[zfs] / module / 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 2009 Sun Microsystems, Inc.  All rights reserved.
 * Use is subject to license terms.
 */

#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/zio.h>
#include <sys/zap.h>
#include <sys/fs/zfs.h>
#include <sys/arc.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,
        NULL
};

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

/*
 * 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;
        uint64_t c;

        for (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 replaceable or attachable device size.
 * If the parent is a mirror or raidz, the replaceable size is the minimum
 * psize of all its children. For the rest, just return our own psize.
 *
 * e.g.
 *                      psize   rsize
 * root                 -       -
 *      mirror/raidz    -       -
 *          disk1       20g     20g
 *          disk2       40g     20g
 *      disk3           80g     80g
 */
uint64_t
vdev_get_rsize(vdev_t *vd)
{
        vdev_t *pvd, *cvd;
        uint64_t c, rsize;

        pvd = vd->vdev_parent;

        /*
         * If our parent is NULL or the root, just return our own psize.
         */
        if (pvd == NULL || pvd->vdev_parent == NULL)
                return (vd->vdev_psize);

        rsize = 0;

        for (c = 0; c < pvd->vdev_children; c++) {
                cvd = pvd->vdev_child[c];
                rsize = MIN(rsize - 1, cvd->vdev_psize - 1) + 1;
        }

        return (rsize);
}

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)
{
        int c;
        vdev_t *mvd;

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

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

        return (NULL);
}

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

        ASSERT(spa_config_held(cvd->vdev_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;

        if (cvd->vdev_ops->vdev_op_leaf)
                cvd->vdev_spa->spa_scrub_maxinflight += zfs_scrub_limit;
}

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;

        if (cvd->vdev_ops->vdev_op_leaf)
                cvd->vdev_spa->spa_scrub_maxinflight -= zfs_scrub_limit;
}

/*
 * 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, c;

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

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

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

        for (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.
 */
static 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;
        }

        if (guid == 0) {
                if (spa->spa_root_vdev == vd) {
                        /*
                         * The root vdev's guid will also be the pool guid,
                         * which must be unique among all pools.
                         */
                        while (guid == 0 || spa_guid_exists(guid, 0))
                                guid = spa_get_random(-1ULL);
                } else {
                        /*
                         * Any other vdev's guid must be unique within the pool.
                         */
                        while (guid == 0 ||
                            spa_guid_exists(spa_guid(spa), guid))
                                guid = spa_get_random(-1ULL);
                }
                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;

        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++) {
                space_map_create(&vd->vdev_dtl[t], 0, -1ULL, 0,
                    &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 (EINVAL);

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

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

        /*
         * The first allocated vdev must be of type 'root'.
         */
        if (ops != &vdev_root_ops && spa->spa_root_vdev == NULL)
                return (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 (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) {
                        /*
                         * Currently, we can only support 2 parity devices.
                         */
                        if (nparity == 0 || nparity > 2)
                                return (EINVAL);
                        /*
                         * Older versions can only support 1 parity device.
                         */
                        if (nparity == 2 &&
                            spa_version(spa) < SPA_VERSION_RAID6)
                                return (ENOTSUP);
                } else {
                        /*
                         * We require the parity to be specified for SPAs that
                         * support multiple parity levels.
                         */
                        if (spa_version(spa) >= SPA_VERSION_RAID6)
                                return (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);

        /*
         * 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.
         */
        if (!spa->spa_import_faulted)
                (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);

        /*
         * If we're a top-level vdev, try to load the allocation parameters.
         */
        if (parent && !parent->vdev_parent && alloctype == VDEV_ALLOC_LOAD) {
                (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);
        }

        /*
         * 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)) {
                if (alloctype == VDEV_ALLOC_LOAD) {
                        (void) nvlist_lookup_uint64(nv, ZPOOL_CONFIG_DTL,
                            &vd->vdev_dtl_smo.smo_object);
                        (void) nvlist_lookup_uint64(nv, ZPOOL_CONFIG_UNSPARE,
                            &vd->vdev_unspare);
                }
                (void) nvlist_lookup_uint64(nv, ZPOOL_CONFIG_OFFLINE,
                    &vd->vdev_offline);

                /*
                 * 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.
                 */
                if (spa->spa_load_state == 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);
                }
        }

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

        *vdp = vd;

        return (0);
}

void
vdev_free(vdev_t *vd)
{
        int c;
        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));

        /*
         * Free all children.
         */
        for (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 == vd->vdev_top)
                vdev_metaslab_fini(vd);

        ASSERT3U(vd->vdev_stat.vs_space, ==, 0);
        ASSERT3U(vd->vdev_stat.vs_dspace, ==, 0);
        ASSERT3U(vd->vdev_stat.vs_alloc, ==, 0);

        /*
         * 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_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);
        for (int t = 0; t < DTL_TYPES; t++) {
                space_map_unload(&vd->vdev_dtl[t]);
                space_map_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;

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

        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)
{
        int c;

        if (vd == NULL)
                return;

        vd->vdev_top = tvd;

        for (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_ashift = cvd->vdev_ashift;
        mvd->vdev_state = cvd->vdev_state;

        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_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;
        metaslab_class_t *mc;
        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;

        if (vd->vdev_ms_shift == 0)     /* not being allocated from yet */
                return (0);

        ASSERT(oldc <= newc);

        if (vd->vdev_islog)
                mc = spa->spa_log_class;
        else
                mc = spa->spa_normal_class;

        if (vd->vdev_mg == NULL)
                vd->vdev_mg = metaslab_group_create(mc, vd);

        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++) {
                space_map_obj_t smo = { 0, 0, 0 };
                if (txg == 0) {
                        uint64_t object = 0;
                        error = dmu_read(mos, vd->vdev_ms_array,
                            m * sizeof (uint64_t), sizeof (uint64_t), &object);
                        if (error)
                                return (error);
                        if (object != 0) {
                                dmu_buf_t *db;
                                error = dmu_bonus_hold(mos, object, FTAG, &db);
                                if (error)
                                        return (error);
                                ASSERT3U(db->db_size, >=, sizeof (smo));
                                bcopy(db->db_data, &smo, sizeof (smo));
                                ASSERT3U(smo.smo_object, ==, object);
                                dmu_buf_rele(db, FTAG);
                        }
                }
                vd->vdev_ms[m] = metaslab_init(vd->vdev_mg, &smo,
                    m << vd->vdev_ms_shift, 1ULL << vd->vdev_ms_shift, txg);
        }

        return (0);
}

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

        if (vd->vdev_ms != NULL) {
                for (m = 0; m < count; m++)
                        if (vd->vdev_ms[m] != NULL)
                                metaslab_fini(vd->vdev_ms[m]);
                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 = 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 = ENXIO;

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

/*
 * Determine whether this device is accessible by reading and writing
 * 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_DONT_RETRY;

                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);

                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_pad)),
                    VDEV_SKIP_SIZE, zio_buf_alloc(VDEV_SKIP_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);
}

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

        ASSERT(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;

        if (!vd->vdev_removed && vd->vdev_faulted) {
                ASSERT(vd->vdev_children == 0);
                vdev_set_state(vd, B_TRUE, VDEV_STATE_FAULTED,
                    VDEV_AUX_ERR_EXCEEDED);
                return (ENXIO);
        } else if (vd->vdev_offline) {
                ASSERT(vd->vdev_children == 0);
                vdev_set_state(vd, B_TRUE, VDEV_STATE_OFFLINE, VDEV_AUX_NONE);
                return (ENXIO);
        }

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

        if (zio_injection_enabled && error == 0)
                error = zio_handle_device_injection(vd, 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;

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

        for (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));

        if (vd->vdev_children == 0) {
                if (osize < SPA_MINDEVSIZE) {
                        vdev_set_state(vd, B_TRUE, VDEV_STATE_CANT_OPEN,
                            VDEV_AUX_TOO_SMALL);
                        return (EOVERFLOW);
                }
                psize = osize;
                asize = 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 (EOVERFLOW);
                }
                psize = 0;
                asize = osize;
        }

        vd->vdev_psize = psize;

        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_ashift = MAX(ashift, vd->vdev_ashift);
        } else {
                /*
                 * Make sure the alignment requirement hasn't increased.
                 */
                if (ashift > vd->vdev_top->vdev_ashift) {
                        vdev_set_state(vd, B_TRUE, VDEV_STATE_CANT_OPEN,
                            VDEV_AUX_BAD_LABEL);
                        return (EINVAL);
                }

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

                /*
                 * If all children are healthy and the asize has increased,
                 * then we've experienced dynamic LUN growth.
                 */
                if (vd->vdev_state == VDEV_STATE_HEALTHY &&
                    asize > vd->vdev_asize) {
                        vd->vdev_asize = asize;
                }
        }

        /*
         * 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_CANT_OPEN,
                    VDEV_AUX_IO_FAILURE);
                return (error);
        }

        /*
         * If this is a top-level vdev, compute the raidz-deflation
         * ratio.  Note, we hard-code in 128k (1<<17) because it is the
         * current "typical" blocksize.  Even if SPA_MAXBLOCKSIZE
         * changes, this algorithm must never change, or we will
         * inconsistently account for existing bp's.
         */
        if (vd->vdev_top == vd) {
                vd->vdev_deflate_ratio = (1<<17) /
                    (vdev_psize_to_asize(vd, 1<<17) >> SPA_MINBLOCKSHIFT);
        }

        /*
         * 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.
 *
 * 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)
{
        spa_t *spa = vd->vdev_spa;
        int c;
        nvlist_t *label;
        uint64_t guid, top_guid;
        uint64_t state;

        for (c = 0; c < vd->vdev_children; c++)
                if (vdev_validate(vd->vdev_child[c]) != 0)
                        return (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)) {

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

                if (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 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 (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 != 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 (spa->spa_load_state == SPA_LOAD_OPEN &&
                    state != POOL_STATE_ACTIVE)
                        return (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;

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

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

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

        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) &&
                    !l2arc_vdev_present(vd)) {
                        uint64_t size = vdev_get_rsize(vd);
                        l2arc_add_vdev(spa, vd,
                            VDEV_LABEL_START_SIZE,
                            size - VDEV_LABEL_START_SIZE);
                }
        } else {
                (void) vdev_validate(vd);
        }

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

        return (0);
}

/*
 * The is the latter half of vdev_create().  It is distinct because it
 * involves initiating transactions in order to do metaslab creation.
 * For creation, we want to try to create all vdevs at once and then undo it
 * if anything fails; this is much harder if we have pending transactions.
 */
void
vdev_init(vdev_t *vd, uint64_t txg)
{
        /*
         * Aim for roughly 200 metaslabs per vdev.
         */
        vd->vdev_ms_shift = highbit(vd->vdev_asize / 200);
        vd->vdev_ms_shift = MAX(vd->vdev_ms_shift, SPA_MAXBLOCKSHIFT);

        /*
         * Initialize the vdev's metaslabs.  This can't fail because
         * there's nothing to read when creating all new metaslabs.
         */
        VERIFY(vdev_metaslab_init(vd, txg) == 0);
}

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

        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);
}

/*
 * 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 three 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)
{
        space_map_t *sm = &vd->vdev_dtl[t];

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

        mutex_enter(sm->sm_lock);
        if (!space_map_contains(sm, txg, size))
                space_map_add(sm, txg, size);
        mutex_exit(sm->sm_lock);
}

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

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

        mutex_enter(sm->sm_lock);
        if (sm->sm_space != 0)
                dirty = space_map_contains(sm, txg, size);
        mutex_exit(sm->sm_lock);

        return (dirty);
}

boolean_t
vdev_dtl_empty(vdev_t *vd, vdev_dtl_type_t t)
{
        space_map_t *sm = &vd->vdev_dtl[t];
        boolean_t empty;

        mutex_enter(sm->sm_lock);
        empty = (sm->sm_space == 0);
        mutex_exit(sm->sm_lock);

        return (empty);
}

/*
 * 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)
                return;

        if (vd->vdev_ops->vdev_op_leaf) {
                mutex_enter(&vd->vdev_dtl_lock);
                if (scrub_txg != 0 &&
                    (spa->spa_scrub_started || spa->spa_scrub_errors == 0)) {
                        /* XXX should check scrub_done? */
                        /*
                         * 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_map_ref_create(&reftree);
                        space_map_ref_add_map(&reftree,
                            &vd->vdev_dtl[DTL_MISSING], 1);
                        space_map_ref_add_seg(&reftree, 0, scrub_txg, -1);
                        space_map_ref_add_map(&reftree,
                            &vd->vdev_dtl[DTL_SCRUB], 2);
                        space_map_ref_generate_map(&reftree,
                            &vd->vdev_dtl[DTL_MISSING], 1);
                        space_map_ref_destroy(&reftree);
                }
                space_map_vacate(&vd->vdev_dtl[DTL_PARTIAL], NULL, NULL);
                space_map_walk(&vd->vdev_dtl[DTL_MISSING],
                    space_map_add, &vd->vdev_dtl[DTL_PARTIAL]);
                if (scrub_done)
                        space_map_vacate(&vd->vdev_dtl[DTL_SCRUB], NULL, NULL);
                space_map_vacate(&vd->vdev_dtl[DTL_OUTAGE], NULL, NULL);
                if (!vdev_readable(vd))
                        space_map_add(&vd->vdev_dtl[DTL_OUTAGE], 0, -1ULL);
                else
                        space_map_walk(&vd->vdev_dtl[DTL_MISSING],
                            space_map_add, &vd->vdev_dtl[DTL_OUTAGE]);
                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++) {
                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_map_ref_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_map_ref_add_map(&reftree, &cvd->vdev_dtl[t], 1);
                        mutex_exit(&cvd->vdev_dtl_lock);
                }
                space_map_ref_generate_map(&reftree, &vd->vdev_dtl[t], minref);
                space_map_ref_destroy(&reftree);
        }
        mutex_exit(&vd->vdev_dtl_lock);
}

static int
vdev_dtl_load(vdev_t *vd)
{
        spa_t *spa = vd->vdev_spa;
        space_map_obj_t *smo = &vd->vdev_dtl_smo;
        objset_t *mos = spa->spa_meta_objset;
        dmu_buf_t *db;
        int error;

        ASSERT(vd->vdev_children == 0);

        if (smo->smo_object == 0)
                return (0);

        if ((error = dmu_bonus_hold(mos, smo->smo_object, FTAG, &db)) != 0)
                return (error);

        ASSERT3U(db->db_size, >=, sizeof (*smo));
        bcopy(db->db_data, smo, sizeof (*smo));
        dmu_buf_rele(db, FTAG);

        mutex_enter(&vd->vdev_dtl_lock);
        error = space_map_load(&vd->vdev_dtl[DTL_MISSING],
            NULL, SM_ALLOC, smo, mos);
        mutex_exit(&vd->vdev_dtl_lock);

        return (error);
}

void
vdev_dtl_sync(vdev_t *vd, uint64_t txg)
{
        spa_t *spa = vd->vdev_spa;
        space_map_obj_t *smo = &vd->vdev_dtl_smo;
        space_map_t *sm = &vd->vdev_dtl[DTL_MISSING];
        objset_t *mos = spa->spa_meta_objset;
        space_map_t smsync;
        kmutex_t smlock;
        dmu_buf_t *db;
        dmu_tx_t *tx;

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

        if (vd->vdev_detached) {
                if (smo->smo_object != 0) {
                        int err = dmu_object_free(mos, smo->smo_object, tx);
                        ASSERT3U(err, ==, 0);
                        smo->smo_object = 0;
                }
                dmu_tx_commit(tx);
                return;
        }

        if (smo->smo_object == 0) {
                ASSERT(smo->smo_objsize == 0);
                ASSERT(smo->smo_alloc == 0);
                smo->smo_object = dmu_object_alloc(mos,
                    DMU_OT_SPACE_MAP, 1 << SPACE_MAP_BLOCKSHIFT,
                    DMU_OT_SPACE_MAP_HEADER, sizeof (*smo), tx);
                ASSERT(smo->smo_object != 0);
                vdev_config_dirty(vd->vdev_top);
        }

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

        space_map_create(&smsync, sm->sm_start, sm->sm_size, sm->sm_shift,
            &smlock);

        mutex_enter(&smlock);

        mutex_enter(&vd->vdev_dtl_lock);
        space_map_walk(sm, space_map_add, &smsync);
        mutex_exit(&vd->vdev_dtl_lock);

        space_map_truncate(smo, mos, tx);
        space_map_sync(&smsync, SM_ALLOC, smo, mos, tx);

        space_map_destroy(&smsync);

        mutex_exit(&smlock);
        mutex_destroy(&smlock);

        VERIFY(0 == dmu_bonus_hold(mos, smo->smo_object, FTAG, &db));
        dmu_buf_will_dirty(db, tx);
        ASSERT3U(db->db_size, >=, sizeof (*smo));
        bcopy(smo, db->db_data, sizeof (*smo));
        dmu_buf_rele(db, FTAG);

        dmu_tx_commit(tx);
}

/*
 * 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);

        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 (vd->vdev_dtl[DTL_MISSING].sm_space != 0 &&
                    vdev_writeable(vd)) {
                        space_seg_t *ss;

                        ss = avl_first(&vd->vdev_dtl[DTL_MISSING].sm_root);
                        thismin = ss->ss_start - 1;
                        ss = avl_last(&vd->vdev_dtl[DTL_MISSING].sm_root);
                        thismax = ss->ss_end;
                        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_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)) == 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 ||
            version > SPA_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_sync_done(vdev_t *vd, uint64_t txg)
{
        metaslab_t *msp;

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

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;

        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);
        }

        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_t *vd;

        spa_vdev_state_enter(spa);

        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));

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

        /*
         * If marking the vdev as faulted cause the top-level vdev to become
         * unavailable, then back off and simply mark the vdev as degraded
         * instead.
         */
        if (vdev_is_dead(vd->vdev_top) && vd->vdev_aux == NULL) {
                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(vd);

                if (vdev_readable(vd)) {
                        vdev_set_state(vd, B_FALSE, VDEV_STATE_DEGRADED,
                            VDEV_AUX_ERR_EXCEEDED);
                }
        }

        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_t *vd;

        spa_vdev_state_enter(spa);

        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,
                    VDEV_AUX_ERR_EXCEEDED);

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

/*
 * Online the given vdev.  If '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;

        spa_vdev_state_enter(spa);

        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));

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

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

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

        spa_vdev_state_enter(spa);

        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 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.
                 */
                if (vd->vdev_aux == NULL && vdev_dtl_required(vd))
                        return (spa_vdev_state_exit(spa, NULL, EBUSY));

                /*
                 * Offline this device and reopen its top-level vdev.
                 * If this action results in the top-level vdev becoming
                 * unusable, undo it and fail the request.
                 */
                vd->vdev_offline = B_TRUE;
                vdev_reopen(vd->vdev_top);
                if (vd->vdev_aux == NULL && vdev_is_dead(vd->vdev_top)) {
                        vd->vdev_offline = B_FALSE;
                        vdev_reopen(vd->vdev_top);
                        return (spa_vdev_state_exit(spa, NULL, EBUSY));
                }
        }

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

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

/*
 * 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)) {

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

                vdev_reopen(vd);

                if (vd != rvd)
                        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);
        }
}

boolean_t
vdev_is_dead(vdev_t *vd)
{
        return (vd->vdev_state < VDEV_STATE_DEGRADED);
}

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);
}

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)
{
        vdev_t *rvd = vd->vdev_spa->spa_root_vdev;

        mutex_enter(&vd->vdev_stat_lock);
        bcopy(&vd->vdev_stat, vs, sizeof (*vs));
        vs->vs_scrub_errors = vd->vdev_spa->spa_scrub_errors;
        vs->vs_timestamp = gethrtime() - vs->vs_timestamp;
        vs->vs_state = vd->vdev_state;
        vs->vs_rsize = vdev_get_rsize(vd);
        mutex_exit(&vd->vdev_stat_lock);

        /*
         * 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;

                        mutex_enter(&vd->vdev_stat_lock);
                        for (int t = 0; t < ZIO_TYPES; t++) {
                                vs->vs_ops[t] += cvs->vs_ops[t];
                                vs->vs_bytes[t] += cvs->vs_bytes[t];
                        }
                        vs->vs_scrub_examined += cvs->vs_scrub_examined;
                        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_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_SCRUB_THREAD)
                                vs->vs_scrub_repaired += 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;

        mutex_enter(&vd->vdev_stat_lock);
        if (type == ZIO_TYPE_READ) {
                if (zio->io_error == ECKSUM)
                        vs->vs_checksum_errors++;
                else
                        vs->vs_read_errors++;
        }
        if (type == ZIO_TYPE_WRITE)
                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_SCRUB_THREAD))) {
                /*
                 * This is either a normal write (not a repair), or it's a
                 * repair induced by the scrub thread.  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->spa_syncing_txg.
                 *
                 * 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_SCRUB_THREAD) {
                                ASSERT(flags & ZIO_FLAG_IO_REPAIR);
                                ASSERT(spa_sync_pass(spa) == 1);
                                vdev_dtl_dirty(vd, DTL_SCRUB, txg, 1);
                                commit_txg = spa->spa_syncing_txg;
                        }
                        ASSERT(commit_txg >= spa->spa_syncing_txg);
                        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);
        }
}

void
vdev_scrub_stat_update(vdev_t *vd, pool_scrub_type_t type, boolean_t complete)
{
        int c;
        vdev_stat_t *vs = &vd->vdev_stat;

        for (c = 0; c < vd->vdev_children; c++)
                vdev_scrub_stat_update(vd->vdev_child[c], type, complete);

        mutex_enter(&vd->vdev_stat_lock);

        if (type == POOL_SCRUB_NONE) {
                /*
                 * Update completion and end time.  Leave everything else alone
                 * so we can report what happened during the previous scrub.
                 */
                vs->vs_scrub_complete = complete;
                vs->vs_scrub_end = gethrestime_sec();
        } else {
                vs->vs_scrub_type = type;
                vs->vs_scrub_complete = 0;
                vs->vs_scrub_examined = 0;
                vs->vs_scrub_repaired = 0;
                vs->vs_scrub_start = gethrestime_sec();
                vs->vs_scrub_end = 0;
        }

        mutex_exit(&vd->vdev_stat_lock);
}

/*
 * Update the in-core space usage stats for this vdev and the root vdev.
 */
void
vdev_space_update(vdev_t *vd, int64_t space_delta, int64_t alloc_delta,
    boolean_t update_root)
{
        int64_t dspace_delta = space_delta;
        spa_t *spa = vd->vdev_spa;
        vdev_t *rvd = spa->spa_root_vdev;

        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);
        dspace_delta = (dspace_delta >> SPA_MINBLOCKSHIFT) *
            vd->vdev_deflate_ratio;

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

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

                /*
                 * Don't count non-normal (e.g. intent log) space as part of
                 * the pool's capacity.
                 */
                if (vd->vdev_mg->mg_class != spa->spa_normal_class)
                        return;

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

/*
 * 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;

        /*
         * If this is an aux vdev (as with l2cache 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;

                VERIFY(nvlist_lookup_nvlist_array(sav->sav_config,
                    ZPOOL_CONFIG_L2CACHE, &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, B_FALSE, B_TRUE);

                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))
                        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(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))
                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;
        int c;
        vdev_t *child;

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

                        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.  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 (vdev_is_dead(vd) && vd->vdev_ops->vdev_op_leaf)
                vd->vdev_ops->vdev_op_close(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) {
                /*
                 * Indicate to the ZFS DE that this device has been removed, and
                 * any recent errors should be ignored.
                 */
                zfs_post_remove(spa, vd);
                vd->vdev_removed = B_TRUE;
        } else if (state == VDEV_STATE_CANT_OPEN) {
                /*
                 * If we fail to open a vdev during an import, 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->spa_load_state == SPA_LOAD_IMPORT &&
                    !spa->spa_import_faulted &&
                    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;
                        case VDEV_AUX_IO_FAILURE:
                                class = FM_EREPORT_ZFS_IO_FAILURE;
                                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)
                vdev_propagate_state(vd);
}

/*
 * Check the vdev configuration to ensure that it's capable of supporting
 * a root pool. Currently, we do not support RAID-Z or partial configuration.
 * In addition, only a single top-level vdev is allowed and none of the leaves
 * can be wholedisks.
 */
boolean_t
vdev_is_bootable(vdev_t *vd)
{
        int c;

        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_RAIDZ) == 0 ||
                    strcmp(vdev_type, VDEV_TYPE_MISSING) == 0) {
                        return (B_FALSE);
                }
        } else if (vd->vdev_wholedisk == 1) {
                return (B_FALSE);
        }

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