xref: /illumos-gate/usr/src/uts/common/fs/zfs/vdev.c (revision c8811bd3)

/*
 * 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);
	mutex_init(&vd->vdev_queue_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_queue_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);

		zio_link_t *zl = NULL;
		while ((pio = zio_walk_parents(zio, &zl)) != 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 &&
	    vd->vdev_mg->mg_initialized);
}

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;
	vdev_t *tvd = vd->vdev_top;

	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;
	/*
	 * Report expandable space on top-level, non-auxillary devices only.
	 * The expandable space is reported in terms of metaslab sized units
	 * since that determines how much space the pool can expand.
	 */
	if (vd->vdev_aux == NULL && tvd != NULL) {
		vs->vs_esize = P2ALIGN(vd->vdev_max_asize - vd->vdev_asize,
		    1ULL << tvd->vdev_ms_shift);
	}
	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);
	}
}