[mirror_zfs.git] / module / zfs / spa.c

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

/*
 * Copyright (c) 2005, 2010, Oracle and/or its affiliates. All rights reserved.
 * Copyright (c) 2011, 2017 by Delphix. All rights reserved.
 * Copyright (c) 2015, Nexenta Systems, Inc.  All rights reserved.
 * Copyright (c) 2013, 2014, Nexenta Systems, Inc.  All rights reserved.
 * Copyright (c) 2014 Spectra Logic Corporation, All rights reserved.
 * Copyright 2013 Saso Kiselkov. All rights reserved.
 * Copyright (c) 2014 Integros [integros.com]
 * Copyright 2016 Toomas Soome <tsoome@me.com>
 * Copyright (c) 2016 Actifio, Inc. All rights reserved.
 * Copyright (c) 2017 Datto Inc.
 * Copyright 2017 Joyent, Inc.
 */

/*
 * SPA: Storage Pool Allocator
 *
 * This file contains all the routines used when modifying on-disk SPA state.
 * This includes opening, importing, destroying, exporting a pool, and syncing a
 * pool.
 */

#include <sys/zfs_context.h>
#include <sys/fm/fs/zfs.h>
#include <sys/spa_impl.h>
#include <sys/zio.h>
#include <sys/zio_checksum.h>
#include <sys/dmu.h>
#include <sys/dmu_tx.h>
#include <sys/zap.h>
#include <sys/zil.h>
#include <sys/ddt.h>
#include <sys/vdev_impl.h>
#include <sys/vdev_disk.h>
#include <sys/metaslab.h>
#include <sys/metaslab_impl.h>
#include <sys/mmp.h>
#include <sys/uberblock_impl.h>
#include <sys/txg.h>
#include <sys/avl.h>
#include <sys/dmu_traverse.h>
#include <sys/dmu_objset.h>
#include <sys/unique.h>
#include <sys/dsl_pool.h>
#include <sys/dsl_dataset.h>
#include <sys/dsl_dir.h>
#include <sys/dsl_prop.h>
#include <sys/dsl_synctask.h>
#include <sys/fs/zfs.h>
#include <sys/arc.h>
#include <sys/callb.h>
#include <sys/systeminfo.h>
#include <sys/spa_boot.h>
#include <sys/zfs_ioctl.h>
#include <sys/dsl_scan.h>
#include <sys/zfeature.h>
#include <sys/dsl_destroy.h>
#include <sys/zvol.h>

#ifdef  _KERNEL
#include <sys/fm/protocol.h>
#include <sys/fm/util.h>
#include <sys/bootprops.h>
#include <sys/callb.h>
#include <sys/cpupart.h>
#include <sys/pool.h>
#include <sys/sysdc.h>
#include <sys/zone.h>
#endif  /* _KERNEL */

#include "zfs_prop.h"
#include "zfs_comutil.h"

/*
 * The interval, in seconds, at which failed configuration cache file writes
 * should be retried.
 */
static int zfs_ccw_retry_interval = 300;

typedef enum zti_modes {
        ZTI_MODE_FIXED,                 /* value is # of threads (min 1) */
        ZTI_MODE_BATCH,                 /* cpu-intensive; value is ignored */
        ZTI_MODE_NULL,                  /* don't create a taskq */
        ZTI_NMODES
} zti_modes_t;

#define ZTI_P(n, q)     { ZTI_MODE_FIXED, (n), (q) }
#define ZTI_PCT(n)      { ZTI_MODE_ONLINE_PERCENT, (n), 1 }
#define ZTI_BATCH       { ZTI_MODE_BATCH, 0, 1 }
#define ZTI_NULL        { ZTI_MODE_NULL, 0, 0 }

#define ZTI_N(n)        ZTI_P(n, 1)
#define ZTI_ONE         ZTI_N(1)

typedef struct zio_taskq_info {
        zti_modes_t zti_mode;
        uint_t zti_value;
        uint_t zti_count;
} zio_taskq_info_t;

static const char *const zio_taskq_types[ZIO_TASKQ_TYPES] = {
        "iss", "iss_h", "int", "int_h"
};

/*
 * This table defines the taskq settings for each ZFS I/O type. When
 * initializing a pool, we use this table to create an appropriately sized
 * taskq. Some operations are low volume and therefore have a small, static
 * number of threads assigned to their taskqs using the ZTI_N(#) or ZTI_ONE
 * macros. Other operations process a large amount of data; the ZTI_BATCH
 * macro causes us to create a taskq oriented for throughput. Some operations
 * are so high frequency and short-lived that the taskq itself can become a a
 * point of lock contention. The ZTI_P(#, #) macro indicates that we need an
 * additional degree of parallelism specified by the number of threads per-
 * taskq and the number of taskqs; when dispatching an event in this case, the
 * particular taskq is chosen at random.
 *
 * The different taskq priorities are to handle the different contexts (issue
 * and interrupt) and then to reserve threads for ZIO_PRIORITY_NOW I/Os that
 * need to be handled with minimum delay.
 */
const zio_taskq_info_t zio_taskqs[ZIO_TYPES][ZIO_TASKQ_TYPES] = {
        /* ISSUE        ISSUE_HIGH      INTR            INTR_HIGH */
        { ZTI_ONE,      ZTI_NULL,       ZTI_ONE,        ZTI_NULL }, /* NULL */
        { ZTI_N(8),     ZTI_NULL,       ZTI_P(12, 8),   ZTI_NULL }, /* READ */
        { ZTI_BATCH,    ZTI_N(5),       ZTI_P(12, 8),   ZTI_N(5) }, /* WRITE */
        { ZTI_P(12, 8), ZTI_NULL,       ZTI_ONE,        ZTI_NULL }, /* FREE */
        { ZTI_ONE,      ZTI_NULL,       ZTI_ONE,        ZTI_NULL }, /* CLAIM */
        { ZTI_ONE,      ZTI_NULL,       ZTI_ONE,        ZTI_NULL }, /* IOCTL */
};

static sysevent_t *spa_event_create(spa_t *spa, vdev_t *vd, nvlist_t *hist_nvl,
    const char *name);
static void spa_event_post(sysevent_t *ev);
static void spa_sync_version(void *arg, dmu_tx_t *tx);
static void spa_sync_props(void *arg, dmu_tx_t *tx);
static boolean_t spa_has_active_shared_spare(spa_t *spa);
static inline int spa_load_impl(spa_t *spa, uint64_t, nvlist_t *config,
    spa_load_state_t state, spa_import_type_t type, boolean_t mosconfig,
    char **ereport);
static void spa_vdev_resilver_done(spa_t *spa);

uint_t          zio_taskq_batch_pct = 75;       /* 1 thread per cpu in pset */
id_t            zio_taskq_psrset_bind = PS_NONE;
boolean_t       zio_taskq_sysdc = B_TRUE;       /* use SDC scheduling class */
uint_t          zio_taskq_basedc = 80;          /* base duty cycle */

boolean_t       spa_create_process = B_TRUE;    /* no process ==> no sysdc */

/*
 * This (illegal) pool name is used when temporarily importing a spa_t in order
 * to get the vdev stats associated with the imported devices.
 */
#define TRYIMPORT_NAME  "$import"

/*
 * ==========================================================================
 * SPA properties routines
 * ==========================================================================
 */

/*
 * Add a (source=src, propname=propval) list to an nvlist.
 */
static void
spa_prop_add_list(nvlist_t *nvl, zpool_prop_t prop, char *strval,
    uint64_t intval, zprop_source_t src)
{
        const char *propname = zpool_prop_to_name(prop);
        nvlist_t *propval;

        VERIFY(nvlist_alloc(&propval, NV_UNIQUE_NAME, KM_SLEEP) == 0);
        VERIFY(nvlist_add_uint64(propval, ZPROP_SOURCE, src) == 0);

        if (strval != NULL)
                VERIFY(nvlist_add_string(propval, ZPROP_VALUE, strval) == 0);
        else
                VERIFY(nvlist_add_uint64(propval, ZPROP_VALUE, intval) == 0);

        VERIFY(nvlist_add_nvlist(nvl, propname, propval) == 0);
        nvlist_free(propval);
}

/*
 * Get property values from the spa configuration.
 */
static void
spa_prop_get_config(spa_t *spa, nvlist_t **nvp)
{
        vdev_t *rvd = spa->spa_root_vdev;
        dsl_pool_t *pool = spa->spa_dsl_pool;
        uint64_t size, alloc, cap, version;
        const zprop_source_t src = ZPROP_SRC_NONE;
        spa_config_dirent_t *dp;
        metaslab_class_t *mc = spa_normal_class(spa);

        ASSERT(MUTEX_HELD(&spa->spa_props_lock));

        if (rvd != NULL) {
                alloc = metaslab_class_get_alloc(spa_normal_class(spa));
                size = metaslab_class_get_space(spa_normal_class(spa));
                spa_prop_add_list(*nvp, ZPOOL_PROP_NAME, spa_name(spa), 0, src);
                spa_prop_add_list(*nvp, ZPOOL_PROP_SIZE, NULL, size, src);
                spa_prop_add_list(*nvp, ZPOOL_PROP_ALLOCATED, NULL, alloc, src);
                spa_prop_add_list(*nvp, ZPOOL_PROP_FREE, NULL,
                    size - alloc, src);

                spa_prop_add_list(*nvp, ZPOOL_PROP_FRAGMENTATION, NULL,
                    metaslab_class_fragmentation(mc), src);
                spa_prop_add_list(*nvp, ZPOOL_PROP_EXPANDSZ, NULL,
                    metaslab_class_expandable_space(mc), src);
                spa_prop_add_list(*nvp, ZPOOL_PROP_READONLY, NULL,
                    (spa_mode(spa) == FREAD), src);

                cap = (size == 0) ? 0 : (alloc * 100 / size);
                spa_prop_add_list(*nvp, ZPOOL_PROP_CAPACITY, NULL, cap, src);

                spa_prop_add_list(*nvp, ZPOOL_PROP_DEDUPRATIO, NULL,
                    ddt_get_pool_dedup_ratio(spa), src);

                spa_prop_add_list(*nvp, ZPOOL_PROP_HEALTH, NULL,
                    rvd->vdev_state, src);

                version = spa_version(spa);
                if (version == zpool_prop_default_numeric(ZPOOL_PROP_VERSION)) {
                        spa_prop_add_list(*nvp, ZPOOL_PROP_VERSION, NULL,
                            version, ZPROP_SRC_DEFAULT);
                } else {
                        spa_prop_add_list(*nvp, ZPOOL_PROP_VERSION, NULL,
                            version, ZPROP_SRC_LOCAL);
                }
        }

        if (pool != NULL) {
                /*
                 * The $FREE directory was introduced in SPA_VERSION_DEADLISTS,
                 * when opening pools before this version freedir will be NULL.
                 */
                if (pool->dp_free_dir != NULL) {
                        spa_prop_add_list(*nvp, ZPOOL_PROP_FREEING, NULL,
                            dsl_dir_phys(pool->dp_free_dir)->dd_used_bytes,
                            src);
                } else {
                        spa_prop_add_list(*nvp, ZPOOL_PROP_FREEING,
                            NULL, 0, src);
                }

                if (pool->dp_leak_dir != NULL) {
                        spa_prop_add_list(*nvp, ZPOOL_PROP_LEAKED, NULL,
                            dsl_dir_phys(pool->dp_leak_dir)->dd_used_bytes,
                            src);
                } else {
                        spa_prop_add_list(*nvp, ZPOOL_PROP_LEAKED,
                            NULL, 0, src);
                }
        }

        spa_prop_add_list(*nvp, ZPOOL_PROP_GUID, NULL, spa_guid(spa), src);

        if (spa->spa_comment != NULL) {
                spa_prop_add_list(*nvp, ZPOOL_PROP_COMMENT, spa->spa_comment,
                    0, ZPROP_SRC_LOCAL);
        }

        if (spa->spa_root != NULL)
                spa_prop_add_list(*nvp, ZPOOL_PROP_ALTROOT, spa->spa_root,
                    0, ZPROP_SRC_LOCAL);

        if (spa_feature_is_enabled(spa, SPA_FEATURE_LARGE_BLOCKS)) {
                spa_prop_add_list(*nvp, ZPOOL_PROP_MAXBLOCKSIZE, NULL,
                    MIN(zfs_max_recordsize, SPA_MAXBLOCKSIZE), ZPROP_SRC_NONE);
        } else {
                spa_prop_add_list(*nvp, ZPOOL_PROP_MAXBLOCKSIZE, NULL,
                    SPA_OLD_MAXBLOCKSIZE, ZPROP_SRC_NONE);
        }

        if (spa_feature_is_enabled(spa, SPA_FEATURE_LARGE_DNODE)) {
                spa_prop_add_list(*nvp, ZPOOL_PROP_MAXDNODESIZE, NULL,
                    DNODE_MAX_SIZE, ZPROP_SRC_NONE);
        } else {
                spa_prop_add_list(*nvp, ZPOOL_PROP_MAXDNODESIZE, NULL,
                    DNODE_MIN_SIZE, ZPROP_SRC_NONE);
        }

        if ((dp = list_head(&spa->spa_config_list)) != NULL) {
                if (dp->scd_path == NULL) {
                        spa_prop_add_list(*nvp, ZPOOL_PROP_CACHEFILE,
                            "none", 0, ZPROP_SRC_LOCAL);
                } else if (strcmp(dp->scd_path, spa_config_path) != 0) {
                        spa_prop_add_list(*nvp, ZPOOL_PROP_CACHEFILE,
                            dp->scd_path, 0, ZPROP_SRC_LOCAL);
                }
        }
}

/*
 * Get zpool property values.
 */
int
spa_prop_get(spa_t *spa, nvlist_t **nvp)
{
        objset_t *mos = spa->spa_meta_objset;
        zap_cursor_t zc;
        zap_attribute_t za;
        int err;

        err = nvlist_alloc(nvp, NV_UNIQUE_NAME, KM_SLEEP);
        if (err)
                return (err);

        mutex_enter(&spa->spa_props_lock);

        /*
         * Get properties from the spa config.
         */
        spa_prop_get_config(spa, nvp);

        /* If no pool property object, no more prop to get. */
        if (mos == NULL || spa->spa_pool_props_object == 0) {
                mutex_exit(&spa->spa_props_lock);
                goto out;
        }

        /*
         * Get properties from the MOS pool property object.
         */
        for (zap_cursor_init(&zc, mos, spa->spa_pool_props_object);
            (err = zap_cursor_retrieve(&zc, &za)) == 0;
            zap_cursor_advance(&zc)) {
                uint64_t intval = 0;
                char *strval = NULL;
                zprop_source_t src = ZPROP_SRC_DEFAULT;
                zpool_prop_t prop;

                if ((prop = zpool_name_to_prop(za.za_name)) == ZPOOL_PROP_INVAL)
                        continue;

                switch (za.za_integer_length) {
                case 8:
                        /* integer property */
                        if (za.za_first_integer !=
                            zpool_prop_default_numeric(prop))
                                src = ZPROP_SRC_LOCAL;

                        if (prop == ZPOOL_PROP_BOOTFS) {
                                dsl_pool_t *dp;
                                dsl_dataset_t *ds = NULL;

                                dp = spa_get_dsl(spa);
                                dsl_pool_config_enter(dp, FTAG);
                                if ((err = dsl_dataset_hold_obj(dp,
                                    za.za_first_integer, FTAG, &ds))) {
                                        dsl_pool_config_exit(dp, FTAG);
                                        break;
                                }

                                strval = kmem_alloc(ZFS_MAX_DATASET_NAME_LEN,
                                    KM_SLEEP);
                                dsl_dataset_name(ds, strval);
                                dsl_dataset_rele(ds, FTAG);
                                dsl_pool_config_exit(dp, FTAG);
                        } else {
                                strval = NULL;
                                intval = za.za_first_integer;
                        }

                        spa_prop_add_list(*nvp, prop, strval, intval, src);

                        if (strval != NULL)
                                kmem_free(strval, ZFS_MAX_DATASET_NAME_LEN);

                        break;

                case 1:
                        /* string property */
                        strval = kmem_alloc(za.za_num_integers, KM_SLEEP);
                        err = zap_lookup(mos, spa->spa_pool_props_object,
                            za.za_name, 1, za.za_num_integers, strval);
                        if (err) {
                                kmem_free(strval, za.za_num_integers);
                                break;
                        }
                        spa_prop_add_list(*nvp, prop, strval, 0, src);
                        kmem_free(strval, za.za_num_integers);
                        break;

                default:
                        break;
                }
        }
        zap_cursor_fini(&zc);
        mutex_exit(&spa->spa_props_lock);
out:
        if (err && err != ENOENT) {
                nvlist_free(*nvp);
                *nvp = NULL;
                return (err);
        }

        return (0);
}

/*
 * Validate the given pool properties nvlist and modify the list
 * for the property values to be set.
 */
static int
spa_prop_validate(spa_t *spa, nvlist_t *props)
{
        nvpair_t *elem;
        int error = 0, reset_bootfs = 0;
        uint64_t objnum = 0;
        boolean_t has_feature = B_FALSE;

        elem = NULL;
        while ((elem = nvlist_next_nvpair(props, elem)) != NULL) {
                uint64_t intval;
                char *strval, *slash, *check, *fname;
                const char *propname = nvpair_name(elem);
                zpool_prop_t prop = zpool_name_to_prop(propname);

                switch (prop) {
                case ZPOOL_PROP_INVAL:
                        if (!zpool_prop_feature(propname)) {
                                error = SET_ERROR(EINVAL);
                                break;
                        }

                        /*
                         * Sanitize the input.
                         */
                        if (nvpair_type(elem) != DATA_TYPE_UINT64) {
                                error = SET_ERROR(EINVAL);
                                break;
                        }

                        if (nvpair_value_uint64(elem, &intval) != 0) {
                                error = SET_ERROR(EINVAL);
                                break;
                        }

                        if (intval != 0) {
                                error = SET_ERROR(EINVAL);
                                break;
                        }

                        fname = strchr(propname, '@') + 1;
                        if (zfeature_lookup_name(fname, NULL) != 0) {
                                error = SET_ERROR(EINVAL);
                                break;
                        }

                        has_feature = B_TRUE;
                        break;

                case ZPOOL_PROP_VERSION:
                        error = nvpair_value_uint64(elem, &intval);
                        if (!error &&
                            (intval < spa_version(spa) ||
                            intval > SPA_VERSION_BEFORE_FEATURES ||
                            has_feature))
                                error = SET_ERROR(EINVAL);
                        break;

                case ZPOOL_PROP_DELEGATION:
                case ZPOOL_PROP_AUTOREPLACE:
                case ZPOOL_PROP_LISTSNAPS:
                case ZPOOL_PROP_AUTOEXPAND:
                        error = nvpair_value_uint64(elem, &intval);
                        if (!error && intval > 1)
                                error = SET_ERROR(EINVAL);
                        break;

                case ZPOOL_PROP_MULTIHOST:
                        error = nvpair_value_uint64(elem, &intval);
                        if (!error && intval > 1)
                                error = SET_ERROR(EINVAL);

                        if (!error && !spa_get_hostid())
                                error = SET_ERROR(ENOTSUP);

                        break;

                case ZPOOL_PROP_BOOTFS:
                        /*
                         * If the pool version is less than SPA_VERSION_BOOTFS,
                         * or the pool is still being created (version == 0),
                         * the bootfs property cannot be set.
                         */
                        if (spa_version(spa) < SPA_VERSION_BOOTFS) {
                                error = SET_ERROR(ENOTSUP);
                                break;
                        }

                        /*
                         * Make sure the vdev config is bootable
                         */
                        if (!vdev_is_bootable(spa->spa_root_vdev)) {
                                error = SET_ERROR(ENOTSUP);
                                break;
                        }

                        reset_bootfs = 1;

                        error = nvpair_value_string(elem, &strval);

                        if (!error) {
                                objset_t *os;
                                uint64_t propval;

                                if (strval == NULL || strval[0] == '\0') {
                                        objnum = zpool_prop_default_numeric(
                                            ZPOOL_PROP_BOOTFS);
                                        break;
                                }

                                error = dmu_objset_hold(strval, FTAG, &os);
                                if (error)
                                        break;

                                /*
                                 * Must be ZPL, and its property settings
                                 * must be supported by GRUB (compression
                                 * is not gzip, and large blocks or large
                                 * dnodes are not used).
                                 */

                                if (dmu_objset_type(os) != DMU_OST_ZFS) {
                                        error = SET_ERROR(ENOTSUP);
                                } else if ((error =
                                    dsl_prop_get_int_ds(dmu_objset_ds(os),
                                    zfs_prop_to_name(ZFS_PROP_COMPRESSION),
                                    &propval)) == 0 &&
                                    !BOOTFS_COMPRESS_VALID(propval)) {
                                        error = SET_ERROR(ENOTSUP);
                                } else if ((error =
                                    dsl_prop_get_int_ds(dmu_objset_ds(os),
                                    zfs_prop_to_name(ZFS_PROP_DNODESIZE),
                                    &propval)) == 0 &&
                                    propval != ZFS_DNSIZE_LEGACY) {
                                        error = SET_ERROR(ENOTSUP);
                                } else {
                                        objnum = dmu_objset_id(os);
                                }
                                dmu_objset_rele(os, FTAG);
                        }
                        break;

                case ZPOOL_PROP_FAILUREMODE:
                        error = nvpair_value_uint64(elem, &intval);
                        if (!error && intval > ZIO_FAILURE_MODE_PANIC)
                                error = SET_ERROR(EINVAL);

                        /*
                         * This is a special case which only occurs when
                         * the pool has completely failed. This allows
                         * the user to change the in-core failmode property
                         * without syncing it out to disk (I/Os might
                         * currently be blocked). We do this by returning
                         * EIO to the caller (spa_prop_set) to trick it
                         * into thinking we encountered a property validation
                         * error.
                         */
                        if (!error && spa_suspended(spa)) {
                                spa->spa_failmode = intval;
                                error = SET_ERROR(EIO);
                        }
                        break;

                case ZPOOL_PROP_CACHEFILE:
                        if ((error = nvpair_value_string(elem, &strval)) != 0)
                                break;

                        if (strval[0] == '\0')
                                break;

                        if (strcmp(strval, "none") == 0)
                                break;

                        if (strval[0] != '/') {
                                error = SET_ERROR(EINVAL);
                                break;
                        }

                        slash = strrchr(strval, '/');
                        ASSERT(slash != NULL);

                        if (slash[1] == '\0' || strcmp(slash, "/.") == 0 ||
                            strcmp(slash, "/..") == 0)
                                error = SET_ERROR(EINVAL);
                        break;

                case ZPOOL_PROP_COMMENT:
                        if ((error = nvpair_value_string(elem, &strval)) != 0)
                                break;
                        for (check = strval; *check != '\0'; check++) {
                                if (!isprint(*check)) {
                                        error = SET_ERROR(EINVAL);
                                        break;
                                }
                        }
                        if (strlen(strval) > ZPROP_MAX_COMMENT)
                                error = SET_ERROR(E2BIG);
                        break;

                case ZPOOL_PROP_DEDUPDITTO:
                        if (spa_version(spa) < SPA_VERSION_DEDUP)
                                error = SET_ERROR(ENOTSUP);
                        else
                                error = nvpair_value_uint64(elem, &intval);
                        if (error == 0 &&
                            intval != 0 && intval < ZIO_DEDUPDITTO_MIN)
                                error = SET_ERROR(EINVAL);
                        break;

                default:
                        break;
                }

                if (error)
                        break;
        }

        if (!error && reset_bootfs) {
                error = nvlist_remove(props,
                    zpool_prop_to_name(ZPOOL_PROP_BOOTFS), DATA_TYPE_STRING);

                if (!error) {
                        error = nvlist_add_uint64(props,
                            zpool_prop_to_name(ZPOOL_PROP_BOOTFS), objnum);
                }
        }

        return (error);
}

void
spa_configfile_set(spa_t *spa, nvlist_t *nvp, boolean_t need_sync)
{
        char *cachefile;
        spa_config_dirent_t *dp;

        if (nvlist_lookup_string(nvp, zpool_prop_to_name(ZPOOL_PROP_CACHEFILE),
            &cachefile) != 0)
                return;

        dp = kmem_alloc(sizeof (spa_config_dirent_t),
            KM_SLEEP);

        if (cachefile[0] == '\0')
                dp->scd_path = spa_strdup(spa_config_path);
        else if (strcmp(cachefile, "none") == 0)
                dp->scd_path = NULL;
        else
                dp->scd_path = spa_strdup(cachefile);

        list_insert_head(&spa->spa_config_list, dp);
        if (need_sync)
                spa_async_request(spa, SPA_ASYNC_CONFIG_UPDATE);
}

int
spa_prop_set(spa_t *spa, nvlist_t *nvp)
{
        int error;
        nvpair_t *elem = NULL;
        boolean_t need_sync = B_FALSE;

        if ((error = spa_prop_validate(spa, nvp)) != 0)
                return (error);

        while ((elem = nvlist_next_nvpair(nvp, elem)) != NULL) {
                zpool_prop_t prop = zpool_name_to_prop(nvpair_name(elem));

                if (prop == ZPOOL_PROP_CACHEFILE ||
                    prop == ZPOOL_PROP_ALTROOT ||
                    prop == ZPOOL_PROP_READONLY)
                        continue;

                if (prop == ZPOOL_PROP_VERSION || prop == ZPOOL_PROP_INVAL) {
                        uint64_t ver;

                        if (prop == ZPOOL_PROP_VERSION) {
                                VERIFY(nvpair_value_uint64(elem, &ver) == 0);
                        } else {
                                ASSERT(zpool_prop_feature(nvpair_name(elem)));
                                ver = SPA_VERSION_FEATURES;
                                need_sync = B_TRUE;
                        }

                        /* Save time if the version is already set. */
                        if (ver == spa_version(spa))
                                continue;

                        /*
                         * In addition to the pool directory object, we might
                         * create the pool properties object, the features for
                         * read object, the features for write object, or the
                         * feature descriptions object.
                         */
                        error = dsl_sync_task(spa->spa_name, NULL,
                            spa_sync_version, &ver,
                            6, ZFS_SPACE_CHECK_RESERVED);
                        if (error)
                                return (error);
                        continue;
                }

                need_sync = B_TRUE;
                break;
        }

        if (need_sync) {
                return (dsl_sync_task(spa->spa_name, NULL, spa_sync_props,
                    nvp, 6, ZFS_SPACE_CHECK_RESERVED));
        }

        return (0);
}

/*
 * If the bootfs property value is dsobj, clear it.
 */
void
spa_prop_clear_bootfs(spa_t *spa, uint64_t dsobj, dmu_tx_t *tx)
{
        if (spa->spa_bootfs == dsobj && spa->spa_pool_props_object != 0) {
                VERIFY(zap_remove(spa->spa_meta_objset,
                    spa->spa_pool_props_object,
                    zpool_prop_to_name(ZPOOL_PROP_BOOTFS), tx) == 0);
                spa->spa_bootfs = 0;
        }
}

/*ARGSUSED*/
static int
spa_change_guid_check(void *arg, dmu_tx_t *tx)
{
        ASSERTV(uint64_t *newguid = arg);
        spa_t *spa = dmu_tx_pool(tx)->dp_spa;
        vdev_t *rvd = spa->spa_root_vdev;
        uint64_t vdev_state;

        spa_config_enter(spa, SCL_STATE, FTAG, RW_READER);
        vdev_state = rvd->vdev_state;
        spa_config_exit(spa, SCL_STATE, FTAG);

        if (vdev_state != VDEV_STATE_HEALTHY)
                return (SET_ERROR(ENXIO));

        ASSERT3U(spa_guid(spa), !=, *newguid);

        return (0);
}

static void
spa_change_guid_sync(void *arg, dmu_tx_t *tx)
{
        uint64_t *newguid = arg;
        spa_t *spa = dmu_tx_pool(tx)->dp_spa;
        uint64_t oldguid;
        vdev_t *rvd = spa->spa_root_vdev;

        oldguid = spa_guid(spa);

        spa_config_enter(spa, SCL_STATE, FTAG, RW_READER);
        rvd->vdev_guid = *newguid;
        rvd->vdev_guid_sum += (*newguid - oldguid);
        vdev_config_dirty(rvd);
        spa_config_exit(spa, SCL_STATE, FTAG);

        spa_history_log_internal(spa, "guid change", tx, "old=%llu new=%llu",
            oldguid, *newguid);
}

/*
 * Change the GUID for the pool.  This is done so that we can later
 * re-import a pool built from a clone of our own vdevs.  We will modify
 * the root vdev's guid, our own pool guid, and then mark all of our
 * vdevs dirty.  Note that we must make sure that all our vdevs are
 * online when we do this, or else any vdevs that weren't present
 * would be orphaned from our pool.  We are also going to issue a
 * sysevent to update any watchers.
 */
int
spa_change_guid(spa_t *spa)
{
        int error;
        uint64_t guid;

        mutex_enter(&spa->spa_vdev_top_lock);
        mutex_enter(&spa_namespace_lock);
        guid = spa_generate_guid(NULL);

        error = dsl_sync_task(spa->spa_name, spa_change_guid_check,
            spa_change_guid_sync, &guid, 5, ZFS_SPACE_CHECK_RESERVED);

        if (error == 0) {
                spa_config_sync(spa, B_FALSE, B_TRUE);
                spa_event_notify(spa, NULL, NULL, ESC_ZFS_POOL_REGUID);
        }

        mutex_exit(&spa_namespace_lock);
        mutex_exit(&spa->spa_vdev_top_lock);

        return (error);
}

/*
 * ==========================================================================
 * SPA state manipulation (open/create/destroy/import/export)
 * ==========================================================================
 */

static int
spa_error_entry_compare(const void *a, const void *b)
{
        const spa_error_entry_t *sa = (const spa_error_entry_t *)a;
        const spa_error_entry_t *sb = (const spa_error_entry_t *)b;
        int ret;

        ret = memcmp(&sa->se_bookmark, &sb->se_bookmark,
            sizeof (zbookmark_phys_t));

        return (AVL_ISIGN(ret));
}

/*
 * Utility function which retrieves copies of the current logs and
 * re-initializes them in the process.
 */
void
spa_get_errlists(spa_t *spa, avl_tree_t *last, avl_tree_t *scrub)
{
        ASSERT(MUTEX_HELD(&spa->spa_errlist_lock));

        bcopy(&spa->spa_errlist_last, last, sizeof (avl_tree_t));
        bcopy(&spa->spa_errlist_scrub, scrub, sizeof (avl_tree_t));

        avl_create(&spa->spa_errlist_scrub,
            spa_error_entry_compare, sizeof (spa_error_entry_t),
            offsetof(spa_error_entry_t, se_avl));
        avl_create(&spa->spa_errlist_last,
            spa_error_entry_compare, sizeof (spa_error_entry_t),
            offsetof(spa_error_entry_t, se_avl));
}

static void
spa_taskqs_init(spa_t *spa, zio_type_t t, zio_taskq_type_t q)
{
        const zio_taskq_info_t *ztip = &zio_taskqs[t][q];
        enum zti_modes mode = ztip->zti_mode;
        uint_t value = ztip->zti_value;
        uint_t count = ztip->zti_count;
        spa_taskqs_t *tqs = &spa->spa_zio_taskq[t][q];
        char name[32];
        uint_t flags = 0;
        boolean_t batch = B_FALSE;

        if (mode == ZTI_MODE_NULL) {
                tqs->stqs_count = 0;
                tqs->stqs_taskq = NULL;
                return;
        }

        ASSERT3U(count, >, 0);

        tqs->stqs_count = count;
        tqs->stqs_taskq = kmem_alloc(count * sizeof (taskq_t *), KM_SLEEP);

        switch (mode) {
        case ZTI_MODE_FIXED:
                ASSERT3U(value, >=, 1);
                value = MAX(value, 1);
                flags |= TASKQ_DYNAMIC;
                break;

        case ZTI_MODE_BATCH:
                batch = B_TRUE;
                flags |= TASKQ_THREADS_CPU_PCT;
                value = MIN(zio_taskq_batch_pct, 100);
                break;

        default:
                panic("unrecognized mode for %s_%s taskq (%u:%u) in "
                    "spa_activate()",
                    zio_type_name[t], zio_taskq_types[q], mode, value);
                break;
        }

        for (uint_t i = 0; i < count; i++) {
                taskq_t *tq;

                if (count > 1) {
                        (void) snprintf(name, sizeof (name), "%s_%s_%u",
                            zio_type_name[t], zio_taskq_types[q], i);
                } else {
                        (void) snprintf(name, sizeof (name), "%s_%s",
                            zio_type_name[t], zio_taskq_types[q]);
                }

                if (zio_taskq_sysdc && spa->spa_proc != &p0) {
                        if (batch)
                                flags |= TASKQ_DC_BATCH;

                        tq = taskq_create_sysdc(name, value, 50, INT_MAX,
                            spa->spa_proc, zio_taskq_basedc, flags);
                } else {
                        pri_t pri = maxclsyspri;
                        /*
                         * The write issue taskq can be extremely CPU
                         * intensive.  Run it at slightly less important
                         * priority than the other taskqs.  Under Linux this
                         * means incrementing the priority value on platforms
                         * like illumos it should be decremented.
                         */
                        if (t == ZIO_TYPE_WRITE && q == ZIO_TASKQ_ISSUE)
                                pri++;

                        tq = taskq_create_proc(name, value, pri, 50,
                            INT_MAX, spa->spa_proc, flags);
                }

                tqs->stqs_taskq[i] = tq;
        }
}

static void
spa_taskqs_fini(spa_t *spa, zio_type_t t, zio_taskq_type_t q)
{
        spa_taskqs_t *tqs = &spa->spa_zio_taskq[t][q];

        if (tqs->stqs_taskq == NULL) {
                ASSERT3U(tqs->stqs_count, ==, 0);
                return;
        }

        for (uint_t i = 0; i < tqs->stqs_count; i++) {
                ASSERT3P(tqs->stqs_taskq[i], !=, NULL);
                taskq_destroy(tqs->stqs_taskq[i]);
        }

        kmem_free(tqs->stqs_taskq, tqs->stqs_count * sizeof (taskq_t *));
        tqs->stqs_taskq = NULL;
}

/*
 * Dispatch a task to the appropriate taskq for the ZFS I/O type and priority.
 * Note that a type may have multiple discrete taskqs to avoid lock contention
 * on the taskq itself. In that case we choose which taskq at random by using
 * the low bits of gethrtime().
 */
void
spa_taskq_dispatch_ent(spa_t *spa, zio_type_t t, zio_taskq_type_t q,
    task_func_t *func, void *arg, uint_t flags, taskq_ent_t *ent)
{
        spa_taskqs_t *tqs = &spa->spa_zio_taskq[t][q];
        taskq_t *tq;

        ASSERT3P(tqs->stqs_taskq, !=, NULL);
        ASSERT3U(tqs->stqs_count, !=, 0);

        if (tqs->stqs_count == 1) {
                tq = tqs->stqs_taskq[0];
        } else {
                tq = tqs->stqs_taskq[((uint64_t)gethrtime()) % tqs->stqs_count];
        }

        taskq_dispatch_ent(tq, func, arg, flags, ent);
}

/*
 * Same as spa_taskq_dispatch_ent() but block on the task until completion.
 */
void
spa_taskq_dispatch_sync(spa_t *spa, zio_type_t t, zio_taskq_type_t q,
    task_func_t *func, void *arg, uint_t flags)
{
        spa_taskqs_t *tqs = &spa->spa_zio_taskq[t][q];
        taskq_t *tq;
        taskqid_t id;

        ASSERT3P(tqs->stqs_taskq, !=, NULL);
        ASSERT3U(tqs->stqs_count, !=, 0);

        if (tqs->stqs_count == 1) {
                tq = tqs->stqs_taskq[0];
        } else {
                tq = tqs->stqs_taskq[((uint64_t)gethrtime()) % tqs->stqs_count];
        }

        id = taskq_dispatch(tq, func, arg, flags);
        if (id)
                taskq_wait_id(tq, id);
}

static void
spa_create_zio_taskqs(spa_t *spa)
{
        for (int t = 0; t < ZIO_TYPES; t++) {
                for (int q = 0; q < ZIO_TASKQ_TYPES; q++) {
                        spa_taskqs_init(spa, t, q);
                }
        }
}

/*
 * Disabled until spa_thread() can be adapted for Linux.
 */
#undef HAVE_SPA_THREAD

#if defined(_KERNEL) && defined(HAVE_SPA_THREAD)
static void
spa_thread(void *arg)
{
        callb_cpr_t cprinfo;

        spa_t *spa = arg;
        user_t *pu = PTOU(curproc);

        CALLB_CPR_INIT(&cprinfo, &spa->spa_proc_lock, callb_generic_cpr,
            spa->spa_name);

        ASSERT(curproc != &p0);
        (void) snprintf(pu->u_psargs, sizeof (pu->u_psargs),
            "zpool-%s", spa->spa_name);
        (void) strlcpy(pu->u_comm, pu->u_psargs, sizeof (pu->u_comm));

        /* bind this thread to the requested psrset */
        if (zio_taskq_psrset_bind != PS_NONE) {
                pool_lock();
                mutex_enter(&cpu_lock);
                mutex_enter(&pidlock);
                mutex_enter(&curproc->p_lock);

                if (cpupart_bind_thread(curthread, zio_taskq_psrset_bind,
                    0, NULL, NULL) == 0)  {
                        curthread->t_bind_pset = zio_taskq_psrset_bind;
                } else {
                        cmn_err(CE_WARN,
                            "Couldn't bind process for zfs pool \"%s\" to "
                            "pset %d\n", spa->spa_name, zio_taskq_psrset_bind);
                }

                mutex_exit(&curproc->p_lock);
                mutex_exit(&pidlock);
                mutex_exit(&cpu_lock);
                pool_unlock();
        }

        if (zio_taskq_sysdc) {
                sysdc_thread_enter(curthread, 100, 0);
        }

        spa->spa_proc = curproc;
        spa->spa_did = curthread->t_did;

        spa_create_zio_taskqs(spa);

        mutex_enter(&spa->spa_proc_lock);
        ASSERT(spa->spa_proc_state == SPA_PROC_CREATED);

        spa->spa_proc_state = SPA_PROC_ACTIVE;
        cv_broadcast(&spa->spa_proc_cv);

        CALLB_CPR_SAFE_BEGIN(&cprinfo);
        while (spa->spa_proc_state == SPA_PROC_ACTIVE)
                cv_wait(&spa->spa_proc_cv, &spa->spa_proc_lock);
        CALLB_CPR_SAFE_END(&cprinfo, &spa->spa_proc_lock);

        ASSERT(spa->spa_proc_state == SPA_PROC_DEACTIVATE);
        spa->spa_proc_state = SPA_PROC_GONE;
        spa->spa_proc = &p0;
        cv_broadcast(&spa->spa_proc_cv);
        CALLB_CPR_EXIT(&cprinfo);       /* drops spa_proc_lock */

        mutex_enter(&curproc->p_lock);
        lwp_exit();
}
#endif

/*
 * Activate an uninitialized pool.
 */
static void
spa_activate(spa_t *spa, int mode)
{
        ASSERT(spa->spa_state == POOL_STATE_UNINITIALIZED);

        spa->spa_state = POOL_STATE_ACTIVE;
        spa->spa_mode = mode;

        spa->spa_normal_class = metaslab_class_create(spa, zfs_metaslab_ops);
        spa->spa_log_class = metaslab_class_create(spa, zfs_metaslab_ops);

        /* Try to create a covering process */
        mutex_enter(&spa->spa_proc_lock);
        ASSERT(spa->spa_proc_state == SPA_PROC_NONE);
        ASSERT(spa->spa_proc == &p0);
        spa->spa_did = 0;

#ifdef HAVE_SPA_THREAD
        /* Only create a process if we're going to be around a while. */
        if (spa_create_process && strcmp(spa->spa_name, TRYIMPORT_NAME) != 0) {
                if (newproc(spa_thread, (caddr_t)spa, syscid, maxclsyspri,
                    NULL, 0) == 0) {
                        spa->spa_proc_state = SPA_PROC_CREATED;
                        while (spa->spa_proc_state == SPA_PROC_CREATED) {
                                cv_wait(&spa->spa_proc_cv,
                                    &spa->spa_proc_lock);
                        }
                        ASSERT(spa->spa_proc_state == SPA_PROC_ACTIVE);
                        ASSERT(spa->spa_proc != &p0);
                        ASSERT(spa->spa_did != 0);
                } else {
#ifdef _KERNEL
                        cmn_err(CE_WARN,
                            "Couldn't create process for zfs pool \"%s\"\n",
                            spa->spa_name);
#endif
                }
        }
#endif /* HAVE_SPA_THREAD */
        mutex_exit(&spa->spa_proc_lock);

        /* If we didn't create a process, we need to create our taskqs. */
        if (spa->spa_proc == &p0) {
                spa_create_zio_taskqs(spa);
        }

        list_create(&spa->spa_config_dirty_list, sizeof (vdev_t),
            offsetof(vdev_t, vdev_config_dirty_node));
        list_create(&spa->spa_evicting_os_list, sizeof (objset_t),
            offsetof(objset_t, os_evicting_node));
        list_create(&spa->spa_state_dirty_list, sizeof (vdev_t),
            offsetof(vdev_t, vdev_state_dirty_node));

        txg_list_create(&spa->spa_vdev_txg_list, spa,
            offsetof(struct vdev, vdev_txg_node));

        avl_create(&spa->spa_errlist_scrub,
            spa_error_entry_compare, sizeof (spa_error_entry_t),
            offsetof(spa_error_entry_t, se_avl));
        avl_create(&spa->spa_errlist_last,
            spa_error_entry_compare, sizeof (spa_error_entry_t),
            offsetof(spa_error_entry_t, se_avl));

        spa_keystore_init(&spa->spa_keystore);

        /*
         * This taskq is used to perform zvol-minor-related tasks
         * asynchronously. This has several advantages, including easy
         * resolution of various deadlocks (zfsonlinux bug #3681).
         *
         * The taskq must be single threaded to ensure tasks are always
         * processed in the order in which they were dispatched.
         *
         * A taskq per pool allows one to keep the pools independent.
         * This way if one pool is suspended, it will not impact another.
         *
         * The preferred location to dispatch a zvol minor task is a sync
         * task. In this context, there is easy access to the spa_t and minimal
         * error handling is required because the sync task must succeed.
         */
        spa->spa_zvol_taskq = taskq_create("z_zvol", 1, defclsyspri,
            1, INT_MAX, 0);

        /*
         * The taskq to upgrade datasets in this pool. Currently used by
         * feature SPA_FEATURE_USEROBJ_ACCOUNTING/SPA_FEATURE_PROJECT_QUOTA.
         */
        spa->spa_upgrade_taskq = taskq_create("z_upgrade", boot_ncpus,
            defclsyspri, 1, INT_MAX, TASKQ_DYNAMIC);
}

/*
 * Opposite of spa_activate().
 */
static void
spa_deactivate(spa_t *spa)
{
        ASSERT(spa->spa_sync_on == B_FALSE);
        ASSERT(spa->spa_dsl_pool == NULL);
        ASSERT(spa->spa_root_vdev == NULL);
        ASSERT(spa->spa_async_zio_root == NULL);
        ASSERT(spa->spa_state != POOL_STATE_UNINITIALIZED);

        spa_evicting_os_wait(spa);

        if (spa->spa_zvol_taskq) {
                taskq_destroy(spa->spa_zvol_taskq);
                spa->spa_zvol_taskq = NULL;
        }

        if (spa->spa_upgrade_taskq) {
                taskq_destroy(spa->spa_upgrade_taskq);
                spa->spa_upgrade_taskq = NULL;
        }

        txg_list_destroy(&spa->spa_vdev_txg_list);

        list_destroy(&spa->spa_config_dirty_list);
        list_destroy(&spa->spa_evicting_os_list);
        list_destroy(&spa->spa_state_dirty_list);

        taskq_cancel_id(system_delay_taskq, spa->spa_deadman_tqid);

        for (int t = 0; t < ZIO_TYPES; t++) {
                for (int q = 0; q < ZIO_TASKQ_TYPES; q++) {
                        spa_taskqs_fini(spa, t, q);
                }
        }

        metaslab_class_destroy(spa->spa_normal_class);
        spa->spa_normal_class = NULL;

        metaslab_class_destroy(spa->spa_log_class);
        spa->spa_log_class = NULL;

        /*
         * If this was part of an import or the open otherwise failed, we may
         * still have errors left in the queues.  Empty them just in case.
         */
        spa_errlog_drain(spa);
        avl_destroy(&spa->spa_errlist_scrub);
        avl_destroy(&spa->spa_errlist_last);

        spa_keystore_fini(&spa->spa_keystore);

        spa->spa_state = POOL_STATE_UNINITIALIZED;

        mutex_enter(&spa->spa_proc_lock);
        if (spa->spa_proc_state != SPA_PROC_NONE) {
                ASSERT(spa->spa_proc_state == SPA_PROC_ACTIVE);
                spa->spa_proc_state = SPA_PROC_DEACTIVATE;
                cv_broadcast(&spa->spa_proc_cv);
                while (spa->spa_proc_state == SPA_PROC_DEACTIVATE) {
                        ASSERT(spa->spa_proc != &p0);
                        cv_wait(&spa->spa_proc_cv, &spa->spa_proc_lock);
                }
                ASSERT(spa->spa_proc_state == SPA_PROC_GONE);
                spa->spa_proc_state = SPA_PROC_NONE;
        }
        ASSERT(spa->spa_proc == &p0);
        mutex_exit(&spa->spa_proc_lock);

        /*
         * We want to make sure spa_thread() has actually exited the ZFS
         * module, so that the module can't be unloaded out from underneath
         * it.
         */
        if (spa->spa_did != 0) {
                thread_join(spa->spa_did);
                spa->spa_did = 0;
        }
}

/*
 * Verify a pool configuration, and construct the vdev tree appropriately.  This
 * will create all the necessary vdevs in the appropriate layout, with each vdev
 * in the CLOSED state.  This will prep the pool before open/creation/import.
 * All vdev validation is done by the vdev_alloc() routine.
 */
static int
spa_config_parse(spa_t *spa, vdev_t **vdp, nvlist_t *nv, vdev_t *parent,
    uint_t id, int atype)
{
        nvlist_t **child;
        uint_t children;
        int error;

        if ((error = vdev_alloc(spa, vdp, nv, parent, id, atype)) != 0)
                return (error);

        if ((*vdp)->vdev_ops->vdev_op_leaf)
                return (0);

        error = nvlist_lookup_nvlist_array(nv, ZPOOL_CONFIG_CHILDREN,
            &child, &children);

        if (error == ENOENT)
                return (0);

        if (error) {
                vdev_free(*vdp);
                *vdp = NULL;
                return (SET_ERROR(EINVAL));
        }

        for (int c = 0; c < children; c++) {
                vdev_t *vd;
                if ((error = spa_config_parse(spa, &vd, child[c], *vdp, c,
                    atype)) != 0) {
                        vdev_free(*vdp);
                        *vdp = NULL;
                        return (error);
                }
        }

        ASSERT(*vdp != NULL);

        return (0);
}

/*
 * Opposite of spa_load().
 */
static void
spa_unload(spa_t *spa)
{
        int i;

        ASSERT(MUTEX_HELD(&spa_namespace_lock));

        /*
         * Stop async tasks.
         */
        spa_async_suspend(spa);

        /*
         * Stop syncing.
         */
        if (spa->spa_sync_on) {
                txg_sync_stop(spa->spa_dsl_pool);
                spa->spa_sync_on = B_FALSE;
        }

        /*
         * Even though vdev_free() also calls vdev_metaslab_fini, we need
         * to call it earlier, before we wait for async i/o to complete.
         * This ensures that there is no async metaslab prefetching, by
         * calling taskq_wait(mg_taskq).
         */
        if (spa->spa_root_vdev != NULL) {
                spa_config_enter(spa, SCL_ALL, FTAG, RW_WRITER);
                for (int c = 0; c < spa->spa_root_vdev->vdev_children; c++)
                        vdev_metaslab_fini(spa->spa_root_vdev->vdev_child[c]);
                spa_config_exit(spa, SCL_ALL, FTAG);
        }

        if (spa->spa_mmp.mmp_thread)
                mmp_thread_stop(spa);

        /*
         * Wait for any outstanding async I/O to complete.
         */
        if (spa->spa_async_zio_root != NULL) {
                for (int i = 0; i < max_ncpus; i++)
                        (void) zio_wait(spa->spa_async_zio_root[i]);
                kmem_free(spa->spa_async_zio_root, max_ncpus * sizeof (void *));
                spa->spa_async_zio_root = NULL;
        }

        bpobj_close(&spa->spa_deferred_bpobj);

        spa_config_enter(spa, SCL_ALL, FTAG, RW_WRITER);

        /*
         * Close all vdevs.
         */
        if (spa->spa_root_vdev)
                vdev_free(spa->spa_root_vdev);
        ASSERT(spa->spa_root_vdev == NULL);

        /*
         * Close the dsl pool.
         */
        if (spa->spa_dsl_pool) {
                dsl_pool_close(spa->spa_dsl_pool);
                spa->spa_dsl_pool = NULL;
                spa->spa_meta_objset = NULL;
        }

        ddt_unload(spa);

        /*
         * Drop and purge level 2 cache
         */
        spa_l2cache_drop(spa);

        for (i = 0; i < spa->spa_spares.sav_count; i++)
                vdev_free(spa->spa_spares.sav_vdevs[i]);
        if (spa->spa_spares.sav_vdevs) {
                kmem_free(spa->spa_spares.sav_vdevs,
                    spa->spa_spares.sav_count * sizeof (void *));
                spa->spa_spares.sav_vdevs = NULL;
        }
        if (spa->spa_spares.sav_config) {
                nvlist_free(spa->spa_spares.sav_config);
                spa->spa_spares.sav_config = NULL;
        }
        spa->spa_spares.sav_count = 0;

        for (i = 0; i < spa->spa_l2cache.sav_count; i++) {
                vdev_clear_stats(spa->spa_l2cache.sav_vdevs[i]);
                vdev_free(spa->spa_l2cache.sav_vdevs[i]);
        }
        if (spa->spa_l2cache.sav_vdevs) {
                kmem_free(spa->spa_l2cache.sav_vdevs,
                    spa->spa_l2cache.sav_count * sizeof (void *));
                spa->spa_l2cache.sav_vdevs = NULL;
        }
        if (spa->spa_l2cache.sav_config) {
                nvlist_free(spa->spa_l2cache.sav_config);
                spa->spa_l2cache.sav_config = NULL;
        }
        spa->spa_l2cache.sav_count = 0;

        spa->spa_async_suspended = 0;

        if (spa->spa_comment != NULL) {
                spa_strfree(spa->spa_comment);
                spa->spa_comment = NULL;
        }

        spa_config_exit(spa, SCL_ALL, FTAG);
}

/*
 * Load (or re-load) the current list of vdevs describing the active spares for
 * this pool.  When this is called, we have some form of basic information in
 * 'spa_spares.sav_config'.  We parse this into vdevs, try to open them, and
 * then re-generate a more complete list including status information.
 */
static void
spa_load_spares(spa_t *spa)
{
        nvlist_t **spares;
        uint_t nspares;
        int i;
        vdev_t *vd, *tvd;

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

        /*
         * First, close and free any existing spare vdevs.
         */
        for (i = 0; i < spa->spa_spares.sav_count; i++) {
                vd = spa->spa_spares.sav_vdevs[i];

                /* Undo the call to spa_activate() below */
                if ((tvd = spa_lookup_by_guid(spa, vd->vdev_guid,
                    B_FALSE)) != NULL && tvd->vdev_isspare)
                        spa_spare_remove(tvd);
                vdev_close(vd);
                vdev_free(vd);
        }

        if (spa->spa_spares.sav_vdevs)
                kmem_free(spa->spa_spares.sav_vdevs,
                    spa->spa_spares.sav_count * sizeof (void *));

        if (spa->spa_spares.sav_config == NULL)
                nspares = 0;
        else
                VERIFY(nvlist_lookup_nvlist_array(spa->spa_spares.sav_config,
                    ZPOOL_CONFIG_SPARES, &spares, &nspares) == 0);

        spa->spa_spares.sav_count = (int)nspares;
        spa->spa_spares.sav_vdevs = NULL;

        if (nspares == 0)
                return;

        /*
         * Construct the array of vdevs, opening them to get status in the
         * process.   For each spare, there is potentially two different vdev_t
         * structures associated with it: one in the list of spares (used only
         * for basic validation purposes) and one in the active vdev
         * configuration (if it's spared in).  During this phase we open and
         * validate each vdev on the spare list.  If the vdev also exists in the
         * active configuration, then we also mark this vdev as an active spare.
         */
        spa->spa_spares.sav_vdevs = kmem_zalloc(nspares * sizeof (void *),
            KM_SLEEP);
        for (i = 0; i < spa->spa_spares.sav_count; i++) {
                VERIFY(spa_config_parse(spa, &vd, spares[i], NULL, 0,
                    VDEV_ALLOC_SPARE) == 0);
                ASSERT(vd != NULL);

                spa->spa_spares.sav_vdevs[i] = vd;

                if ((tvd = spa_lookup_by_guid(spa, vd->vdev_guid,
                    B_FALSE)) != NULL) {
                        if (!tvd->vdev_isspare)
                                spa_spare_add(tvd);

                        /*
                         * We only mark the spare active if we were successfully
                         * able to load the vdev.  Otherwise, importing a pool
                         * with a bad active spare would result in strange
                         * behavior, because multiple pool would think the spare
                         * is actively in use.
                         *
                         * There is a vulnerability here to an equally bizarre
                         * circumstance, where a dead active spare is later
                         * brought back to life (onlined or otherwise).  Given
                         * the rarity of this scenario, and the extra complexity
                         * it adds, we ignore the possibility.
                         */
                        if (!vdev_is_dead(tvd))
                                spa_spare_activate(tvd);
                }

                vd->vdev_top = vd;
                vd->vdev_aux = &spa->spa_spares;

                if (vdev_open(vd) != 0)
                        continue;

                if (vdev_validate_aux(vd) == 0)
                        spa_spare_add(vd);
        }

        /*
         * Recompute the stashed list of spares, with status information
         * this time.
         */
        VERIFY(nvlist_remove(spa->spa_spares.sav_config, ZPOOL_CONFIG_SPARES,
            DATA_TYPE_NVLIST_ARRAY) == 0);

        spares = kmem_alloc(spa->spa_spares.sav_count * sizeof (void *),
            KM_SLEEP);
        for (i = 0; i < spa->spa_spares.sav_count; i++)
                spares[i] = vdev_config_generate(spa,
                    spa->spa_spares.sav_vdevs[i], B_TRUE, VDEV_CONFIG_SPARE);
        VERIFY(nvlist_add_nvlist_array(spa->spa_spares.sav_config,
            ZPOOL_CONFIG_SPARES, spares, spa->spa_spares.sav_count) == 0);
        for (i = 0; i < spa->spa_spares.sav_count; i++)
                nvlist_free(spares[i]);
        kmem_free(spares, spa->spa_spares.sav_count * sizeof (void *));
}

/*
 * Load (or re-load) the current list of vdevs describing the active l2cache for
 * this pool.  When this is called, we have some form of basic information in
 * 'spa_l2cache.sav_config'.  We parse this into vdevs, try to open them, and
 * then re-generate a more complete list including status information.
 * Devices which are already active have their details maintained, and are
 * not re-opened.
 */
static void
spa_load_l2cache(spa_t *spa)
{
        nvlist_t **l2cache = NULL;
        uint_t nl2cache;
        int i, j, oldnvdevs;
        uint64_t guid;
        vdev_t *vd, **oldvdevs, **newvdevs;
        spa_aux_vdev_t *sav = &spa->spa_l2cache;

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

        oldvdevs = sav->sav_vdevs;
        oldnvdevs = sav->sav_count;
        sav->sav_vdevs = NULL;
        sav->sav_count = 0;

        if (sav->sav_config == NULL) {
                nl2cache = 0;
                newvdevs = NULL;
                goto out;
        }

        VERIFY(nvlist_lookup_nvlist_array(sav->sav_config,
            ZPOOL_CONFIG_L2CACHE, &l2cache, &nl2cache) == 0);
        newvdevs = kmem_alloc(nl2cache * sizeof (void *), KM_SLEEP);

        /*
         * Process new nvlist of vdevs.
         */
        for (i = 0; i < nl2cache; i++) {
                VERIFY(nvlist_lookup_uint64(l2cache[i], ZPOOL_CONFIG_GUID,
                    &guid) == 0);

                newvdevs[i] = NULL;
                for (j = 0; j < oldnvdevs; j++) {
                        vd = oldvdevs[j];
                        if (vd != NULL && guid == vd->vdev_guid) {
                                /*
                                 * Retain previous vdev for add/remove ops.
                                 */
                                newvdevs[i] = vd;
                                oldvdevs[j] = NULL;
                                break;
                        }
                }

                if (newvdevs[i] == NULL) {
                        /*
                         * Create new vdev
                         */
                        VERIFY(spa_config_parse(spa, &vd, l2cache[i], NULL, 0,
                            VDEV_ALLOC_L2CACHE) == 0);
                        ASSERT(vd != NULL);
                        newvdevs[i] = vd;

                        /*
                         * Commit this vdev as an l2cache device,
                         * even if it fails to open.
                         */
                        spa_l2cache_add(vd);

                        vd->vdev_top = vd;
                        vd->vdev_aux = sav;

                        spa_l2cache_activate(vd);

                        if (vdev_open(vd) != 0)
                                continue;

                        (void) vdev_validate_aux(vd);

                        if (!vdev_is_dead(vd))
                                l2arc_add_vdev(spa, vd);
                }
        }

        sav->sav_vdevs = newvdevs;
        sav->sav_count = (int)nl2cache;

        /*
         * Recompute the stashed list of l2cache devices, with status
         * information this time.
         */
        VERIFY(nvlist_remove(sav->sav_config, ZPOOL_CONFIG_L2CACHE,
            DATA_TYPE_NVLIST_ARRAY) == 0);

        if (sav->sav_count > 0)
                l2cache = kmem_alloc(sav->sav_count * sizeof (void *),
                    KM_SLEEP);
        for (i = 0; i < sav->sav_count; i++)
                l2cache[i] = vdev_config_generate(spa,
                    sav->sav_vdevs[i], B_TRUE, VDEV_CONFIG_L2CACHE);
        VERIFY(nvlist_add_nvlist_array(sav->sav_config,
            ZPOOL_CONFIG_L2CACHE, l2cache, sav->sav_count) == 0);

out:
        /*
         * Purge vdevs that were dropped
         */
        for (i = 0; i < oldnvdevs; i++) {
                uint64_t pool;

                vd = oldvdevs[i];
                if (vd != NULL) {
                        ASSERT(vd->vdev_isl2cache);

                        if (spa_l2cache_exists(vd->vdev_guid, &pool) &&
                            pool != 0ULL && l2arc_vdev_present(vd))
                                l2arc_remove_vdev(vd);
                        vdev_clear_stats(vd);
                        vdev_free(vd);
                }
        }

        if (oldvdevs)
                kmem_free(oldvdevs, oldnvdevs * sizeof (void *));

        for (i = 0; i < sav->sav_count; i++)
                nvlist_free(l2cache[i]);
        if (sav->sav_count)
                kmem_free(l2cache, sav->sav_count * sizeof (void *));
}

static int
load_nvlist(spa_t *spa, uint64_t obj, nvlist_t **value)
{
        dmu_buf_t *db;
        char *packed = NULL;
        size_t nvsize = 0;
        int error;
        *value = NULL;

        error = dmu_bonus_hold(spa->spa_meta_objset, obj, FTAG, &db);
        if (error)
                return (error);

        nvsize = *(uint64_t *)db->db_data;
        dmu_buf_rele(db, FTAG);

        packed = vmem_alloc(nvsize, KM_SLEEP);
        error = dmu_read(spa->spa_meta_objset, obj, 0, nvsize, packed,
            DMU_READ_PREFETCH);
        if (error == 0)
                error = nvlist_unpack(packed, nvsize, value, 0);
        vmem_free(packed, nvsize);

        return (error);
}

/*
 * Checks to see if the given vdev could not be opened, in which case we post a
 * sysevent to notify the autoreplace code that the device has been removed.
 */
static void
spa_check_removed(vdev_t *vd)
{
        for (int c = 0; c < vd->vdev_children; c++)
                spa_check_removed(vd->vdev_child[c]);

        if (vd->vdev_ops->vdev_op_leaf && vdev_is_dead(vd) &&
            !vd->vdev_ishole) {
                zfs_post_autoreplace(vd->vdev_spa, vd);
                spa_event_notify(vd->vdev_spa, vd, NULL, ESC_ZFS_VDEV_CHECK);
        }
}

static void
spa_config_valid_zaps(vdev_t *vd, vdev_t *mvd)
{
        ASSERT3U(vd->vdev_children, ==, mvd->vdev_children);

        vd->vdev_top_zap = mvd->vdev_top_zap;
        vd->vdev_leaf_zap = mvd->vdev_leaf_zap;

        for (uint64_t i = 0; i < vd->vdev_children; i++) {
                spa_config_valid_zaps(vd->vdev_child[i], mvd->vdev_child[i]);
        }
}

/*
 * Validate the current config against the MOS config
 */
static boolean_t
spa_config_valid(spa_t *spa, nvlist_t *config)
{
        vdev_t *mrvd, *rvd = spa->spa_root_vdev;
        nvlist_t *nv;

        VERIFY(nvlist_lookup_nvlist(config, ZPOOL_CONFIG_VDEV_TREE, &nv) == 0);

        spa_config_enter(spa, SCL_ALL, FTAG, RW_WRITER);
        VERIFY(spa_config_parse(spa, &mrvd, nv, NULL, 0, VDEV_ALLOC_LOAD) == 0);

        ASSERT3U(rvd->vdev_children, ==, mrvd->vdev_children);

        /*
         * If we're doing a normal import, then build up any additional
         * diagnostic information about missing devices in this config.
         * We'll pass this up to the user for further processing.
         */
        if (!(spa->spa_import_flags & ZFS_IMPORT_MISSING_LOG)) {
                nvlist_t **child, *nv;
                uint64_t idx = 0;

                child = kmem_alloc(rvd->vdev_children * sizeof (nvlist_t *),
                    KM_SLEEP);
                VERIFY(nvlist_alloc(&nv, NV_UNIQUE_NAME, KM_SLEEP) == 0);

                for (int c = 0; c < rvd->vdev_children; c++) {
                        vdev_t *tvd = rvd->vdev_child[c];
                        vdev_t *mtvd  = mrvd->vdev_child[c];

                        if (tvd->vdev_ops == &vdev_missing_ops &&
                            mtvd->vdev_ops != &vdev_missing_ops &&
                            mtvd->vdev_islog)
                                child[idx++] = vdev_config_generate(spa, mtvd,
                                    B_FALSE, 0);
                }

                if (idx) {
                        VERIFY(nvlist_add_nvlist_array(nv,
                            ZPOOL_CONFIG_CHILDREN, child, idx) == 0);
                        VERIFY(nvlist_add_nvlist(spa->spa_load_info,
                            ZPOOL_CONFIG_MISSING_DEVICES, nv) == 0);

                        for (int i = 0; i < idx; i++)
                                nvlist_free(child[i]);
                }
                nvlist_free(nv);
                kmem_free(child, rvd->vdev_children * sizeof (char **));
        }

        /*
         * Compare the root vdev tree with the information we have
         * from the MOS config (mrvd). Check each top-level vdev
         * with the corresponding MOS config top-level (mtvd).
         */
        for (int c = 0; c < rvd->vdev_children; c++) {
                vdev_t *tvd = rvd->vdev_child[c];
                vdev_t *mtvd  = mrvd->vdev_child[c];

                /*
                 * Resolve any "missing" vdevs in the current configuration.
                 * If we find that the MOS config has more accurate information
                 * about the top-level vdev then use that vdev instead.
                 */
                if (tvd->vdev_ops == &vdev_missing_ops &&
                    mtvd->vdev_ops != &vdev_missing_ops) {

                        if (!(spa->spa_import_flags & ZFS_IMPORT_MISSING_LOG))
                                continue;

                        /*
                         * Device specific actions.
                         */
                        if (mtvd->vdev_islog) {
                                spa_set_log_state(spa, SPA_LOG_CLEAR);
                        } else {
                                /*
                                 * XXX - once we have 'readonly' pool
                                 * support we should be able to handle
                                 * missing data devices by transitioning
                                 * the pool to readonly.
                                 */
                                continue;
                        }

                        /*
                         * Swap the missing vdev with the data we were
                         * able to obtain from the MOS config.
                         */
                        vdev_remove_child(rvd, tvd);
                        vdev_remove_child(mrvd, mtvd);

                        vdev_add_child(rvd, mtvd);
                        vdev_add_child(mrvd, tvd);

                        spa_config_exit(spa, SCL_ALL, FTAG);
                        vdev_load(mtvd);
                        spa_config_enter(spa, SCL_ALL, FTAG, RW_WRITER);

                        vdev_reopen(rvd);
                } else {
                        if (mtvd->vdev_islog) {
                                /*
                                 * Load the slog device's state from the MOS
                                 * config since it's possible that the label
                                 * does not contain the most up-to-date
                                 * information.
                                 */
                                vdev_load_log_state(tvd, mtvd);
                                vdev_reopen(tvd);
                        }

                        /*
                         * Per-vdev ZAP info is stored exclusively in the MOS.
                         */
                        spa_config_valid_zaps(tvd, mtvd);
                }
        }

        vdev_free(mrvd);
        spa_config_exit(spa, SCL_ALL, FTAG);

        /*
         * Ensure we were able to validate the config.
         */
        return (rvd->vdev_guid_sum == spa->spa_uberblock.ub_guid_sum);
}

/*
 * Check for missing log devices
 */
static boolean_t
spa_check_logs(spa_t *spa)
{
        boolean_t rv = B_FALSE;
        dsl_pool_t *dp = spa_get_dsl(spa);

        switch (spa->spa_log_state) {
        default:
                break;
        case SPA_LOG_MISSING:
                /* need to recheck in case slog has been restored */
        case SPA_LOG_UNKNOWN:
                rv = (dmu_objset_find_dp(dp, dp->dp_root_dir_obj,
                    zil_check_log_chain, NULL, DS_FIND_CHILDREN) != 0);
                if (rv)
                        spa_set_log_state(spa, SPA_LOG_MISSING);
                break;
        }
        return (rv);
}

static boolean_t
spa_passivate_log(spa_t *spa)
{
        vdev_t *rvd = spa->spa_root_vdev;
        boolean_t slog_found = B_FALSE;

        ASSERT(spa_config_held(spa, SCL_ALLOC, RW_WRITER));

        if (!spa_has_slogs(spa))
                return (B_FALSE);

        for (int c = 0; c < rvd->vdev_children; c++) {
                vdev_t *tvd = rvd->vdev_child[c];
                metaslab_group_t *mg = tvd->vdev_mg;

                if (tvd->vdev_islog) {
                        metaslab_group_passivate(mg);
                        slog_found = B_TRUE;
                }
        }

        return (slog_found);
}

static void
spa_activate_log(spa_t *spa)
{
        vdev_t *rvd = spa->spa_root_vdev;

        ASSERT(spa_config_held(spa, SCL_ALLOC, RW_WRITER));

        for (int c = 0; c < rvd->vdev_children; c++) {
                vdev_t *tvd = rvd->vdev_child[c];
                metaslab_group_t *mg = tvd->vdev_mg;

                if (tvd->vdev_islog)
                        metaslab_group_activate(mg);
        }
}

int
spa_offline_log(spa_t *spa)
{
        int error;

        error = dmu_objset_find(spa_name(spa), zil_vdev_offline,
            NULL, DS_FIND_CHILDREN);
        if (error == 0) {
                /*
                 * We successfully offlined the log device, sync out the
                 * current txg so that the "stubby" block can be removed
                 * by zil_sync().
                 */
                txg_wait_synced(spa->spa_dsl_pool, 0);
        }
        return (error);
}

static void
spa_aux_check_removed(spa_aux_vdev_t *sav)
{
        for (int i = 0; i < sav->sav_count; i++)
                spa_check_removed(sav->sav_vdevs[i]);
}

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

        if (zio->io_error)
                return;

        mutex_enter(&spa->spa_props_lock);      /* any mutex will do */
        if (spa->spa_claim_max_txg < zio->io_bp->blk_birth)
                spa->spa_claim_max_txg = zio->io_bp->blk_birth;
        mutex_exit(&spa->spa_props_lock);
}

typedef struct spa_load_error {
        uint64_t        sle_meta_count;
        uint64_t        sle_data_count;
} spa_load_error_t;

static void
spa_load_verify_done(zio_t *zio)
{
        blkptr_t *bp = zio->io_bp;
        spa_load_error_t *sle = zio->io_private;
        dmu_object_type_t type = BP_GET_TYPE(bp);
        int error = zio->io_error;
        spa_t *spa = zio->io_spa;

        abd_free(zio->io_abd);
        if (error) {
                if ((BP_GET_LEVEL(bp) != 0 || DMU_OT_IS_METADATA(type)) &&
                    type != DMU_OT_INTENT_LOG)
                        atomic_inc_64(&sle->sle_meta_count);
                else
                        atomic_inc_64(&sle->sle_data_count);
        }

        mutex_enter(&spa->spa_scrub_lock);
        spa->spa_load_verify_ios--;
        cv_broadcast(&spa->spa_scrub_io_cv);
        mutex_exit(&spa->spa_scrub_lock);
}

/*
 * Maximum number of concurrent scrub i/os to create while verifying
 * a pool while importing it.
 */
int spa_load_verify_maxinflight = 10000;
int spa_load_verify_metadata = B_TRUE;
int spa_load_verify_data = B_TRUE;

/*ARGSUSED*/
static int
spa_load_verify_cb(spa_t *spa, zilog_t *zilog, const blkptr_t *bp,
    const zbookmark_phys_t *zb, const dnode_phys_t *dnp, void *arg)
{
        if (bp == NULL || BP_IS_HOLE(bp) || BP_IS_EMBEDDED(bp))
                return (0);
        /*
         * Note: normally this routine will not be called if
         * spa_load_verify_metadata is not set.  However, it may be useful
         * to manually set the flag after the traversal has begun.
         */
        if (!spa_load_verify_metadata)
                return (0);
        if (!BP_IS_METADATA(bp) && !spa_load_verify_data)
                return (0);

        zio_t *rio = arg;
        size_t size = BP_GET_PSIZE(bp);

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

        zio_nowait(zio_read(rio, spa, bp, abd_alloc_for_io(size, B_FALSE), size,
            spa_load_verify_done, rio->io_private, ZIO_PRIORITY_SCRUB,
            ZIO_FLAG_SPECULATIVE | ZIO_FLAG_CANFAIL |
            ZIO_FLAG_SCRUB | ZIO_FLAG_RAW, zb));
        return (0);
}

/* ARGSUSED */
int
verify_dataset_name_len(dsl_pool_t *dp, dsl_dataset_t *ds, void *arg)
{
        if (dsl_dataset_namelen(ds) >= ZFS_MAX_DATASET_NAME_LEN)
                return (SET_ERROR(ENAMETOOLONG));

        return (0);
}

static int
spa_load_verify(spa_t *spa)
{
        zio_t *rio;
        spa_load_error_t sle = { 0 };
        zpool_rewind_policy_t policy;
        boolean_t verify_ok = B_FALSE;
        int error = 0;

        zpool_get_rewind_policy(spa->spa_config, &policy);

        if (policy.zrp_request & ZPOOL_NEVER_REWIND)
                return (0);

        dsl_pool_config_enter(spa->spa_dsl_pool, FTAG);
        error = dmu_objset_find_dp(spa->spa_dsl_pool,
            spa->spa_dsl_pool->dp_root_dir_obj, verify_dataset_name_len, NULL,
            DS_FIND_CHILDREN);
        dsl_pool_config_exit(spa->spa_dsl_pool, FTAG);
        if (error != 0)
                return (error);

        rio = zio_root(spa, NULL, &sle,
            ZIO_FLAG_CANFAIL | ZIO_FLAG_SPECULATIVE);

        if (spa_load_verify_metadata) {
                error = traverse_pool(spa, spa->spa_verify_min_txg,
                    TRAVERSE_PRE | TRAVERSE_PREFETCH_METADATA |
                    TRAVERSE_NO_DECRYPT, spa_load_verify_cb, rio);
        }

        (void) zio_wait(rio);

        spa->spa_load_meta_errors = sle.sle_meta_count;
        spa->spa_load_data_errors = sle.sle_data_count;

        if (!error && sle.sle_meta_count <= policy.zrp_maxmeta &&
            sle.sle_data_count <= policy.zrp_maxdata) {
                int64_t loss = 0;

                verify_ok = B_TRUE;
                spa->spa_load_txg = spa->spa_uberblock.ub_txg;
                spa->spa_load_txg_ts = spa->spa_uberblock.ub_timestamp;

                loss = spa->spa_last_ubsync_txg_ts - spa->spa_load_txg_ts;
                VERIFY(nvlist_add_uint64(spa->spa_load_info,
                    ZPOOL_CONFIG_LOAD_TIME, spa->spa_load_txg_ts) == 0);
                VERIFY(nvlist_add_int64(spa->spa_load_info,
                    ZPOOL_CONFIG_REWIND_TIME, loss) == 0);
                VERIFY(nvlist_add_uint64(spa->spa_load_info,
                    ZPOOL_CONFIG_LOAD_DATA_ERRORS, sle.sle_data_count) == 0);
        } else {
                spa->spa_load_max_txg = spa->spa_uberblock.ub_txg;
        }

        if (error) {
                if (error != ENXIO && error != EIO)
                        error = SET_ERROR(EIO);
                return (error);
        }

        return (verify_ok ? 0 : EIO);
}

/*
 * Find a value in the pool props object.
 */
static void
spa_prop_find(spa_t *spa, zpool_prop_t prop, uint64_t *val)
{
        (void) zap_lookup(spa->spa_meta_objset, spa->spa_pool_props_object,
            zpool_prop_to_name(prop), sizeof (uint64_t), 1, val);
}

/*
 * Find a value in the pool directory object.
 */
static int
spa_dir_prop(spa_t *spa, const char *name, uint64_t *val)
{
        return (zap_lookup(spa->spa_meta_objset, DMU_POOL_DIRECTORY_OBJECT,
            name, sizeof (uint64_t), 1, val));
}

static int
spa_vdev_err(vdev_t *vdev, vdev_aux_t aux, int err)
{
        vdev_set_state(vdev, B_TRUE, VDEV_STATE_CANT_OPEN, aux);
        return (err);
}

/*
 * Fix up config after a partly-completed split.  This is done with the
 * ZPOOL_CONFIG_SPLIT nvlist.  Both the splitting pool and the split-off
 * pool have that entry in their config, but only the splitting one contains
 * a list of all the guids of the vdevs that are being split off.
 *
 * This function determines what to do with that list: either rejoin
 * all the disks to the pool, or complete the splitting process.  To attempt
 * the rejoin, each disk that is offlined is marked online again, and
 * we do a reopen() call.  If the vdev label for every disk that was
 * marked online indicates it was successfully split off (VDEV_AUX_SPLIT_POOL)
 * then we call vdev_split() on each disk, and complete the split.
 *
 * Otherwise we leave the config alone, with all the vdevs in place in
 * the original pool.
 */
static void
spa_try_repair(spa_t *spa, nvlist_t *config)
{
        uint_t extracted;
        uint64_t *glist;
        uint_t i, gcount;
        nvlist_t *nvl;
        vdev_t **vd;
        boolean_t attempt_reopen;

        if (nvlist_lookup_nvlist(config, ZPOOL_CONFIG_SPLIT, &nvl) != 0)
                return;

        /* check that the config is complete */
        if (nvlist_lookup_uint64_array(nvl, ZPOOL_CONFIG_SPLIT_LIST,
            &glist, &gcount) != 0)
                return;

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

        /* attempt to online all the vdevs & validate */
        attempt_reopen = B_TRUE;
        for (i = 0; i < gcount; i++) {
                if (glist[i] == 0)      /* vdev is hole */
                        continue;

                vd[i] = spa_lookup_by_guid(spa, glist[i], B_FALSE);
                if (vd[i] == NULL) {
                        /*
                         * Don't bother attempting to reopen the disks;
                         * just do the split.
                         */
                        attempt_reopen = B_FALSE;
                } else {
                        /* attempt to re-online it */
                        vd[i]->vdev_offline = B_FALSE;
                }
        }

        if (attempt_reopen) {
                vdev_reopen(spa->spa_root_vdev);

                /* check each device to see what state it's in */
                for (extracted = 0, i = 0; i < gcount; i++) {
                        if (vd[i] != NULL &&
                            vd[i]->vdev_stat.vs_aux != VDEV_AUX_SPLIT_POOL)
                                break;
                        ++extracted;
                }
        }

        /*
         * If every disk has been moved to the new pool, or if we never
         * even attempted to look at them, then we split them off for
         * good.
         */
        if (!attempt_reopen || gcount == extracted) {
                for (i = 0; i < gcount; i++)
                        if (vd[i] != NULL)
                                vdev_split(vd[i]);
                vdev_reopen(spa->spa_root_vdev);
        }

        kmem_free(vd, gcount * sizeof (vdev_t *));
}

static int
spa_load(spa_t *spa, spa_load_state_t state, spa_import_type_t type,
    boolean_t mosconfig)
{
        nvlist_t *config = spa->spa_config;
        char *ereport = FM_EREPORT_ZFS_POOL;
        char *comment;
        int error;
        uint64_t pool_guid;
        nvlist_t *nvl;

        if (nvlist_lookup_uint64(config, ZPOOL_CONFIG_POOL_GUID, &pool_guid))
                return (SET_ERROR(EINVAL));

        ASSERT(spa->spa_comment == NULL);
        if (nvlist_lookup_string(config, ZPOOL_CONFIG_COMMENT, &comment) == 0)
                spa->spa_comment = spa_strdup(comment);

        /*
         * Versioning wasn't explicitly added to the label until later, so if
         * it's not present treat it as the initial version.
         */
        if (nvlist_lookup_uint64(config, ZPOOL_CONFIG_VERSION,
            &spa->spa_ubsync.ub_version) != 0)
                spa->spa_ubsync.ub_version = SPA_VERSION_INITIAL;

        (void) nvlist_lookup_uint64(config, ZPOOL_CONFIG_POOL_TXG,
            &spa->spa_config_txg);

        if ((state == SPA_LOAD_IMPORT || state == SPA_LOAD_TRYIMPORT) &&
            spa_guid_exists(pool_guid, 0)) {
                error = SET_ERROR(EEXIST);
        } else {
                spa->spa_config_guid = pool_guid;

                if (nvlist_lookup_nvlist(config, ZPOOL_CONFIG_SPLIT,
                    &nvl) == 0) {
                        VERIFY(nvlist_dup(nvl, &spa->spa_config_splitting,
                            KM_SLEEP) == 0);
                }

                nvlist_free(spa->spa_load_info);
                spa->spa_load_info = fnvlist_alloc();

                gethrestime(&spa->spa_loaded_ts);
                error = spa_load_impl(spa, pool_guid, config, state, type,
                    mosconfig, &ereport);
        }

        /*
         * Don't count references from objsets that are already closed
         * and are making their way through the eviction process.
         */
        spa_evicting_os_wait(spa);
        spa->spa_minref = refcount_count(&spa->spa_refcount);
        if (error) {
                if (error != EEXIST) {
                        spa->spa_loaded_ts.tv_sec = 0;
                        spa->spa_loaded_ts.tv_nsec = 0;
                }
                if (error != EBADF) {
                        zfs_ereport_post(ereport, spa, NULL, NULL, NULL, 0, 0);
                }
        }
        spa->spa_load_state = error ? SPA_LOAD_ERROR : SPA_LOAD_NONE;
        spa->spa_ena = 0;

        return (error);
}

#ifdef ZFS_DEBUG
/*
 * Count the number of per-vdev ZAPs associated with all of the vdevs in the
 * vdev tree rooted in the given vd, and ensure that each ZAP is present in the
 * spa's per-vdev ZAP list.
 */
static uint64_t
vdev_count_verify_zaps(vdev_t *vd)
{
        spa_t *spa = vd->vdev_spa;
        uint64_t total = 0;

        if (vd->vdev_top_zap != 0) {
                total++;
                ASSERT0(zap_lookup_int(spa->spa_meta_objset,
                    spa->spa_all_vdev_zaps, vd->vdev_top_zap));
        }
        if (vd->vdev_leaf_zap != 0) {
                total++;
                ASSERT0(zap_lookup_int(spa->spa_meta_objset,
                    spa->spa_all_vdev_zaps, vd->vdev_leaf_zap));
        }

        for (uint64_t i = 0; i < vd->vdev_children; i++) {
                total += vdev_count_verify_zaps(vd->vdev_child[i]);
        }

        return (total);
}
#endif

/*
 * Determine whether the activity check is required.
 */
static boolean_t
spa_activity_check_required(spa_t *spa, uberblock_t *ub, nvlist_t *label,
    nvlist_t *config)
{
        uint64_t state = 0;
        uint64_t hostid = 0;
        uint64_t tryconfig_txg = 0;
        uint64_t tryconfig_timestamp = 0;
        nvlist_t *nvinfo;

        if (nvlist_exists(config, ZPOOL_CONFIG_LOAD_INFO)) {
                nvinfo = fnvlist_lookup_nvlist(config, ZPOOL_CONFIG_LOAD_INFO);
                (void) nvlist_lookup_uint64(nvinfo, ZPOOL_CONFIG_MMP_TXG,
                    &tryconfig_txg);
                (void) nvlist_lookup_uint64(config, ZPOOL_CONFIG_TIMESTAMP,
                    &tryconfig_timestamp);
        }

        (void) nvlist_lookup_uint64(config, ZPOOL_CONFIG_POOL_STATE, &state);

        /*
         * Disable the MMP activity check - This is used by zdb which
         * is intended to be used on potentially active pools.
         */
        if (spa->spa_import_flags & ZFS_IMPORT_SKIP_MMP)
                return (B_FALSE);

        /*
         * Skip the activity check when the MMP feature is disabled.
         */
        if (ub->ub_mmp_magic == MMP_MAGIC && ub->ub_mmp_delay == 0)
                return (B_FALSE);
        /*
         * If the tryconfig_* values are nonzero, they are the results of an
         * earlier tryimport.  If they match the uberblock we just found, then
         * the pool has not changed and we return false so we do not test a
         * second time.
         */
        if (tryconfig_txg && tryconfig_txg == ub->ub_txg &&
            tryconfig_timestamp && tryconfig_timestamp == ub->ub_timestamp)
                return (B_FALSE);

        /*
         * Allow the activity check to be skipped when importing the pool
         * on the same host which last imported it.  Since the hostid from
         * configuration may be stale use the one read from the label.
         */
        if (nvlist_exists(label, ZPOOL_CONFIG_HOSTID))
                hostid = fnvlist_lookup_uint64(label, ZPOOL_CONFIG_HOSTID);

        if (hostid == spa_get_hostid())
                return (B_FALSE);

        /*
         * Skip the activity test when the pool was cleanly exported.
         */
        if (state != POOL_STATE_ACTIVE)
                return (B_FALSE);

        return (B_TRUE);
}

/*
 * Perform the import activity check.  If the user canceled the import or
 * we detected activity then fail.
 */
static int
spa_activity_check(spa_t *spa, uberblock_t *ub, nvlist_t *config)
{
        uint64_t import_intervals = MAX(zfs_multihost_import_intervals, 1);
        uint64_t txg = ub->ub_txg;
        uint64_t timestamp = ub->ub_timestamp;
        uint64_t import_delay = NANOSEC;
        hrtime_t import_expire;
        nvlist_t *mmp_label = NULL;
        vdev_t *rvd = spa->spa_root_vdev;
        kcondvar_t cv;
        kmutex_t mtx;
        int error = 0;

        cv_init(&cv, NULL, CV_DEFAULT, NULL);
        mutex_init(&mtx, NULL, MUTEX_DEFAULT, NULL);
        mutex_enter(&mtx);

        /*
         * If ZPOOL_CONFIG_MMP_TXG is present an activity check was performed
         * during the earlier tryimport.  If the txg recorded there is 0 then
         * the pool is known to be active on another host.
         *
         * Otherwise, the pool might be in use on another node.  Check for
         * changes in the uberblocks on disk if necessary.
         */
        if (nvlist_exists(config, ZPOOL_CONFIG_LOAD_INFO)) {
                nvlist_t *nvinfo = fnvlist_lookup_nvlist(config,
                    ZPOOL_CONFIG_LOAD_INFO);

                if (nvlist_exists(nvinfo, ZPOOL_CONFIG_MMP_TXG) &&
                    fnvlist_lookup_uint64(nvinfo, ZPOOL_CONFIG_MMP_TXG) == 0) {
                        vdev_uberblock_load(rvd, ub, &mmp_label);
                        error = SET_ERROR(EREMOTEIO);
                        goto out;
                }
        }

        /*
         * Preferentially use the zfs_multihost_interval from the node which
         * last imported the pool.  This value is stored in an MMP uberblock as.
         *
         * ub_mmp_delay * vdev_count_leaves() == zfs_multihost_interval
         */
        if (ub->ub_mmp_magic == MMP_MAGIC && ub->ub_mmp_delay)
                import_delay = MAX(import_delay, import_intervals *
                    ub->ub_mmp_delay * MAX(vdev_count_leaves(spa), 1));

        /* Apply a floor using the local default values. */
        import_delay = MAX(import_delay, import_intervals *
            MSEC2NSEC(MAX(zfs_multihost_interval, MMP_MIN_INTERVAL)));

        /* Add a small random factor in case of simultaneous imports (0-25%) */
        import_expire = gethrtime() + import_delay +
            (import_delay * spa_get_random(250) / 1000);

        while (gethrtime() < import_expire) {
                vdev_uberblock_load(rvd, ub, &mmp_label);

                if (txg != ub->ub_txg || timestamp != ub->ub_timestamp) {
                        error = SET_ERROR(EREMOTEIO);
                        break;
                }

                if (mmp_label) {
                        nvlist_free(mmp_label);
                        mmp_label = NULL;
                }

                error = cv_timedwait_sig(&cv, &mtx, ddi_get_lbolt() + hz);
                if (error != -1) {
                        error = SET_ERROR(EINTR);
                        break;
                }
                error = 0;
        }

out:
        mutex_exit(&mtx);
        mutex_destroy(&mtx);
        cv_destroy(&cv);

        /*
         * If the pool is determined to be active store the status in the
         * spa->spa_load_info nvlist.  If the remote hostname or hostid are
         * available from configuration read from disk store them as well.
         * This allows 'zpool import' to generate a more useful message.
         *
         * ZPOOL_CONFIG_MMP_STATE    - observed pool status (mandatory)
         * ZPOOL_CONFIG_MMP_HOSTNAME - hostname from the active pool
         * ZPOOL_CONFIG_MMP_HOSTID   - hostid from the active pool
         */
        if (error == EREMOTEIO) {
                char *hostname = "<unknown>";
                uint64_t hostid = 0;

                if (mmp_label) {
                        if (nvlist_exists(mmp_label, ZPOOL_CONFIG_HOSTNAME)) {
                                hostname = fnvlist_lookup_string(mmp_label,
                                    ZPOOL_CONFIG_HOSTNAME);
                                fnvlist_add_string(spa->spa_load_info,
                                    ZPOOL_CONFIG_MMP_HOSTNAME, hostname);
                        }

                        if (nvlist_exists(mmp_label, ZPOOL_CONFIG_HOSTID)) {
                                hostid = fnvlist_lookup_uint64(mmp_label,
                                    ZPOOL_CONFIG_HOSTID);
                                fnvlist_add_uint64(spa->spa_load_info,
                                    ZPOOL_CONFIG_MMP_HOSTID, hostid);
                        }
                }

                fnvlist_add_uint64(spa->spa_load_info,
                    ZPOOL_CONFIG_MMP_STATE, MMP_STATE_ACTIVE);
                fnvlist_add_uint64(spa->spa_load_info,
                    ZPOOL_CONFIG_MMP_TXG, 0);

                error = spa_vdev_err(rvd, VDEV_AUX_ACTIVE, EREMOTEIO);
        }

        if (mmp_label)
                nvlist_free(mmp_label);

        return (error);
}

/*
 * Load an existing storage pool, using the pool's builtin spa_config as a
 * source of configuration information.
 */
__attribute__((always_inline))
static inline int
spa_load_impl(spa_t *spa, uint64_t pool_guid, nvlist_t *config,
    spa_load_state_t state, spa_import_type_t type, boolean_t mosconfig,
    char **ereport)
{
        int error = 0;
        nvlist_t *nvroot = NULL;
        nvlist_t *label;
        vdev_t *rvd;
        uberblock_t *ub = &spa->spa_uberblock;
        uint64_t children, config_cache_txg = spa->spa_config_txg;
        int orig_mode = spa->spa_mode;
        int parse;
        uint64_t obj;
        boolean_t missing_feat_write = B_FALSE;
        boolean_t activity_check = B_FALSE;

        /*
         * If this is an untrusted config, access the pool in read-only mode.
         * This prevents things like resilvering recently removed devices.
         */
        if (!mosconfig)
                spa->spa_mode = FREAD;

        ASSERT(MUTEX_HELD(&spa_namespace_lock));

        spa->spa_load_state = state;

        if (nvlist_lookup_nvlist(config, ZPOOL_CONFIG_VDEV_TREE, &nvroot))
                return (SET_ERROR(EINVAL));

        parse = (type == SPA_IMPORT_EXISTING ?
            VDEV_ALLOC_LOAD : VDEV_ALLOC_SPLIT);

        /*
         * Create "The Godfather" zio to hold all async IOs
         */
        spa->spa_async_zio_root = kmem_alloc(max_ncpus * sizeof (void *),
            KM_SLEEP);
        for (int i = 0; i < max_ncpus; i++) {
                spa->spa_async_zio_root[i] = zio_root(spa, NULL, NULL,
                    ZIO_FLAG_CANFAIL | ZIO_FLAG_SPECULATIVE |
                    ZIO_FLAG_GODFATHER);
        }

        /*
         * Parse the configuration into a vdev tree.  We explicitly set the
         * value that will be returned by spa_version() since parsing the
         * configuration requires knowing the version number.
         */
        spa_config_enter(spa, SCL_ALL, FTAG, RW_WRITER);
        error = spa_config_parse(spa, &rvd, nvroot, NULL, 0, parse);
        spa_config_exit(spa, SCL_ALL, FTAG);

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

        ASSERT(spa->spa_root_vdev == rvd);
        ASSERT3U(spa->spa_min_ashift, >=, SPA_MINBLOCKSHIFT);
        ASSERT3U(spa->spa_max_ashift, <=, SPA_MAXBLOCKSHIFT);

        if (type != SPA_IMPORT_ASSEMBLE) {
                ASSERT(spa_guid(spa) == pool_guid);
        }

        /*
         * Try to open all vdevs, loading each label in the process.
         */
        spa_config_enter(spa, SCL_ALL, FTAG, RW_WRITER);
        error = vdev_open(rvd);
        spa_config_exit(spa, SCL_ALL, FTAG);
        if (error != 0)
                return (error);

        /*
         * We need to validate the vdev labels against the configuration that
         * we have in hand, which is dependent on the setting of mosconfig. If
         * mosconfig is true then we're validating the vdev labels based on
         * that config.  Otherwise, we're validating against the cached config
         * (zpool.cache) that was read when we loaded the zfs module, and then
         * later we will recursively call spa_load() and validate against
         * the vdev config.
         *
         * If we're assembling a new pool that's been split off from an
         * existing pool, the labels haven't yet been updated so we skip
         * validation for now.
         */
        if (type != SPA_IMPORT_ASSEMBLE) {
                spa_config_enter(spa, SCL_ALL, FTAG, RW_WRITER);
                error = vdev_validate(rvd, mosconfig);
                spa_config_exit(spa, SCL_ALL, FTAG);

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

                if (rvd->vdev_state <= VDEV_STATE_CANT_OPEN)
                        return (SET_ERROR(ENXIO));
        }

        /*
         * Find the best uberblock.
         */
        vdev_uberblock_load(rvd, ub, &label);

        /*
         * If we weren't able to find a single valid uberblock, return failure.
         */
        if (ub->ub_txg == 0) {
                nvlist_free(label);
                return (spa_vdev_err(rvd, VDEV_AUX_CORRUPT_DATA, ENXIO));
        }

        /*
         * For pools which have the multihost property on determine if the
         * pool is truly inactive and can be safely imported.  Prevent
         * hosts which don't have a hostid set from importing the pool.
         */
        activity_check = spa_activity_check_required(spa, ub, label, config);
        if (activity_check) {
                if (ub->ub_mmp_magic == MMP_MAGIC && ub->ub_mmp_delay &&
                    spa_get_hostid() == 0) {
                        nvlist_free(label);
                        fnvlist_add_uint64(spa->spa_load_info,
                            ZPOOL_CONFIG_MMP_STATE, MMP_STATE_NO_HOSTID);
                        return (spa_vdev_err(rvd, VDEV_AUX_ACTIVE, EREMOTEIO));
                }

                error = spa_activity_check(spa, ub, config);
                if (error) {
                        nvlist_free(label);
                        return (error);
                }

                fnvlist_add_uint64(spa->spa_load_info,
                    ZPOOL_CONFIG_MMP_STATE, MMP_STATE_INACTIVE);
                fnvlist_add_uint64(spa->spa_load_info,
                    ZPOOL_CONFIG_MMP_TXG, ub->ub_txg);
        }

        /*
         * If the pool has an unsupported version we can't open it.
         */
        if (!SPA_VERSION_IS_SUPPORTED(ub->ub_version)) {
                nvlist_free(label);
                return (spa_vdev_err(rvd, VDEV_AUX_VERSION_NEWER, ENOTSUP));
        }

        if (ub->ub_version >= SPA_VERSION_FEATURES) {
                nvlist_t *features;

                /*
                 * If we weren't able to find what's necessary for reading the
                 * MOS in the label, return failure.
                 */
                if (label == NULL || nvlist_lookup_nvlist(label,
                    ZPOOL_CONFIG_FEATURES_FOR_READ, &features) != 0) {
                        nvlist_free(label);
                        return (spa_vdev_err(rvd, VDEV_AUX_CORRUPT_DATA,
                            ENXIO));
                }

                /*
                 * Update our in-core representation with the definitive values
                 * from the label.
                 */
                nvlist_free(spa->spa_label_features);
                VERIFY(nvlist_dup(features, &spa->spa_label_features, 0) == 0);
        }

        nvlist_free(label);

        /*
         * Look through entries in the label nvlist's features_for_read. If
         * there is a feature listed there which we don't understand then we
         * cannot open a pool.
         */
        if (ub->ub_version >= SPA_VERSION_FEATURES) {
                nvlist_t *unsup_feat;

                VERIFY(nvlist_alloc(&unsup_feat, NV_UNIQUE_NAME, KM_SLEEP) ==
                    0);

                for (nvpair_t *nvp = nvlist_next_nvpair(spa->spa_label_features,
                    NULL); nvp != NULL;
                    nvp = nvlist_next_nvpair(spa->spa_label_features, nvp)) {
                        if (!zfeature_is_supported(nvpair_name(nvp))) {
                                VERIFY(nvlist_add_string(unsup_feat,
                                    nvpair_name(nvp), "") == 0);
                        }
                }

                if (!nvlist_empty(unsup_feat)) {
                        VERIFY(nvlist_add_nvlist(spa->spa_load_info,
                            ZPOOL_CONFIG_UNSUP_FEAT, unsup_feat) == 0);
                        nvlist_free(unsup_feat);
                        return (spa_vdev_err(rvd, VDEV_AUX_UNSUP_FEAT,
                            ENOTSUP));
                }

                nvlist_free(unsup_feat);
        }

        /*
         * If the vdev guid sum doesn't match the uberblock, we have an
         * incomplete configuration.  We first check to see if the pool
         * is aware of the complete config (i.e ZPOOL_CONFIG_VDEV_CHILDREN).
         * If it is, defer the vdev_guid_sum check till later so we
         * can handle missing vdevs.
         */
        if (nvlist_lookup_uint64(config, ZPOOL_CONFIG_VDEV_CHILDREN,
            &children) != 0 && mosconfig && type != SPA_IMPORT_ASSEMBLE &&
            rvd->vdev_guid_sum != ub->ub_guid_sum)
                return (spa_vdev_err(rvd, VDEV_AUX_BAD_GUID_SUM, ENXIO));

        if (type != SPA_IMPORT_ASSEMBLE && spa->spa_config_splitting) {
                spa_config_enter(spa, SCL_ALL, FTAG, RW_WRITER);
                spa_try_repair(spa, config);
                spa_config_exit(spa, SCL_ALL, FTAG);
                nvlist_free(spa->spa_config_splitting);
                spa->spa_config_splitting = NULL;
        }

        /*
         * Initialize internal SPA structures.
         */
        spa->spa_state = POOL_STATE_ACTIVE;
        spa->spa_ubsync = spa->spa_uberblock;
        spa->spa_verify_min_txg = spa->spa_extreme_rewind ?
            TXG_INITIAL - 1 : spa_last_synced_txg(spa) - TXG_DEFER_SIZE - 1;
        spa->spa_first_txg = spa->spa_last_ubsync_txg ?
            spa->spa_last_ubsync_txg : spa_last_synced_txg(spa) + 1;
        spa->spa_claim_max_txg = spa->spa_first_txg;
        spa->spa_prev_software_version = ub->ub_software_version;

        error = dsl_pool_init(spa, spa->spa_first_txg, &spa->spa_dsl_pool);
        if (error)
                return (spa_vdev_err(rvd, VDEV_AUX_CORRUPT_DATA, EIO));
        spa->spa_meta_objset = spa->spa_dsl_pool->dp_meta_objset;

        if (spa_dir_prop(spa, DMU_POOL_CONFIG, &spa->spa_config_object) != 0)
                return (spa_vdev_err(rvd, VDEV_AUX_CORRUPT_DATA, EIO));

        if (spa_version(spa) >= SPA_VERSION_FEATURES) {
                boolean_t missing_feat_read = B_FALSE;
                nvlist_t *unsup_feat, *enabled_feat;

                if (spa_dir_prop(spa, DMU_POOL_FEATURES_FOR_READ,
                    &spa->spa_feat_for_read_obj) != 0) {
                        return (spa_vdev_err(rvd, VDEV_AUX_CORRUPT_DATA, EIO));
                }

                if (spa_dir_prop(spa, DMU_POOL_FEATURES_FOR_WRITE,
                    &spa->spa_feat_for_write_obj) != 0) {
                        return (spa_vdev_err(rvd, VDEV_AUX_CORRUPT_DATA, EIO));
                }

                if (spa_dir_prop(spa, DMU_POOL_FEATURE_DESCRIPTIONS,
                    &spa->spa_feat_desc_obj) != 0) {
                        return (spa_vdev_err(rvd, VDEV_AUX_CORRUPT_DATA, EIO));
                }

                enabled_feat = fnvlist_alloc();
                unsup_feat = fnvlist_alloc();

                if (!spa_features_check(spa, B_FALSE,
                    unsup_feat, enabled_feat))
                        missing_feat_read = B_TRUE;

                if (spa_writeable(spa) || state == SPA_LOAD_TRYIMPORT) {
                        if (!spa_features_check(spa, B_TRUE,
                            unsup_feat, enabled_feat)) {
                                missing_feat_write = B_TRUE;
                        }
                }

                fnvlist_add_nvlist(spa->spa_load_info,
                    ZPOOL_CONFIG_ENABLED_FEAT, enabled_feat);

                if (!nvlist_empty(unsup_feat)) {
                        fnvlist_add_nvlist(spa->spa_load_info,
                            ZPOOL_CONFIG_UNSUP_FEAT, unsup_feat);
                }

                fnvlist_free(enabled_feat);
                fnvlist_free(unsup_feat);

                if (!missing_feat_read) {
                        fnvlist_add_boolean(spa->spa_load_info,
                            ZPOOL_CONFIG_CAN_RDONLY);
                }

                /*
                 * If the state is SPA_LOAD_TRYIMPORT, our objective is
                 * twofold: to determine whether the pool is available for
                 * import in read-write mode and (if it is not) whether the
                 * pool is available for import in read-only mode. If the pool
                 * is available for import in read-write mode, it is displayed
                 * as available in userland; if it is not available for import
                 * in read-only mode, it is displayed as unavailable in
                 * userland. If the pool is available for import in read-only
                 * mode but not read-write mode, it is displayed as unavailable
                 * in userland with a special note that the pool is actually
                 * available for open in read-only mode.
                 *
                 * As a result, if the state is SPA_LOAD_TRYIMPORT and we are
                 * missing a feature for write, we must first determine whether
                 * the pool can be opened read-only before returning to
                 * userland in order to know whether to display the
                 * abovementioned note.
                 */
                if (missing_feat_read || (missing_feat_write &&
                    spa_writeable(spa))) {
                        return (spa_vdev_err(rvd, VDEV_AUX_UNSUP_FEAT,
                            ENOTSUP));
                }

                /*
                 * Load refcounts for ZFS features from disk into an in-memory
                 * cache during SPA initialization.
                 */
                for (spa_feature_t i = 0; i < SPA_FEATURES; i++) {
                        uint64_t refcount;

                        error = feature_get_refcount_from_disk(spa,
                            &spa_feature_table[i], &refcount);
                        if (error == 0) {
                                spa->spa_feat_refcount_cache[i] = refcount;
                        } else if (error == ENOTSUP) {
                                spa->spa_feat_refcount_cache[i] =
                                    SPA_FEATURE_DISABLED;
                        } else {
                                return (spa_vdev_err(rvd,
                                    VDEV_AUX_CORRUPT_DATA, EIO));
                        }
                }
        }

        if (spa_feature_is_active(spa, SPA_FEATURE_ENABLED_TXG)) {
                if (spa_dir_prop(spa, DMU_POOL_FEATURE_ENABLED_TXG,
                    &spa->spa_feat_enabled_txg_obj) != 0)
                        return (spa_vdev_err(rvd, VDEV_AUX_CORRUPT_DATA, EIO));
        }

        spa->spa_is_initializing = B_TRUE;
        error = dsl_pool_open(spa->spa_dsl_pool);
        spa->spa_is_initializing = B_FALSE;
        if (error != 0)
                return (spa_vdev_err(rvd, VDEV_AUX_CORRUPT_DATA, EIO));

        if (!mosconfig) {
                uint64_t hostid;
                nvlist_t *policy = NULL, *nvconfig;

                if (load_nvlist(spa, spa->spa_config_object, &nvconfig) != 0)
                        return (spa_vdev_err(rvd, VDEV_AUX_CORRUPT_DATA, EIO));

                if (!spa_is_root(spa) && nvlist_lookup_uint64(nvconfig,
                    ZPOOL_CONFIG_HOSTID, &hostid) == 0) {
                        char *hostname;
                        unsigned long myhostid = 0;

                        VERIFY(nvlist_lookup_string(nvconfig,
                            ZPOOL_CONFIG_HOSTNAME, &hostname) == 0);

                        myhostid = spa_get_hostid();
                        if (hostid && myhostid && hostid != myhostid) {
                                nvlist_free(nvconfig);
                                return (SET_ERROR(EBADF));
                        }
                }
                if (nvlist_lookup_nvlist(spa->spa_config,
                    ZPOOL_REWIND_POLICY, &policy) == 0)
                        VERIFY(nvlist_add_nvlist(nvconfig,
                            ZPOOL_REWIND_POLICY, policy) == 0);

                spa_config_set(spa, nvconfig);
                spa_unload(spa);
                spa_deactivate(spa);
                spa_activate(spa, orig_mode);

                return (spa_load(spa, state, SPA_IMPORT_EXISTING, B_TRUE));
        }

        /* Grab the checksum salt from the MOS. */
        error = zap_lookup(spa->spa_meta_objset, DMU_POOL_DIRECTORY_OBJECT,
            DMU_POOL_CHECKSUM_SALT, 1,
            sizeof (spa->spa_cksum_salt.zcs_bytes),
            spa->spa_cksum_salt.zcs_bytes);
        if (error == ENOENT) {
                /* Generate a new salt for subsequent use */
                (void) random_get_pseudo_bytes(spa->spa_cksum_salt.zcs_bytes,
                    sizeof (spa->spa_cksum_salt.zcs_bytes));
        } else if (error != 0) {
                return (spa_vdev_err(rvd, VDEV_AUX_CORRUPT_DATA, EIO));
        }

        if (spa_dir_prop(spa, DMU_POOL_SYNC_BPOBJ, &obj) != 0)
                return (spa_vdev_err(rvd, VDEV_AUX_CORRUPT_DATA, EIO));
        error = bpobj_open(&spa->spa_deferred_bpobj, spa->spa_meta_objset, obj);
        if (error != 0)
                return (spa_vdev_err(rvd, VDEV_AUX_CORRUPT_DATA, EIO));

        /*
         * Load the bit that tells us to use the new accounting function
         * (raid-z deflation).  If we have an older pool, this will not
         * be present.
         */
        error = spa_dir_prop(spa, DMU_POOL_DEFLATE, &spa->spa_deflate);
        if (error != 0 && error != ENOENT)
                return (spa_vdev_err(rvd, VDEV_AUX_CORRUPT_DATA, EIO));

        error = spa_dir_prop(spa, DMU_POOL_CREATION_VERSION,
            &spa->spa_creation_version);
        if (error != 0 && error != ENOENT)
                return (spa_vdev_err(rvd, VDEV_AUX_CORRUPT_DATA, EIO));

        /*
         * Load the persistent error log.  If we have an older pool, this will
         * not be present.
         */
        error = spa_dir_prop(spa, DMU_POOL_ERRLOG_LAST, &spa->spa_errlog_last);
        if (error != 0 && error != ENOENT)
                return (spa_vdev_err(rvd, VDEV_AUX_CORRUPT_DATA, EIO));

        error = spa_dir_prop(spa, DMU_POOL_ERRLOG_SCRUB,
            &spa->spa_errlog_scrub);
        if (error != 0 && error != ENOENT)
                return (spa_vdev_err(rvd, VDEV_AUX_CORRUPT_DATA, EIO));

        /*
         * Load the history object.  If we have an older pool, this
         * will not be present.
         */
        error = spa_dir_prop(spa, DMU_POOL_HISTORY, &spa->spa_history);
        if (error != 0 && error != ENOENT)
                return (spa_vdev_err(rvd, VDEV_AUX_CORRUPT_DATA, EIO));

        /*
         * Load the per-vdev ZAP map. If we have an older pool, this will not
         * be present; in this case, defer its creation to a later time to
         * avoid dirtying the MOS this early / out of sync context. See
         * spa_sync_config_object.
         */

        /* The sentinel is only available in the MOS config. */
        nvlist_t *mos_config;
        if (load_nvlist(spa, spa->spa_config_object, &mos_config) != 0)
                return (spa_vdev_err(rvd, VDEV_AUX_CORRUPT_DATA, EIO));

        error = spa_dir_prop(spa, DMU_POOL_VDEV_ZAP_MAP,
            &spa->spa_all_vdev_zaps);

        if (error == ENOENT) {
                VERIFY(!nvlist_exists(mos_config,
                    ZPOOL_CONFIG_HAS_PER_VDEV_ZAPS));
                spa->spa_avz_action = AVZ_ACTION_INITIALIZE;
                ASSERT0(vdev_count_verify_zaps(spa->spa_root_vdev));
        } else if (error != 0) {
                return (spa_vdev_err(rvd, VDEV_AUX_CORRUPT_DATA, EIO));
        } else if (!nvlist_exists(mos_config, ZPOOL_CONFIG_HAS_PER_VDEV_ZAPS)) {
                /*
                 * An older version of ZFS overwrote the sentinel value, so
                 * we have orphaned per-vdev ZAPs in the MOS. Defer their
                 * destruction to later; see spa_sync_config_object.
                 */
                spa->spa_avz_action = AVZ_ACTION_DESTROY;
                /*
                 * We're assuming that no vdevs have had their ZAPs created
                 * before this. Better be sure of it.
                 */
                ASSERT0(vdev_count_verify_zaps(spa->spa_root_vdev));
        }
        nvlist_free(mos_config);

        /*
         * If we're assembling the pool from the split-off vdevs of
         * an existing pool, we don't want to attach the spares & cache
         * devices.
         */

        /*
         * Load any hot spares for this pool.
         */
        error = spa_dir_prop(spa, DMU_POOL_SPARES, &spa->spa_spares.sav_object);
        if (error != 0 && error != ENOENT)
                return (spa_vdev_err(rvd, VDEV_AUX_CORRUPT_DATA, EIO));
        if (error == 0 && type != SPA_IMPORT_ASSEMBLE) {
                ASSERT(spa_version(spa) >= SPA_VERSION_SPARES);
                if (load_nvlist(spa, spa->spa_spares.sav_object,
                    &spa->spa_spares.sav_config) != 0)
                        return (spa_vdev_err(rvd, VDEV_AUX_CORRUPT_DATA, EIO));

                spa_config_enter(spa, SCL_ALL, FTAG, RW_WRITER);
                spa_load_spares(spa);
                spa_config_exit(spa, SCL_ALL, FTAG);
        } else if (error == 0) {
                spa->spa_spares.sav_sync = B_TRUE;
        }

        /*
         * Load any level 2 ARC devices for this pool.
         */
        error = spa_dir_prop(spa, DMU_POOL_L2CACHE,
            &spa->spa_l2cache.sav_object);
        if (error != 0 && error != ENOENT)
                return (spa_vdev_err(rvd, VDEV_AUX_CORRUPT_DATA, EIO));
        if (error == 0 && type != SPA_IMPORT_ASSEMBLE) {
                ASSERT(spa_version(spa) >= SPA_VERSION_L2CACHE);
                if (load_nvlist(spa, spa->spa_l2cache.sav_object,
                    &spa->spa_l2cache.sav_config) != 0)
                        return (spa_vdev_err(rvd, VDEV_AUX_CORRUPT_DATA, EIO));

                spa_config_enter(spa, SCL_ALL, FTAG, RW_WRITER);
                spa_load_l2cache(spa);
                spa_config_exit(spa, SCL_ALL, FTAG);
        } else if (error == 0) {
                spa->spa_l2cache.sav_sync = B_TRUE;
        }

        spa->spa_delegation = zpool_prop_default_numeric(ZPOOL_PROP_DELEGATION);

        error = spa_dir_prop(spa, DMU_POOL_PROPS, &spa->spa_pool_props_object);
        if (error && error != ENOENT)
                return (spa_vdev_err(rvd, VDEV_AUX_CORRUPT_DATA, EIO));

        if (error == 0) {
                uint64_t autoreplace = 0;

                spa_prop_find(spa, ZPOOL_PROP_BOOTFS, &spa->spa_bootfs);
                spa_prop_find(spa, ZPOOL_PROP_AUTOREPLACE, &autoreplace);
                spa_prop_find(spa, ZPOOL_PROP_DELEGATION, &spa->spa_delegation);
                spa_prop_find(spa, ZPOOL_PROP_FAILUREMODE, &spa->spa_failmode);
                spa_prop_find(spa, ZPOOL_PROP_AUTOEXPAND, &spa->spa_autoexpand);
                spa_prop_find(spa, ZPOOL_PROP_MULTIHOST, &spa->spa_multihost);
                spa_prop_find(spa, ZPOOL_PROP_DEDUPDITTO,
                    &spa->spa_dedup_ditto);

                spa->spa_autoreplace = (autoreplace != 0);
        }

        /*
         * If the 'multihost' property is set, then never allow a pool to
         * be imported when the system hostid is zero.  The exception to
         * this rule is zdb which is always allowed to access pools.
         */
        if (spa_multihost(spa) && spa_get_hostid() == 0 &&
            (spa->spa_import_flags & ZFS_IMPORT_SKIP_MMP) == 0) {
                fnvlist_add_uint64(spa->spa_load_info,
                    ZPOOL_CONFIG_MMP_STATE, MMP_STATE_NO_HOSTID);
                return (spa_vdev_err(rvd, VDEV_AUX_ACTIVE, EREMOTEIO));
        }

        /*
         * If the 'autoreplace' property is set, then post a resource notifying
         * the ZFS DE that it should not issue any faults for unopenable
         * devices.  We also iterate over the vdevs, and post a sysevent for any
         * unopenable vdevs so that the normal autoreplace handler can take
         * over.
         */
        if (spa->spa_autoreplace && state != SPA_LOAD_TRYIMPORT) {
                spa_check_removed(spa->spa_root_vdev);
                /*
                 * For the import case, this is done in spa_import(), because
                 * at this point we're using the spare definitions from
                 * the MOS config, not necessarily from the userland config.
                 */
                if (state != SPA_LOAD_IMPORT) {
                        spa_aux_check_removed(&spa->spa_spares);
                        spa_aux_check_removed(&spa->spa_l2cache);
                }
        }

        /*
         * Load the vdev state for all toplevel vdevs.
         */
        vdev_load(rvd);

        /*
         * Propagate the leaf DTLs we just loaded all the way up the tree.
         */
        spa_config_enter(spa, SCL_ALL, FTAG, RW_WRITER);
        vdev_dtl_reassess(rvd, 0, 0, B_FALSE);
        spa_config_exit(spa, SCL_ALL, FTAG);

        /*
         * Load the DDTs (dedup tables).
         */
        error = ddt_load(spa);
        if (error != 0)
                return (spa_vdev_err(rvd, VDEV_AUX_CORRUPT_DATA, EIO));

        spa_update_dspace(spa);

        /*
         * Validate the config, using the MOS config to fill in any
         * information which might be missing.  If we fail to validate
         * the config then declare the pool unfit for use. If we're
         * assembling a pool from a split, the log is not transferred
         * over.
         */
        if (type != SPA_IMPORT_ASSEMBLE) {
                nvlist_t *nvconfig;

                if (load_nvlist(spa, spa->spa_config_object, &nvconfig) != 0)
                        return (spa_vdev_err(rvd, VDEV_AUX_CORRUPT_DATA, EIO));

                if (!spa_config_valid(spa, nvconfig)) {
                        nvlist_free(nvconfig);
                        return (spa_vdev_err(rvd, VDEV_AUX_BAD_GUID_SUM,
                            ENXIO));
                }
                nvlist_free(nvconfig);

                /*
                 * Now that we've validated the config, check the state of the
                 * root vdev.  If it can't be opened, it indicates one or
                 * more toplevel vdevs are faulted.
                 */
                if (rvd->vdev_state <= VDEV_STATE_CANT_OPEN)
                        return (SET_ERROR(ENXIO));

                if (spa_writeable(spa) && spa_check_logs(spa)) {
                        *ereport = FM_EREPORT_ZFS_LOG_REPLAY;
                        return (spa_vdev_err(rvd, VDEV_AUX_BAD_LOG, ENXIO));
                }
        }

        if (missing_feat_write) {
                ASSERT(state == SPA_LOAD_TRYIMPORT);

                /*
                 * At this point, we know that we can open the pool in
                 * read-only mode but not read-write mode. We now have enough
                 * information and can return to userland.
                 */
                return (spa_vdev_err(rvd, VDEV_AUX_UNSUP_FEAT, ENOTSUP));
        }

        /*
         * We've successfully opened the pool, verify that we're ready
         * to start pushing transactions.
         */
        if (state != SPA_LOAD_TRYIMPORT) {
                if ((error = spa_load_verify(spa)))
                        return (spa_vdev_err(rvd, VDEV_AUX_CORRUPT_DATA,
                            error));
        }

        if (spa_writeable(spa) && (state == SPA_LOAD_RECOVER ||
            spa->spa_load_max_txg == UINT64_MAX)) {
                dmu_tx_t *tx;
                int need_update = B_FALSE;
                dsl_pool_t *dp = spa_get_dsl(spa);

                ASSERT(state != SPA_LOAD_TRYIMPORT);

                /*
                 * Claim log blocks that haven't been committed yet.
                 * This must all happen in a single txg.
                 * Note: spa_claim_max_txg is updated by spa_claim_notify(),
                 * invoked from zil_claim_log_block()'s i/o done callback.
                 * Price of rollback is that we abandon the log.
                 */
                spa->spa_claiming = B_TRUE;

                tx = dmu_tx_create_assigned(dp, spa_first_txg(spa));
                (void) dmu_objset_find_dp(dp, dp->dp_root_dir_obj,
                    zil_claim, tx, DS_FIND_CHILDREN);
                dmu_tx_commit(tx);

                spa->spa_claiming = B_FALSE;

                spa_set_log_state(spa, SPA_LOG_GOOD);
                spa->spa_sync_on = B_TRUE;
                txg_sync_start(spa->spa_dsl_pool);
                mmp_thread_start(spa);

                /*
                 * Wait for all claims to sync.  We sync up to the highest
                 * claimed log block birth time so that claimed log blocks
                 * don't appear to be from the future.  spa_claim_max_txg
                 * will have been set for us by either zil_check_log_chain()
                 * (invoked from spa_check_logs()) or zil_claim() above.
                 */
                txg_wait_synced(spa->spa_dsl_pool, spa->spa_claim_max_txg);

                /*
                 * If the config cache is stale, or we have uninitialized
                 * metaslabs (see spa_vdev_add()), then update the config.
                 *
                 * If this is a verbatim import, trust the current
                 * in-core spa_config and update the disk labels.
                 */
                if (config_cache_txg != spa->spa_config_txg ||
                    state == SPA_LOAD_IMPORT ||
                    state == SPA_LOAD_RECOVER ||
                    (spa->spa_import_flags & ZFS_IMPORT_VERBATIM))
                        need_update = B_TRUE;

                for (int c = 0; c < rvd->vdev_children; c++)
                        if (rvd->vdev_child[c]->vdev_ms_array == 0)
                                need_update = B_TRUE;

                /*
                 * Update the config cache asychronously in case we're the
                 * root pool, in which case the config cache isn't writable yet.
                 */
                if (need_update)
                        spa_async_request(spa, SPA_ASYNC_CONFIG_UPDATE);

                /*
                 * Check all DTLs to see if anything needs resilvering.
                 */
                if (!dsl_scan_resilvering(spa->spa_dsl_pool) &&
                    vdev_resilver_needed(rvd, NULL, NULL))
                        spa_async_request(spa, SPA_ASYNC_RESILVER);

                /*
                 * Log the fact that we booted up (so that we can detect if
                 * we rebooted in the middle of an operation).
                 */
                spa_history_log_version(spa, "open", NULL);

                /*
                 * Delete any inconsistent datasets.
                 */
                (void) dmu_objset_find(spa_name(spa),
                    dsl_destroy_inconsistent, NULL, DS_FIND_CHILDREN);

                /*
                 * Clean up any stale temporary dataset userrefs.
                 */
                dsl_pool_clean_tmp_userrefs(spa->spa_dsl_pool);
        }

        return (0);
}

static int
spa_load_retry(spa_t *spa, spa_load_state_t state, int mosconfig)
{
        int mode = spa->spa_mode;

        spa_unload(spa);
        spa_deactivate(spa);

        spa->spa_load_max_txg = spa->spa_uberblock.ub_txg - 1;

        spa_activate(spa, mode);
        spa_async_suspend(spa);

        return (spa_load(spa, state, SPA_IMPORT_EXISTING, mosconfig));
}

/*
 * If spa_load() fails this function will try loading prior txg's. If
 * 'state' is SPA_LOAD_RECOVER and one of these loads succeeds the pool
 * will be rewound to that txg. If 'state' is not SPA_LOAD_RECOVER this
 * function will not rewind the pool and will return the same error as
 * spa_load().
 */
static int
spa_load_best(spa_t *spa, spa_load_state_t state, int mosconfig,
    uint64_t max_request, int rewind_flags)
{
        nvlist_t *loadinfo = NULL;
        nvlist_t *config = NULL;
        int load_error, rewind_error;
        uint64_t safe_rewind_txg;
        uint64_t min_txg;

        if (spa->spa_load_txg && state == SPA_LOAD_RECOVER) {
                spa->spa_load_max_txg = spa->spa_load_txg;
                spa_set_log_state(spa, SPA_LOG_CLEAR);
        } else {
                spa->spa_load_max_txg = max_request;
                if (max_request != UINT64_MAX)
                        spa->spa_extreme_rewind = B_TRUE;
        }

        load_error = rewind_error = spa_load(spa, state, SPA_IMPORT_EXISTING,
            mosconfig);
        if (load_error == 0)
                return (0);

        if (spa->spa_root_vdev != NULL)
                config = spa_config_generate(spa, NULL, -1ULL, B_TRUE);

        spa->spa_last_ubsync_txg = spa->spa_uberblock.ub_txg;
        spa->spa_last_ubsync_txg_ts = spa->spa_uberblock.ub_timestamp;

        if (rewind_flags & ZPOOL_NEVER_REWIND) {
                nvlist_free(config);
                return (load_error);
        }

        if (state == SPA_LOAD_RECOVER) {
                /* Price of rolling back is discarding txgs, including log */
                spa_set_log_state(spa, SPA_LOG_CLEAR);
        } else {
                /*
                 * If we aren't rolling back save the load info from our first
                 * import attempt so that we can restore it after attempting
                 * to rewind.
                 */
                loadinfo = spa->spa_load_info;
                spa->spa_load_info = fnvlist_alloc();
        }

        spa->spa_load_max_txg = spa->spa_last_ubsync_txg;
        safe_rewind_txg = spa->spa_last_ubsync_txg - TXG_DEFER_SIZE;
        min_txg = (rewind_flags & ZPOOL_EXTREME_REWIND) ?
            TXG_INITIAL : safe_rewind_txg;

        /*
         * Continue as long as we're finding errors, we're still within
         * the acceptable rewind range, and we're still finding uberblocks
         */
        while (rewind_error && spa->spa_uberblock.ub_txg >= min_txg &&
            spa->spa_uberblock.ub_txg <= spa->spa_load_max_txg) {
                if (spa->spa_load_max_txg < safe_rewind_txg)
                        spa->spa_extreme_rewind = B_TRUE;
                rewind_error = spa_load_retry(spa, state, mosconfig);
        }

        spa->spa_extreme_rewind = B_FALSE;
        spa->spa_load_max_txg = UINT64_MAX;

        if (config && (rewind_error || state != SPA_LOAD_RECOVER))
                spa_config_set(spa, config);
        else
                nvlist_free(config);

        if (state == SPA_LOAD_RECOVER) {
                ASSERT3P(loadinfo, ==, NULL);
                return (rewind_error);
        } else {
                /* Store the rewind info as part of the initial load info */
                fnvlist_add_nvlist(loadinfo, ZPOOL_CONFIG_REWIND_INFO,
                    spa->spa_load_info);

                /* Restore the initial load info */
                fnvlist_free(spa->spa_load_info);
                spa->spa_load_info = loadinfo;

                return (load_error);
        }
}

/*
 * Pool Open/Import
 *
 * The import case is identical to an open except that the configuration is sent
 * down from userland, instead of grabbed from the configuration cache.  For the
 * case of an open, the pool configuration will exist in the
 * POOL_STATE_UNINITIALIZED state.
 *
 * The stats information (gen/count/ustats) is used to gather vdev statistics at
 * the same time open the pool, without having to keep around the spa_t in some
 * ambiguous state.
 */
static int
spa_open_common(const char *pool, spa_t **spapp, void *tag, nvlist_t *nvpolicy,
    nvlist_t **config)
{
        spa_t *spa;
        spa_load_state_t state = SPA_LOAD_OPEN;
        int error;
        int locked = B_FALSE;
        int firstopen = B_FALSE;

        *spapp = NULL;

        /*
         * As disgusting as this is, we need to support recursive calls to this
         * function because dsl_dir_open() is called during spa_load(), and ends
         * up calling spa_open() again.  The real fix is to figure out how to
         * avoid dsl_dir_open() calling this in the first place.
         */
        if (MUTEX_NOT_HELD(&spa_namespace_lock)) {
                mutex_enter(&spa_namespace_lock);
                locked = B_TRUE;
        }

        if ((spa = spa_lookup(pool)) == NULL) {
                if (locked)
                        mutex_exit(&spa_namespace_lock);
                return (SET_ERROR(ENOENT));
        }

        if (spa->spa_state == POOL_STATE_UNINITIALIZED) {
                zpool_rewind_policy_t policy;

                firstopen = B_TRUE;

                zpool_get_rewind_policy(nvpolicy ? nvpolicy : spa->spa_config,
                    &policy);
                if (policy.zrp_request & ZPOOL_DO_REWIND)
                        state = SPA_LOAD_RECOVER;

                spa_activate(spa, spa_mode_global);

                if (state != SPA_LOAD_RECOVER)
                        spa->spa_last_ubsync_txg = spa->spa_load_txg = 0;

                error = spa_load_best(spa, state, B_FALSE, policy.zrp_txg,
                    policy.zrp_request);

                if (error == EBADF) {
                        /*
                         * If vdev_validate() returns failure (indicated by
                         * EBADF), it indicates that one of the vdevs indicates
                         * that the pool has been exported or destroyed.  If
                         * this is the case, the config cache is out of sync and
                         * we should remove the pool from the namespace.
                         */
                        spa_unload(spa);
                        spa_deactivate(spa);
                        spa_config_sync(spa, B_TRUE, B_TRUE);
                        spa_remove(spa);
                        if (locked)
                                mutex_exit(&spa_namespace_lock);
                        return (SET_ERROR(ENOENT));
                }

                if (error) {
                        /*
                         * We can't open the pool, but we still have useful
                         * information: the state of each vdev after the
                         * attempted vdev_open().  Return this to the user.
                         */
                        if (config != NULL && spa->spa_config) {
                                VERIFY(nvlist_dup(spa->spa_config, config,
                                    KM_SLEEP) == 0);
                                VERIFY(nvlist_add_nvlist(*config,
                                    ZPOOL_CONFIG_LOAD_INFO,
                                    spa->spa_load_info) == 0);
                        }
                        spa_unload(spa);
                        spa_deactivate(spa);
                        spa->spa_last_open_failed = error;
                        if (locked)
                                mutex_exit(&spa_namespace_lock);
                        *spapp = NULL;
                        return (error);
                }
        }

        spa_open_ref(spa, tag);

        if (config != NULL)
                *config = spa_config_generate(spa, NULL, -1ULL, B_TRUE);

        /*
         * If we've recovered the pool, pass back any information we
         * gathered while doing the load.
         */
        if (state == SPA_LOAD_RECOVER) {
                VERIFY(nvlist_add_nvlist(*config, ZPOOL_CONFIG_LOAD_INFO,
                    spa->spa_load_info) == 0);
        }

        if (locked) {
                spa->spa_last_open_failed = 0;
                spa->spa_last_ubsync_txg = 0;
                spa->spa_load_txg = 0;
                mutex_exit(&spa_namespace_lock);
        }

        if (firstopen)
                zvol_create_minors(spa, spa_name(spa), B_TRUE);

        *spapp = spa;

        return (0);
}

int
spa_open_rewind(const char *name, spa_t **spapp, void *tag, nvlist_t *policy,
    nvlist_t **config)
{
        return (spa_open_common(name, spapp, tag, policy, config));
}

int
spa_open(const char *name, spa_t **spapp, void *tag)
{
        return (spa_open_common(name, spapp, tag, NULL, NULL));
}

/*
 * Lookup the given spa_t, incrementing the inject count in the process,
 * preventing it from being exported or destroyed.
 */
spa_t *
spa_inject_addref(char *name)
{
        spa_t *spa;

        mutex_enter(&spa_namespace_lock);
        if ((spa = spa_lookup(name)) == NULL) {
                mutex_exit(&spa_namespace_lock);
                return (NULL);
        }
        spa->spa_inject_ref++;
        mutex_exit(&spa_namespace_lock);

        return (spa);
}

void
spa_inject_delref(spa_t *spa)
{
        mutex_enter(&spa_namespace_lock);
        spa->spa_inject_ref--;
        mutex_exit(&spa_namespace_lock);
}

/*
 * Add spares device information to the nvlist.
 */
static void
spa_add_spares(spa_t *spa, nvlist_t *config)
{
        nvlist_t **spares;
        uint_t i, nspares;
        nvlist_t *nvroot;
        uint64_t guid;
        vdev_stat_t *vs;
        uint_t vsc;
        uint64_t pool;

        ASSERT(spa_config_held(spa, SCL_CONFIG, RW_READER));

        if (spa->spa_spares.sav_count == 0)
                return;

        VERIFY(nvlist_lookup_nvlist(config,
            ZPOOL_CONFIG_VDEV_TREE, &nvroot) == 0);
        VERIFY(nvlist_lookup_nvlist_array(spa->spa_spares.sav_config,
            ZPOOL_CONFIG_SPARES, &spares, &nspares) == 0);
        if (nspares != 0) {
                VERIFY(nvlist_add_nvlist_array(nvroot,
                    ZPOOL_CONFIG_SPARES, spares, nspares) == 0);
                VERIFY(nvlist_lookup_nvlist_array(nvroot,
                    ZPOOL_CONFIG_SPARES, &spares, &nspares) == 0);

                /*
                 * Go through and find any spares which have since been
                 * repurposed as an active spare.  If this is the case, update
                 * their status appropriately.
                 */
                for (i = 0; i < nspares; i++) {
                        VERIFY(nvlist_lookup_uint64(spares[i],
                            ZPOOL_CONFIG_GUID, &guid) == 0);
                        if (spa_spare_exists(guid, &pool, NULL) &&
                            pool != 0ULL) {
                                VERIFY(nvlist_lookup_uint64_array(
                                    spares[i], ZPOOL_CONFIG_VDEV_STATS,
                                    (uint64_t **)&vs, &vsc) == 0);
                                vs->vs_state = VDEV_STATE_CANT_OPEN;
                                vs->vs_aux = VDEV_AUX_SPARED;
                        }
                }
        }
}

/*
 * Add l2cache device information to the nvlist, including vdev stats.
 */
static void
spa_add_l2cache(spa_t *spa, nvlist_t *config)
{
        nvlist_t **l2cache;
        uint_t i, j, nl2cache;
        nvlist_t *nvroot;
        uint64_t guid;
        vdev_t *vd;
        vdev_stat_t *vs;
        uint_t vsc;

        ASSERT(spa_config_held(spa, SCL_CONFIG, RW_READER));

        if (spa->spa_l2cache.sav_count == 0)
                return;

        VERIFY(nvlist_lookup_nvlist(config,
            ZPOOL_CONFIG_VDEV_TREE, &nvroot) == 0);
        VERIFY(nvlist_lookup_nvlist_array(spa->spa_l2cache.sav_config,
            ZPOOL_CONFIG_L2CACHE, &l2cache, &nl2cache) == 0);
        if (nl2cache != 0) {
                VERIFY(nvlist_add_nvlist_array(nvroot,
                    ZPOOL_CONFIG_L2CACHE, l2cache, nl2cache) == 0);
                VERIFY(nvlist_lookup_nvlist_array(nvroot,
                    ZPOOL_CONFIG_L2CACHE, &l2cache, &nl2cache) == 0);

                /*
                 * Update level 2 cache device stats.
                 */

                for (i = 0; i < nl2cache; i++) {
                        VERIFY(nvlist_lookup_uint64(l2cache[i],
                            ZPOOL_CONFIG_GUID, &guid) == 0);

                        vd = NULL;
                        for (j = 0; j < spa->spa_l2cache.sav_count; j++) {
                                if (guid ==
                                    spa->spa_l2cache.sav_vdevs[j]->vdev_guid) {
                                        vd = spa->spa_l2cache.sav_vdevs[j];
                                        break;
                                }
                        }
                        ASSERT(vd != NULL);

                        VERIFY(nvlist_lookup_uint64_array(l2cache[i],
                            ZPOOL_CONFIG_VDEV_STATS, (uint64_t **)&vs, &vsc)
                            == 0);
                        vdev_get_stats(vd, vs);
                        vdev_config_generate_stats(vd, l2cache[i]);

                }
        }
}

static void
spa_feature_stats_from_disk(spa_t *spa, nvlist_t *features)
{
        zap_cursor_t zc;
        zap_attribute_t za;

        if (spa->spa_feat_for_read_obj != 0) {
                for (zap_cursor_init(&zc, spa->spa_meta_objset,
                    spa->spa_feat_for_read_obj);
                    zap_cursor_retrieve(&zc, &za) == 0;
                    zap_cursor_advance(&zc)) {
                        ASSERT(za.za_integer_length == sizeof (uint64_t) &&
                            za.za_num_integers == 1);
                        VERIFY0(nvlist_add_uint64(features, za.za_name,
                            za.za_first_integer));
                }
                zap_cursor_fini(&zc);
        }

        if (spa->spa_feat_for_write_obj != 0) {
                for (zap_cursor_init(&zc, spa->spa_meta_objset,
                    spa->spa_feat_for_write_obj);
                    zap_cursor_retrieve(&zc, &za) == 0;
                    zap_cursor_advance(&zc)) {
                        ASSERT(za.za_integer_length == sizeof (uint64_t) &&
                            za.za_num_integers == 1);
                        VERIFY0(nvlist_add_uint64(features, za.za_name,
                            za.za_first_integer));
                }
                zap_cursor_fini(&zc);
        }
}

static void
spa_feature_stats_from_cache(spa_t *spa, nvlist_t *features)
{
        int i;

        for (i = 0; i < SPA_FEATURES; i++) {
                zfeature_info_t feature = spa_feature_table[i];
                uint64_t refcount;

                if (feature_get_refcount(spa, &feature, &refcount) != 0)
                        continue;

                VERIFY0(nvlist_add_uint64(features, feature.fi_guid, refcount));
        }
}

/*
 * Store a list of pool features and their reference counts in the
 * config.
 *
 * The first time this is called on a spa, allocate a new nvlist, fetch
 * the pool features and reference counts from disk, then save the list
 * in the spa. In subsequent calls on the same spa use the saved nvlist
 * and refresh its values from the cached reference counts.  This
 * ensures we don't block here on I/O on a suspended pool so 'zpool
 * clear' can resume the pool.
 */
static void
spa_add_feature_stats(spa_t *spa, nvlist_t *config)
{
        nvlist_t *features;

        ASSERT(spa_config_held(spa, SCL_CONFIG, RW_READER));

        mutex_enter(&spa->spa_feat_stats_lock);
        features = spa->spa_feat_stats;

        if (features != NULL) {
                spa_feature_stats_from_cache(spa, features);
        } else {
                VERIFY0(nvlist_alloc(&features, NV_UNIQUE_NAME, KM_SLEEP));
                spa->spa_feat_stats = features;
                spa_feature_stats_from_disk(spa, features);
        }

        VERIFY0(nvlist_add_nvlist(config, ZPOOL_CONFIG_FEATURE_STATS,
            features));

        mutex_exit(&spa->spa_feat_stats_lock);
}

int
spa_get_stats(const char *name, nvlist_t **config,
    char *altroot, size_t buflen)
{
        int error;
        spa_t *spa;

        *config = NULL;
        error = spa_open_common(name, &spa, FTAG, NULL, config);

        if (spa != NULL) {
                /*
                 * This still leaves a window of inconsistency where the spares
                 * or l2cache devices could change and the config would be
                 * self-inconsistent.
                 */
                spa_config_enter(spa, SCL_CONFIG, FTAG, RW_READER);

                if (*config != NULL) {
                        uint64_t loadtimes[2];

                        loadtimes[0] = spa->spa_loaded_ts.tv_sec;
                        loadtimes[1] = spa->spa_loaded_ts.tv_nsec;
                        VERIFY(nvlist_add_uint64_array(*config,
                            ZPOOL_CONFIG_LOADED_TIME, loadtimes, 2) == 0);

                        VERIFY(nvlist_add_uint64(*config,
                            ZPOOL_CONFIG_ERRCOUNT,
                            spa_get_errlog_size(spa)) == 0);

                        if (spa_suspended(spa))
                                VERIFY(nvlist_add_uint64(*config,
                                    ZPOOL_CONFIG_SUSPENDED,
                                    spa->spa_failmode) == 0);

                        spa_add_spares(spa, *config);
                        spa_add_l2cache(spa, *config);
                        spa_add_feature_stats(spa, *config);
                }
        }

        /*
         * We want to get the alternate root even for faulted pools, so we cheat
         * and call spa_lookup() directly.
         */
        if (altroot) {
                if (spa == NULL) {
                        mutex_enter(&spa_namespace_lock);
                        spa = spa_lookup(name);
                        if (spa)
                                spa_altroot(spa, altroot, buflen);
                        else
                                altroot[0] = '\0';
                        spa = NULL;
                        mutex_exit(&spa_namespace_lock);
                } else {
                        spa_altroot(spa, altroot, buflen);
                }
        }

        if (spa != NULL) {
                spa_config_exit(spa, SCL_CONFIG, FTAG);
                spa_close(spa, FTAG);
        }

        return (error);
}

/*
 * Validate that the auxiliary device array is well formed.  We must have an
 * array of nvlists, each which describes a valid leaf vdev.  If this is an
 * import (mode is VDEV_ALLOC_SPARE), then we allow corrupted spares to be
 * specified, as long as they are well-formed.
 */
static int
spa_validate_aux_devs(spa_t *spa, nvlist_t *nvroot, uint64_t crtxg, int mode,
    spa_aux_vdev_t *sav, const char *config, uint64_t version,
    vdev_labeltype_t label)
{
        nvlist_t **dev;
        uint_t i, ndev;
        vdev_t *vd;
        int error;

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

        /*
         * It's acceptable to have no devs specified.
         */
        if (nvlist_lookup_nvlist_array(nvroot, config, &dev, &ndev) != 0)
                return (0);

        if (ndev == 0)
                return (SET_ERROR(EINVAL));

        /*
         * Make sure the pool is formatted with a version that supports this
         * device type.
         */
        if (spa_version(spa) < version)
                return (SET_ERROR(ENOTSUP));

        /*
         * Set the pending device list so we correctly handle device in-use
         * checking.
         */
        sav->sav_pending = dev;
        sav->sav_npending = ndev;

        for (i = 0; i < ndev; i++) {
                if ((error = spa_config_parse(spa, &vd, dev[i], NULL, 0,
                    mode)) != 0)
                        goto out;

                if (!vd->vdev_ops->vdev_op_leaf) {
                        vdev_free(vd);
                        error = SET_ERROR(EINVAL);
                        goto out;
                }

                vd->vdev_top = vd;

                if ((error = vdev_open(vd)) == 0 &&
                    (error = vdev_label_init(vd, crtxg, label)) == 0) {
                        VERIFY(nvlist_add_uint64(dev[i], ZPOOL_CONFIG_GUID,
                            vd->vdev_guid) == 0);
                }

                vdev_free(vd);

                if (error &&
                    (mode != VDEV_ALLOC_SPARE && mode != VDEV_ALLOC_L2CACHE))
                        goto out;
                else
                        error = 0;
        }

out:
        sav->sav_pending = NULL;
        sav->sav_npending = 0;
        return (error);
}

static int
spa_validate_aux(spa_t *spa, nvlist_t *nvroot, uint64_t crtxg, int mode)
{
        int error;

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

        if ((error = spa_validate_aux_devs(spa, nvroot, crtxg, mode,
            &spa->spa_spares, ZPOOL_CONFIG_SPARES, SPA_VERSION_SPARES,
            VDEV_LABEL_SPARE)) != 0) {
                return (error);
        }

        return (spa_validate_aux_devs(spa, nvroot, crtxg, mode,
            &spa->spa_l2cache, ZPOOL_CONFIG_L2CACHE, SPA_VERSION_L2CACHE,
            VDEV_LABEL_L2CACHE));
}

static void
spa_set_aux_vdevs(spa_aux_vdev_t *sav, nvlist_t **devs, int ndevs,
    const char *config)
{
        int i;

        if (sav->sav_config != NULL) {
                nvlist_t **olddevs;
                uint_t oldndevs;
                nvlist_t **newdevs;

                /*
                 * Generate new dev list by concatenating with the
                 * current dev list.
                 */
                VERIFY(nvlist_lookup_nvlist_array(sav->sav_config, config,
                    &olddevs, &oldndevs) == 0);

                newdevs = kmem_alloc(sizeof (void *) *
                    (ndevs + oldndevs), KM_SLEEP);
                for (i = 0; i < oldndevs; i++)
                        VERIFY(nvlist_dup(olddevs[i], &newdevs[i],
                            KM_SLEEP) == 0);
                for (i = 0; i < ndevs; i++)
                        VERIFY(nvlist_dup(devs[i], &newdevs[i + oldndevs],
                            KM_SLEEP) == 0);

                VERIFY(nvlist_remove(sav->sav_config, config,
                    DATA_TYPE_NVLIST_ARRAY) == 0);

                VERIFY(nvlist_add_nvlist_array(sav->sav_config,
                    config, newdevs, ndevs + oldndevs) == 0);
                for (i = 0; i < oldndevs + ndevs; i++)
                        nvlist_free(newdevs[i]);
                kmem_free(newdevs, (oldndevs + ndevs) * sizeof (void *));
        } else {
                /*
                 * Generate a new dev list.
                 */
                VERIFY(nvlist_alloc(&sav->sav_config, NV_UNIQUE_NAME,
                    KM_SLEEP) == 0);
                VERIFY(nvlist_add_nvlist_array(sav->sav_config, config,
                    devs, ndevs) == 0);
        }
}

/*
 * Stop and drop level 2 ARC devices
 */
void
spa_l2cache_drop(spa_t *spa)
{
        vdev_t *vd;
        int i;
        spa_aux_vdev_t *sav = &spa->spa_l2cache;

        for (i = 0; i < sav->sav_count; i++) {
                uint64_t pool;

                vd = sav->sav_vdevs[i];
                ASSERT(vd != NULL);

                if (spa_l2cache_exists(vd->vdev_guid, &pool) &&
                    pool != 0ULL && l2arc_vdev_present(vd))
                        l2arc_remove_vdev(vd);
        }
}

/*
 * Verify encryption parameters for spa creation. If we are encrypting, we must
 * have the encryption feature flag enabled.
 */
static int
spa_create_check_encryption_params(dsl_crypto_params_t *dcp,
    boolean_t has_encryption)
{
        if (dcp->cp_crypt != ZIO_CRYPT_OFF &&
            dcp->cp_crypt != ZIO_CRYPT_INHERIT &&
            !has_encryption)
                return (SET_ERROR(ENOTSUP));

        return (dmu_objset_create_crypt_check(NULL, dcp));
}

/*
 * Pool Creation
 */
int
spa_create(const char *pool, nvlist_t *nvroot, nvlist_t *props,
    nvlist_t *zplprops, dsl_crypto_params_t *dcp)
{
        spa_t *spa;
        char *altroot = NULL;
        vdev_t *rvd;
        dsl_pool_t *dp;
        dmu_tx_t *tx;
        int error = 0;
        uint64_t txg = TXG_INITIAL;
        nvlist_t **spares, **l2cache;
        uint_t nspares, nl2cache;
        uint64_t version, obj, root_dsobj = 0;
        boolean_t has_features;
        boolean_t has_encryption;
        spa_feature_t feat;
        char *feat_name;
        char *poolname;
        nvlist_t *nvl;

        if (nvlist_lookup_string(props, "tname", &poolname) != 0)
                poolname = (char *)pool;

        /*
         * If this pool already exists, return failure.
         */
        mutex_enter(&spa_namespace_lock);
        if (spa_lookup(poolname) != NULL) {
                mutex_exit(&spa_namespace_lock);
                return (SET_ERROR(EEXIST));
        }

        /*
         * Allocate a new spa_t structure.
         */
        nvl = fnvlist_alloc();
        fnvlist_add_string(nvl, ZPOOL_CONFIG_POOL_NAME, pool);
        (void) nvlist_lookup_string(props,
            zpool_prop_to_name(ZPOOL_PROP_ALTROOT), &altroot);
        spa = spa_add(poolname, nvl, altroot);
        fnvlist_free(nvl);
        spa_activate(spa, spa_mode_global);

        if (props && (error = spa_prop_validate(spa, props))) {
                spa_deactivate(spa);
                spa_remove(spa);
                mutex_exit(&spa_namespace_lock);
                return (error);
        }

        /*
         * Temporary pool names should never be written to disk.
         */
        if (poolname != pool)
                spa->spa_import_flags |= ZFS_IMPORT_TEMP_NAME;

        has_features = B_FALSE;
        has_encryption = B_FALSE;
        for (nvpair_t *elem = nvlist_next_nvpair(props, NULL);
            elem != NULL; elem = nvlist_next_nvpair(props, elem)) {
                if (zpool_prop_feature(nvpair_name(elem))) {
                        has_features = B_TRUE;

                        feat_name = strchr(nvpair_name(elem), '@') + 1;
                        VERIFY0(zfeature_lookup_name(feat_name, &feat));
                        if (feat == SPA_FEATURE_ENCRYPTION)
                                has_encryption = B_TRUE;
                }
        }

        /* verify encryption params, if they were provided */
        if (dcp != NULL) {
                error = spa_create_check_encryption_params(dcp, has_encryption);
                if (error != 0) {
                        spa_deactivate(spa);
                        spa_remove(spa);
                        mutex_exit(&spa_namespace_lock);
                        return (error);
                }
        }

        if (has_features || nvlist_lookup_uint64(props,
            zpool_prop_to_name(ZPOOL_PROP_VERSION), &version) != 0) {
                version = SPA_VERSION;
        }
        ASSERT(SPA_VERSION_IS_SUPPORTED(version));

        spa->spa_first_txg = txg;
        spa->spa_uberblock.ub_txg = txg - 1;
        spa->spa_uberblock.ub_version = version;
        spa->spa_ubsync = spa->spa_uberblock;
        spa->spa_load_state = SPA_LOAD_CREATE;

        /*
         * Create "The Godfather" zio to hold all async IOs
         */
        spa->spa_async_zio_root = kmem_alloc(max_ncpus * sizeof (void *),
            KM_SLEEP);
        for (int i = 0; i < max_ncpus; i++) {
                spa->spa_async_zio_root[i] = zio_root(spa, NULL, NULL,
                    ZIO_FLAG_CANFAIL | ZIO_FLAG_SPECULATIVE |
                    ZIO_FLAG_GODFATHER);
        }

        /*
         * Create the root vdev.
         */
        spa_config_enter(spa, SCL_ALL, FTAG, RW_WRITER);

        error = spa_config_parse(spa, &rvd, nvroot, NULL, 0, VDEV_ALLOC_ADD);

        ASSERT(error != 0 || rvd != NULL);
        ASSERT(error != 0 || spa->spa_root_vdev == rvd);

        if (error == 0 && !zfs_allocatable_devs(nvroot))
                error = SET_ERROR(EINVAL);

        if (error == 0 &&
            (error = vdev_create(rvd, txg, B_FALSE)) == 0 &&
            (error = spa_validate_aux(spa, nvroot, txg,
            VDEV_ALLOC_ADD)) == 0) {
                for (int c = 0; c < rvd->vdev_children; c++) {
                        vdev_metaslab_set_size(rvd->vdev_child[c]);
                        vdev_expand(rvd->vdev_child[c], txg);
                }
        }

        spa_config_exit(spa, SCL_ALL, FTAG);

        if (error != 0) {
                spa_unload(spa);
                spa_deactivate(spa);
                spa_remove(spa);
                mutex_exit(&spa_namespace_lock);
                return (error);
        }

        /*
         * Get the list of spares, if specified.
         */
        if (nvlist_lookup_nvlist_array(nvroot, ZPOOL_CONFIG_SPARES,
            &spares, &nspares) == 0) {
                VERIFY(nvlist_alloc(&spa->spa_spares.sav_config, NV_UNIQUE_NAME,
                    KM_SLEEP) == 0);
                VERIFY(nvlist_add_nvlist_array(spa->spa_spares.sav_config,
                    ZPOOL_CONFIG_SPARES, spares, nspares) == 0);
                spa_config_enter(spa, SCL_ALL, FTAG, RW_WRITER);
                spa_load_spares(spa);
                spa_config_exit(spa, SCL_ALL, FTAG);
                spa->spa_spares.sav_sync = B_TRUE;
        }

        /*
         * Get the list of level 2 cache devices, if specified.
         */
        if (nvlist_lookup_nvlist_array(nvroot, ZPOOL_CONFIG_L2CACHE,
            &l2cache, &nl2cache) == 0) {
                VERIFY(nvlist_alloc(&spa->spa_l2cache.sav_config,
                    NV_UNIQUE_NAME, KM_SLEEP) == 0);
                VERIFY(nvlist_add_nvlist_array(spa->spa_l2cache.sav_config,
                    ZPOOL_CONFIG_L2CACHE, l2cache, nl2cache) == 0);
                spa_config_enter(spa, SCL_ALL, FTAG, RW_WRITER);
                spa_load_l2cache(spa);
                spa_config_exit(spa, SCL_ALL, FTAG);
                spa->spa_l2cache.sav_sync = B_TRUE;
        }

        spa->spa_is_initializing = B_TRUE;
        spa->spa_dsl_pool = dp = dsl_pool_create(spa, zplprops, dcp, txg);
        spa->spa_is_initializing = B_FALSE;

        /*
         * Create DDTs (dedup tables).
         */
        ddt_create(spa);

        spa_update_dspace(spa);

        tx = dmu_tx_create_assigned(dp, txg);

        /*
         * Create the pool's history object.
         */
        if (version >= SPA_VERSION_ZPOOL_HISTORY && !spa->spa_history)
                spa_history_create_obj(spa, tx);

        spa_event_notify(spa, NULL, NULL, ESC_ZFS_POOL_CREATE);
        spa_history_log_version(spa, "create", tx);

        /*
         * Create the pool config object.
         */
        spa->spa_config_object = dmu_object_alloc(spa->spa_meta_objset,
            DMU_OT_PACKED_NVLIST, SPA_CONFIG_BLOCKSIZE,
            DMU_OT_PACKED_NVLIST_SIZE, sizeof (uint64_t), tx);

        if (zap_add(spa->spa_meta_objset,
            DMU_POOL_DIRECTORY_OBJECT, DMU_POOL_CONFIG,
            sizeof (uint64_t), 1, &spa->spa_config_object, tx) != 0) {
                cmn_err(CE_PANIC, "failed to add pool config");
        }

        if (zap_add(spa->spa_meta_objset,
            DMU_POOL_DIRECTORY_OBJECT, DMU_POOL_CREATION_VERSION,
            sizeof (uint64_t), 1, &version, tx) != 0) {
                cmn_err(CE_PANIC, "failed to add pool version");
        }

        /* Newly created pools with the right version are always deflated. */
        if (version >= SPA_VERSION_RAIDZ_DEFLATE) {
                spa->spa_deflate = TRUE;
                if (zap_add(spa->spa_meta_objset,
                    DMU_POOL_DIRECTORY_OBJECT, DMU_POOL_DEFLATE,
                    sizeof (uint64_t), 1, &spa->spa_deflate, tx) != 0) {
                        cmn_err(CE_PANIC, "failed to add deflate");
                }
        }

        /*
         * Create the deferred-free bpobj.  Turn off compression
         * because sync-to-convergence takes longer if the blocksize
         * keeps changing.
         */
        obj = bpobj_alloc(spa->spa_meta_objset, 1 << 14, tx);
        dmu_object_set_compress(spa->spa_meta_objset, obj,
            ZIO_COMPRESS_OFF, tx);
        if (zap_add(spa->spa_meta_objset,
            DMU_POOL_DIRECTORY_OBJECT, DMU_POOL_SYNC_BPOBJ,
            sizeof (uint64_t), 1, &obj, tx) != 0) {
                cmn_err(CE_PANIC, "failed to add bpobj");
        }
        VERIFY3U(0, ==, bpobj_open(&spa->spa_deferred_bpobj,
            spa->spa_meta_objset, obj));

        /*
         * Generate some random noise for salted checksums to operate on.
         */
        (void) random_get_pseudo_bytes(spa->spa_cksum_salt.zcs_bytes,
            sizeof (spa->spa_cksum_salt.zcs_bytes));

        /*
         * Set pool properties.
         */
        spa->spa_bootfs = zpool_prop_default_numeric(ZPOOL_PROP_BOOTFS);
        spa->spa_delegation = zpool_prop_default_numeric(ZPOOL_PROP_DELEGATION);
        spa->spa_failmode = zpool_prop_default_numeric(ZPOOL_PROP_FAILUREMODE);
        spa->spa_autoexpand = zpool_prop_default_numeric(ZPOOL_PROP_AUTOEXPAND);
        spa->spa_multihost = zpool_prop_default_numeric(ZPOOL_PROP_MULTIHOST);

        if (props != NULL) {
                spa_configfile_set(spa, props, B_FALSE);
                spa_sync_props(props, tx);
        }

        dmu_tx_commit(tx);

        /*
         * If the root dataset is encrypted we will need to create key mappings
         * for the zio layer before we start to write any data to disk and hold
         * them until after the first txg has been synced. Waiting for the first
         * transaction to complete also ensures that our bean counters are
         * appropriately updated.
         */
        if (dp->dp_root_dir->dd_crypto_obj != 0) {
                root_dsobj = dsl_dir_phys(dp->dp_root_dir)->dd_head_dataset_obj;
                VERIFY0(spa_keystore_create_mapping_impl(spa, root_dsobj,
                    dp->dp_root_dir, FTAG));
        }

        spa->spa_sync_on = B_TRUE;
        txg_sync_start(dp);
        mmp_thread_start(spa);
        txg_wait_synced(dp, txg);

        if (dp->dp_root_dir->dd_crypto_obj != 0)
                VERIFY0(spa_keystore_remove_mapping(spa, root_dsobj, FTAG));

        spa_config_sync(spa, B_FALSE, B_TRUE);

        /*
         * Don't count references from objsets that are already closed
         * and are making their way through the eviction process.
         */
        spa_evicting_os_wait(spa);
        spa->spa_minref = refcount_count(&spa->spa_refcount);
        spa->spa_load_state = SPA_LOAD_NONE;

        mutex_exit(&spa_namespace_lock);

        return (0);
}

/*
 * Import a non-root pool into the system.
 */
int
spa_import(char *pool, nvlist_t *config, nvlist_t *props, uint64_t flags)
{
        spa_t *spa;
        char *altroot = NULL;
        spa_load_state_t state = SPA_LOAD_IMPORT;
        zpool_rewind_policy_t policy;
        uint64_t mode = spa_mode_global;
        uint64_t readonly = B_FALSE;
        int error;
        nvlist_t *nvroot;
        nvlist_t **spares, **l2cache;
        uint_t nspares, nl2cache;

        /*
         * If a pool with this name exists, return failure.
         */
        mutex_enter(&spa_namespace_lock);
        if (spa_lookup(pool) != NULL) {
                mutex_exit(&spa_namespace_lock);
                return (SET_ERROR(EEXIST));
        }

        /*
         * Create and initialize the spa structure.
         */
        (void) nvlist_lookup_string(props,
            zpool_prop_to_name(ZPOOL_PROP_ALTROOT), &altroot);
        (void) nvlist_lookup_uint64(props,
            zpool_prop_to_name(ZPOOL_PROP_READONLY), &readonly);
        if (readonly)
                mode = FREAD;
        spa = spa_add(pool, config, altroot);
        spa->spa_import_flags = flags;

        /*
         * Verbatim import - Take a pool and insert it into the namespace
         * as if it had been loaded at boot.
         */
        if (spa->spa_import_flags & ZFS_IMPORT_VERBATIM) {
                if (props != NULL)
                        spa_configfile_set(spa, props, B_FALSE);

                spa_config_sync(spa, B_FALSE, B_TRUE);
                spa_event_notify(spa, NULL, NULL, ESC_ZFS_POOL_IMPORT);

                mutex_exit(&spa_namespace_lock);
                return (0);
        }

        spa_activate(spa, mode);

        /*
         * Don't start async tasks until we know everything is healthy.
         */
        spa_async_suspend(spa);

        zpool_get_rewind_policy(config, &policy);
        if (policy.zrp_request & ZPOOL_DO_REWIND)
                state = SPA_LOAD_RECOVER;

        /*
         * Pass off the heavy lifting to spa_load().  Pass TRUE for mosconfig
         * because the user-supplied config is actually the one to trust when
         * doing an import.
         */
        if (state != SPA_LOAD_RECOVER)
                spa->spa_last_ubsync_txg = spa->spa_load_txg = 0;

        error = spa_load_best(spa, state, B_TRUE, policy.zrp_txg,
            policy.zrp_request);

        /*
         * Propagate anything learned while loading the pool and pass it
         * back to caller (i.e. rewind info, missing devices, etc).
         */
        VERIFY(nvlist_add_nvlist(config, ZPOOL_CONFIG_LOAD_INFO,
            spa->spa_load_info) == 0);

        spa_config_enter(spa, SCL_ALL, FTAG, RW_WRITER);
        /*
         * Toss any existing sparelist, as it doesn't have any validity
         * anymore, and conflicts with spa_has_spare().
         */
        if (spa->spa_spares.sav_config) {
                nvlist_free(spa->spa_spares.sav_config);
                spa->spa_spares.sav_config = NULL;
                spa_load_spares(spa);
        }
        if (spa->spa_l2cache.sav_config) {
                nvlist_free(spa->spa_l2cache.sav_config);
                spa->spa_l2cache.sav_config = NULL;
                spa_load_l2cache(spa);
        }

        VERIFY(nvlist_lookup_nvlist(config, ZPOOL_CONFIG_VDEV_TREE,
            &nvroot) == 0);
        spa_config_exit(spa, SCL_ALL, FTAG);

        if (props != NULL)
                spa_configfile_set(spa, props, B_FALSE);

        if (error != 0 || (props && spa_writeable(spa) &&
            (error = spa_prop_set(spa, props)))) {
                spa_unload(spa);
                spa_deactivate(spa);
                spa_remove(spa);
                mutex_exit(&spa_namespace_lock);
                return (error);
        }

        spa_async_resume(spa);

        /*
         * Override any spares and level 2 cache devices as specified by
         * the user, as these may have correct device names/devids, etc.
         */
        if (nvlist_lookup_nvlist_array(nvroot, ZPOOL_CONFIG_SPARES,
            &spares, &nspares) == 0) {
                if (spa->spa_spares.sav_config)
                        VERIFY(nvlist_remove(spa->spa_spares.sav_config,
                            ZPOOL_CONFIG_SPARES, DATA_TYPE_NVLIST_ARRAY) == 0);
                else
                        VERIFY(nvlist_alloc(&spa->spa_spares.sav_config,
                            NV_UNIQUE_NAME, KM_SLEEP) == 0);
                VERIFY(nvlist_add_nvlist_array(spa->spa_spares.sav_config,
                    ZPOOL_CONFIG_SPARES, spares, nspares) == 0);
                spa_config_enter(spa, SCL_ALL, FTAG, RW_WRITER);
                spa_load_spares(spa);
                spa_config_exit(spa, SCL_ALL, FTAG);
                spa->spa_spares.sav_sync = B_TRUE;
        }
        if (nvlist_lookup_nvlist_array(nvroot, ZPOOL_CONFIG_L2CACHE,
            &l2cache, &nl2cache) == 0) {
                if (spa->spa_l2cache.sav_config)
                        VERIFY(nvlist_remove(spa->spa_l2cache.sav_config,
                            ZPOOL_CONFIG_L2CACHE, DATA_TYPE_NVLIST_ARRAY) == 0);
                else
                        VERIFY(nvlist_alloc(&spa->spa_l2cache.sav_config,
                            NV_UNIQUE_NAME, KM_SLEEP) == 0);
                VERIFY(nvlist_add_nvlist_array(spa->spa_l2cache.sav_config,
                    ZPOOL_CONFIG_L2CACHE, l2cache, nl2cache) == 0);
                spa_config_enter(spa, SCL_ALL, FTAG, RW_WRITER);
                spa_load_l2cache(spa);
                spa_config_exit(spa, SCL_ALL, FTAG);
                spa->spa_l2cache.sav_sync = B_TRUE;
        }

        /*
         * Check for any removed devices.
         */
        if (spa->spa_autoreplace) {
                spa_aux_check_removed(&spa->spa_spares);
                spa_aux_check_removed(&spa->spa_l2cache);
        }

        if (spa_writeable(spa)) {
                /*
                 * Update the config cache to include the newly-imported pool.
                 */
                spa_config_update(spa, SPA_CONFIG_UPDATE_POOL);
        }

        /*
         * It's possible that the pool was expanded while it was exported.
         * We kick off an async task to handle this for us.
         */
        spa_async_request(spa, SPA_ASYNC_AUTOEXPAND);

        spa_history_log_version(spa, "import", NULL);

        spa_event_notify(spa, NULL, NULL, ESC_ZFS_POOL_IMPORT);

        zvol_create_minors(spa, pool, B_TRUE);

        mutex_exit(&spa_namespace_lock);

        return (0);
}

nvlist_t *
spa_tryimport(nvlist_t *tryconfig)
{
        nvlist_t *config = NULL;
        char *poolname;
        spa_t *spa;
        uint64_t state;
        int error;

        if (nvlist_lookup_string(tryconfig, ZPOOL_CONFIG_POOL_NAME, &poolname))
                return (NULL);

        if (nvlist_lookup_uint64(tryconfig, ZPOOL_CONFIG_POOL_STATE, &state))
                return (NULL);

        /*
         * Create and initialize the spa structure.
         */
        mutex_enter(&spa_namespace_lock);
        spa = spa_add(TRYIMPORT_NAME, tryconfig, NULL);
        spa_activate(spa, FREAD);

        /*
         * Pass off the heavy lifting to spa_load().
         * Pass TRUE for mosconfig because the user-supplied config
         * is actually the one to trust when doing an import.
         */
        error = spa_load(spa, SPA_LOAD_TRYIMPORT, SPA_IMPORT_EXISTING, B_TRUE);

        /*
         * If 'tryconfig' was at least parsable, return the current config.
         */
        if (spa->spa_root_vdev != NULL) {
                config = spa_config_generate(spa, NULL, -1ULL, B_TRUE);
                VERIFY(nvlist_add_string(config, ZPOOL_CONFIG_POOL_NAME,
                    poolname) == 0);
                VERIFY(nvlist_add_uint64(config, ZPOOL_CONFIG_POOL_STATE,
                    state) == 0);
                VERIFY(nvlist_add_uint64(config, ZPOOL_CONFIG_TIMESTAMP,
                    spa->spa_uberblock.ub_timestamp) == 0);
                VERIFY(nvlist_add_nvlist(config, ZPOOL_CONFIG_LOAD_INFO,
                    spa->spa_load_info) == 0);
                VERIFY(nvlist_add_uint64(config, ZPOOL_CONFIG_ERRATA,
                    spa->spa_errata) == 0);

                /*
                 * If the bootfs property exists on this pool then we
                 * copy it out so that external consumers can tell which
                 * pools are bootable.
                 */
                if ((!error || error == EEXIST) && spa->spa_bootfs) {
                        char *tmpname = kmem_alloc(MAXPATHLEN, KM_SLEEP);

                        /*
                         * We have to play games with the name since the
                         * pool was opened as TRYIMPORT_NAME.
                         */
                        if (dsl_dsobj_to_dsname(spa_name(spa),
                            spa->spa_bootfs, tmpname) == 0) {
                                char *cp;
                                char *dsname;

                                dsname = kmem_alloc(MAXPATHLEN, KM_SLEEP);

                                cp = strchr(tmpname, '/');
                                if (cp == NULL) {
                                        (void) strlcpy(dsname, tmpname,
                                            MAXPATHLEN);
                                } else {
                                        (void) snprintf(dsname, MAXPATHLEN,
                                            "%s/%s", poolname, ++cp);
                                }
                                VERIFY(nvlist_add_string(config,
                                    ZPOOL_CONFIG_BOOTFS, dsname) == 0);
                                kmem_free(dsname, MAXPATHLEN);
                        }
                        kmem_free(tmpname, MAXPATHLEN);
                }

                /*
                 * Add the list of hot spares and level 2 cache devices.
                 */
                spa_config_enter(spa, SCL_CONFIG, FTAG, RW_READER);
                spa_add_spares(spa, config);
                spa_add_l2cache(spa, config);
                spa_config_exit(spa, SCL_CONFIG, FTAG);
        }

        spa_unload(spa);
        spa_deactivate(spa);
        spa_remove(spa);
        mutex_exit(&spa_namespace_lock);

        return (config);
}

/*
 * Pool export/destroy
 *
 * The act of destroying or exporting a pool is very simple.  We make sure there
 * is no more pending I/O and any references to the pool are gone.  Then, we
 * update the pool state and sync all the labels to disk, removing the
 * configuration from the cache afterwards. If the 'hardforce' flag is set, then
 * we don't sync the labels or remove the configuration cache.
 */
static int
spa_export_common(char *pool, int new_state, nvlist_t **oldconfig,
    boolean_t force, boolean_t hardforce)
{
        spa_t *spa;

        if (oldconfig)
                *oldconfig = NULL;

        if (!(spa_mode_global & FWRITE))
                return (SET_ERROR(EROFS));

        mutex_enter(&spa_namespace_lock);
        if ((spa = spa_lookup(pool)) == NULL) {
                mutex_exit(&spa_namespace_lock);
                return (SET_ERROR(ENOENT));
        }

        /*
         * Put a hold on the pool, drop the namespace lock, stop async tasks,
         * reacquire the namespace lock, and see if we can export.
         */
        spa_open_ref(spa, FTAG);
        mutex_exit(&spa_namespace_lock);
        spa_async_suspend(spa);
        if (spa->spa_zvol_taskq) {
                zvol_remove_minors(spa, spa_name(spa), B_TRUE);
                taskq_wait(spa->spa_zvol_taskq);
        }
        mutex_enter(&spa_namespace_lock);
        spa_close(spa, FTAG);

        if (spa->spa_state == POOL_STATE_UNINITIALIZED)
                goto export_spa;
        /*
         * The pool will be in core if it's openable, in which case we can
         * modify its state.  Objsets may be open only because they're dirty,
         * so we have to force it to sync before checking spa_refcnt.
         */
        if (spa->spa_sync_on) {
                txg_wait_synced(spa->spa_dsl_pool, 0);
                spa_evicting_os_wait(spa);
        }

        /*
         * A pool cannot be exported or destroyed if there are active
         * references.  If we are resetting a pool, allow references by
         * fault injection handlers.
         */
        if (!spa_refcount_zero(spa) ||
            (spa->spa_inject_ref != 0 &&
            new_state != POOL_STATE_UNINITIALIZED)) {
                spa_async_resume(spa);
                mutex_exit(&spa_namespace_lock);
                return (SET_ERROR(EBUSY));
        }

        if (spa->spa_sync_on) {
                /*
                 * A pool cannot be exported if it has an active shared spare.
                 * This is to prevent other pools stealing the active spare
                 * from an exported pool. At user's own will, such pool can
                 * be forcedly exported.
                 */
                if (!force && new_state == POOL_STATE_EXPORTED &&
                    spa_has_active_shared_spare(spa)) {
                        spa_async_resume(spa);
                        mutex_exit(&spa_namespace_lock);
                        return (SET_ERROR(EXDEV));
                }

                /*
                 * We want this to be reflected on every label,
                 * so mark them all dirty.  spa_unload() will do the
                 * final sync that pushes these changes out.
                 */
                if (new_state != POOL_STATE_UNINITIALIZED && !hardforce) {
                        spa_config_enter(spa, SCL_ALL, FTAG, RW_WRITER);
                        spa->spa_state = new_state;
                        spa->spa_final_txg = spa_last_synced_txg(spa) +
                            TXG_DEFER_SIZE + 1;
                        vdev_config_dirty(spa->spa_root_vdev);
                        spa_config_exit(spa, SCL_ALL, FTAG);
                }
        }

export_spa:
        if (new_state == POOL_STATE_DESTROYED)
                spa_event_notify(spa, NULL, NULL, ESC_ZFS_POOL_DESTROY);
        else if (new_state == POOL_STATE_EXPORTED)
                spa_event_notify(spa, NULL, NULL, ESC_ZFS_POOL_EXPORT);

        if (spa->spa_state != POOL_STATE_UNINITIALIZED) {
                spa_unload(spa);
                spa_deactivate(spa);
        }

        if (oldconfig && spa->spa_config)
                VERIFY(nvlist_dup(spa->spa_config, oldconfig, 0) == 0);

        if (new_state != POOL_STATE_UNINITIALIZED) {
                if (!hardforce)
                        spa_config_sync(spa, B_TRUE, B_TRUE);
                spa_remove(spa);
        }
        mutex_exit(&spa_namespace_lock);

        return (0);
}

/*
 * Destroy a storage pool.
 */
int
spa_destroy(char *pool)
{
        return (spa_export_common(pool, POOL_STATE_DESTROYED, NULL,
            B_FALSE, B_FALSE));
}

/*
 * Export a storage pool.
 */
int
spa_export(char *pool, nvlist_t **oldconfig, boolean_t force,
    boolean_t hardforce)
{
        return (spa_export_common(pool, POOL_STATE_EXPORTED, oldconfig,
            force, hardforce));
}

/*
 * Similar to spa_export(), this unloads the spa_t without actually removing it
 * from the namespace in any way.
 */
int
spa_reset(char *pool)
{
        return (spa_export_common(pool, POOL_STATE_UNINITIALIZED, NULL,
            B_FALSE, B_FALSE));
}

/*
 * ==========================================================================
 * Device manipulation
 * ==========================================================================
 */

/*
 * Add a device to a storage pool.
 */
int
spa_vdev_add(spa_t *spa, nvlist_t *nvroot)
{
        uint64_t txg, id;
        int error;
        vdev_t *rvd = spa->spa_root_vdev;
        vdev_t *vd, *tvd;
        nvlist_t **spares, **l2cache;
        uint_t nspares, nl2cache;

        ASSERT(spa_writeable(spa));

        txg = spa_vdev_enter(spa);

        if ((error = spa_config_parse(spa, &vd, nvroot, NULL, 0,
            VDEV_ALLOC_ADD)) != 0)
                return (spa_vdev_exit(spa, NULL, txg, error));

        spa->spa_pending_vdev = vd;     /* spa_vdev_exit() will clear this */

        if (nvlist_lookup_nvlist_array(nvroot, ZPOOL_CONFIG_SPARES, &spares,
            &nspares) != 0)
                nspares = 0;

        if (nvlist_lookup_nvlist_array(nvroot, ZPOOL_CONFIG_L2CACHE, &l2cache,
            &nl2cache) != 0)
                nl2cache = 0;

        if (vd->vdev_children == 0 && nspares == 0 && nl2cache == 0)
                return (spa_vdev_exit(spa, vd, txg, EINVAL));

        if (vd->vdev_children != 0 &&
            (error = vdev_create(vd, txg, B_FALSE)) != 0)
                return (spa_vdev_exit(spa, vd, txg, error));

        /*
         * We must validate the spares and l2cache devices after checking the
         * children.  Otherwise, vdev_inuse() will blindly overwrite the spare.
         */
        if ((error = spa_validate_aux(spa, nvroot, txg, VDEV_ALLOC_ADD)) != 0)
                return (spa_vdev_exit(spa, vd, txg, error));

        /*
         * Transfer each new top-level vdev from vd to rvd.
         */
        for (int c = 0; c < vd->vdev_children; c++) {

                /*
                 * Set the vdev id to the first hole, if one exists.
                 */
                for (id = 0; id < rvd->vdev_children; id++) {
                        if (rvd->vdev_child[id]->vdev_ishole) {
                                vdev_free(rvd->vdev_child[id]);
                                break;
                        }
                }
                tvd = vd->vdev_child[c];
                vdev_remove_child(vd, tvd);
                tvd->vdev_id = id;
                vdev_add_child(rvd, tvd);
                vdev_config_dirty(tvd);
        }

        if (nspares != 0) {
                spa_set_aux_vdevs(&spa->spa_spares, spares, nspares,
                    ZPOOL_CONFIG_SPARES);
                spa_load_spares(spa);
                spa->spa_spares.sav_sync = B_TRUE;
        }

        if (nl2cache != 0) {
                spa_set_aux_vdevs(&spa->spa_l2cache, l2cache, nl2cache,
                    ZPOOL_CONFIG_L2CACHE);
                spa_load_l2cache(spa);
                spa->spa_l2cache.sav_sync = B_TRUE;
        }

        /*
         * We have to be careful when adding new vdevs to an existing pool.
         * If other threads start allocating from these vdevs before we
         * sync the config cache, and we lose power, then upon reboot we may
         * fail to open the pool because there are DVAs that the config cache
         * can't translate.  Therefore, we first add the vdevs without
         * initializing metaslabs; sync the config cache (via spa_vdev_exit());
         * and then let spa_config_update() initialize the new metaslabs.
         *
         * spa_load() checks for added-but-not-initialized vdevs, so that
         * if we lose power at any point in this sequence, the remaining
         * steps will be completed the next time we load the pool.
         */
        (void) spa_vdev_exit(spa, vd, txg, 0);

        mutex_enter(&spa_namespace_lock);
        spa_config_update(spa, SPA_CONFIG_UPDATE_POOL);
        spa_event_notify(spa, NULL, NULL, ESC_ZFS_VDEV_ADD);
        mutex_exit(&spa_namespace_lock);

        return (0);
}

/*
 * Attach a device to a mirror.  The arguments are the path to any device
 * in the mirror, and the nvroot for the new device.  If the path specifies
 * a device that is not mirrored, we automatically insert the mirror vdev.
 *
 * If 'replacing' is specified, the new device is intended to replace the
 * existing device; in this case the two devices are made into their own
 * mirror using the 'replacing' vdev, which is functionally identical to
 * the mirror vdev (it actually reuses all the same ops) but has a few
 * extra rules: you can't attach to it after it's been created, and upon
 * completion of resilvering, the first disk (the one being replaced)
 * is automatically detached.
 */
int
spa_vdev_attach(spa_t *spa, uint64_t guid, nvlist_t *nvroot, int replacing)
{
        uint64_t txg, dtl_max_txg;
        ASSERTV(vdev_t *rvd = spa->spa_root_vdev);
        vdev_t *oldvd, *newvd, *newrootvd, *pvd, *tvd;
        vdev_ops_t *pvops;
        char *oldvdpath, *newvdpath;
        int newvd_isspare;
        int error;

        ASSERT(spa_writeable(spa));

        txg = spa_vdev_enter(spa);

        oldvd = spa_lookup_by_guid(spa, guid, B_FALSE);

        if (oldvd == NULL)
                return (spa_vdev_exit(spa, NULL, txg, ENODEV));

        if (!oldvd->vdev_ops->vdev_op_leaf)
                return (spa_vdev_exit(spa, NULL, txg, ENOTSUP));

        pvd = oldvd->vdev_parent;

        if ((error = spa_config_parse(spa, &newrootvd, nvroot, NULL, 0,
            VDEV_ALLOC_ATTACH)) != 0)
                return (spa_vdev_exit(spa, NULL, txg, EINVAL));

        if (newrootvd->vdev_children != 1)
                return (spa_vdev_exit(spa, newrootvd, txg, EINVAL));

        newvd = newrootvd->vdev_child[0];

        if (!newvd->vdev_ops->vdev_op_leaf)
                return (spa_vdev_exit(spa, newrootvd, txg, EINVAL));

        if ((error = vdev_create(newrootvd, txg, replacing)) != 0)
                return (spa_vdev_exit(spa, newrootvd, txg, error));

        /*
         * Spares can't replace logs
         */
        if (oldvd->vdev_top->vdev_islog && newvd->vdev_isspare)
                return (spa_vdev_exit(spa, newrootvd, txg, ENOTSUP));

        if (!replacing) {
                /*
                 * For attach, the only allowable parent is a mirror or the root
                 * vdev.
                 */
                if (pvd->vdev_ops != &vdev_mirror_ops &&
                    pvd->vdev_ops != &vdev_root_ops)
                        return (spa_vdev_exit(spa, newrootvd, txg, ENOTSUP));

                pvops = &vdev_mirror_ops;
        } else {
                /*
                 * Active hot spares can only be replaced by inactive hot
                 * spares.
                 */
                if (pvd->vdev_ops == &vdev_spare_ops &&
                    oldvd->vdev_isspare &&
                    !spa_has_spare(spa, newvd->vdev_guid))
                        return (spa_vdev_exit(spa, newrootvd, txg, ENOTSUP));

                /*
                 * If the source is a hot spare, and the parent isn't already a
                 * spare, then we want to create a new hot spare.  Otherwise, we
                 * want to create a replacing vdev.  The user is not allowed to
                 * attach to a spared vdev child unless the 'isspare' state is
                 * the same (spare replaces spare, non-spare replaces
                 * non-spare).
                 */
                if (pvd->vdev_ops == &vdev_replacing_ops &&
                    spa_version(spa) < SPA_VERSION_MULTI_REPLACE) {
                        return (spa_vdev_exit(spa, newrootvd, txg, ENOTSUP));
                } else if (pvd->vdev_ops == &vdev_spare_ops &&
                    newvd->vdev_isspare != oldvd->vdev_isspare) {
                        return (spa_vdev_exit(spa, newrootvd, txg, ENOTSUP));
                }

                if (newvd->vdev_isspare)
                        pvops = &vdev_spare_ops;
                else
                        pvops = &vdev_replacing_ops;
        }

        /*
         * Make sure the new device is big enough.
         */
        if (newvd->vdev_asize < vdev_get_min_asize(oldvd))
                return (spa_vdev_exit(spa, newrootvd, txg, EOVERFLOW));

        /*
         * The new device cannot have a higher alignment requirement
         * than the top-level vdev.
         */
        if (newvd->vdev_ashift > oldvd->vdev_top->vdev_ashift)
                return (spa_vdev_exit(spa, newrootvd, txg, EDOM));

        /*
         * If this is an in-place replacement, update oldvd's path and devid
         * to make it distinguishable from newvd, and unopenable from now on.
         */
        if (strcmp(oldvd->vdev_path, newvd->vdev_path) == 0) {
                spa_strfree(oldvd->vdev_path);
                oldvd->vdev_path = kmem_alloc(strlen(newvd->vdev_path) + 5,
                    KM_SLEEP);
                (void) sprintf(oldvd->vdev_path, "%s/%s",
                    newvd->vdev_path, "old");
                if (oldvd->vdev_devid != NULL) {
                        spa_strfree(oldvd->vdev_devid);
                        oldvd->vdev_devid = NULL;
                }
        }

        /* mark the device being resilvered */
        newvd->vdev_resilver_txg = txg;

        /*
         * If the parent is not a mirror, or if we're replacing, insert the new
         * mirror/replacing/spare vdev above oldvd.
         */
        if (pvd->vdev_ops != pvops)
                pvd = vdev_add_parent(oldvd, pvops);

        ASSERT(pvd->vdev_top->vdev_parent == rvd);
        ASSERT(pvd->vdev_ops == pvops);
        ASSERT(oldvd->vdev_parent == pvd);

        /*
         * Extract the new device from its root and add it to pvd.
         */
        vdev_remove_child(newrootvd, newvd);
        newvd->vdev_id = pvd->vdev_children;
        newvd->vdev_crtxg = oldvd->vdev_crtxg;
        vdev_add_child(pvd, newvd);

        /*
         * Reevaluate the parent vdev state.
         */
        vdev_propagate_state(pvd);

        tvd = newvd->vdev_top;
        ASSERT(pvd->vdev_top == tvd);
        ASSERT(tvd->vdev_parent == rvd);

        vdev_config_dirty(tvd);

        /*
         * Set newvd's DTL to [TXG_INITIAL, dtl_max_txg) so that we account
         * for any dmu_sync-ed blocks.  It will propagate upward when
         * spa_vdev_exit() calls vdev_dtl_reassess().
         */
        dtl_max_txg = txg + TXG_CONCURRENT_STATES;

        vdev_dtl_dirty(newvd, DTL_MISSING, TXG_INITIAL,
            dtl_max_txg - TXG_INITIAL);

        if (newvd->vdev_isspare) {
                spa_spare_activate(newvd);
                spa_event_notify(spa, newvd, NULL, ESC_ZFS_VDEV_SPARE);
        }

        oldvdpath = spa_strdup(oldvd->vdev_path);
        newvdpath = spa_strdup(newvd->vdev_path);
        newvd_isspare = newvd->vdev_isspare;

        /*
         * Mark newvd's DTL dirty in this txg.
         */
        vdev_dirty(tvd, VDD_DTL, newvd, txg);

        /*
         * Schedule the resilver to restart in the future. We do this to
         * ensure that dmu_sync-ed blocks have been stitched into the
         * respective datasets.
         */
        dsl_resilver_restart(spa->spa_dsl_pool, dtl_max_txg);

        if (spa->spa_bootfs)
                spa_event_notify(spa, newvd, NULL, ESC_ZFS_BOOTFS_VDEV_ATTACH);

        spa_event_notify(spa, newvd, NULL, ESC_ZFS_VDEV_ATTACH);

        /*
         * Commit the config
         */
        (void) spa_vdev_exit(spa, newrootvd, dtl_max_txg, 0);

        spa_history_log_internal(spa, "vdev attach", NULL,
            "%s vdev=%s %s vdev=%s",
            replacing && newvd_isspare ? "spare in" :
            replacing ? "replace" : "attach", newvdpath,
            replacing ? "for" : "to", oldvdpath);

        spa_strfree(oldvdpath);
        spa_strfree(newvdpath);

        return (0);
}

/*
 * Detach a device from a mirror or replacing vdev.
 *
 * If 'replace_done' is specified, only detach if the parent
 * is a replacing vdev.
 */
int
spa_vdev_detach(spa_t *spa, uint64_t guid, uint64_t pguid, int replace_done)
{
        uint64_t txg;
        int error;
        ASSERTV(vdev_t *rvd = spa->spa_root_vdev);
        vdev_t *vd, *pvd, *cvd, *tvd;
        boolean_t unspare = B_FALSE;
        uint64_t unspare_guid = 0;
        char *vdpath;

        ASSERT(spa_writeable(spa));

        txg = spa_vdev_enter(spa);

        vd = spa_lookup_by_guid(spa, guid, B_FALSE);

        if (vd == NULL)
                return (spa_vdev_exit(spa, NULL, txg, ENODEV));

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

        pvd = vd->vdev_parent;

        /*
         * If the parent/child relationship is not as expected, don't do it.
         * Consider M(A,R(B,C)) -- that is, a mirror of A with a replacing
         * vdev that's replacing B with C.  The user's intent in replacing
         * is to go from M(A,B) to M(A,C).  If the user decides to cancel
         * the replace by detaching C, the expected behavior is to end up
         * M(A,B).  But suppose that right after deciding to detach C,
         * the replacement of B completes.  We would have M(A,C), and then
         * ask to detach C, which would leave us with just A -- not what
         * the user wanted.  To prevent this, we make sure that the
         * parent/child relationship hasn't changed -- in this example,
         * that C's parent is still the replacing vdev R.
         */
        if (pvd->vdev_guid != pguid && pguid != 0)
                return (spa_vdev_exit(spa, NULL, txg, EBUSY));

        /*
         * Only 'replacing' or 'spare' vdevs can be replaced.
         */
        if (replace_done && pvd->vdev_ops != &vdev_replacing_ops &&
            pvd->vdev_ops != &vdev_spare_ops)
                return (spa_vdev_exit(spa, NULL, txg, ENOTSUP));

        ASSERT(pvd->vdev_ops != &vdev_spare_ops ||
            spa_version(spa) >= SPA_VERSION_SPARES);

        /*
         * Only mirror, replacing, and spare vdevs support detach.
         */
        if (pvd->vdev_ops != &vdev_replacing_ops &&
            pvd->vdev_ops != &vdev_mirror_ops &&
            pvd->vdev_ops != &vdev_spare_ops)
                return (spa_vdev_exit(spa, NULL, txg, ENOTSUP));

        /*
         * If this device has the only valid copy of some data,
         * we cannot safely detach it.
         */
        if (vdev_dtl_required(vd))
                return (spa_vdev_exit(spa, NULL, txg, EBUSY));

        ASSERT(pvd->vdev_children >= 2);

        /*
         * If we are detaching the second disk from a replacing vdev, then
         * check to see if we changed the original vdev's path to have "/old"
         * at the end in spa_vdev_attach().  If so, undo that change now.
         */
        if (pvd->vdev_ops == &vdev_replacing_ops && vd->vdev_id > 0 &&
            vd->vdev_path != NULL) {
                size_t len = strlen(vd->vdev_path);

                for (int c = 0; c < pvd->vdev_children; c++) {
                        cvd = pvd->vdev_child[c];

                        if (cvd == vd || cvd->vdev_path == NULL)
                                continue;

                        if (strncmp(cvd->vdev_path, vd->vdev_path, len) == 0 &&
                            strcmp(cvd->vdev_path + len, "/old") == 0) {
                                spa_strfree(cvd->vdev_path);
                                cvd->vdev_path = spa_strdup(vd->vdev_path);
                                break;
                        }
                }
        }

        /*
         * If we are detaching the original disk from a spare, then it implies
         * that the spare should become a real disk, and be removed from the
         * active spare list for the pool.
         */
        if (pvd->vdev_ops == &vdev_spare_ops &&
            vd->vdev_id == 0 &&
            pvd->vdev_child[pvd->vdev_children - 1]->vdev_isspare)
                unspare = B_TRUE;

        /*
         * Erase the disk labels so the disk can be used for other things.
         * This must be done after all other error cases are handled,
         * but before we disembowel vd (so we can still do I/O to it).
         * But if we can't do it, don't treat the error as fatal --
         * it may be that the unwritability of the disk is the reason
         * it's being detached!
         */
        error = vdev_label_init(vd, 0, VDEV_LABEL_REMOVE);

        /*
         * Remove vd from its parent and compact the parent's children.
         */
        vdev_remove_child(pvd, vd);
        vdev_compact_children(pvd);

        /*
         * Remember one of the remaining children so we can get tvd below.
         */
        cvd = pvd->vdev_child[pvd->vdev_children - 1];

        /*
         * If we need to remove the remaining child from the list of hot spares,
         * do it now, marking the vdev as no longer a spare in the process.
         * We must do this before vdev_remove_parent(), because that can
         * change the GUID if it creates a new toplevel GUID.  For a similar
         * reason, we must remove the spare now, in the same txg as the detach;
         * otherwise someone could attach a new sibling, change the GUID, and
         * the subsequent attempt to spa_vdev_remove(unspare_guid) would fail.
         */
        if (unspare) {
                ASSERT(cvd->vdev_isspare);
                spa_spare_remove(cvd);
                unspare_guid = cvd->vdev_guid;
                (void) spa_vdev_remove(spa, unspare_guid, B_TRUE);
                cvd->vdev_unspare = B_TRUE;
        }

        /*
         * If the parent mirror/replacing vdev only has one child,
         * the parent is no longer needed.  Remove it from the tree.
         */
        if (pvd->vdev_children == 1) {
                if (pvd->vdev_ops == &vdev_spare_ops)
                        cvd->vdev_unspare = B_FALSE;
                vdev_remove_parent(cvd);
        }


        /*
         * We don't set tvd until now because the parent we just removed
         * may have been the previous top-level vdev.
         */
        tvd = cvd->vdev_top;
        ASSERT(tvd->vdev_parent == rvd);

        /*
         * Reevaluate the parent vdev state.
         */
        vdev_propagate_state(cvd);

        /*
         * If the 'autoexpand' property is set on the pool then automatically
         * try to expand the size of the pool. For example if the device we
         * just detached was smaller than the others, it may be possible to
         * add metaslabs (i.e. grow the pool). We need to reopen the vdev
         * first so that we can obtain the updated sizes of the leaf vdevs.
         */
        if (spa->spa_autoexpand) {
                vdev_reopen(tvd);
                vdev_expand(tvd, txg);
        }

        vdev_config_dirty(tvd);

        /*
         * Mark vd's DTL as dirty in this txg.  vdev_dtl_sync() will see that
         * vd->vdev_detached is set and free vd's DTL object in syncing context.
         * But first make sure we're not on any *other* txg's DTL list, to
         * prevent vd from being accessed after it's freed.
         */
        vdpath = spa_strdup(vd->vdev_path ? vd->vdev_path : "none");
        for (int t = 0; t < TXG_SIZE; t++)
                (void) txg_list_remove_this(&tvd->vdev_dtl_list, vd, t);
        vd->vdev_detached = B_TRUE;
        vdev_dirty(tvd, VDD_DTL, vd, txg);

        spa_event_notify(spa, vd, NULL, ESC_ZFS_VDEV_REMOVE);

        /* hang on to the spa before we release the lock */
        spa_open_ref(spa, FTAG);

        error = spa_vdev_exit(spa, vd, txg, 0);

        spa_history_log_internal(spa, "detach", NULL,
            "vdev=%s", vdpath);
        spa_strfree(vdpath);

        /*
         * If this was the removal of the original device in a hot spare vdev,
         * then we want to go through and remove the device from the hot spare
         * list of every other pool.
         */
        if (unspare) {
                spa_t *altspa = NULL;

                mutex_enter(&spa_namespace_lock);
                while ((altspa = spa_next(altspa)) != NULL) {
                        if (altspa->spa_state != POOL_STATE_ACTIVE ||
                            altspa == spa)
                                continue;

                        spa_open_ref(altspa, FTAG);
                        mutex_exit(&spa_namespace_lock);
                        (void) spa_vdev_remove(altspa, unspare_guid, B_TRUE);
                        mutex_enter(&spa_namespace_lock);
                        spa_close(altspa, FTAG);
                }
                mutex_exit(&spa_namespace_lock);

                /* search the rest of the vdevs for spares to remove */
                spa_vdev_resilver_done(spa);
        }

        /* all done with the spa; OK to release */
        mutex_enter(&spa_namespace_lock);
        spa_close(spa, FTAG);
        mutex_exit(&spa_namespace_lock);

        return (error);
}

/*
 * Split a set of devices from their mirrors, and create a new pool from them.
 */
int
spa_vdev_split_mirror(spa_t *spa, char *newname, nvlist_t *config,
    nvlist_t *props, boolean_t exp)
{
        int error = 0;
        uint64_t txg, *glist;
        spa_t *newspa;
        uint_t c, children, lastlog;
        nvlist_t **child, *nvl, *tmp;
        dmu_tx_t *tx;
        char *altroot = NULL;
        vdev_t *rvd, **vml = NULL;                      /* vdev modify list */
        boolean_t activate_slog;

        ASSERT(spa_writeable(spa));

        txg = spa_vdev_enter(spa);

        /* clear the log and flush everything up to now */
        activate_slog = spa_passivate_log(spa);
        (void) spa_vdev_config_exit(spa, NULL, txg, 0, FTAG);
        error = spa_offline_log(spa);
        txg = spa_vdev_config_enter(spa);

        if (activate_slog)
                spa_activate_log(spa);

        if (error != 0)
                return (spa_vdev_exit(spa, NULL, txg, error));

        /* check new spa name before going any further */
        if (spa_lookup(newname) != NULL)
                return (spa_vdev_exit(spa, NULL, txg, EEXIST));

        /*
         * scan through all the children to ensure they're all mirrors
         */
        if (nvlist_lookup_nvlist(config, ZPOOL_CONFIG_VDEV_TREE, &nvl) != 0 ||
            nvlist_lookup_nvlist_array(nvl, ZPOOL_CONFIG_CHILDREN, &child,
            &children) != 0)
                return (spa_vdev_exit(spa, NULL, txg, EINVAL));

        /* first, check to ensure we've got the right child count */
        rvd = spa->spa_root_vdev;
        lastlog = 0;
        for (c = 0; c < rvd->vdev_children; c++) {
                vdev_t *vd = rvd->vdev_child[c];

                /* don't count the holes & logs as children */
                if (vd->vdev_islog || vd->vdev_ishole) {
                        if (lastlog == 0)
                                lastlog = c;
                        continue;
                }

                lastlog = 0;
        }
        if (children != (lastlog != 0 ? lastlog : rvd->vdev_children))
                return (spa_vdev_exit(spa, NULL, txg, EINVAL));

        /* next, ensure no spare or cache devices are part of the split */
        if (nvlist_lookup_nvlist(nvl, ZPOOL_CONFIG_SPARES, &tmp) == 0 ||
            nvlist_lookup_nvlist(nvl, ZPOOL_CONFIG_L2CACHE, &tmp) == 0)
                return (spa_vdev_exit(spa, NULL, txg, EINVAL));

        vml = kmem_zalloc(children * sizeof (vdev_t *), KM_SLEEP);
        glist = kmem_zalloc(children * sizeof (uint64_t), KM_SLEEP);

        /* then, loop over each vdev and validate it */
        for (c = 0; c < children; c++) {
                uint64_t is_hole = 0;

                (void) nvlist_lookup_uint64(child[c], ZPOOL_CONFIG_IS_HOLE,
                    &is_hole);

                if (is_hole != 0) {
                        if (spa->spa_root_vdev->vdev_child[c]->vdev_ishole ||
                            spa->spa_root_vdev->vdev_child[c]->vdev_islog) {
                                continue;
                        } else {
                                error = SET_ERROR(EINVAL);
                                break;
                        }
                }

                /* which disk is going to be split? */
                if (nvlist_lookup_uint64(child[c], ZPOOL_CONFIG_GUID,
                    &glist[c]) != 0) {
                        error = SET_ERROR(EINVAL);
                        break;
                }

                /* look it up in the spa */
                vml[c] = spa_lookup_by_guid(spa, glist[c], B_FALSE);
                if (vml[c] == NULL) {
                        error = SET_ERROR(ENODEV);
                        break;
                }

                /* make sure there's nothing stopping the split */
                if (vml[c]->vdev_parent->vdev_ops != &vdev_mirror_ops ||
                    vml[c]->vdev_islog ||
                    vml[c]->vdev_ishole ||
                    vml[c]->vdev_isspare ||
                    vml[c]->vdev_isl2cache ||
                    !vdev_writeable(vml[c]) ||
                    vml[c]->vdev_children != 0 ||
                    vml[c]->vdev_state != VDEV_STATE_HEALTHY ||
                    c != spa->spa_root_vdev->vdev_child[c]->vdev_id) {
                        error = SET_ERROR(EINVAL);
                        break;
                }

                if (vdev_dtl_required(vml[c])) {
                        error = SET_ERROR(EBUSY);
                        break;
                }

                /* we need certain info from the top level */
                VERIFY(nvlist_add_uint64(child[c], ZPOOL_CONFIG_METASLAB_ARRAY,
                    vml[c]->vdev_top->vdev_ms_array) == 0);
                VERIFY(nvlist_add_uint64(child[c], ZPOOL_CONFIG_METASLAB_SHIFT,
                    vml[c]->vdev_top->vdev_ms_shift) == 0);
                VERIFY(nvlist_add_uint64(child[c], ZPOOL_CONFIG_ASIZE,
                    vml[c]->vdev_top->vdev_asize) == 0);
                VERIFY(nvlist_add_uint64(child[c], ZPOOL_CONFIG_ASHIFT,
                    vml[c]->vdev_top->vdev_ashift) == 0);

                /* transfer per-vdev ZAPs */
                ASSERT3U(vml[c]->vdev_leaf_zap, !=, 0);
                VERIFY0(nvlist_add_uint64(child[c],
                    ZPOOL_CONFIG_VDEV_LEAF_ZAP, vml[c]->vdev_leaf_zap));

                ASSERT3U(vml[c]->vdev_top->vdev_top_zap, !=, 0);
                VERIFY0(nvlist_add_uint64(child[c],
                    ZPOOL_CONFIG_VDEV_TOP_ZAP,
                    vml[c]->vdev_parent->vdev_top_zap));
        }

        if (error != 0) {
                kmem_free(vml, children * sizeof (vdev_t *));
                kmem_free(glist, children * sizeof (uint64_t));
                return (spa_vdev_exit(spa, NULL, txg, error));
        }

        /* stop writers from using the disks */
        for (c = 0; c < children; c++) {
                if (vml[c] != NULL)
                        vml[c]->vdev_offline = B_TRUE;
        }
        vdev_reopen(spa->spa_root_vdev);

        /*
         * Temporarily record the splitting vdevs in the spa config.  This
         * will disappear once the config is regenerated.
         */
        VERIFY(nvlist_alloc(&nvl, NV_UNIQUE_NAME, KM_SLEEP) == 0);
        VERIFY(nvlist_add_uint64_array(nvl, ZPOOL_CONFIG_SPLIT_LIST,
            glist, children) == 0);
        kmem_free(glist, children * sizeof (uint64_t));

        mutex_enter(&spa->spa_props_lock);
        VERIFY(nvlist_add_nvlist(spa->spa_config, ZPOOL_CONFIG_SPLIT,
            nvl) == 0);
        mutex_exit(&spa->spa_props_lock);
        spa->spa_config_splitting = nvl;
        vdev_config_dirty(spa->spa_root_vdev);

        /* configure and create the new pool */
        VERIFY(nvlist_add_string(config, ZPOOL_CONFIG_POOL_NAME, newname) == 0);
        VERIFY(nvlist_add_uint64(config, ZPOOL_CONFIG_POOL_STATE,
            exp ? POOL_STATE_EXPORTED : POOL_STATE_ACTIVE) == 0);
        VERIFY(nvlist_add_uint64(config, ZPOOL_CONFIG_VERSION,
            spa_version(spa)) == 0);
        VERIFY(nvlist_add_uint64(config, ZPOOL_CONFIG_POOL_TXG,
            spa->spa_config_txg) == 0);
        VERIFY(nvlist_add_uint64(config, ZPOOL_CONFIG_POOL_GUID,
            spa_generate_guid(NULL)) == 0);
        VERIFY0(nvlist_add_boolean(config, ZPOOL_CONFIG_HAS_PER_VDEV_ZAPS));
        (void) nvlist_lookup_string(props,
            zpool_prop_to_name(ZPOOL_PROP_ALTROOT), &altroot);

        /* add the new pool to the namespace */
        newspa = spa_add(newname, config, altroot);
        newspa->spa_avz_action = AVZ_ACTION_REBUILD;
        newspa->spa_config_txg = spa->spa_config_txg;
        spa_set_log_state(newspa, SPA_LOG_CLEAR);

        /* release the spa config lock, retaining the namespace lock */
        spa_vdev_config_exit(spa, NULL, txg, 0, FTAG);

        if (zio_injection_enabled)
                zio_handle_panic_injection(spa, FTAG, 1);

        spa_activate(newspa, spa_mode_global);
        spa_async_suspend(newspa);

        /* create the new pool from the disks of the original pool */
        error = spa_load(newspa, SPA_LOAD_IMPORT, SPA_IMPORT_ASSEMBLE, B_TRUE);
        if (error)
                goto out;

        /* if that worked, generate a real config for the new pool */
        if (newspa->spa_root_vdev != NULL) {
                VERIFY(nvlist_alloc(&newspa->spa_config_splitting,
                    NV_UNIQUE_NAME, KM_SLEEP) == 0);
                VERIFY(nvlist_add_uint64(newspa->spa_config_splitting,
                    ZPOOL_CONFIG_SPLIT_GUID, spa_guid(spa)) == 0);
                spa_config_set(newspa, spa_config_generate(newspa, NULL, -1ULL,
                    B_TRUE));
        }

        /* set the props */
        if (props != NULL) {
                spa_configfile_set(newspa, props, B_FALSE);
                error = spa_prop_set(newspa, props);
                if (error)
                        goto out;
        }

        /* flush everything */
        txg = spa_vdev_config_enter(newspa);
        vdev_config_dirty(newspa->spa_root_vdev);
        (void) spa_vdev_config_exit(newspa, NULL, txg, 0, FTAG);

        if (zio_injection_enabled)
                zio_handle_panic_injection(spa, FTAG, 2);

        spa_async_resume(newspa);

        /* finally, update the original pool's config */
        txg = spa_vdev_config_enter(spa);
        tx = dmu_tx_create_dd(spa_get_dsl(spa)->dp_mos_dir);
        error = dmu_tx_assign(tx, TXG_WAIT);
        if (error != 0)
                dmu_tx_abort(tx);
        for (c = 0; c < children; c++) {
                if (vml[c] != NULL) {
                        vdev_split(vml[c]);
                        if (error == 0)
                                spa_history_log_internal(spa, "detach", tx,
                                    "vdev=%s", vml[c]->vdev_path);

                        vdev_free(vml[c]);
                }
        }
        spa->spa_avz_action = AVZ_ACTION_REBUILD;
        vdev_config_dirty(spa->spa_root_vdev);
        spa->spa_config_splitting = NULL;
        nvlist_free(nvl);
        if (error == 0)
                dmu_tx_commit(tx);
        (void) spa_vdev_exit(spa, NULL, txg, 0);

        if (zio_injection_enabled)
                zio_handle_panic_injection(spa, FTAG, 3);

        /* split is complete; log a history record */
        spa_history_log_internal(newspa, "split", NULL,
            "from pool %s", spa_name(spa));

        kmem_free(vml, children * sizeof (vdev_t *));

        /* if we're not going to mount the filesystems in userland, export */
        if (exp)
                error = spa_export_common(newname, POOL_STATE_EXPORTED, NULL,
                    B_FALSE, B_FALSE);

        return (error);

out:
        spa_unload(newspa);
        spa_deactivate(newspa);
        spa_remove(newspa);

        txg = spa_vdev_config_enter(spa);

        /* re-online all offlined disks */
        for (c = 0; c < children; c++) {
                if (vml[c] != NULL)
                        vml[c]->vdev_offline = B_FALSE;
        }
        vdev_reopen(spa->spa_root_vdev);

        nvlist_free(spa->spa_config_splitting);
        spa->spa_config_splitting = NULL;
        (void) spa_vdev_exit(spa, NULL, txg, error);

        kmem_free(vml, children * sizeof (vdev_t *));
        return (error);
}

static nvlist_t *
spa_nvlist_lookup_by_guid(nvlist_t **nvpp, int count, uint64_t target_guid)
{
        for (int i = 0; i < count; i++) {
                uint64_t guid;

                VERIFY(nvlist_lookup_uint64(nvpp[i], ZPOOL_CONFIG_GUID,
                    &guid) == 0);

                if (guid == target_guid)
                        return (nvpp[i]);
        }

        return (NULL);
}

static void
spa_vdev_remove_aux(nvlist_t *config, char *name, nvlist_t **dev, int count,
    nvlist_t *dev_to_remove)
{
        nvlist_t **newdev = NULL;

        if (count > 1)
                newdev = kmem_alloc((count - 1) * sizeof (void *), KM_SLEEP);

        for (int i = 0, j = 0; i < count; i++) {
                if (dev[i] == dev_to_remove)
                        continue;
                VERIFY(nvlist_dup(dev[i], &newdev[j++], KM_SLEEP) == 0);
        }

        VERIFY(nvlist_remove(config, name, DATA_TYPE_NVLIST_ARRAY) == 0);
        VERIFY(nvlist_add_nvlist_array(config, name, newdev, count - 1) == 0);

        for (int i = 0; i < count - 1; i++)
                nvlist_free(newdev[i]);

        if (count > 1)
                kmem_free(newdev, (count - 1) * sizeof (void *));
}

/*
 * Evacuate the device.
 */
static int
spa_vdev_remove_evacuate(spa_t *spa, vdev_t *vd)
{
        uint64_t txg;
        int error = 0;

        ASSERT(MUTEX_HELD(&spa_namespace_lock));
        ASSERT(spa_config_held(spa, SCL_ALL, RW_WRITER) == 0);
        ASSERT(vd == vd->vdev_top);

        /*
         * Evacuate the device.  We don't hold the config lock as writer
         * since we need to do I/O but we do keep the
         * spa_namespace_lock held.  Once this completes the device
         * should no longer have any blocks allocated on it.
         */
        if (vd->vdev_islog) {
                if (vd->vdev_stat.vs_alloc != 0)
                        error = spa_offline_log(spa);
        } else {
                error = SET_ERROR(ENOTSUP);
        }

        if (error)
                return (error);

        /*
         * The evacuation succeeded.  Remove any remaining MOS metadata
         * associated with this vdev, and wait for these changes to sync.
         */
        ASSERT0(vd->vdev_stat.vs_alloc);
        txg = spa_vdev_config_enter(spa);
        vd->vdev_removing = B_TRUE;
        vdev_dirty_leaves(vd, VDD_DTL, txg);
        vdev_config_dirty(vd);
        spa_vdev_config_exit(spa, NULL, txg, 0, FTAG);

        return (0);
}

/*
 * Complete the removal by cleaning up the namespace.
 */
static void
spa_vdev_remove_from_namespace(spa_t *spa, vdev_t *vd)
{
        vdev_t *rvd = spa->spa_root_vdev;
        uint64_t id = vd->vdev_id;
        boolean_t last_vdev = (id == (rvd->vdev_children - 1));

        ASSERT(MUTEX_HELD(&spa_namespace_lock));
        ASSERT(spa_config_held(spa, SCL_ALL, RW_WRITER) == SCL_ALL);
        ASSERT(vd == vd->vdev_top);

        /*
         * Only remove any devices which are empty.
         */
        if (vd->vdev_stat.vs_alloc != 0)
                return;

        (void) vdev_label_init(vd, 0, VDEV_LABEL_REMOVE);

        if (list_link_active(&vd->vdev_state_dirty_node))
                vdev_state_clean(vd);
        if (list_link_active(&vd->vdev_config_dirty_node))
                vdev_config_clean(vd);

        vdev_free(vd);

        if (last_vdev) {
                vdev_compact_children(rvd);
        } else {
                vd = vdev_alloc_common(spa, id, 0, &vdev_hole_ops);
                vdev_add_child(rvd, vd);
        }
        vdev_config_dirty(rvd);

        /*
         * Reassess the health of our root vdev.
         */
        vdev_reopen(rvd);
}

/*
 * Remove a device from the pool -
 *
 * Removing a device from the vdev namespace requires several steps
 * and can take a significant amount of time.  As a result we use
 * the spa_vdev_config_[enter/exit] functions which allow us to
 * grab and release the spa_config_lock while still holding the namespace
 * lock.  During each step the configuration is synced out.
 *
 * Currently, this supports removing only hot spares, slogs, and level 2 ARC
 * devices.
 */
int
spa_vdev_remove(spa_t *spa, uint64_t guid, boolean_t unspare)
{
        vdev_t *vd;
        sysevent_t *ev = NULL;
        metaslab_group_t *mg;
        nvlist_t **spares, **l2cache, *nv;
        uint64_t txg = 0;
        uint_t nspares, nl2cache;
        int error = 0;
        boolean_t locked = MUTEX_HELD(&spa_namespace_lock);

        ASSERT(spa_writeable(spa));

        if (!locked)
                txg = spa_vdev_enter(spa);

        vd = spa_lookup_by_guid(spa, guid, B_FALSE);

        if (spa->spa_spares.sav_vdevs != NULL &&
            nvlist_lookup_nvlist_array(spa->spa_spares.sav_config,
            ZPOOL_CONFIG_SPARES, &spares, &nspares) == 0 &&
            (nv = spa_nvlist_lookup_by_guid(spares, nspares, guid)) != NULL) {
                /*
                 * Only remove the hot spare if it's not currently in use
                 * in this pool.
                 */
                if (vd == NULL || unspare) {
                        if (vd == NULL)
                                vd = spa_lookup_by_guid(spa, guid, B_TRUE);
                        ev = spa_event_create(spa, vd, NULL,
                            ESC_ZFS_VDEV_REMOVE_AUX);
                        spa_vdev_remove_aux(spa->spa_spares.sav_config,
                            ZPOOL_CONFIG_SPARES, spares, nspares, nv);
                        spa_load_spares(spa);
                        spa->spa_spares.sav_sync = B_TRUE;
                } else {
                        error = SET_ERROR(EBUSY);
                }
        } else if (spa->spa_l2cache.sav_vdevs != NULL &&
            nvlist_lookup_nvlist_array(spa->spa_l2cache.sav_config,
            ZPOOL_CONFIG_L2CACHE, &l2cache, &nl2cache) == 0 &&
            (nv = spa_nvlist_lookup_by_guid(l2cache, nl2cache, guid)) != NULL) {
                /*
                 * Cache devices can always be removed.
                 */
                vd = spa_lookup_by_guid(spa, guid, B_TRUE);
                ev = spa_event_create(spa, vd, NULL, ESC_ZFS_VDEV_REMOVE_AUX);
                spa_vdev_remove_aux(spa->spa_l2cache.sav_config,
                    ZPOOL_CONFIG_L2CACHE, l2cache, nl2cache, nv);
                spa_load_l2cache(spa);
                spa->spa_l2cache.sav_sync = B_TRUE;
        } else if (vd != NULL && vd->vdev_islog) {
                ASSERT(!locked);
                ASSERT(vd == vd->vdev_top);

                mg = vd->vdev_mg;

                /*
                 * Stop allocating from this vdev.
                 */
                metaslab_group_passivate(mg);

                /*
                 * Wait for the youngest allocations and frees to sync,
                 * and then wait for the deferral of those frees to finish.
                 */
                spa_vdev_config_exit(spa, NULL,
                    txg + TXG_CONCURRENT_STATES + TXG_DEFER_SIZE, 0, FTAG);

                /*
                 * Attempt to evacuate the vdev.
                 */
                error = spa_vdev_remove_evacuate(spa, vd);

                txg = spa_vdev_config_enter(spa);

                /*
                 * If we couldn't evacuate the vdev, unwind.
                 */
                if (error) {
                        metaslab_group_activate(mg);
                        return (spa_vdev_exit(spa, NULL, txg, error));
                }

                /*
                 * Clean up the vdev namespace.
                 */
                ev = spa_event_create(spa, vd, NULL, ESC_ZFS_VDEV_REMOVE_DEV);
                spa_vdev_remove_from_namespace(spa, vd);

        } else if (vd != NULL) {
                /*
                 * Normal vdevs cannot be removed (yet).
                 */
                error = SET_ERROR(ENOTSUP);
        } else {
                /*
                 * There is no vdev of any kind with the specified guid.
                 */
                error = SET_ERROR(ENOENT);
        }

        if (!locked)
                error = spa_vdev_exit(spa, NULL, txg, error);

        if (ev)
                spa_event_post(ev);

        return (error);
}

/*
 * Find any device that's done replacing, or a vdev marked 'unspare' that's
 * currently spared, so we can detach it.
 */
static vdev_t *
spa_vdev_resilver_done_hunt(vdev_t *vd)
{
        vdev_t *newvd, *oldvd;

        for (int c = 0; c < vd->vdev_children; c++) {
                oldvd = spa_vdev_resilver_done_hunt(vd->vdev_child[c]);
                if (oldvd != NULL)
                        return (oldvd);
        }

        /*
         * Check for a completed replacement.  We always consider the first
         * vdev in the list to be the oldest vdev, and the last one to be
         * the newest (see spa_vdev_attach() for how that works).  In
         * the case where the newest vdev is faulted, we will not automatically
         * remove it after a resilver completes.  This is OK as it will require
         * user intervention to determine which disk the admin wishes to keep.
         */
        if (vd->vdev_ops == &vdev_replacing_ops) {
                ASSERT(vd->vdev_children > 1);

                newvd = vd->vdev_child[vd->vdev_children - 1];
                oldvd = vd->vdev_child[0];

                if (vdev_dtl_empty(newvd, DTL_MISSING) &&
                    vdev_dtl_empty(newvd, DTL_OUTAGE) &&
                    !vdev_dtl_required(oldvd))
                        return (oldvd);
        }

        /*
         * Check for a completed resilver with the 'unspare' flag set.
         */
        if (vd->vdev_ops == &vdev_spare_ops) {
                vdev_t *first = vd->vdev_child[0];
                vdev_t *last = vd->vdev_child[vd->vdev_children - 1];

                if (last->vdev_unspare) {
                        oldvd = first;
                        newvd = last;
                } else if (first->vdev_unspare) {
                        oldvd = last;
                        newvd = first;
                } else {
                        oldvd = NULL;
                }

                if (oldvd != NULL &&
                    vdev_dtl_empty(newvd, DTL_MISSING) &&
                    vdev_dtl_empty(newvd, DTL_OUTAGE) &&
                    !vdev_dtl_required(oldvd))
                        return (oldvd);

                /*
                 * If there are more than two spares attached to a disk,
                 * and those spares are not required, then we want to
                 * attempt to free them up now so that they can be used
                 * by other pools.  Once we're back down to a single
                 * disk+spare, we stop removing them.
                 */
                if (vd->vdev_children > 2) {
                        newvd = vd->vdev_child[1];

                        if (newvd->vdev_isspare && last->vdev_isspare &&
                            vdev_dtl_empty(last, DTL_MISSING) &&
                            vdev_dtl_empty(last, DTL_OUTAGE) &&
                            !vdev_dtl_required(newvd))
                                return (newvd);
                }
        }

        return (NULL);
}

static void
spa_vdev_resilver_done(spa_t *spa)
{
        vdev_t *vd, *pvd, *ppvd;
        uint64_t guid, sguid, pguid, ppguid;

        spa_config_enter(spa, SCL_ALL, FTAG, RW_WRITER);

        while ((vd = spa_vdev_resilver_done_hunt(spa->spa_root_vdev)) != NULL) {
                pvd = vd->vdev_parent;
                ppvd = pvd->vdev_parent;
                guid = vd->vdev_guid;
                pguid = pvd->vdev_guid;
                ppguid = ppvd->vdev_guid;
                sguid = 0;
                /*
                 * If we have just finished replacing a hot spared device, then
                 * we need to detach the parent's first child (the original hot
                 * spare) as well.
                 */
                if (ppvd->vdev_ops == &vdev_spare_ops && pvd->vdev_id == 0 &&
                    ppvd->vdev_children == 2) {
                        ASSERT(pvd->vdev_ops == &vdev_replacing_ops);
                        sguid = ppvd->vdev_child[1]->vdev_guid;
                }
                ASSERT(vd->vdev_resilver_txg == 0 || !vdev_dtl_required(vd));

                spa_config_exit(spa, SCL_ALL, FTAG);
                if (spa_vdev_detach(spa, guid, pguid, B_TRUE) != 0)
                        return;
                if (sguid && spa_vdev_detach(spa, sguid, ppguid, B_TRUE) != 0)
                        return;
                spa_config_enter(spa, SCL_ALL, FTAG, RW_WRITER);
        }

        spa_config_exit(spa, SCL_ALL, FTAG);
}

/*
 * Update the stored path or FRU for this vdev.
 */
int
spa_vdev_set_common(spa_t *spa, uint64_t guid, const char *value,
    boolean_t ispath)
{
        vdev_t *vd;
        boolean_t sync = B_FALSE;

        ASSERT(spa_writeable(spa));

        spa_vdev_state_enter(spa, SCL_ALL);

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

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

        if (ispath) {
                if (strcmp(value, vd->vdev_path) != 0) {
                        spa_strfree(vd->vdev_path);
                        vd->vdev_path = spa_strdup(value);
                        sync = B_TRUE;
                }
        } else {
                if (vd->vdev_fru == NULL) {
                        vd->vdev_fru = spa_strdup(value);
                        sync = B_TRUE;
                } else if (strcmp(value, vd->vdev_fru) != 0) {
                        spa_strfree(vd->vdev_fru);
                        vd->vdev_fru = spa_strdup(value);
                        sync = B_TRUE;
                }
        }

        return (spa_vdev_state_exit(spa, sync ? vd : NULL, 0));
}

int
spa_vdev_setpath(spa_t *spa, uint64_t guid, const char *newpath)
{
        return (spa_vdev_set_common(spa, guid, newpath, B_TRUE));
}

int
spa_vdev_setfru(spa_t *spa, uint64_t guid, const char *newfru)
{
        return (spa_vdev_set_common(spa, guid, newfru, B_FALSE));
}

/*
 * ==========================================================================
 * SPA Scanning
 * ==========================================================================
 */
int
spa_scrub_pause_resume(spa_t *spa, pool_scrub_cmd_t cmd)
{
        ASSERT(spa_config_held(spa, SCL_ALL, RW_WRITER) == 0);

        if (dsl_scan_resilvering(spa->spa_dsl_pool))
                return (SET_ERROR(EBUSY));

        return (dsl_scrub_set_pause_resume(spa->spa_dsl_pool, cmd));
}

int
spa_scan_stop(spa_t *spa)
{
        ASSERT(spa_config_held(spa, SCL_ALL, RW_WRITER) == 0);
        if (dsl_scan_resilvering(spa->spa_dsl_pool))
                return (SET_ERROR(EBUSY));
        return (dsl_scan_cancel(spa->spa_dsl_pool));
}

int
spa_scan(spa_t *spa, pool_scan_func_t func)
{
        ASSERT(spa_config_held(spa, SCL_ALL, RW_WRITER) == 0);

        if (func >= POOL_SCAN_FUNCS || func == POOL_SCAN_NONE)
                return (SET_ERROR(ENOTSUP));

        /*
         * If a resilver was requested, but there is no DTL on a
         * writeable leaf device, we have nothing to do.
         */
        if (func == POOL_SCAN_RESILVER &&
            !vdev_resilver_needed(spa->spa_root_vdev, NULL, NULL)) {
                spa_async_request(spa, SPA_ASYNC_RESILVER_DONE);
                return (0);
        }

        return (dsl_scan(spa->spa_dsl_pool, func));
}

/*
 * ==========================================================================
 * SPA async task processing
 * ==========================================================================
 */

static void
spa_async_remove(spa_t *spa, vdev_t *vd)
{
        if (vd->vdev_remove_wanted) {
                vd->vdev_remove_wanted = B_FALSE;
                vd->vdev_delayed_close = B_FALSE;
                vdev_set_state(vd, B_FALSE, VDEV_STATE_REMOVED, VDEV_AUX_NONE);

                /*
                 * We want to clear the stats, but we don't want to do a full
                 * vdev_clear() as that will cause us to throw away
                 * degraded/faulted state as well as attempt to reopen the
                 * device, all of which is a waste.
                 */
                vd->vdev_stat.vs_read_errors = 0;
                vd->vdev_stat.vs_write_errors = 0;
                vd->vdev_stat.vs_checksum_errors = 0;

                vdev_state_dirty(vd->vdev_top);
        }

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

static void
spa_async_probe(spa_t *spa, vdev_t *vd)
{
        if (vd->vdev_probe_wanted) {
                vd->vdev_probe_wanted = B_FALSE;
                vdev_reopen(vd);        /* vdev_open() does the actual probe */
        }

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

static void
spa_async_autoexpand(spa_t *spa, vdev_t *vd)
{
        if (!spa->spa_autoexpand)
                return;

        for (int c = 0; c < vd->vdev_children; c++) {
                vdev_t *cvd = vd->vdev_child[c];
                spa_async_autoexpand(spa, cvd);
        }

        if (!vd->vdev_ops->vdev_op_leaf || vd->vdev_physpath == NULL)
                return;

        spa_event_notify(vd->vdev_spa, vd, NULL, ESC_ZFS_VDEV_AUTOEXPAND);
}

static void
spa_async_thread(void *arg)
{
        spa_t *spa = (spa_t *)arg;
        int tasks;

        ASSERT(spa->spa_sync_on);

        mutex_enter(&spa->spa_async_lock);
        tasks = spa->spa_async_tasks;
        spa->spa_async_tasks = 0;
        mutex_exit(&spa->spa_async_lock);

        /*
         * See if the config needs to be updated.
         */
        if (tasks & SPA_ASYNC_CONFIG_UPDATE) {
                uint64_t old_space, new_space;

                mutex_enter(&spa_namespace_lock);
                old_space = metaslab_class_get_space(spa_normal_class(spa));
                spa_config_update(spa, SPA_CONFIG_UPDATE_POOL);
                new_space = metaslab_class_get_space(spa_normal_class(spa));
                mutex_exit(&spa_namespace_lock);

                /*
                 * If the pool grew as a result of the config update,
                 * then log an internal history event.
                 */
                if (new_space != old_space) {
                        spa_history_log_internal(spa, "vdev online", NULL,
                            "pool '%s' size: %llu(+%llu)",
                            spa_name(spa), new_space, new_space - old_space);
                }
        }

        /*
         * See if any devices need to be marked REMOVED.
         */
        if (tasks & SPA_ASYNC_REMOVE) {
                spa_vdev_state_enter(spa, SCL_NONE);
                spa_async_remove(spa, spa->spa_root_vdev);
                for (int i = 0; i < spa->spa_l2cache.sav_count; i++)
                        spa_async_remove(spa, spa->spa_l2cache.sav_vdevs[i]);
                for (int i = 0; i < spa->spa_spares.sav_count; i++)
                        spa_async_remove(spa, spa->spa_spares.sav_vdevs[i]);
                (void) spa_vdev_state_exit(spa, NULL, 0);
        }

        if ((tasks & SPA_ASYNC_AUTOEXPAND) && !spa_suspended(spa)) {
                spa_config_enter(spa, SCL_CONFIG, FTAG, RW_READER);
                spa_async_autoexpand(spa, spa->spa_root_vdev);
                spa_config_exit(spa, SCL_CONFIG, FTAG);
        }

        /*
         * See if any devices need to be probed.
         */
        if (tasks & SPA_ASYNC_PROBE) {
                spa_vdev_state_enter(spa, SCL_NONE);
                spa_async_probe(spa, spa->spa_root_vdev);
                (void) spa_vdev_state_exit(spa, NULL, 0);
        }

        /*
         * If any devices are done replacing, detach them.
         */
        if (tasks & SPA_ASYNC_RESILVER_DONE)
                spa_vdev_resilver_done(spa);

        /*
         * Kick off a resilver.
         */
        if (tasks & SPA_ASYNC_RESILVER)
                dsl_resilver_restart(spa->spa_dsl_pool, 0);

        /*
         * Let the world know that we're done.
         */
        mutex_enter(&spa->spa_async_lock);
        spa->spa_async_thread = NULL;
        cv_broadcast(&spa->spa_async_cv);
        mutex_exit(&spa->spa_async_lock);
        thread_exit();
}

void
spa_async_suspend(spa_t *spa)
{
        mutex_enter(&spa->spa_async_lock);
        spa->spa_async_suspended++;
        while (spa->spa_async_thread != NULL)
                cv_wait(&spa->spa_async_cv, &spa->spa_async_lock);
        mutex_exit(&spa->spa_async_lock);
}

void
spa_async_resume(spa_t *spa)
{
        mutex_enter(&spa->spa_async_lock);
        ASSERT(spa->spa_async_suspended != 0);
        spa->spa_async_suspended--;
        mutex_exit(&spa->spa_async_lock);
}

static boolean_t
spa_async_tasks_pending(spa_t *spa)
{
        uint_t non_config_tasks;
        uint_t config_task;
        boolean_t config_task_suspended;

        non_config_tasks = spa->spa_async_tasks & ~SPA_ASYNC_CONFIG_UPDATE;
        config_task = spa->spa_async_tasks & SPA_ASYNC_CONFIG_UPDATE;
        if (spa->spa_ccw_fail_time == 0) {
                config_task_suspended = B_FALSE;
        } else {
                config_task_suspended =
                    (gethrtime() - spa->spa_ccw_fail_time) <
                    ((hrtime_t)zfs_ccw_retry_interval * NANOSEC);
        }

        return (non_config_tasks || (config_task && !config_task_suspended));
}

static void
spa_async_dispatch(spa_t *spa)
{
        mutex_enter(&spa->spa_async_lock);
        if (spa_async_tasks_pending(spa) &&
            !spa->spa_async_suspended &&
            spa->spa_async_thread == NULL &&
            rootdir != NULL)
                spa->spa_async_thread = thread_create(NULL, 0,
                    spa_async_thread, spa, 0, &p0, TS_RUN, maxclsyspri);
        mutex_exit(&spa->spa_async_lock);
}

void
spa_async_request(spa_t *spa, int task)
{
        zfs_dbgmsg("spa=%s async request task=%u", spa->spa_name, task);
        mutex_enter(&spa->spa_async_lock);
        spa->spa_async_tasks |= task;
        mutex_exit(&spa->spa_async_lock);
}

/*
 * ==========================================================================
 * SPA syncing routines
 * ==========================================================================
 */

static int
bpobj_enqueue_cb(void *arg, const blkptr_t *bp, dmu_tx_t *tx)
{
        bpobj_t *bpo = arg;
        bpobj_enqueue(bpo, bp, tx);
        return (0);
}

static int
spa_free_sync_cb(void *arg, const blkptr_t *bp, dmu_tx_t *tx)
{
        zio_t *zio = arg;

        zio_nowait(zio_free_sync(zio, zio->io_spa, dmu_tx_get_txg(tx), bp,
            zio->io_flags));
        return (0);
}

/*
 * Note: this simple function is not inlined to make it easier to dtrace the
 * amount of time spent syncing frees.
 */
static void
spa_sync_frees(spa_t *spa, bplist_t *bpl, dmu_tx_t *tx)
{
        zio_t *zio = zio_root(spa, NULL, NULL, 0);
        bplist_iterate(bpl, spa_free_sync_cb, zio, tx);
        VERIFY(zio_wait(zio) == 0);
}

/*
 * Note: this simple function is not inlined to make it easier to dtrace the
 * amount of time spent syncing deferred frees.
 */
static void
spa_sync_deferred_frees(spa_t *spa, dmu_tx_t *tx)
{
        zio_t *zio = zio_root(spa, NULL, NULL, 0);
        VERIFY3U(bpobj_iterate(&spa->spa_deferred_bpobj,
            spa_free_sync_cb, zio, tx), ==, 0);
        VERIFY0(zio_wait(zio));
}

static void
spa_sync_nvlist(spa_t *spa, uint64_t obj, nvlist_t *nv, dmu_tx_t *tx)
{
        char *packed = NULL;
        size_t bufsize;
        size_t nvsize = 0;
        dmu_buf_t *db;

        VERIFY(nvlist_size(nv, &nvsize, NV_ENCODE_XDR) == 0);

        /*
         * Write full (SPA_CONFIG_BLOCKSIZE) blocks of configuration
         * information.  This avoids the dmu_buf_will_dirty() path and
         * saves us a pre-read to get data we don't actually care about.
         */
        bufsize = P2ROUNDUP((uint64_t)nvsize, SPA_CONFIG_BLOCKSIZE);
        packed = vmem_alloc(bufsize, KM_SLEEP);

        VERIFY(nvlist_pack(nv, &packed, &nvsize, NV_ENCODE_XDR,
            KM_SLEEP) == 0);
        bzero(packed + nvsize, bufsize - nvsize);

        dmu_write(spa->spa_meta_objset, obj, 0, bufsize, packed, tx);

        vmem_free(packed, bufsize);

        VERIFY(0 == dmu_bonus_hold(spa->spa_meta_objset, obj, FTAG, &db));
        dmu_buf_will_dirty(db, tx);
        *(uint64_t *)db->db_data = nvsize;
        dmu_buf_rele(db, FTAG);
}

static void
spa_sync_aux_dev(spa_t *spa, spa_aux_vdev_t *sav, dmu_tx_t *tx,
    const char *config, const char *entry)
{
        nvlist_t *nvroot;
        nvlist_t **list;
        int i;

        if (!sav->sav_sync)
                return;

        /*
         * Update the MOS nvlist describing the list of available devices.
         * spa_validate_aux() will have already made sure this nvlist is
         * valid and the vdevs are labeled appropriately.
         */
        if (sav->sav_object == 0) {
                sav->sav_object = dmu_object_alloc(spa->spa_meta_objset,
                    DMU_OT_PACKED_NVLIST, 1 << 14, DMU_OT_PACKED_NVLIST_SIZE,
                    sizeof (uint64_t), tx);
                VERIFY(zap_update(spa->spa_meta_objset,
                    DMU_POOL_DIRECTORY_OBJECT, entry, sizeof (uint64_t), 1,
                    &sav->sav_object, tx) == 0);
        }

        VERIFY(nvlist_alloc(&nvroot, NV_UNIQUE_NAME, KM_SLEEP) == 0);
        if (sav->sav_count == 0) {
                VERIFY(nvlist_add_nvlist_array(nvroot, config, NULL, 0) == 0);
        } else {
                list = kmem_alloc(sav->sav_count*sizeof (void *), KM_SLEEP);
                for (i = 0; i < sav->sav_count; i++)
                        list[i] = vdev_config_generate(spa, sav->sav_vdevs[i],
                            B_FALSE, VDEV_CONFIG_L2CACHE);
                VERIFY(nvlist_add_nvlist_array(nvroot, config, list,
                    sav->sav_count) == 0);
                for (i = 0; i < sav->sav_count; i++)
                        nvlist_free(list[i]);
                kmem_free(list, sav->sav_count * sizeof (void *));
        }

        spa_sync_nvlist(spa, sav->sav_object, nvroot, tx);
        nvlist_free(nvroot);

        sav->sav_sync = B_FALSE;
}

/*
 * Rebuild spa's all-vdev ZAP from the vdev ZAPs indicated in each vdev_t.
 * The all-vdev ZAP must be empty.
 */
static void
spa_avz_build(vdev_t *vd, uint64_t avz, dmu_tx_t *tx)
{
        spa_t *spa = vd->vdev_spa;

        if (vd->vdev_top_zap != 0) {
                VERIFY0(zap_add_int(spa->spa_meta_objset, avz,
                    vd->vdev_top_zap, tx));
        }
        if (vd->vdev_leaf_zap != 0) {
                VERIFY0(zap_add_int(spa->spa_meta_objset, avz,
                    vd->vdev_leaf_zap, tx));
        }
        for (uint64_t i = 0; i < vd->vdev_children; i++) {
                spa_avz_build(vd->vdev_child[i], avz, tx);
        }
}

static void
spa_sync_config_object(spa_t *spa, dmu_tx_t *tx)
{
        nvlist_t *config;

        /*
         * If the pool is being imported from a pre-per-vdev-ZAP version of ZFS,
         * its config may not be dirty but we still need to build per-vdev ZAPs.
         * Similarly, if the pool is being assembled (e.g. after a split), we
         * need to rebuild the AVZ although the config may not be dirty.
         */
        if (list_is_empty(&spa->spa_config_dirty_list) &&
            spa->spa_avz_action == AVZ_ACTION_NONE)
                return;

        spa_config_enter(spa, SCL_STATE, FTAG, RW_READER);

        ASSERT(spa->spa_avz_action == AVZ_ACTION_NONE ||
            spa->spa_avz_action == AVZ_ACTION_INITIALIZE ||
            spa->spa_all_vdev_zaps != 0);

        if (spa->spa_avz_action == AVZ_ACTION_REBUILD) {
                /* Make and build the new AVZ */
                uint64_t new_avz = zap_create(spa->spa_meta_objset,
                    DMU_OTN_ZAP_METADATA, DMU_OT_NONE, 0, tx);
                spa_avz_build(spa->spa_root_vdev, new_avz, tx);

                /* Diff old AVZ with new one */
                zap_cursor_t zc;
                zap_attribute_t za;

                for (zap_cursor_init(&zc, spa->spa_meta_objset,
                    spa->spa_all_vdev_zaps);
                    zap_cursor_retrieve(&zc, &za) == 0;
                    zap_cursor_advance(&zc)) {
                        uint64_t vdzap = za.za_first_integer;
                        if (zap_lookup_int(spa->spa_meta_objset, new_avz,
                            vdzap) == ENOENT) {
                                /*
                                 * ZAP is listed in old AVZ but not in new one;
                                 * destroy it
                                 */
                                VERIFY0(zap_destroy(spa->spa_meta_objset, vdzap,
                                    tx));
                        }
                }

                zap_cursor_fini(&zc);

                /* Destroy the old AVZ */
                VERIFY0(zap_destroy(spa->spa_meta_objset,
                    spa->spa_all_vdev_zaps, tx));

                /* Replace the old AVZ in the dir obj with the new one */
                VERIFY0(zap_update(spa->spa_meta_objset,
                    DMU_POOL_DIRECTORY_OBJECT, DMU_POOL_VDEV_ZAP_MAP,
                    sizeof (new_avz), 1, &new_avz, tx));

                spa->spa_all_vdev_zaps = new_avz;
        } else if (spa->spa_avz_action == AVZ_ACTION_DESTROY) {
                zap_cursor_t zc;
                zap_attribute_t za;

                /* Walk through the AVZ and destroy all listed ZAPs */
                for (zap_cursor_init(&zc, spa->spa_meta_objset,
                    spa->spa_all_vdev_zaps);
                    zap_cursor_retrieve(&zc, &za) == 0;
                    zap_cursor_advance(&zc)) {
                        uint64_t zap = za.za_first_integer;
                        VERIFY0(zap_destroy(spa->spa_meta_objset, zap, tx));
                }

                zap_cursor_fini(&zc);

                /* Destroy and unlink the AVZ itself */
                VERIFY0(zap_destroy(spa->spa_meta_objset,
                    spa->spa_all_vdev_zaps, tx));
                VERIFY0(zap_remove(spa->spa_meta_objset,
                    DMU_POOL_DIRECTORY_OBJECT, DMU_POOL_VDEV_ZAP_MAP, tx));
                spa->spa_all_vdev_zaps = 0;
        }

        if (spa->spa_all_vdev_zaps == 0) {
                spa->spa_all_vdev_zaps = zap_create_link(spa->spa_meta_objset,
                    DMU_OTN_ZAP_METADATA, DMU_POOL_DIRECTORY_OBJECT,
                    DMU_POOL_VDEV_ZAP_MAP, tx);
        }
        spa->spa_avz_action = AVZ_ACTION_NONE;

        /* Create ZAPs for vdevs that don't have them. */
        vdev_construct_zaps(spa->spa_root_vdev, tx);

        config = spa_config_generate(spa, spa->spa_root_vdev,
            dmu_tx_get_txg(tx), B_FALSE);

        /*
         * If we're upgrading the spa version then make sure that
         * the config object gets updated with the correct version.
         */
        if (spa->spa_ubsync.ub_version < spa->spa_uberblock.ub_version)
                fnvlist_add_uint64(config, ZPOOL_CONFIG_VERSION,
                    spa->spa_uberblock.ub_version);

        spa_config_exit(spa, SCL_STATE, FTAG);

        nvlist_free(spa->spa_config_syncing);
        spa->spa_config_syncing = config;

        spa_sync_nvlist(spa, spa->spa_config_object, config, tx);
}

static void
spa_sync_version(void *arg, dmu_tx_t *tx)
{
        uint64_t *versionp = arg;
        uint64_t version = *versionp;
        spa_t *spa = dmu_tx_pool(tx)->dp_spa;

        /*
         * Setting the version is special cased when first creating the pool.
         */
        ASSERT(tx->tx_txg != TXG_INITIAL);

        ASSERT(SPA_VERSION_IS_SUPPORTED(version));
        ASSERT(version >= spa_version(spa));

        spa->spa_uberblock.ub_version = version;
        vdev_config_dirty(spa->spa_root_vdev);
        spa_history_log_internal(spa, "set", tx, "version=%lld", version);
}

/*
 * Set zpool properties.
 */
static void
spa_sync_props(void *arg, dmu_tx_t *tx)
{
        nvlist_t *nvp = arg;
        spa_t *spa = dmu_tx_pool(tx)->dp_spa;
        objset_t *mos = spa->spa_meta_objset;
        nvpair_t *elem = NULL;

        mutex_enter(&spa->spa_props_lock);

        while ((elem = nvlist_next_nvpair(nvp, elem))) {
                uint64_t intval;
                char *strval, *fname;
                zpool_prop_t prop;
                const char *propname;
                zprop_type_t proptype;
                spa_feature_t fid;

                switch (prop = zpool_name_to_prop(nvpair_name(elem))) {
                case ZPOOL_PROP_INVAL:
                        /*
                         * We checked this earlier in spa_prop_validate().
                         */
                        ASSERT(zpool_prop_feature(nvpair_name(elem)));

                        fname = strchr(nvpair_name(elem), '@') + 1;
                        VERIFY0(zfeature_lookup_name(fname, &fid));

                        spa_feature_enable(spa, fid, tx);
                        spa_history_log_internal(spa, "set", tx,
                            "%s=enabled", nvpair_name(elem));
                        break;

                case ZPOOL_PROP_VERSION:
                        intval = fnvpair_value_uint64(elem);
                        /*
                         * The version is synced separately before other
                         * properties and should be correct by now.
                         */
                        ASSERT3U(spa_version(spa), >=, intval);
                        break;

                case ZPOOL_PROP_ALTROOT:
                        /*
                         * 'altroot' is a non-persistent property. It should
                         * have been set temporarily at creation or import time.
                         */
                        ASSERT(spa->spa_root != NULL);
                        break;

                case ZPOOL_PROP_READONLY:
                case ZPOOL_PROP_CACHEFILE:
                        /*
                         * 'readonly' and 'cachefile' are also non-persisitent
                         * properties.
                         */
                        break;
                case ZPOOL_PROP_COMMENT:
                        strval = fnvpair_value_string(elem);
                        if (spa->spa_comment != NULL)
                                spa_strfree(spa->spa_comment);
                        spa->spa_comment = spa_strdup(strval);
                        /*
                         * We need to dirty the configuration on all the vdevs
                         * so that their labels get updated.  It's unnecessary
                         * to do this for pool creation since the vdev's
                         * configuration has already been dirtied.
                         */
                        if (tx->tx_txg != TXG_INITIAL)
                                vdev_config_dirty(spa->spa_root_vdev);
                        spa_history_log_internal(spa, "set", tx,
                            "%s=%s", nvpair_name(elem), strval);
                        break;
                default:
                        /*
                         * Set pool property values in the poolprops mos object.
                         */
                        if (spa->spa_pool_props_object == 0) {
                                spa->spa_pool_props_object =
                                    zap_create_link(mos, DMU_OT_POOL_PROPS,
                                    DMU_POOL_DIRECTORY_OBJECT, DMU_POOL_PROPS,
                                    tx);
                        }

                        /* normalize the property name */
                        propname = zpool_prop_to_name(prop);
                        proptype = zpool_prop_get_type(prop);

                        if (nvpair_type(elem) == DATA_TYPE_STRING) {
                                ASSERT(proptype == PROP_TYPE_STRING);
                                strval = fnvpair_value_string(elem);
                                VERIFY0(zap_update(mos,
                                    spa->spa_pool_props_object, propname,
                                    1, strlen(strval) + 1, strval, tx));
                                spa_history_log_internal(spa, "set", tx,
                                    "%s=%s", nvpair_name(elem), strval);
                        } else if (nvpair_type(elem) == DATA_TYPE_UINT64) {
                                intval = fnvpair_value_uint64(elem);

                                if (proptype == PROP_TYPE_INDEX) {
                                        const char *unused;
                                        VERIFY0(zpool_prop_index_to_string(
                                            prop, intval, &unused));
                                }
                                VERIFY0(zap_update(mos,
                                    spa->spa_pool_props_object, propname,
                                    8, 1, &intval, tx));
                                spa_history_log_internal(spa, "set", tx,
                                    "%s=%lld", nvpair_name(elem), intval);
                        } else {
                                ASSERT(0); /* not allowed */
                        }

                        switch (prop) {
                        case ZPOOL_PROP_DELEGATION:
                                spa->spa_delegation = intval;
                                break;
                        case ZPOOL_PROP_BOOTFS:
                                spa->spa_bootfs = intval;
                                break;
                        case ZPOOL_PROP_FAILUREMODE:
                                spa->spa_failmode = intval;
                                break;
                        case ZPOOL_PROP_AUTOEXPAND:
                                spa->spa_autoexpand = intval;
                                if (tx->tx_txg != TXG_INITIAL)
                                        spa_async_request(spa,
                                            SPA_ASYNC_AUTOEXPAND);
                                break;
                        case ZPOOL_PROP_MULTIHOST:
                                spa->spa_multihost = intval;
                                break;
                        case ZPOOL_PROP_DEDUPDITTO:
                                spa->spa_dedup_ditto = intval;
                                break;
                        default:
                                break;
                        }
                }

        }

        mutex_exit(&spa->spa_props_lock);
}

/*
 * Perform one-time upgrade on-disk changes.  spa_version() does not
 * reflect the new version this txg, so there must be no changes this
 * txg to anything that the upgrade code depends on after it executes.
 * Therefore this must be called after dsl_pool_sync() does the sync
 * tasks.
 */
static void
spa_sync_upgrades(spa_t *spa, dmu_tx_t *tx)
{
        dsl_pool_t *dp = spa->spa_dsl_pool;

        ASSERT(spa->spa_sync_pass == 1);

        rrw_enter(&dp->dp_config_rwlock, RW_WRITER, FTAG);

        if (spa->spa_ubsync.ub_version < SPA_VERSION_ORIGIN &&
            spa->spa_uberblock.ub_version >= SPA_VERSION_ORIGIN) {
                dsl_pool_create_origin(dp, tx);

                /* Keeping the origin open increases spa_minref */
                spa->spa_minref += 3;
        }

        if (spa->spa_ubsync.ub_version < SPA_VERSION_NEXT_CLONES &&
            spa->spa_uberblock.ub_version >= SPA_VERSION_NEXT_CLONES) {
                dsl_pool_upgrade_clones(dp, tx);
        }

        if (spa->spa_ubsync.ub_version < SPA_VERSION_DIR_CLONES &&
            spa->spa_uberblock.ub_version >= SPA_VERSION_DIR_CLONES) {
                dsl_pool_upgrade_dir_clones(dp, tx);

                /* Keeping the freedir open increases spa_minref */
                spa->spa_minref += 3;
        }

        if (spa->spa_ubsync.ub_version < SPA_VERSION_FEATURES &&
            spa->spa_uberblock.ub_version >= SPA_VERSION_FEATURES) {
                spa_feature_create_zap_objects(spa, tx);
        }

        /*
         * LZ4_COMPRESS feature's behaviour was changed to activate_on_enable
         * when possibility to use lz4 compression for metadata was added
         * Old pools that have this feature enabled must be upgraded to have
         * this feature active
         */
        if (spa->spa_uberblock.ub_version >= SPA_VERSION_FEATURES) {
                boolean_t lz4_en = spa_feature_is_enabled(spa,
                    SPA_FEATURE_LZ4_COMPRESS);
                boolean_t lz4_ac = spa_feature_is_active(spa,
                    SPA_FEATURE_LZ4_COMPRESS);

                if (lz4_en && !lz4_ac)
                        spa_feature_incr(spa, SPA_FEATURE_LZ4_COMPRESS, tx);
        }

        /*
         * If we haven't written the salt, do so now.  Note that the
         * feature may not be activated yet, but that's fine since
         * the presence of this ZAP entry is backwards compatible.
         */
        if (zap_contains(spa->spa_meta_objset, DMU_POOL_DIRECTORY_OBJECT,
            DMU_POOL_CHECKSUM_SALT) == ENOENT) {
                VERIFY0(zap_add(spa->spa_meta_objset,
                    DMU_POOL_DIRECTORY_OBJECT, DMU_POOL_CHECKSUM_SALT, 1,
                    sizeof (spa->spa_cksum_salt.zcs_bytes),
                    spa->spa_cksum_salt.zcs_bytes, tx));
        }

        rrw_exit(&dp->dp_config_rwlock, FTAG);
}

/*
 * Sync the specified transaction group.  New blocks may be dirtied as
 * part of the process, so we iterate until it converges.
 */
void
spa_sync(spa_t *spa, uint64_t txg)
{
        dsl_pool_t *dp = spa->spa_dsl_pool;
        objset_t *mos = spa->spa_meta_objset;
        bplist_t *free_bpl = &spa->spa_free_bplist[txg & TXG_MASK];
        vdev_t *rvd = spa->spa_root_vdev;
        vdev_t *vd;
        dmu_tx_t *tx;
        int error;
        uint32_t max_queue_depth = zfs_vdev_async_write_max_active *
            zfs_vdev_queue_depth_pct / 100;

        VERIFY(spa_writeable(spa));

        /*
         * Lock out configuration changes.
         */
        spa_config_enter(spa, SCL_CONFIG, FTAG, RW_READER);

        spa->spa_syncing_txg = txg;
        spa->spa_sync_pass = 0;

        mutex_enter(&spa->spa_alloc_lock);
        VERIFY0(avl_numnodes(&spa->spa_alloc_tree));
        mutex_exit(&spa->spa_alloc_lock);

        /*
         * If there are any pending vdev state changes, convert them
         * into config changes that go out with this transaction group.
         */
        spa_config_enter(spa, SCL_STATE, FTAG, RW_READER);
        while (list_head(&spa->spa_state_dirty_list) != NULL) {
                /*
                 * We need the write lock here because, for aux vdevs,
                 * calling vdev_config_dirty() modifies sav_config.
                 * This is ugly and will become unnecessary when we
                 * eliminate the aux vdev wart by integrating all vdevs
                 * into the root vdev tree.
                 */
                spa_config_exit(spa, SCL_CONFIG | SCL_STATE, FTAG);
                spa_config_enter(spa, SCL_CONFIG | SCL_STATE, FTAG, RW_WRITER);
                while ((vd = list_head(&spa->spa_state_dirty_list)) != NULL) {
                        vdev_state_clean(vd);
                        vdev_config_dirty(vd);
                }
                spa_config_exit(spa, SCL_CONFIG | SCL_STATE, FTAG);
                spa_config_enter(spa, SCL_CONFIG | SCL_STATE, FTAG, RW_READER);
        }
        spa_config_exit(spa, SCL_STATE, FTAG);

        tx = dmu_tx_create_assigned(dp, txg);

        spa->spa_sync_starttime = gethrtime();
        taskq_cancel_id(system_delay_taskq, spa->spa_deadman_tqid);
        spa->spa_deadman_tqid = taskq_dispatch_delay(system_delay_taskq,
            spa_deadman, spa, TQ_SLEEP, ddi_get_lbolt() +
            NSEC_TO_TICK(spa->spa_deadman_synctime));

        /*
         * If we are upgrading to SPA_VERSION_RAIDZ_DEFLATE this txg,
         * set spa_deflate if we have no raid-z vdevs.
         */
        if (spa->spa_ubsync.ub_version < SPA_VERSION_RAIDZ_DEFLATE &&
            spa->spa_uberblock.ub_version >= SPA_VERSION_RAIDZ_DEFLATE) {
                int i;

                for (i = 0; i < rvd->vdev_children; i++) {
                        vd = rvd->vdev_child[i];
                        if (vd->vdev_deflate_ratio != SPA_MINBLOCKSIZE)
                                break;
                }
                if (i == rvd->vdev_children) {
                        spa->spa_deflate = TRUE;
                        VERIFY(0 == zap_add(spa->spa_meta_objset,
                            DMU_POOL_DIRECTORY_OBJECT, DMU_POOL_DEFLATE,
                            sizeof (uint64_t), 1, &spa->spa_deflate, tx));
                }
        }

        /*
         * Set the top-level vdev's max queue depth. Evaluate each
         * top-level's async write queue depth in case it changed.
         * The max queue depth will not change in the middle of syncing
         * out this txg.
         */
        uint64_t queue_depth_total = 0;
        for (int c = 0; c < rvd->vdev_children; c++) {
                vdev_t *tvd = rvd->vdev_child[c];
                metaslab_group_t *mg = tvd->vdev_mg;

                if (mg == NULL || mg->mg_class != spa_normal_class(spa) ||
                    !metaslab_group_initialized(mg))
                        continue;

                /*
                 * It is safe to do a lock-free check here because only async
                 * allocations look at mg_max_alloc_queue_depth, and async
                 * allocations all happen from spa_sync().
                 */
                ASSERT0(refcount_count(&mg->mg_alloc_queue_depth));
                mg->mg_max_alloc_queue_depth = max_queue_depth;
                queue_depth_total += mg->mg_max_alloc_queue_depth;
        }
        metaslab_class_t *mc = spa_normal_class(spa);
        ASSERT0(refcount_count(&mc->mc_alloc_slots));
        mc->mc_alloc_max_slots = queue_depth_total;
        mc->mc_alloc_throttle_enabled = zio_dva_throttle_enabled;

        ASSERT3U(mc->mc_alloc_max_slots, <=,
            max_queue_depth * rvd->vdev_children);

        /*
         * Iterate to convergence.
         */
        do {
                int pass = ++spa->spa_sync_pass;

                spa_sync_config_object(spa, tx);
                spa_sync_aux_dev(spa, &spa->spa_spares, tx,
                    ZPOOL_CONFIG_SPARES, DMU_POOL_SPARES);
                spa_sync_aux_dev(spa, &spa->spa_l2cache, tx,
                    ZPOOL_CONFIG_L2CACHE, DMU_POOL_L2CACHE);
                spa_errlog_sync(spa, txg);
                dsl_pool_sync(dp, txg);

                if (pass < zfs_sync_pass_deferred_free) {
                        spa_sync_frees(spa, free_bpl, tx);
                } else {
                        /*
                         * We can not defer frees in pass 1, because
                         * we sync the deferred frees later in pass 1.
                         */
                        ASSERT3U(pass, >, 1);
                        bplist_iterate(free_bpl, bpobj_enqueue_cb,
                            &spa->spa_deferred_bpobj, tx);
                }

                ddt_sync(spa, txg);
                dsl_scan_sync(dp, tx);

                while ((vd = txg_list_remove(&spa->spa_vdev_txg_list, txg)))
                        vdev_sync(vd, txg);

                if (pass == 1) {
                        spa_sync_upgrades(spa, tx);
                        ASSERT3U(txg, >=,
                            spa->spa_uberblock.ub_rootbp.blk_birth);
                        /*
                         * Note: We need to check if the MOS is dirty
                         * because we could have marked the MOS dirty
                         * without updating the uberblock (e.g. if we
                         * have sync tasks but no dirty user data).  We
                         * need to check the uberblock's rootbp because
                         * it is updated if we have synced out dirty
                         * data (though in this case the MOS will most
                         * likely also be dirty due to second order
                         * effects, we don't want to rely on that here).
                         */
                        if (spa->spa_uberblock.ub_rootbp.blk_birth < txg &&
                            !dmu_objset_is_dirty(mos, txg)) {
                                /*
                                 * Nothing changed on the first pass,
                                 * therefore this TXG is a no-op.  Avoid
                                 * syncing deferred frees, so that we
                                 * can keep this TXG as a no-op.
                                 */
                                ASSERT(txg_list_empty(&dp->dp_dirty_datasets,
                                    txg));
                                ASSERT(txg_list_empty(&dp->dp_dirty_dirs, txg));
                                ASSERT(txg_list_empty(&dp->dp_sync_tasks, txg));
                                break;
                        }
                        spa_sync_deferred_frees(spa, tx);
                }

        } while (dmu_objset_is_dirty(mos, txg));

#ifdef ZFS_DEBUG
        if (!list_is_empty(&spa->spa_config_dirty_list)) {
                /*
                 * Make sure that the number of ZAPs for all the vdevs matches
                 * the number of ZAPs in the per-vdev ZAP list. This only gets
                 * called if the config is dirty; otherwise there may be
                 * outstanding AVZ operations that weren't completed in
                 * spa_sync_config_object.
                 */
                uint64_t all_vdev_zap_entry_count;
                ASSERT0(zap_count(spa->spa_meta_objset,
                    spa->spa_all_vdev_zaps, &all_vdev_zap_entry_count));
                ASSERT3U(vdev_count_verify_zaps(spa->spa_root_vdev), ==,
                    all_vdev_zap_entry_count);
        }
#endif

        /*
         * Rewrite the vdev configuration (which includes the uberblock)
         * to commit the transaction group.
         *
         * If there are no dirty vdevs, we sync the uberblock to a few
         * random top-level vdevs that are known to be visible in the
         * config cache (see spa_vdev_add() for a complete description).
         * If there *are* dirty vdevs, sync the uberblock to all vdevs.
         */
        for (;;) {
                /*
                 * We hold SCL_STATE to prevent vdev open/close/etc.
                 * while we're attempting to write the vdev labels.
                 */
                spa_config_enter(spa, SCL_STATE, FTAG, RW_READER);

                if (list_is_empty(&spa->spa_config_dirty_list)) {
                        vdev_t *svd[SPA_DVAS_PER_BP];
                        int svdcount = 0;
                        int children = rvd->vdev_children;
                        int c0 = spa_get_random(children);

                        for (int c = 0; c < children; c++) {
                                vd = rvd->vdev_child[(c0 + c) % children];
                                if (vd->vdev_ms_array == 0 || vd->vdev_islog)
                                        continue;
                                svd[svdcount++] = vd;
                                if (svdcount == SPA_DVAS_PER_BP)
                                        break;
                        }
                        error = vdev_config_sync(svd, svdcount, txg);
                } else {
                        error = vdev_config_sync(rvd->vdev_child,
                            rvd->vdev_children, txg);
                }

                if (error == 0)
                        spa->spa_last_synced_guid = rvd->vdev_guid;

                spa_config_exit(spa, SCL_STATE, FTAG);

                if (error == 0)
                        break;
                zio_suspend(spa, NULL);
                zio_resume_wait(spa);
        }
        dmu_tx_commit(tx);

        taskq_cancel_id(system_delay_taskq, spa->spa_deadman_tqid);
        spa->spa_deadman_tqid = 0;

        /*
         * Clear the dirty config list.
         */
        while ((vd = list_head(&spa->spa_config_dirty_list)) != NULL)
                vdev_config_clean(vd);

        /*
         * Now that the new config has synced transactionally,
         * let it become visible to the config cache.
         */
        if (spa->spa_config_syncing != NULL) {
                spa_config_set(spa, spa->spa_config_syncing);
                spa->spa_config_txg = txg;
                spa->spa_config_syncing = NULL;
        }

        dsl_pool_sync_done(dp, txg);

        mutex_enter(&spa->spa_alloc_lock);
        VERIFY0(avl_numnodes(&spa->spa_alloc_tree));
        mutex_exit(&spa->spa_alloc_lock);

        /*
         * Update usable space statistics.
         */
        while ((vd = txg_list_remove(&spa->spa_vdev_txg_list, TXG_CLEAN(txg))))
                vdev_sync_done(vd, txg);

        spa_update_dspace(spa);

        /*
         * It had better be the case that we didn't dirty anything
         * since vdev_config_sync().
         */
        ASSERT(txg_list_empty(&dp->dp_dirty_datasets, txg));
        ASSERT(txg_list_empty(&dp->dp_dirty_dirs, txg));
        ASSERT(txg_list_empty(&spa->spa_vdev_txg_list, txg));

        spa->spa_sync_pass = 0;

        /*
         * Update the last synced uberblock here. We want to do this at
         * the end of spa_sync() so that consumers of spa_last_synced_txg()
         * will be guaranteed that all the processing associated with
         * that txg has been completed.
         */
        spa->spa_ubsync = spa->spa_uberblock;
        spa_config_exit(spa, SCL_CONFIG, FTAG);

        spa_handle_ignored_writes(spa);

        /*
         * If any async tasks have been requested, kick them off.
         */
        spa_async_dispatch(spa);
}

/*
 * Sync all pools.  We don't want to hold the namespace lock across these
 * operations, so we take a reference on the spa_t and drop the lock during the
 * sync.
 */
void
spa_sync_allpools(void)
{
        spa_t *spa = NULL;
        mutex_enter(&spa_namespace_lock);
        while ((spa = spa_next(spa)) != NULL) {
                if (spa_state(spa) != POOL_STATE_ACTIVE ||
                    !spa_writeable(spa) || spa_suspended(spa))
                        continue;
                spa_open_ref(spa, FTAG);
                mutex_exit(&spa_namespace_lock);
                txg_wait_synced(spa_get_dsl(spa), 0);
                mutex_enter(&spa_namespace_lock);
                spa_close(spa, FTAG);
        }
        mutex_exit(&spa_namespace_lock);
}

/*
 * ==========================================================================
 * Miscellaneous routines
 * ==========================================================================
 */

/*
 * Remove all pools in the system.
 */
void
spa_evict_all(void)
{
        spa_t *spa;

        /*
         * Remove all cached state.  All pools should be closed now,
         * so every spa in the AVL tree should be unreferenced.
         */
        mutex_enter(&spa_namespace_lock);
        while ((spa = spa_next(NULL)) != NULL) {
                /*
                 * Stop async tasks.  The async thread may need to detach
                 * a device that's been replaced, which requires grabbing
                 * spa_namespace_lock, so we must drop it here.
                 */
                spa_open_ref(spa, FTAG);
                mutex_exit(&spa_namespace_lock);
                spa_async_suspend(spa);
                mutex_enter(&spa_namespace_lock);
                spa_close(spa, FTAG);

                if (spa->spa_state != POOL_STATE_UNINITIALIZED) {
                        spa_unload(spa);
                        spa_deactivate(spa);
                }
                spa_remove(spa);
        }
        mutex_exit(&spa_namespace_lock);
}

vdev_t *
spa_lookup_by_guid(spa_t *spa, uint64_t guid, boolean_t aux)
{
        vdev_t *vd;
        int i;

        if ((vd = vdev_lookup_by_guid(spa->spa_root_vdev, guid)) != NULL)
                return (vd);

        if (aux) {
                for (i = 0; i < spa->spa_l2cache.sav_count; i++) {
                        vd = spa->spa_l2cache.sav_vdevs[i];
                        if (vd->vdev_guid == guid)
                                return (vd);
                }

                for (i = 0; i < spa->spa_spares.sav_count; i++) {
                        vd = spa->spa_spares.sav_vdevs[i];
                        if (vd->vdev_guid == guid)
                                return (vd);
                }
        }

        return (NULL);
}

void
spa_upgrade(spa_t *spa, uint64_t version)
{
        ASSERT(spa_writeable(spa));

        spa_config_enter(spa, SCL_ALL, FTAG, RW_WRITER);

        /*
         * This should only be called for a non-faulted pool, and since a
         * future version would result in an unopenable pool, this shouldn't be
         * possible.
         */
        ASSERT(SPA_VERSION_IS_SUPPORTED(spa->spa_uberblock.ub_version));
        ASSERT3U(version, >=, spa->spa_uberblock.ub_version);

        spa->spa_uberblock.ub_version = version;
        vdev_config_dirty(spa->spa_root_vdev);

        spa_config_exit(spa, SCL_ALL, FTAG);

        txg_wait_synced(spa_get_dsl(spa), 0);
}

boolean_t
spa_has_spare(spa_t *spa, uint64_t guid)
{
        int i;
        uint64_t spareguid;
        spa_aux_vdev_t *sav = &spa->spa_spares;

        for (i = 0; i < sav->sav_count; i++)
                if (sav->sav_vdevs[i]->vdev_guid == guid)
                        return (B_TRUE);

        for (i = 0; i < sav->sav_npending; i++) {
                if (nvlist_lookup_uint64(sav->sav_pending[i], ZPOOL_CONFIG_GUID,
                    &spareguid) == 0 && spareguid == guid)
                        return (B_TRUE);
        }

        return (B_FALSE);
}

/*
 * Check if a pool has an active shared spare device.
 * Note: reference count of an active spare is 2, as a spare and as a replace
 */
static boolean_t
spa_has_active_shared_spare(spa_t *spa)
{
        int i, refcnt;
        uint64_t pool;
        spa_aux_vdev_t *sav = &spa->spa_spares;

        for (i = 0; i < sav->sav_count; i++) {
                if (spa_spare_exists(sav->sav_vdevs[i]->vdev_guid, &pool,
                    &refcnt) && pool != 0ULL && pool == spa_guid(spa) &&
                    refcnt > 2)
                        return (B_TRUE);
        }

        return (B_FALSE);
}

static sysevent_t *
spa_event_create(spa_t *spa, vdev_t *vd, nvlist_t *hist_nvl, const char *name)
{
        sysevent_t *ev = NULL;
#ifdef _KERNEL
        nvlist_t *resource;

        resource = zfs_event_create(spa, vd, FM_SYSEVENT_CLASS, name, hist_nvl);
        if (resource) {
                ev = kmem_alloc(sizeof (sysevent_t), KM_SLEEP);
                ev->resource = resource;
        }
#endif
        return (ev);
}

static void
spa_event_post(sysevent_t *ev)
{
#ifdef _KERNEL
        if (ev) {
                zfs_zevent_post(ev->resource, NULL, zfs_zevent_post_cb);
                kmem_free(ev, sizeof (*ev));
        }
#endif
}

/*
 * Post a zevent corresponding to the given sysevent.   The 'name' must be one
 * of the event definitions in sys/sysevent/eventdefs.h.  The payload will be
 * filled in from the spa and (optionally) the vdev.  This doesn't do anything
 * in the userland libzpool, as we don't want consumers to misinterpret ztest
 * or zdb as real changes.
 */
void
spa_event_notify(spa_t *spa, vdev_t *vd, nvlist_t *hist_nvl, const char *name)
{
        spa_event_post(spa_event_create(spa, vd, hist_nvl, name));
}

#if defined(_KERNEL) && defined(HAVE_SPL)
/* state manipulation functions */
EXPORT_SYMBOL(spa_open);
EXPORT_SYMBOL(spa_open_rewind);
EXPORT_SYMBOL(spa_get_stats);
EXPORT_SYMBOL(spa_create);
EXPORT_SYMBOL(spa_import);
EXPORT_SYMBOL(spa_tryimport);
EXPORT_SYMBOL(spa_destroy);
EXPORT_SYMBOL(spa_export);
EXPORT_SYMBOL(spa_reset);
EXPORT_SYMBOL(spa_async_request);
EXPORT_SYMBOL(spa_async_suspend);
EXPORT_SYMBOL(spa_async_resume);
EXPORT_SYMBOL(spa_inject_addref);
EXPORT_SYMBOL(spa_inject_delref);
EXPORT_SYMBOL(spa_scan_stat_init);
EXPORT_SYMBOL(spa_scan_get_stats);

/* device maniion */
EXPORT_SYMBOL(spa_vdev_add);
EXPORT_SYMBOL(spa_vdev_attach);
EXPORT_SYMBOL(spa_vdev_detach);
EXPORT_SYMBOL(spa_vdev_remove);
EXPORT_SYMBOL(spa_vdev_setpath);
EXPORT_SYMBOL(spa_vdev_setfru);
EXPORT_SYMBOL(spa_vdev_split_mirror);

/* spare statech is global across all pools) */
EXPORT_SYMBOL(spa_spare_add);
EXPORT_SYMBOL(spa_spare_remove);
EXPORT_SYMBOL(spa_spare_exists);
EXPORT_SYMBOL(spa_spare_activate);

/* L2ARC statech is global across all pools) */
EXPORT_SYMBOL(spa_l2cache_add);
EXPORT_SYMBOL(spa_l2cache_remove);
EXPORT_SYMBOL(spa_l2cache_exists);
EXPORT_SYMBOL(spa_l2cache_activate);
EXPORT_SYMBOL(spa_l2cache_drop);

/* scanning */
EXPORT_SYMBOL(spa_scan);
EXPORT_SYMBOL(spa_scan_stop);

/* spa syncing */
EXPORT_SYMBOL(spa_sync); /* only for DMU use */
EXPORT_SYMBOL(spa_sync_allpools);

/* properties */
EXPORT_SYMBOL(spa_prop_set);
EXPORT_SYMBOL(spa_prop_get);
EXPORT_SYMBOL(spa_prop_clear_bootfs);

/* asynchronous event notification */
EXPORT_SYMBOL(spa_event_notify);
#endif

#if defined(_KERNEL) && defined(HAVE_SPL)
module_param(spa_load_verify_maxinflight, int, 0644);
MODULE_PARM_DESC(spa_load_verify_maxinflight,
        "Max concurrent traversal I/Os while verifying pool during import -X");

module_param(spa_load_verify_metadata, int, 0644);
MODULE_PARM_DESC(spa_load_verify_metadata,
        "Set to traverse metadata on pool import");

module_param(spa_load_verify_data, int, 0644);
MODULE_PARM_DESC(spa_load_verify_data,
        "Set to traverse data on pool import");

/* CSTYLED */
module_param(zio_taskq_batch_pct, uint, 0444);
MODULE_PARM_DESC(zio_taskq_batch_pct,
        "Percentage of CPUs to run an IO worker thread");

#endif