FreeBSD/Linux Kernel Cross Reference
sys/contrib/openzfs/module/zfs/vdev_removal.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 https://opensource.org/licenses/CDDL-1.0.
     * 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, 2020 by Delphix. All rights reserved.
     * Copyright (c) 2019, loli10K <ezomori.nozomu@gmail.com>. All rights reserved.
     */
    
    #include <sys/zfs_context.h>
    #include <sys/spa_impl.h>
    #include <sys/dmu.h>
    #include <sys/dmu_tx.h>
    #include <sys/zap.h>
    #include <sys/vdev_impl.h>
    #include <sys/metaslab.h>
    #include <sys/metaslab_impl.h>
    #include <sys/uberblock_impl.h>
    #include <sys/txg.h>
    #include <sys/avl.h>
    #include <sys/bpobj.h>
    #include <sys/dsl_pool.h>
    #include <sys/dsl_synctask.h>
    #include <sys/dsl_dir.h>
    #include <sys/arc.h>
    #include <sys/zfeature.h>
    #include <sys/vdev_indirect_births.h>
    #include <sys/vdev_indirect_mapping.h>
    #include <sys/abd.h>
    #include <sys/vdev_initialize.h>
    #include <sys/vdev_trim.h>
    #include <sys/trace_zfs.h>
    
    /*
     * This file contains the necessary logic to remove vdevs from a
     * storage pool.  Currently, the only devices that can be removed
     * are log, cache, and spare devices; and top level vdevs from a pool
     * w/o raidz or mirrors.  (Note that members of a mirror can be removed
     * by the detach operation.)
     *
     * Log vdevs are removed by evacuating them and then turning the vdev
     * into a hole vdev while holding spa config locks.
     *
     * Top level vdevs are removed and converted into an indirect vdev via
     * a multi-step process:
     *
     *  - Disable allocations from this device (spa_vdev_remove_top).
     *
     *  - From a new thread (spa_vdev_remove_thread), copy data from
     *    the removing vdev to a different vdev.  The copy happens in open
     *    context (spa_vdev_copy_impl) and issues a sync task
     *    (vdev_mapping_sync) so the sync thread can update the partial
     *    indirect mappings in core and on disk.
     *
     *  - If a free happens during a removal, it is freed from the
     *    removing vdev, and if it has already been copied, from the new
     *    location as well (free_from_removing_vdev).
     *
     *  - After the removal is completed, the copy thread converts the vdev
     *    into an indirect vdev (vdev_remove_complete) before instructing
     *    the sync thread to destroy the space maps and finish the removal
     *    (spa_finish_removal).
     */
    
    typedef struct vdev_copy_arg {
            metaslab_t      *vca_msp;
            uint64_t        vca_outstanding_bytes;
            uint64_t        vca_read_error_bytes;
            uint64_t        vca_write_error_bytes;
            kcondvar_t      vca_cv;
            kmutex_t        vca_lock;
    } vdev_copy_arg_t;
    
    /*
     * The maximum amount of memory we can use for outstanding i/o while
     * doing a device removal.  This determines how much i/o we can have
     * in flight concurrently.
     */
    static const uint_t zfs_remove_max_copy_bytes = 64 * 1024 * 1024;
    
    /*
    * The largest contiguous segment that we will attempt to allocate when
    * removing a device.  This can be no larger than SPA_MAXBLOCKSIZE.  If
    * there is a performance problem with attempting to allocate large blocks,
    * consider decreasing this.
    *
    * See also the accessor function spa_remove_max_segment().
    */
   uint_t zfs_remove_max_segment = SPA_MAXBLOCKSIZE;
   
   /*
    * Ignore hard IO errors during device removal.  When set if a device
    * encounters hard IO error during the removal process the removal will
    * not be cancelled.  This can result in a normally recoverable block
    * becoming permanently damaged and is not recommended.
    */
   static int zfs_removal_ignore_errors = 0;
   
   /*
    * Allow a remap segment to span free chunks of at most this size. The main
    * impact of a larger span is that we will read and write larger, more
    * contiguous chunks, with more "unnecessary" data -- trading off bandwidth
    * for iops.  The value here was chosen to align with
    * zfs_vdev_read_gap_limit, which is a similar concept when doing regular
    * reads (but there's no reason it has to be the same).
    *
    * Additionally, a higher span will have the following relatively minor
    * effects:
    *  - the mapping will be smaller, since one entry can cover more allocated
    *    segments
    *  - more of the fragmentation in the removing device will be preserved
    *  - we'll do larger allocations, which may fail and fall back on smaller
    *    allocations
    */
   uint_t vdev_removal_max_span = 32 * 1024;
   
   /*
    * This is used by the test suite so that it can ensure that certain
    * actions happen while in the middle of a removal.
    */
   int zfs_removal_suspend_progress = 0;
   
   #define VDEV_REMOVAL_ZAP_OBJS   "lzap"
   
   static __attribute__((noreturn)) void spa_vdev_remove_thread(void *arg);
   static int spa_vdev_remove_cancel_impl(spa_t *spa);
   
   static void
   spa_sync_removing_state(spa_t *spa, dmu_tx_t *tx)
   {
           VERIFY0(zap_update(spa->spa_dsl_pool->dp_meta_objset,
               DMU_POOL_DIRECTORY_OBJECT,
               DMU_POOL_REMOVING, sizeof (uint64_t),
               sizeof (spa->spa_removing_phys) / sizeof (uint64_t),
               &spa->spa_removing_phys, tx));
   }
   
   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 =
                       fnvlist_lookup_uint64(nvpp[i], ZPOOL_CONFIG_GUID);
   
                   if (guid == target_guid)
                           return (nvpp[i]);
           }
   
           return (NULL);
   }
   
   static void
   vdev_activate(vdev_t *vd)
   {
           metaslab_group_t *mg = vd->vdev_mg;
           spa_t *spa = vd->vdev_spa;
           uint64_t vdev_space = spa_deflate(spa) ?
               vd->vdev_stat.vs_dspace : vd->vdev_stat.vs_space;
   
           ASSERT(!vd->vdev_islog);
           ASSERT(vd->vdev_noalloc);
   
           metaslab_group_activate(mg);
           metaslab_group_activate(vd->vdev_log_mg);
   
           ASSERT3U(spa->spa_nonallocating_dspace, >=, vdev_space);
   
           spa->spa_nonallocating_dspace -= vdev_space;
   
           vd->vdev_noalloc = B_FALSE;
   }
   
   static int
   vdev_passivate(vdev_t *vd, uint64_t *txg)
   {
           spa_t *spa = vd->vdev_spa;
           int error;
   
           ASSERT(!vd->vdev_noalloc);
   
           vdev_t *rvd = spa->spa_root_vdev;
           metaslab_group_t *mg = vd->vdev_mg;
           metaslab_class_t *normal = spa_normal_class(spa);
           if (mg->mg_class == normal) {
                   /*
                    * We must check that this is not the only allocating device in
                    * the pool before passivating, otherwise we will not be able
                    * to make progress because we can't allocate from any vdevs.
                    */
                   boolean_t last = B_TRUE;
                   for (uint64_t id = 0; id < rvd->vdev_children; id++) {
                           vdev_t *cvd = rvd->vdev_child[id];
   
                           if (cvd == vd ||
                               cvd->vdev_ops == &vdev_indirect_ops)
                                   continue;
   
                           metaslab_class_t *mc = cvd->vdev_mg->mg_class;
                           if (mc != normal)
                                   continue;
   
                           if (!cvd->vdev_noalloc) {
                                   last = B_FALSE;
                                   break;
                           }
                   }
                   if (last)
                           return (SET_ERROR(EINVAL));
           }
   
           metaslab_group_passivate(mg);
           ASSERT(!vd->vdev_islog);
           metaslab_group_passivate(vd->vdev_log_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);
   
           /*
            * We must ensure that no "stubby" log blocks are allocated
            * on the device to be removed.  These blocks could be
            * written at any time, including while we are in the middle
            * of copying them.
            */
           error = spa_reset_logs(spa);
   
           *txg = spa_vdev_config_enter(spa);
   
           if (error != 0) {
                   metaslab_group_activate(mg);
                   ASSERT(!vd->vdev_islog);
                   if (vd->vdev_log_mg != NULL)
                           metaslab_group_activate(vd->vdev_log_mg);
                   return (error);
           }
   
           spa->spa_nonallocating_dspace += spa_deflate(spa) ?
               vd->vdev_stat.vs_dspace : vd->vdev_stat.vs_space;
           vd->vdev_noalloc = B_TRUE;
   
           return (0);
   }
   
   /*
    * Turn off allocations for a top-level device from the pool.
    *
    * Turning off allocations for a top-level device 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.
    */
   int
   spa_vdev_noalloc(spa_t *spa, uint64_t guid)
   {
           vdev_t *vd;
           uint64_t txg;
           int error = 0;
   
           ASSERT(!MUTEX_HELD(&spa_namespace_lock));
           ASSERT(spa_writeable(spa));
   
           txg = spa_vdev_enter(spa);
   
           ASSERT(MUTEX_HELD(&spa_namespace_lock));
   
           vd = spa_lookup_by_guid(spa, guid, B_FALSE);
   
           if (vd == NULL)
                   error = SET_ERROR(ENOENT);
           else if (vd->vdev_mg == NULL)
                   error = SET_ERROR(ZFS_ERR_VDEV_NOTSUP);
           else if (!vd->vdev_noalloc)
                   error = vdev_passivate(vd, &txg);
   
           if (error == 0) {
                   vdev_dirty_leaves(vd, VDD_DTL, txg);
                   vdev_config_dirty(vd);
           }
   
           error = spa_vdev_exit(spa, NULL, txg, error);
   
           return (error);
   }
   
   int
   spa_vdev_alloc(spa_t *spa, uint64_t guid)
   {
           vdev_t *vd;
           uint64_t txg;
           int error = 0;
   
           ASSERT(!MUTEX_HELD(&spa_namespace_lock));
           ASSERT(spa_writeable(spa));
   
           txg = spa_vdev_enter(spa);
   
           ASSERT(MUTEX_HELD(&spa_namespace_lock));
   
           vd = spa_lookup_by_guid(spa, guid, B_FALSE);
   
           if (vd == NULL)
                   error = SET_ERROR(ENOENT);
           else if (vd->vdev_mg == NULL)
                   error = SET_ERROR(ZFS_ERR_VDEV_NOTSUP);
           else if (!vd->vdev_removing)
                   vdev_activate(vd);
   
           if (error == 0) {
                   vdev_dirty_leaves(vd, VDD_DTL, txg);
                   vdev_config_dirty(vd);
           }
   
           (void) spa_vdev_exit(spa, NULL, txg, error);
   
           return (error);
   }
   
   static void
   spa_vdev_remove_aux(nvlist_t *config, const 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);
           fnvlist_add_nvlist_array(config, name, (const nvlist_t * const *)newdev,
               count - 1);
   
           for (int i = 0; i < count - 1; i++)
                   nvlist_free(newdev[i]);
   
           if (count > 1)
                   kmem_free(newdev, (count - 1) * sizeof (void *));
   }
   
   static spa_vdev_removal_t *
   spa_vdev_removal_create(vdev_t *vd)
   {
           spa_vdev_removal_t *svr = kmem_zalloc(sizeof (*svr), KM_SLEEP);
           mutex_init(&svr->svr_lock, NULL, MUTEX_DEFAULT, NULL);
           cv_init(&svr->svr_cv, NULL, CV_DEFAULT, NULL);
           svr->svr_allocd_segs = range_tree_create(NULL, RANGE_SEG64, NULL, 0, 0);
           svr->svr_vdev_id = vd->vdev_id;
   
           for (int i = 0; i < TXG_SIZE; i++) {
                   svr->svr_frees[i] = range_tree_create(NULL, RANGE_SEG64, NULL,
                       0, 0);
                   list_create(&svr->svr_new_segments[i],
                       sizeof (vdev_indirect_mapping_entry_t),
                       offsetof(vdev_indirect_mapping_entry_t, vime_node));
           }
   
           return (svr);
   }
   
   void
   spa_vdev_removal_destroy(spa_vdev_removal_t *svr)
   {
           for (int i = 0; i < TXG_SIZE; i++) {
                   ASSERT0(svr->svr_bytes_done[i]);
                   ASSERT0(svr->svr_max_offset_to_sync[i]);
                   range_tree_destroy(svr->svr_frees[i]);
                   list_destroy(&svr->svr_new_segments[i]);
           }
   
           range_tree_destroy(svr->svr_allocd_segs);
           mutex_destroy(&svr->svr_lock);
           cv_destroy(&svr->svr_cv);
           kmem_free(svr, sizeof (*svr));
   }
   
   /*
    * This is called as a synctask in the txg in which we will mark this vdev
    * as removing (in the config stored in the MOS).
    *
    * It begins the evacuation of a toplevel vdev by:
    * - initializing the spa_removing_phys which tracks this removal
    * - computing the amount of space to remove for accounting purposes
    * - dirtying all dbufs in the spa_config_object
    * - creating the spa_vdev_removal
    * - starting the spa_vdev_remove_thread
    */
   static void
   vdev_remove_initiate_sync(void *arg, dmu_tx_t *tx)
   {
           int vdev_id = (uintptr_t)arg;
           spa_t *spa = dmu_tx_pool(tx)->dp_spa;
           vdev_t *vd = vdev_lookup_top(spa, vdev_id);
           vdev_indirect_config_t *vic = &vd->vdev_indirect_config;
           objset_t *mos = spa->spa_dsl_pool->dp_meta_objset;
           spa_vdev_removal_t *svr = NULL;
           uint64_t txg __maybe_unused = dmu_tx_get_txg(tx);
   
           ASSERT0(vdev_get_nparity(vd));
           svr = spa_vdev_removal_create(vd);
   
           ASSERT(vd->vdev_removing);
           ASSERT3P(vd->vdev_indirect_mapping, ==, NULL);
   
           spa_feature_incr(spa, SPA_FEATURE_DEVICE_REMOVAL, tx);
           if (spa_feature_is_enabled(spa, SPA_FEATURE_OBSOLETE_COUNTS)) {
                   /*
                    * By activating the OBSOLETE_COUNTS feature, we prevent
                    * the pool from being downgraded and ensure that the
                    * refcounts are precise.
                    */
                   spa_feature_incr(spa, SPA_FEATURE_OBSOLETE_COUNTS, tx);
                   uint64_t one = 1;
                   VERIFY0(zap_add(spa->spa_meta_objset, vd->vdev_top_zap,
                       VDEV_TOP_ZAP_OBSOLETE_COUNTS_ARE_PRECISE, sizeof (one), 1,
                       &one, tx));
                   boolean_t are_precise __maybe_unused;
                   ASSERT0(vdev_obsolete_counts_are_precise(vd, &are_precise));
                   ASSERT3B(are_precise, ==, B_TRUE);
           }
   
           vic->vic_mapping_object = vdev_indirect_mapping_alloc(mos, tx);
           vd->vdev_indirect_mapping =
               vdev_indirect_mapping_open(mos, vic->vic_mapping_object);
           vic->vic_births_object = vdev_indirect_births_alloc(mos, tx);
           vd->vdev_indirect_births =
               vdev_indirect_births_open(mos, vic->vic_births_object);
           spa->spa_removing_phys.sr_removing_vdev = vd->vdev_id;
           spa->spa_removing_phys.sr_start_time = gethrestime_sec();
           spa->spa_removing_phys.sr_end_time = 0;
           spa->spa_removing_phys.sr_state = DSS_SCANNING;
           spa->spa_removing_phys.sr_to_copy = 0;
           spa->spa_removing_phys.sr_copied = 0;
   
           /*
            * Note: We can't use vdev_stat's vs_alloc for sr_to_copy, because
            * there may be space in the defer tree, which is free, but still
            * counted in vs_alloc.
            */
           for (uint64_t i = 0; i < vd->vdev_ms_count; i++) {
                   metaslab_t *ms = vd->vdev_ms[i];
                   if (ms->ms_sm == NULL)
                           continue;
   
                   spa->spa_removing_phys.sr_to_copy +=
                       metaslab_allocated_space(ms);
   
                   /*
                    * Space which we are freeing this txg does not need to
                    * be copied.
                    */
                   spa->spa_removing_phys.sr_to_copy -=
                       range_tree_space(ms->ms_freeing);
   
                   ASSERT0(range_tree_space(ms->ms_freed));
                   for (int t = 0; t < TXG_SIZE; t++)
                           ASSERT0(range_tree_space(ms->ms_allocating[t]));
           }
   
           /*
            * Sync tasks are called before metaslab_sync(), so there should
            * be no already-synced metaslabs in the TXG_CLEAN list.
            */
           ASSERT3P(txg_list_head(&vd->vdev_ms_list, TXG_CLEAN(txg)), ==, NULL);
   
           spa_sync_removing_state(spa, tx);
   
           /*
            * All blocks that we need to read the most recent mapping must be
            * stored on concrete vdevs.  Therefore, we must dirty anything that
            * is read before spa_remove_init().  Specifically, the
            * spa_config_object.  (Note that although we already modified the
            * spa_config_object in spa_sync_removing_state, that may not have
            * modified all blocks of the object.)
            */
           dmu_object_info_t doi;
           VERIFY0(dmu_object_info(mos, DMU_POOL_DIRECTORY_OBJECT, &doi));
           for (uint64_t offset = 0; offset < doi.doi_max_offset; ) {
                   dmu_buf_t *dbuf;
                   VERIFY0(dmu_buf_hold(mos, DMU_POOL_DIRECTORY_OBJECT,
                       offset, FTAG, &dbuf, 0));
                   dmu_buf_will_dirty(dbuf, tx);
                   offset += dbuf->db_size;
                   dmu_buf_rele(dbuf, FTAG);
           }
   
           /*
            * Now that we've allocated the im_object, dirty the vdev to ensure
            * that the object gets written to the config on disk.
            */
           vdev_config_dirty(vd);
   
           zfs_dbgmsg("starting removal thread for vdev %llu (%px) in txg %llu "
               "im_obj=%llu", (u_longlong_t)vd->vdev_id, vd,
               (u_longlong_t)dmu_tx_get_txg(tx),
               (u_longlong_t)vic->vic_mapping_object);
   
           spa_history_log_internal(spa, "vdev remove started", tx,
               "%s vdev %llu %s", spa_name(spa), (u_longlong_t)vd->vdev_id,
               (vd->vdev_path != NULL) ? vd->vdev_path : "-");
           /*
            * Setting spa_vdev_removal causes subsequent frees to call
            * free_from_removing_vdev().  Note that we don't need any locking
            * because we are the sync thread, and metaslab_free_impl() is only
            * called from syncing context (potentially from a zio taskq thread,
            * but in any case only when there are outstanding free i/os, which
            * there are not).
            */
           ASSERT3P(spa->spa_vdev_removal, ==, NULL);
           spa->spa_vdev_removal = svr;
           svr->svr_thread = thread_create(NULL, 0,
               spa_vdev_remove_thread, spa, 0, &p0, TS_RUN, minclsyspri);
   }
   
   /*
    * When we are opening a pool, we must read the mapping for each
    * indirect vdev in order from most recently removed to least
    * recently removed.  We do this because the blocks for the mapping
    * of older indirect vdevs may be stored on more recently removed vdevs.
    * In order to read each indirect mapping object, we must have
    * initialized all more recently removed vdevs.
    */
   int
   spa_remove_init(spa_t *spa)
   {
           int error;
   
           error = zap_lookup(spa->spa_dsl_pool->dp_meta_objset,
               DMU_POOL_DIRECTORY_OBJECT,
               DMU_POOL_REMOVING, sizeof (uint64_t),
               sizeof (spa->spa_removing_phys) / sizeof (uint64_t),
               &spa->spa_removing_phys);
   
           if (error == ENOENT) {
                   spa->spa_removing_phys.sr_state = DSS_NONE;
                   spa->spa_removing_phys.sr_removing_vdev = -1;
                   spa->spa_removing_phys.sr_prev_indirect_vdev = -1;
                   spa->spa_indirect_vdevs_loaded = B_TRUE;
                   return (0);
           } else if (error != 0) {
                   return (error);
           }
   
           if (spa->spa_removing_phys.sr_state == DSS_SCANNING) {
                   /*
                    * We are currently removing a vdev.  Create and
                    * initialize a spa_vdev_removal_t from the bonus
                    * buffer of the removing vdevs vdev_im_object, and
                    * initialize its partial mapping.
                    */
                   spa_config_enter(spa, SCL_STATE, FTAG, RW_READER);
                   vdev_t *vd = vdev_lookup_top(spa,
                       spa->spa_removing_phys.sr_removing_vdev);
   
                   if (vd == NULL) {
                           spa_config_exit(spa, SCL_STATE, FTAG);
                           return (EINVAL);
                   }
   
                   vdev_indirect_config_t *vic = &vd->vdev_indirect_config;
   
                   ASSERT(vdev_is_concrete(vd));
                   spa_vdev_removal_t *svr = spa_vdev_removal_create(vd);
                   ASSERT3U(svr->svr_vdev_id, ==, vd->vdev_id);
                   ASSERT(vd->vdev_removing);
   
                   vd->vdev_indirect_mapping = vdev_indirect_mapping_open(
                       spa->spa_meta_objset, vic->vic_mapping_object);
                   vd->vdev_indirect_births = vdev_indirect_births_open(
                       spa->spa_meta_objset, vic->vic_births_object);
                   spa_config_exit(spa, SCL_STATE, FTAG);
   
                   spa->spa_vdev_removal = svr;
           }
   
           spa_config_enter(spa, SCL_STATE, FTAG, RW_READER);
           uint64_t indirect_vdev_id =
               spa->spa_removing_phys.sr_prev_indirect_vdev;
           while (indirect_vdev_id != UINT64_MAX) {
                   vdev_t *vd = vdev_lookup_top(spa, indirect_vdev_id);
                   vdev_indirect_config_t *vic = &vd->vdev_indirect_config;
   
                   ASSERT3P(vd->vdev_ops, ==, &vdev_indirect_ops);
                   vd->vdev_indirect_mapping = vdev_indirect_mapping_open(
                       spa->spa_meta_objset, vic->vic_mapping_object);
                   vd->vdev_indirect_births = vdev_indirect_births_open(
                       spa->spa_meta_objset, vic->vic_births_object);
   
                   indirect_vdev_id = vic->vic_prev_indirect_vdev;
           }
           spa_config_exit(spa, SCL_STATE, FTAG);
   
           /*
            * Now that we've loaded all the indirect mappings, we can allow
            * reads from other blocks (e.g. via predictive prefetch).
            */
           spa->spa_indirect_vdevs_loaded = B_TRUE;
           return (0);
   }
   
   void
   spa_restart_removal(spa_t *spa)
   {
           spa_vdev_removal_t *svr = spa->spa_vdev_removal;
   
           if (svr == NULL)
                   return;
   
           /*
            * In general when this function is called there is no
            * removal thread running. The only scenario where this
            * is not true is during spa_import() where this function
            * is called twice [once from spa_import_impl() and
            * spa_async_resume()]. Thus, in the scenario where we
            * import a pool that has an ongoing removal we don't
            * want to spawn a second thread.
            */
           if (svr->svr_thread != NULL)
                   return;
   
           if (!spa_writeable(spa))
                   return;
   
           zfs_dbgmsg("restarting removal of %llu",
               (u_longlong_t)svr->svr_vdev_id);
           svr->svr_thread = thread_create(NULL, 0, spa_vdev_remove_thread, spa,
               0, &p0, TS_RUN, minclsyspri);
   }
   
   /*
    * Process freeing from a device which is in the middle of being removed.
    * We must handle this carefully so that we attempt to copy freed data,
    * and we correctly free already-copied data.
    */
   void
   free_from_removing_vdev(vdev_t *vd, uint64_t offset, uint64_t size)
   {
           spa_t *spa = vd->vdev_spa;
           spa_vdev_removal_t *svr = spa->spa_vdev_removal;
           vdev_indirect_mapping_t *vim = vd->vdev_indirect_mapping;
           uint64_t txg = spa_syncing_txg(spa);
           uint64_t max_offset_yet = 0;
   
           ASSERT(vd->vdev_indirect_config.vic_mapping_object != 0);
           ASSERT3U(vd->vdev_indirect_config.vic_mapping_object, ==,
               vdev_indirect_mapping_object(vim));
           ASSERT3U(vd->vdev_id, ==, svr->svr_vdev_id);
   
           mutex_enter(&svr->svr_lock);
   
           /*
            * Remove the segment from the removing vdev's spacemap.  This
            * ensures that we will not attempt to copy this space (if the
            * removal thread has not yet visited it), and also ensures
            * that we know what is actually allocated on the new vdevs
            * (needed if we cancel the removal).
            *
            * Note: we must do the metaslab_free_concrete() with the svr_lock
            * held, so that the remove_thread can not load this metaslab and then
            * visit this offset between the time that we metaslab_free_concrete()
            * and when we check to see if it has been visited.
            *
            * Note: The checkpoint flag is set to false as having/taking
            * a checkpoint and removing a device can't happen at the same
            * time.
            */
           ASSERT(!spa_has_checkpoint(spa));
           metaslab_free_concrete(vd, offset, size, B_FALSE);
   
           uint64_t synced_size = 0;
           uint64_t synced_offset = 0;
           uint64_t max_offset_synced = vdev_indirect_mapping_max_offset(vim);
           if (offset < max_offset_synced) {
                   /*
                    * The mapping for this offset is already on disk.
                    * Free from the new location.
                    *
                    * Note that we use svr_max_synced_offset because it is
                    * updated atomically with respect to the in-core mapping.
                    * By contrast, vim_max_offset is not.
                    *
                    * This block may be split between a synced entry and an
                    * in-flight or unvisited entry.  Only process the synced
                    * portion of it here.
                    */
                   synced_size = MIN(size, max_offset_synced - offset);
                   synced_offset = offset;
   
                   ASSERT3U(max_offset_yet, <=, max_offset_synced);
                   max_offset_yet = max_offset_synced;
   
                   DTRACE_PROBE3(remove__free__synced,
                       spa_t *, spa,
                       uint64_t, offset,
                       uint64_t, synced_size);
   
                   size -= synced_size;
                   offset += synced_size;
           }
   
           /*
            * Look at all in-flight txgs starting from the currently syncing one
            * and see if a section of this free is being copied. By starting from
            * this txg and iterating forward, we might find that this region
            * was copied in two different txgs and handle it appropriately.
            */
           for (int i = 0; i < TXG_CONCURRENT_STATES; i++) {
                   int txgoff = (txg + i) & TXG_MASK;
                   if (size > 0 && offset < svr->svr_max_offset_to_sync[txgoff]) {
                           /*
                            * The mapping for this offset is in flight, and
                            * will be synced in txg+i.
                            */
                           uint64_t inflight_size = MIN(size,
                               svr->svr_max_offset_to_sync[txgoff] - offset);
   
                           DTRACE_PROBE4(remove__free__inflight,
                               spa_t *, spa,
                               uint64_t, offset,
                               uint64_t, inflight_size,
                               uint64_t, txg + i);
   
                           /*
                            * We copy data in order of increasing offset.
                            * Therefore the max_offset_to_sync[] must increase
                            * (or be zero, indicating that nothing is being
                            * copied in that txg).
                            */
                           if (svr->svr_max_offset_to_sync[txgoff] != 0) {
                                   ASSERT3U(svr->svr_max_offset_to_sync[txgoff],
                                       >=, max_offset_yet);
                                   max_offset_yet =
                                       svr->svr_max_offset_to_sync[txgoff];
                           }
   
                           /*
                            * We've already committed to copying this segment:
                            * we have allocated space elsewhere in the pool for
                            * it and have an IO outstanding to copy the data. We
                            * cannot free the space before the copy has
                            * completed, or else the copy IO might overwrite any
                            * new data. To free that space, we record the
                            * segment in the appropriate svr_frees tree and free
                            * the mapped space later, in the txg where we have
                            * completed the copy and synced the mapping (see
                            * vdev_mapping_sync).
                            */
                           range_tree_add(svr->svr_frees[txgoff],
                               offset, inflight_size);
                           size -= inflight_size;
                           offset += inflight_size;
   
                           /*
                            * This space is already accounted for as being
                            * done, because it is being copied in txg+i.
                            * However, if i!=0, then it is being copied in
                            * a future txg.  If we crash after this txg
                            * syncs but before txg+i syncs, then the space
                            * will be free.  Therefore we must account
                            * for the space being done in *this* txg
                            * (when it is freed) rather than the future txg
                            * (when it will be copied).
                            */
                           ASSERT3U(svr->svr_bytes_done[txgoff], >=,
                               inflight_size);
                           svr->svr_bytes_done[txgoff] -= inflight_size;
                           svr->svr_bytes_done[txg & TXG_MASK] += inflight_size;
                   }
           }
           ASSERT0(svr->svr_max_offset_to_sync[TXG_CLEAN(txg) & TXG_MASK]);
   
           if (size > 0) {
                   /*
                    * The copy thread has not yet visited this offset.  Ensure
                    * that it doesn't.
                    */
   
                   DTRACE_PROBE3(remove__free__unvisited,
                       spa_t *, spa,
                       uint64_t, offset,
                       uint64_t, size);
   
                   if (svr->svr_allocd_segs != NULL)
                           range_tree_clear(svr->svr_allocd_segs, offset, size);
   
                   /*
                    * Since we now do not need to copy this data, for
                    * accounting purposes we have done our job and can count
                    * it as completed.
                    */
                   svr->svr_bytes_done[txg & TXG_MASK] += size;
           }
           mutex_exit(&svr->svr_lock);
   
           /*
            * Now that we have dropped svr_lock, process the synced portion
            * of this free.
            */
           if (synced_size > 0) {
                   vdev_indirect_mark_obsolete(vd, synced_offset, synced_size);
   
                   /*
                    * Note: this can only be called from syncing context,
                    * and the vdev_indirect_mapping is only changed from the
                    * sync thread, so we don't need svr_lock while doing
                    * metaslab_free_impl_cb.
                    */
                   boolean_t checkpoint = B_FALSE;
                   vdev_indirect_ops.vdev_op_remap(vd, synced_offset, synced_size,
                       metaslab_free_impl_cb, &checkpoint);
           }
   }
   
   /*
    * Stop an active removal and update the spa_removing phys.
    */
   static void
   spa_finish_removal(spa_t *spa, dsl_scan_state_t state, dmu_tx_t *tx)
   {
           spa_vdev_removal_t *svr = spa->spa_vdev_removal;
           ASSERT3U(dmu_tx_get_txg(tx), ==, spa_syncing_txg(spa));
   
           /* Ensure the removal thread has completed before we free the svr. */
           spa_vdev_remove_suspend(spa);
   
           ASSERT(state == DSS_FINISHED || state == DSS_CANCELED);
   
           if (state == DSS_FINISHED) {
                   spa_removing_phys_t *srp = &spa->spa_removing_phys;
                   vdev_t *vd = vdev_lookup_top(spa, svr->svr_vdev_id);
                   vdev_indirect_config_t *vic = &vd->vdev_indirect_config;
   
                   if (srp->sr_prev_indirect_vdev != -1) {
                           vdev_t *pvd;
                           pvd = vdev_lookup_top(spa,
                               srp->sr_prev_indirect_vdev);
                           ASSERT3P(pvd->vdev_ops, ==, &vdev_indirect_ops);
                   }
   
                   vic->vic_prev_indirect_vdev = srp->sr_prev_indirect_vdev;
                   srp->sr_prev_indirect_vdev = vd->vdev_id;
           }
           spa->spa_removing_phys.sr_state = state;
           spa->spa_removing_phys.sr_end_time = gethrestime_sec();
   
           spa->spa_vdev_removal = NULL;
           spa_vdev_removal_destroy(svr);
   
           spa_sync_removing_state(spa, tx);
           spa_notify_waiters(spa);
   
           vdev_config_dirty(spa->spa_root_vdev);
   }
   
   static void
   free_mapped_segment_cb(void *arg, uint64_t offset, uint64_t size)
   {
           vdev_t *vd = arg;
           vdev_indirect_mark_obsolete(vd, offset, size);
           boolean_t checkpoint = B_FALSE;
           vdev_indirect_ops.vdev_op_remap(vd, offset, size,
               metaslab_free_impl_cb, &checkpoint);
   }
   
   /*
    * On behalf of the removal thread, syncs an incremental bit more of
    * the indirect mapping to disk and updates the in-memory mapping.
    * Called as a sync task in every txg that the removal thread makes progress.
    */
   static void
   vdev_mapping_sync(void *arg, dmu_tx_t *tx)
   {
           spa_vdev_removal_t *svr = arg;
           spa_t *spa = dmu_tx_pool(tx)->dp_spa;
           vdev_t *vd = vdev_lookup_top(spa, svr->svr_vdev_id);
           vdev_indirect_config_t *vic __maybe_unused = &vd->vdev_indirect_config;
           uint64_t txg = dmu_tx_get_txg(tx);
           vdev_indirect_mapping_t *vim = vd->vdev_indirect_mapping;
   
           ASSERT(vic->vic_mapping_object != 0);
           ASSERT3U(txg, ==, spa_syncing_txg(spa));
   
           vdev_indirect_mapping_add_entries(vim,
               &svr->svr_new_segments[txg & TXG_MASK], tx);
           vdev_indirect_births_add_entry(vd->vdev_indirect_births,
               vdev_indirect_mapping_max_offset(vim), dmu_tx_get_txg(tx), tx);
   
           /*
            * Free the copied data for anything that was freed while the
            * mapping entries were in flight.
            */
           mutex_enter(&svr->svr_lock);
           range_tree_vacate(svr->svr_frees[txg & TXG_MASK],
               free_mapped_segment_cb, vd);
           ASSERT3U(svr->svr_max_offset_to_sync[txg & TXG_MASK], >=,
               vdev_indirect_mapping_max_offset(vim));
           svr->svr_max_offset_to_sync[txg & TXG_MASK] = 0;
           mutex_exit(&svr->svr_lock);
   
           spa_sync_removing_state(spa, tx);
   }
   
   typedef struct vdev_copy_segment_arg {
           spa_t *vcsa_spa;
           dva_t *vcsa_dest_dva;
           uint64_t vcsa_txg;
           range_tree_t *vcsa_obsolete_segs;
   } vdev_copy_segment_arg_t;
   
   static void
   unalloc_seg(void *arg, uint64_t start, uint64_t size)
   {
           vdev_copy_segment_arg_t *vcsa = arg;
           spa_t *spa = vcsa->vcsa_spa;
           blkptr_t bp = { { { {0} } } };
   
           BP_SET_BIRTH(&bp, TXG_INITIAL, TXG_INITIAL);
           BP_SET_LSIZE(&bp, size);
           BP_SET_PSIZE(&bp, size);
           BP_SET_COMPRESS(&bp, ZIO_COMPRESS_OFF);
           BP_SET_CHECKSUM(&bp, ZIO_CHECKSUM_OFF);
           BP_SET_TYPE(&bp, DMU_OT_NONE);
           BP_SET_LEVEL(&bp, 0);
           BP_SET_DEDUP(&bp, 0);
           BP_SET_BYTEORDER(&bp, ZFS_HOST_BYTEORDER);
   
           DVA_SET_VDEV(&bp.blk_dva[0], DVA_GET_VDEV(vcsa->vcsa_dest_dva));
           DVA_SET_OFFSET(&bp.blk_dva[0],
               DVA_GET_OFFSET(vcsa->vcsa_dest_dva) + start);
           DVA_SET_ASIZE(&bp.blk_dva[0], size);
   
           zio_free(spa, vcsa->vcsa_txg, &bp);
   }
   
   /*
    * All reads and writes associated with a call to spa_vdev_copy_segment()
    * are done.
    */
   static void
   spa_vdev_copy_segment_done(zio_t *zio)
   {
           vdev_copy_segment_arg_t *vcsa = zio->io_private;
   
           range_tree_vacate(vcsa->vcsa_obsolete_segs,
               unalloc_seg, vcsa);
           range_tree_destroy(vcsa->vcsa_obsolete_segs);
           kmem_free(vcsa, sizeof (*vcsa));
   
           spa_config_exit(zio->io_spa, SCL_STATE, zio->io_spa);
   }
   
   /*
    * The write of the new location is done.
    */
   static void
   spa_vdev_copy_segment_write_done(zio_t *zio)
   {
           vdev_copy_arg_t *vca = zio->io_private;
   
           abd_free(zio->io_abd);
   
           mutex_enter(&vca->vca_lock);
           vca->vca_outstanding_bytes -= zio->io_size;
   
           if (zio->io_error != 0)
                   vca->vca_write_error_bytes += zio->io_size;
   
           cv_signal(&vca->vca_cv);
           mutex_exit(&vca->vca_lock);
   }
   
   /*
    * The read of the old location is done.  The parent zio is the write to
    * the new location.  Allow it to start.
   */
  static void
  spa_vdev_copy_segment_read_done(zio_t *zio)
  {
          vdev_copy_arg_t *vca = zio->io_private;
  
          if (zio->io_error != 0) {
                  mutex_enter(&vca->vca_lock);
                  vca->vca_read_error_bytes += zio->io_size;
                  mutex_exit(&vca->vca_lock);
          }
  
          zio_nowait(zio_unique_parent(zio));
  }
  
  /*
   * If the old and new vdevs are mirrors, we will read both sides of the old
   * mirror, and write each copy to the corresponding side of the new mirror.
   * If the old and new vdevs have a different number of children, we will do
   * this as best as possible.  Since we aren't verifying checksums, this
   * ensures that as long as there's a good copy of the data, we'll have a
   * good copy after the removal, even if there's silent damage to one side
   * of the mirror. If we're removing a mirror that has some silent damage,
   * we'll have exactly the same damage in the new location (assuming that
   * the new location is also a mirror).
   *
   * We accomplish this by creating a tree of zio_t's, with as many writes as
   * there are "children" of the new vdev (a non-redundant vdev counts as one
   * child, a 2-way mirror has 2 children, etc). Each write has an associated
   * read from a child of the old vdev. Typically there will be the same
   * number of children of the old and new vdevs.  However, if there are more
   * children of the new vdev, some child(ren) of the old vdev will be issued
   * multiple reads.  If there are more children of the old vdev, some copies
   * will be dropped.
   *
   * For example, the tree of zio_t's for a 2-way mirror is:
   *
   *                            null
   *                           /    \
   *    write(new vdev, child 0)      write(new vdev, child 1)
   *      |                             |
   *    read(old vdev, child 0)       read(old vdev, child 1)
   *
   * Child zio's complete before their parents complete.  However, zio's
   * created with zio_vdev_child_io() may be issued before their children
   * complete.  In this case we need to make sure that the children (reads)
   * complete before the parents (writes) are *issued*.  We do this by not
   * calling zio_nowait() on each write until its corresponding read has
   * completed.
   *
   * The spa_config_lock must be held while zio's created by
   * zio_vdev_child_io() are in progress, to ensure that the vdev tree does
   * not change (e.g. due to a concurrent "zpool attach/detach"). The "null"
   * zio is needed to release the spa_config_lock after all the reads and
   * writes complete. (Note that we can't grab the config lock for each read,
   * because it is not reentrant - we could deadlock with a thread waiting
   * for a write lock.)
   */
  static void
  spa_vdev_copy_one_child(vdev_copy_arg_t *vca, zio_t *nzio,
      vdev_t *source_vd, uint64_t source_offset,
      vdev_t *dest_child_vd, uint64_t dest_offset, int dest_id, uint64_t size)
  {
          ASSERT3U(spa_config_held(nzio->io_spa, SCL_ALL, RW_READER), !=, 0);
  
          /*
           * If the destination child in unwritable then there is no point
           * in issuing the source reads which cannot be written.
           */
          if (!vdev_writeable(dest_child_vd))
                  return;
  
          mutex_enter(&vca->vca_lock);
          vca->vca_outstanding_bytes += size;
          mutex_exit(&vca->vca_lock);
  
          abd_t *abd = abd_alloc_for_io(size, B_FALSE);
  
          vdev_t *source_child_vd = NULL;
          if (source_vd->vdev_ops == &vdev_mirror_ops && dest_id != -1) {
                  /*
                   * Source and dest are both mirrors.  Copy from the same
                   * child id as we are copying to (wrapping around if there
                   * are more dest children than source children).  If the
                   * preferred source child is unreadable select another.
                   */
                  for (int i = 0; i < source_vd->vdev_children; i++) {
                          source_child_vd = source_vd->vdev_child[
                              (dest_id + i) % source_vd->vdev_children];
                          if (vdev_readable(source_child_vd))
                                  break;
                  }
          } else {
                  source_child_vd = source_vd;
          }
  
          /*
           * There should always be at least one readable source child or
           * the pool would be in a suspended state.  Somehow selecting an
           * unreadable child would result in IO errors, the removal process
           * being cancelled, and the pool reverting to its pre-removal state.
           */
          ASSERT3P(source_child_vd, !=, NULL);
  
          zio_t *write_zio = zio_vdev_child_io(nzio, NULL,
              dest_child_vd, dest_offset, abd, size,
              ZIO_TYPE_WRITE, ZIO_PRIORITY_REMOVAL,
              ZIO_FLAG_CANFAIL,
              spa_vdev_copy_segment_write_done, vca);
  
          zio_nowait(zio_vdev_child_io(write_zio, NULL,
              source_child_vd, source_offset, abd, size,
              ZIO_TYPE_READ, ZIO_PRIORITY_REMOVAL,
              ZIO_FLAG_CANFAIL,
              spa_vdev_copy_segment_read_done, vca));
  }
  
  /*
   * Allocate a new location for this segment, and create the zio_t's to
   * read from the old location and write to the new location.
   */
  static int
  spa_vdev_copy_segment(vdev_t *vd, range_tree_t *segs,
      uint64_t maxalloc, uint64_t txg,
      vdev_copy_arg_t *vca, zio_alloc_list_t *zal)
  {
          metaslab_group_t *mg = vd->vdev_mg;
          spa_t *spa = vd->vdev_spa;
          spa_vdev_removal_t *svr = spa->spa_vdev_removal;
          vdev_indirect_mapping_entry_t *entry;
          dva_t dst = {{ 0 }};
          uint64_t start = range_tree_min(segs);
          ASSERT0(P2PHASE(start, 1 << spa->spa_min_ashift));
  
          ASSERT3U(maxalloc, <=, SPA_MAXBLOCKSIZE);
          ASSERT0(P2PHASE(maxalloc, 1 << spa->spa_min_ashift));
  
          uint64_t size = range_tree_span(segs);
          if (range_tree_span(segs) > maxalloc) {
                  /*
                   * We can't allocate all the segments.  Prefer to end
                   * the allocation at the end of a segment, thus avoiding
                   * additional split blocks.
                   */
                  range_seg_max_t search;
                  zfs_btree_index_t where;
                  rs_set_start(&search, segs, start + maxalloc);
                  rs_set_end(&search, segs, start + maxalloc);
                  (void) zfs_btree_find(&segs->rt_root, &search, &where);
                  range_seg_t *rs = zfs_btree_prev(&segs->rt_root, &where,
                      &where);
                  if (rs != NULL) {
                          size = rs_get_end(rs, segs) - start;
                  } else {
                          /*
                           * There are no segments that end before maxalloc.
                           * I.e. the first segment is larger than maxalloc,
                           * so we must split it.
                           */
                          size = maxalloc;
                  }
          }
          ASSERT3U(size, <=, maxalloc);
          ASSERT0(P2PHASE(size, 1 << spa->spa_min_ashift));
  
          /*
           * An allocation class might not have any remaining vdevs or space
           */
          metaslab_class_t *mc = mg->mg_class;
          if (mc->mc_groups == 0)
                  mc = spa_normal_class(spa);
          int error = metaslab_alloc_dva(spa, mc, size, &dst, 0, NULL, txg,
              METASLAB_DONT_THROTTLE, zal, 0);
          if (error == ENOSPC && mc != spa_normal_class(spa)) {
                  error = metaslab_alloc_dva(spa, spa_normal_class(spa), size,
                      &dst, 0, NULL, txg, METASLAB_DONT_THROTTLE, zal, 0);
          }
          if (error != 0)
                  return (error);
  
          /*
           * Determine the ranges that are not actually needed.  Offsets are
           * relative to the start of the range to be copied (i.e. relative to the
           * local variable "start").
           */
          range_tree_t *obsolete_segs = range_tree_create(NULL, RANGE_SEG64, NULL,
              0, 0);
  
          zfs_btree_index_t where;
          range_seg_t *rs = zfs_btree_first(&segs->rt_root, &where);
          ASSERT3U(rs_get_start(rs, segs), ==, start);
          uint64_t prev_seg_end = rs_get_end(rs, segs);
          while ((rs = zfs_btree_next(&segs->rt_root, &where, &where)) != NULL) {
                  if (rs_get_start(rs, segs) >= start + size) {
                          break;
                  } else {
                          range_tree_add(obsolete_segs,
                              prev_seg_end - start,
                              rs_get_start(rs, segs) - prev_seg_end);
                  }
                  prev_seg_end = rs_get_end(rs, segs);
          }
          /* We don't end in the middle of an obsolete range */
          ASSERT3U(start + size, <=, prev_seg_end);
  
          range_tree_clear(segs, start, size);
  
          /*
           * We can't have any padding of the allocated size, otherwise we will
           * misunderstand what's allocated, and the size of the mapping. We
           * prevent padding by ensuring that all devices in the pool have the
           * same ashift, and the allocation size is a multiple of the ashift.
           */
          VERIFY3U(DVA_GET_ASIZE(&dst), ==, size);
  
          entry = kmem_zalloc(sizeof (vdev_indirect_mapping_entry_t), KM_SLEEP);
          DVA_MAPPING_SET_SRC_OFFSET(&entry->vime_mapping, start);
          entry->vime_mapping.vimep_dst = dst;
          if (spa_feature_is_enabled(spa, SPA_FEATURE_OBSOLETE_COUNTS)) {
                  entry->vime_obsolete_count = range_tree_space(obsolete_segs);
          }
  
          vdev_copy_segment_arg_t *vcsa = kmem_zalloc(sizeof (*vcsa), KM_SLEEP);
          vcsa->vcsa_dest_dva = &entry->vime_mapping.vimep_dst;
          vcsa->vcsa_obsolete_segs = obsolete_segs;
          vcsa->vcsa_spa = spa;
          vcsa->vcsa_txg = txg;
  
          /*
           * See comment before spa_vdev_copy_one_child().
           */
          spa_config_enter(spa, SCL_STATE, spa, RW_READER);
          zio_t *nzio = zio_null(spa->spa_txg_zio[txg & TXG_MASK], spa, NULL,
              spa_vdev_copy_segment_done, vcsa, 0);
          vdev_t *dest_vd = vdev_lookup_top(spa, DVA_GET_VDEV(&dst));
          if (dest_vd->vdev_ops == &vdev_mirror_ops) {
                  for (int i = 0; i < dest_vd->vdev_children; i++) {
                          vdev_t *child = dest_vd->vdev_child[i];
                          spa_vdev_copy_one_child(vca, nzio, vd, start,
                              child, DVA_GET_OFFSET(&dst), i, size);
                  }
          } else {
                  spa_vdev_copy_one_child(vca, nzio, vd, start,
                      dest_vd, DVA_GET_OFFSET(&dst), -1, size);
          }
          zio_nowait(nzio);
  
          list_insert_tail(&svr->svr_new_segments[txg & TXG_MASK], entry);
          ASSERT3U(start + size, <=, vd->vdev_ms_count << vd->vdev_ms_shift);
          vdev_dirty(vd, 0, NULL, txg);
  
          return (0);
  }
  
  /*
   * Complete the removal of a toplevel vdev. This is called as a
   * synctask in the same txg that we will sync out the new config (to the
   * MOS object) which indicates that this vdev is indirect.
   */
  static void
  vdev_remove_complete_sync(void *arg, dmu_tx_t *tx)
  {
          spa_vdev_removal_t *svr = arg;
          spa_t *spa = dmu_tx_pool(tx)->dp_spa;
          vdev_t *vd = vdev_lookup_top(spa, svr->svr_vdev_id);
  
          ASSERT3P(vd->vdev_ops, ==, &vdev_indirect_ops);
  
          for (int i = 0; i < TXG_SIZE; i++) {
                  ASSERT0(svr->svr_bytes_done[i]);
          }
  
          ASSERT3U(spa->spa_removing_phys.sr_copied, ==,
              spa->spa_removing_phys.sr_to_copy);
  
          vdev_destroy_spacemaps(vd, tx);
  
          /* destroy leaf zaps, if any */
          ASSERT3P(svr->svr_zaplist, !=, NULL);
          for (nvpair_t *pair = nvlist_next_nvpair(svr->svr_zaplist, NULL);
              pair != NULL;
              pair = nvlist_next_nvpair(svr->svr_zaplist, pair)) {
                  vdev_destroy_unlink_zap(vd, fnvpair_value_uint64(pair), tx);
          }
          fnvlist_free(svr->svr_zaplist);
  
          spa_finish_removal(dmu_tx_pool(tx)->dp_spa, DSS_FINISHED, tx);
          /* vd->vdev_path is not available here */
          spa_history_log_internal(spa, "vdev remove completed",  tx,
              "%s vdev %llu", spa_name(spa), (u_longlong_t)vd->vdev_id);
  }
  
  static void
  vdev_remove_enlist_zaps(vdev_t *vd, nvlist_t *zlist)
  {
          ASSERT3P(zlist, !=, NULL);
          ASSERT0(vdev_get_nparity(vd));
  
          if (vd->vdev_leaf_zap != 0) {
                  char zkey[32];
                  (void) snprintf(zkey, sizeof (zkey), "%s-%llu",
                      VDEV_REMOVAL_ZAP_OBJS, (u_longlong_t)vd->vdev_leaf_zap);
                  fnvlist_add_uint64(zlist, zkey, vd->vdev_leaf_zap);
          }
  
          for (uint64_t id = 0; id < vd->vdev_children; id++) {
                  vdev_remove_enlist_zaps(vd->vdev_child[id], zlist);
          }
  }
  
  static void
  vdev_remove_replace_with_indirect(vdev_t *vd, uint64_t txg)
  {
          vdev_t *ivd;
          dmu_tx_t *tx;
          spa_t *spa = vd->vdev_spa;
          spa_vdev_removal_t *svr = spa->spa_vdev_removal;
  
          /*
           * First, build a list of leaf zaps to be destroyed.
           * This is passed to the sync context thread,
           * which does the actual unlinking.
           */
          svr->svr_zaplist = fnvlist_alloc();
          vdev_remove_enlist_zaps(vd, svr->svr_zaplist);
  
          ivd = vdev_add_parent(vd, &vdev_indirect_ops);
          ivd->vdev_removing = 0;
  
          vd->vdev_leaf_zap = 0;
  
          vdev_remove_child(ivd, vd);
          vdev_compact_children(ivd);
  
          ASSERT(!list_link_active(&vd->vdev_state_dirty_node));
  
          mutex_enter(&svr->svr_lock);
          svr->svr_thread = NULL;
          cv_broadcast(&svr->svr_cv);
          mutex_exit(&svr->svr_lock);
  
          /* After this, we can not use svr. */
          tx = dmu_tx_create_assigned(spa->spa_dsl_pool, txg);
          dsl_sync_task_nowait(spa->spa_dsl_pool,
              vdev_remove_complete_sync, svr, tx);
          dmu_tx_commit(tx);
  }
  
  /*
   * Complete the removal of a toplevel vdev. This is called in open
   * context by the removal thread after we have copied all vdev's data.
   */
  static void
  vdev_remove_complete(spa_t *spa)
  {
          uint64_t txg;
  
          /*
           * Wait for any deferred frees to be synced before we call
           * vdev_metaslab_fini()
           */
          txg_wait_synced(spa->spa_dsl_pool, 0);
          txg = spa_vdev_enter(spa);
          vdev_t *vd = vdev_lookup_top(spa, spa->spa_vdev_removal->svr_vdev_id);
          ASSERT3P(vd->vdev_initialize_thread, ==, NULL);
          ASSERT3P(vd->vdev_trim_thread, ==, NULL);
          ASSERT3P(vd->vdev_autotrim_thread, ==, NULL);
          vdev_rebuild_stop_wait(vd);
          ASSERT3P(vd->vdev_rebuild_thread, ==, NULL);
          uint64_t vdev_space = spa_deflate(spa) ?
              vd->vdev_stat.vs_dspace : vd->vdev_stat.vs_space;
  
          sysevent_t *ev = spa_event_create(spa, vd, NULL,
              ESC_ZFS_VDEV_REMOVE_DEV);
  
          zfs_dbgmsg("finishing device removal for vdev %llu in txg %llu",
              (u_longlong_t)vd->vdev_id, (u_longlong_t)txg);
  
          ASSERT3U(0, !=, vdev_space);
          ASSERT3U(spa->spa_nonallocating_dspace, >=, vdev_space);
  
          /* the vdev is no longer part of the dspace */
          spa->spa_nonallocating_dspace -= vdev_space;
  
          /*
           * Discard allocation state.
           */
          if (vd->vdev_mg != NULL) {
                  vdev_metaslab_fini(vd);
                  metaslab_group_destroy(vd->vdev_mg);
                  vd->vdev_mg = NULL;
          }
          if (vd->vdev_log_mg != NULL) {
                  ASSERT0(vd->vdev_ms_count);
                  metaslab_group_destroy(vd->vdev_log_mg);
                  vd->vdev_log_mg = NULL;
          }
          ASSERT0(vd->vdev_stat.vs_space);
          ASSERT0(vd->vdev_stat.vs_dspace);
  
          vdev_remove_replace_with_indirect(vd, txg);
  
          /*
           * We now release the locks, allowing spa_sync to run and finish the
           * removal via vdev_remove_complete_sync in syncing context.
           *
           * Note that we hold on to the vdev_t that has been replaced.  Since
           * it isn't part of the vdev tree any longer, it can't be concurrently
           * manipulated, even while we don't have the config lock.
           */
          (void) spa_vdev_exit(spa, NULL, txg, 0);
  
          /*
           * Top ZAP should have been transferred to the indirect vdev in
           * vdev_remove_replace_with_indirect.
           */
          ASSERT0(vd->vdev_top_zap);
  
          /*
           * Leaf ZAP should have been moved in vdev_remove_replace_with_indirect.
           */
          ASSERT0(vd->vdev_leaf_zap);
  
          txg = spa_vdev_enter(spa);
          (void) vdev_label_init(vd, 0, VDEV_LABEL_REMOVE);
          /*
           * Request to update the config and the config cachefile.
           */
          vdev_config_dirty(spa->spa_root_vdev);
          (void) spa_vdev_exit(spa, vd, txg, 0);
  
          if (ev != NULL)
                  spa_event_post(ev);
  }
  
  /*
   * Evacuates a segment of size at most max_alloc from the vdev
   * via repeated calls to spa_vdev_copy_segment. If an allocation
   * fails, the pool is probably too fragmented to handle such a
   * large size, so decrease max_alloc so that the caller will not try
   * this size again this txg.
   */
  static void
  spa_vdev_copy_impl(vdev_t *vd, spa_vdev_removal_t *svr, vdev_copy_arg_t *vca,
      uint64_t *max_alloc, dmu_tx_t *tx)
  {
          uint64_t txg = dmu_tx_get_txg(tx);
          spa_t *spa = dmu_tx_pool(tx)->dp_spa;
  
          mutex_enter(&svr->svr_lock);
  
          /*
           * Determine how big of a chunk to copy.  We can allocate up
           * to max_alloc bytes, and we can span up to vdev_removal_max_span
           * bytes of unallocated space at a time.  "segs" will track the
           * allocated segments that we are copying.  We may also be copying
           * free segments (of up to vdev_removal_max_span bytes).
           */
          range_tree_t *segs = range_tree_create(NULL, RANGE_SEG64, NULL, 0, 0);
          for (;;) {
                  range_tree_t *rt = svr->svr_allocd_segs;
                  range_seg_t *rs = range_tree_first(rt);
  
                  if (rs == NULL)
                          break;
  
                  uint64_t seg_length;
  
                  if (range_tree_is_empty(segs)) {
                          /* need to truncate the first seg based on max_alloc */
                          seg_length = MIN(rs_get_end(rs, rt) - rs_get_start(rs,
                              rt), *max_alloc);
                  } else {
                          if (rs_get_start(rs, rt) - range_tree_max(segs) >
                              vdev_removal_max_span) {
                                  /*
                                   * Including this segment would cause us to
                                   * copy a larger unneeded chunk than is allowed.
                                   */
                                  break;
                          } else if (rs_get_end(rs, rt) - range_tree_min(segs) >
                              *max_alloc) {
                                  /*
                                   * This additional segment would extend past
                                   * max_alloc. Rather than splitting this
                                   * segment, leave it for the next mapping.
                                   */
                                  break;
                          } else {
                                  seg_length = rs_get_end(rs, rt) -
                                      rs_get_start(rs, rt);
                          }
                  }
  
                  range_tree_add(segs, rs_get_start(rs, rt), seg_length);
                  range_tree_remove(svr->svr_allocd_segs,
                      rs_get_start(rs, rt), seg_length);
          }
  
          if (range_tree_is_empty(segs)) {
                  mutex_exit(&svr->svr_lock);
                  range_tree_destroy(segs);
                  return;
          }
  
          if (svr->svr_max_offset_to_sync[txg & TXG_MASK] == 0) {
                  dsl_sync_task_nowait(dmu_tx_pool(tx), vdev_mapping_sync,
                      svr, tx);
          }
  
          svr->svr_max_offset_to_sync[txg & TXG_MASK] = range_tree_max(segs);
  
          /*
           * Note: this is the amount of *allocated* space
           * that we are taking care of each txg.
           */
          svr->svr_bytes_done[txg & TXG_MASK] += range_tree_space(segs);
  
          mutex_exit(&svr->svr_lock);
  
          zio_alloc_list_t zal;
          metaslab_trace_init(&zal);
          uint64_t thismax = SPA_MAXBLOCKSIZE;
          while (!range_tree_is_empty(segs)) {
                  int error = spa_vdev_copy_segment(vd,
                      segs, thismax, txg, vca, &zal);
  
                  if (error == ENOSPC) {
                          /*
                           * Cut our segment in half, and don't try this
                           * segment size again this txg.  Note that the
                           * allocation size must be aligned to the highest
                           * ashift in the pool, so that the allocation will
                           * not be padded out to a multiple of the ashift,
                           * which could cause us to think that this mapping
                           * is larger than we intended.
                           */
                          ASSERT3U(spa->spa_max_ashift, >=, SPA_MINBLOCKSHIFT);
                          ASSERT3U(spa->spa_max_ashift, ==, spa->spa_min_ashift);
                          uint64_t attempted =
                              MIN(range_tree_span(segs), thismax);
                          thismax = P2ROUNDUP(attempted / 2,
                              1 << spa->spa_max_ashift);
                          /*
                           * The minimum-size allocation can not fail.
                           */
                          ASSERT3U(attempted, >, 1 << spa->spa_max_ashift);
                          *max_alloc = attempted - (1 << spa->spa_max_ashift);
                  } else {
                          ASSERT0(error);
  
                          /*
                           * We've performed an allocation, so reset the
                           * alloc trace list.
                           */
                          metaslab_trace_fini(&zal);
                          metaslab_trace_init(&zal);
                  }
          }
          metaslab_trace_fini(&zal);
          range_tree_destroy(segs);
  }
  
  /*
   * The size of each removal mapping is limited by the tunable
   * zfs_remove_max_segment, but we must adjust this to be a multiple of the
   * pool's ashift, so that we don't try to split individual sectors regardless
   * of the tunable value.  (Note that device removal requires that all devices
   * have the same ashift, so there's no difference between spa_min_ashift and
   * spa_max_ashift.) The raw tunable should not be used elsewhere.
   */
  uint64_t
  spa_remove_max_segment(spa_t *spa)
  {
          return (P2ROUNDUP(zfs_remove_max_segment, 1 << spa->spa_max_ashift));
  }
  
  /*
   * The removal thread operates in open context.  It iterates over all
   * allocated space in the vdev, by loading each metaslab's spacemap.
   * For each contiguous segment of allocated space (capping the segment
   * size at SPA_MAXBLOCKSIZE), we:
   *    - Allocate space for it on another vdev.
   *    - Create a new mapping from the old location to the new location
   *      (as a record in svr_new_segments).
   *    - Initiate a physical read zio to get the data off the removing disk.
   *    - In the read zio's done callback, initiate a physical write zio to
   *      write it to the new vdev.
   * Note that all of this will take effect when a particular TXG syncs.
   * The sync thread ensures that all the phys reads and writes for the syncing
   * TXG have completed (see spa_txg_zio) and writes the new mappings to disk
   * (see vdev_mapping_sync()).
   */
  static __attribute__((noreturn)) void
  spa_vdev_remove_thread(void *arg)
  {
          spa_t *spa = arg;
          spa_vdev_removal_t *svr = spa->spa_vdev_removal;
          vdev_copy_arg_t vca;
          uint64_t max_alloc = spa_remove_max_segment(spa);
          uint64_t last_txg = 0;
  
          spa_config_enter(spa, SCL_CONFIG, FTAG, RW_READER);
          vdev_t *vd = vdev_lookup_top(spa, svr->svr_vdev_id);
          vdev_indirect_mapping_t *vim = vd->vdev_indirect_mapping;
          uint64_t start_offset = vdev_indirect_mapping_max_offset(vim);
  
          ASSERT3P(vd->vdev_ops, !=, &vdev_indirect_ops);
          ASSERT(vdev_is_concrete(vd));
          ASSERT(vd->vdev_removing);
          ASSERT(vd->vdev_indirect_config.vic_mapping_object != 0);
          ASSERT(vim != NULL);
  
          mutex_init(&vca.vca_lock, NULL, MUTEX_DEFAULT, NULL);
          cv_init(&vca.vca_cv, NULL, CV_DEFAULT, NULL);
          vca.vca_outstanding_bytes = 0;
          vca.vca_read_error_bytes = 0;
          vca.vca_write_error_bytes = 0;
  
          mutex_enter(&svr->svr_lock);
  
          /*
           * Start from vim_max_offset so we pick up where we left off
           * if we are restarting the removal after opening the pool.
           */
          uint64_t msi;
          for (msi = start_offset >> vd->vdev_ms_shift;
              msi < vd->vdev_ms_count && !svr->svr_thread_exit; msi++) {
                  metaslab_t *msp = vd->vdev_ms[msi];
                  ASSERT3U(msi, <=, vd->vdev_ms_count);
  
                  ASSERT0(range_tree_space(svr->svr_allocd_segs));
  
                  mutex_enter(&msp->ms_sync_lock);
                  mutex_enter(&msp->ms_lock);
  
                  /*
                   * Assert nothing in flight -- ms_*tree is empty.
                   */
                  for (int i = 0; i < TXG_SIZE; i++) {
                          ASSERT0(range_tree_space(msp->ms_allocating[i]));
                  }
  
                  /*
                   * If the metaslab has ever been allocated from (ms_sm!=NULL),
                   * read the allocated segments from the space map object
                   * into svr_allocd_segs. Since we do this while holding
                   * svr_lock and ms_sync_lock, concurrent frees (which
                   * would have modified the space map) will wait for us
                   * to finish loading the spacemap, and then take the
                   * appropriate action (see free_from_removing_vdev()).
                   */
                  if (msp->ms_sm != NULL) {
                          VERIFY0(space_map_load(msp->ms_sm,
                              svr->svr_allocd_segs, SM_ALLOC));
  
                          range_tree_walk(msp->ms_unflushed_allocs,
                              range_tree_add, svr->svr_allocd_segs);
                          range_tree_walk(msp->ms_unflushed_frees,
                              range_tree_remove, svr->svr_allocd_segs);
                          range_tree_walk(msp->ms_freeing,
                              range_tree_remove, svr->svr_allocd_segs);
  
                          /*
                           * When we are resuming from a paused removal (i.e.
                           * when importing a pool with a removal in progress),
                           * discard any state that we have already processed.
                           */
                          range_tree_clear(svr->svr_allocd_segs, 0, start_offset);
                  }
                  mutex_exit(&msp->ms_lock);
                  mutex_exit(&msp->ms_sync_lock);
  
                  vca.vca_msp = msp;
                  zfs_dbgmsg("copying %llu segments for metaslab %llu",
                      (u_longlong_t)zfs_btree_numnodes(
                      &svr->svr_allocd_segs->rt_root),
                      (u_longlong_t)msp->ms_id);
  
                  while (!svr->svr_thread_exit &&
                      !range_tree_is_empty(svr->svr_allocd_segs)) {
  
                          mutex_exit(&svr->svr_lock);
  
                          /*
                           * We need to periodically drop the config lock so that
                           * writers can get in.  Additionally, we can't wait
                           * for a txg to sync while holding a config lock
                           * (since a waiting writer could cause a 3-way deadlock
                           * with the sync thread, which also gets a config
                           * lock for reader).  So we can't hold the config lock
                           * while calling dmu_tx_assign().
                           */
                          spa_config_exit(spa, SCL_CONFIG, FTAG);
  
                          /*
                           * This delay will pause the removal around the point
                           * specified by zfs_removal_suspend_progress. We do this
                           * solely from the test suite or during debugging.
                           */
                          while (zfs_removal_suspend_progress &&
                              !svr->svr_thread_exit)
                                  delay(hz);
  
                          mutex_enter(&vca.vca_lock);
                          while (vca.vca_outstanding_bytes >
                              zfs_remove_max_copy_bytes) {
                                  cv_wait(&vca.vca_cv, &vca.vca_lock);
                          }
                          mutex_exit(&vca.vca_lock);
  
                          dmu_tx_t *tx =
                              dmu_tx_create_dd(spa_get_dsl(spa)->dp_mos_dir);
  
                          VERIFY0(dmu_tx_assign(tx, TXG_WAIT));
                          uint64_t txg = dmu_tx_get_txg(tx);
  
                          /*
                           * Reacquire the vdev_config lock.  The vdev_t
                           * that we're removing may have changed, e.g. due
                           * to a vdev_attach or vdev_detach.
                           */
                          spa_config_enter(spa, SCL_CONFIG, FTAG, RW_READER);
                          vd = vdev_lookup_top(spa, svr->svr_vdev_id);
  
                          if (txg != last_txg)
                                  max_alloc = spa_remove_max_segment(spa);
                          last_txg = txg;
  
                          spa_vdev_copy_impl(vd, svr, &vca, &max_alloc, tx);
  
                          dmu_tx_commit(tx);
                          mutex_enter(&svr->svr_lock);
                  }
  
                  mutex_enter(&vca.vca_lock);
                  if (zfs_removal_ignore_errors == 0 &&
                      (vca.vca_read_error_bytes > 0 ||
                      vca.vca_write_error_bytes > 0)) {
                          svr->svr_thread_exit = B_TRUE;
                  }
                  mutex_exit(&vca.vca_lock);
          }
  
          mutex_exit(&svr->svr_lock);
  
          spa_config_exit(spa, SCL_CONFIG, FTAG);
  
          /*
           * Wait for all copies to finish before cleaning up the vca.
           */
          txg_wait_synced(spa->spa_dsl_pool, 0);
          ASSERT0(vca.vca_outstanding_bytes);
  
          mutex_destroy(&vca.vca_lock);
          cv_destroy(&vca.vca_cv);
  
          if (svr->svr_thread_exit) {
                  mutex_enter(&svr->svr_lock);
                  range_tree_vacate(svr->svr_allocd_segs, NULL, NULL);
                  svr->svr_thread = NULL;
                  cv_broadcast(&svr->svr_cv);
                  mutex_exit(&svr->svr_lock);
  
                  /*
                   * During the removal process an unrecoverable read or write
                   * error was encountered.  The removal process must be
                   * cancelled or this damage may become permanent.
                   */
                  if (zfs_removal_ignore_errors == 0 &&
                      (vca.vca_read_error_bytes > 0 ||
                      vca.vca_write_error_bytes > 0)) {
                          zfs_dbgmsg("canceling removal due to IO errors: "
                              "[read_error_bytes=%llu] [write_error_bytes=%llu]",
                              (u_longlong_t)vca.vca_read_error_bytes,
                              (u_longlong_t)vca.vca_write_error_bytes);
                          spa_vdev_remove_cancel_impl(spa);
                  }
          } else {
                  ASSERT0(range_tree_space(svr->svr_allocd_segs));
                  vdev_remove_complete(spa);
          }
  
          thread_exit();
  }
  
  void
  spa_vdev_remove_suspend(spa_t *spa)
  {
          spa_vdev_removal_t *svr = spa->spa_vdev_removal;
  
          if (svr == NULL)
                  return;
  
          mutex_enter(&svr->svr_lock);
          svr->svr_thread_exit = B_TRUE;
          while (svr->svr_thread != NULL)
                  cv_wait(&svr->svr_cv, &svr->svr_lock);
          svr->svr_thread_exit = B_FALSE;
          mutex_exit(&svr->svr_lock);
  }
  
  /*
   * Return true if the "allocating" property has been set to "off"
   */
  static boolean_t
  vdev_prop_allocating_off(vdev_t *vd)
  {
          uint64_t objid = vd->vdev_top_zap;
          uint64_t allocating = 1;
  
          /* no vdev property object => no props */
          if (objid != 0) {
                  spa_t *spa = vd->vdev_spa;
                  objset_t *mos = spa->spa_meta_objset;
  
                  mutex_enter(&spa->spa_props_lock);
                  (void) zap_lookup(mos, objid, "allocating", sizeof (uint64_t),
                      1, &allocating);
                  mutex_exit(&spa->spa_props_lock);
          }
          return (allocating == 0);
  }
  
  static int
  spa_vdev_remove_cancel_check(void *arg, dmu_tx_t *tx)
  {
          (void) arg;
          spa_t *spa = dmu_tx_pool(tx)->dp_spa;
  
          if (spa->spa_vdev_removal == NULL)
                  return (ENOTACTIVE);
          return (0);
  }
  
  /*
   * Cancel a removal by freeing all entries from the partial mapping
   * and marking the vdev as no longer being removing.
   */
  static void
  spa_vdev_remove_cancel_sync(void *arg, dmu_tx_t *tx)
  {
          (void) arg;
          spa_t *spa = dmu_tx_pool(tx)->dp_spa;
          spa_vdev_removal_t *svr = spa->spa_vdev_removal;
          vdev_t *vd = vdev_lookup_top(spa, svr->svr_vdev_id);
          vdev_indirect_config_t *vic = &vd->vdev_indirect_config;
          vdev_indirect_mapping_t *vim = vd->vdev_indirect_mapping;
          objset_t *mos = spa->spa_meta_objset;
  
          ASSERT3P(svr->svr_thread, ==, NULL);
  
          spa_feature_decr(spa, SPA_FEATURE_DEVICE_REMOVAL, tx);
  
          boolean_t are_precise;
          VERIFY0(vdev_obsolete_counts_are_precise(vd, &are_precise));
          if (are_precise) {
                  spa_feature_decr(spa, SPA_FEATURE_OBSOLETE_COUNTS, tx);
                  VERIFY0(zap_remove(spa->spa_meta_objset, vd->vdev_top_zap,
                      VDEV_TOP_ZAP_OBSOLETE_COUNTS_ARE_PRECISE, tx));
          }
  
          uint64_t obsolete_sm_object;
          VERIFY0(vdev_obsolete_sm_object(vd, &obsolete_sm_object));
          if (obsolete_sm_object != 0) {
                  ASSERT(vd->vdev_obsolete_sm != NULL);
                  ASSERT3U(obsolete_sm_object, ==,
                      space_map_object(vd->vdev_obsolete_sm));
  
                  space_map_free(vd->vdev_obsolete_sm, tx);
                  VERIFY0(zap_remove(spa->spa_meta_objset, vd->vdev_top_zap,
                      VDEV_TOP_ZAP_INDIRECT_OBSOLETE_SM, tx));
                  space_map_close(vd->vdev_obsolete_sm);
                  vd->vdev_obsolete_sm = NULL;
                  spa_feature_decr(spa, SPA_FEATURE_OBSOLETE_COUNTS, tx);
          }
          for (int i = 0; i < TXG_SIZE; i++) {
                  ASSERT(list_is_empty(&svr->svr_new_segments[i]));
                  ASSERT3U(svr->svr_max_offset_to_sync[i], <=,
                      vdev_indirect_mapping_max_offset(vim));
          }
  
          for (uint64_t msi = 0; msi < vd->vdev_ms_count; msi++) {
                  metaslab_t *msp = vd->vdev_ms[msi];
  
                  if (msp->ms_start >= vdev_indirect_mapping_max_offset(vim))
                          break;
  
                  ASSERT0(range_tree_space(svr->svr_allocd_segs));
  
                  mutex_enter(&msp->ms_lock);
  
                  /*
                   * Assert nothing in flight -- ms_*tree is empty.
                   */
                  for (int i = 0; i < TXG_SIZE; i++)
                          ASSERT0(range_tree_space(msp->ms_allocating[i]));
                  for (int i = 0; i < TXG_DEFER_SIZE; i++)
                          ASSERT0(range_tree_space(msp->ms_defer[i]));
                  ASSERT0(range_tree_space(msp->ms_freed));
  
                  if (msp->ms_sm != NULL) {
                          mutex_enter(&svr->svr_lock);
                          VERIFY0(space_map_load(msp->ms_sm,
                              svr->svr_allocd_segs, SM_ALLOC));
  
                          range_tree_walk(msp->ms_unflushed_allocs,
                              range_tree_add, svr->svr_allocd_segs);
                          range_tree_walk(msp->ms_unflushed_frees,
                              range_tree_remove, svr->svr_allocd_segs);
                          range_tree_walk(msp->ms_freeing,
                              range_tree_remove, svr->svr_allocd_segs);
  
                          /*
                           * Clear everything past what has been synced,
                           * because we have not allocated mappings for it yet.
                           */
                          uint64_t syncd = vdev_indirect_mapping_max_offset(vim);
                          uint64_t sm_end = msp->ms_sm->sm_start +
                              msp->ms_sm->sm_size;
                          if (sm_end > syncd)
                                  range_tree_clear(svr->svr_allocd_segs,
                                      syncd, sm_end - syncd);
  
                          mutex_exit(&svr->svr_lock);
                  }
                  mutex_exit(&msp->ms_lock);
  
                  mutex_enter(&svr->svr_lock);
                  range_tree_vacate(svr->svr_allocd_segs,
                      free_mapped_segment_cb, vd);
                  mutex_exit(&svr->svr_lock);
          }
  
          /*
           * Note: this must happen after we invoke free_mapped_segment_cb,
           * because it adds to the obsolete_segments.
           */
          range_tree_vacate(vd->vdev_obsolete_segments, NULL, NULL);
  
          ASSERT3U(vic->vic_mapping_object, ==,
              vdev_indirect_mapping_object(vd->vdev_indirect_mapping));
          vdev_indirect_mapping_close(vd->vdev_indirect_mapping);
          vd->vdev_indirect_mapping = NULL;
          vdev_indirect_mapping_free(mos, vic->vic_mapping_object, tx);
          vic->vic_mapping_object = 0;
  
          ASSERT3U(vic->vic_births_object, ==,
              vdev_indirect_births_object(vd->vdev_indirect_births));
          vdev_indirect_births_close(vd->vdev_indirect_births);
          vd->vdev_indirect_births = NULL;
          vdev_indirect_births_free(mos, vic->vic_births_object, tx);
          vic->vic_births_object = 0;
  
          /*
           * We may have processed some frees from the removing vdev in this
           * txg, thus increasing svr_bytes_done; discard that here to
           * satisfy the assertions in spa_vdev_removal_destroy().
           * Note that future txg's can not have any bytes_done, because
           * future TXG's are only modified from open context, and we have
           * already shut down the copying thread.
           */
          svr->svr_bytes_done[dmu_tx_get_txg(tx) & TXG_MASK] = 0;
          spa_finish_removal(spa, DSS_CANCELED, tx);
  
          vd->vdev_removing = B_FALSE;
  
          if (!vdev_prop_allocating_off(vd)) {
                  spa_config_enter(spa, SCL_ALLOC | SCL_VDEV, FTAG, RW_WRITER);
                  vdev_activate(vd);
                  spa_config_exit(spa, SCL_ALLOC | SCL_VDEV, FTAG);
          }
  
          vdev_config_dirty(vd);
  
          zfs_dbgmsg("canceled device removal for vdev %llu in %llu",
              (u_longlong_t)vd->vdev_id, (u_longlong_t)dmu_tx_get_txg(tx));
          spa_history_log_internal(spa, "vdev remove canceled", tx,
              "%s vdev %llu %s", spa_name(spa),
              (u_longlong_t)vd->vdev_id,
              (vd->vdev_path != NULL) ? vd->vdev_path : "-");
  }
  
  static int
  spa_vdev_remove_cancel_impl(spa_t *spa)
  {
          int error = dsl_sync_task(spa->spa_name, spa_vdev_remove_cancel_check,
              spa_vdev_remove_cancel_sync, NULL, 0,
              ZFS_SPACE_CHECK_EXTRA_RESERVED);
          return (error);
  }
  
  int
  spa_vdev_remove_cancel(spa_t *spa)
  {
          spa_vdev_remove_suspend(spa);
  
          if (spa->spa_vdev_removal == NULL)
                  return (ENOTACTIVE);
  
          return (spa_vdev_remove_cancel_impl(spa));
  }
  
  void
  svr_sync(spa_t *spa, dmu_tx_t *tx)
  {
          spa_vdev_removal_t *svr = spa->spa_vdev_removal;
          int txgoff = dmu_tx_get_txg(tx) & TXG_MASK;
  
          if (svr == NULL)
                  return;
  
          /*
           * This check is necessary so that we do not dirty the
           * DIRECTORY_OBJECT via spa_sync_removing_state() when there
           * is nothing to do.  Dirtying it every time would prevent us
           * from syncing-to-convergence.
           */
          if (svr->svr_bytes_done[txgoff] == 0)
                  return;
  
          /*
           * Update progress accounting.
           */
          spa->spa_removing_phys.sr_copied += svr->svr_bytes_done[txgoff];
          svr->svr_bytes_done[txgoff] = 0;
  
          spa_sync_removing_state(spa, tx);
  }
  
  static void
  vdev_remove_make_hole_and_free(vdev_t *vd)
  {
          uint64_t id = vd->vdev_id;
          spa_t *spa = vd->vdev_spa;
          vdev_t *rvd = spa->spa_root_vdev;
  
          ASSERT(MUTEX_HELD(&spa_namespace_lock));
          ASSERT(spa_config_held(spa, SCL_ALL, RW_WRITER) == SCL_ALL);
  
          vdev_free(vd);
  
          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 log device.  The config lock is held for the specified TXG.
   */
  static int
  spa_vdev_remove_log(vdev_t *vd, uint64_t *txg)
  {
          metaslab_group_t *mg = vd->vdev_mg;
          spa_t *spa = vd->vdev_spa;
          int error = 0;
  
          ASSERT(vd->vdev_islog);
          ASSERT(vd == vd->vdev_top);
          ASSERT3P(vd->vdev_log_mg, ==, NULL);
          ASSERT(MUTEX_HELD(&spa_namespace_lock));
  
          /*
           * 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);
  
          /*
           * Cancel any initialize or TRIM which was in progress.
           */
          vdev_initialize_stop_all(vd, VDEV_INITIALIZE_CANCELED);
          vdev_trim_stop_all(vd, VDEV_TRIM_CANCELED);
          vdev_autotrim_stop_wait(vd);
  
          /*
           * 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.
           */
          ASSERT(MUTEX_HELD(&spa_namespace_lock));
          if (vd->vdev_stat.vs_alloc != 0)
                  error = spa_reset_logs(spa);
  
          *txg = spa_vdev_config_enter(spa);
  
          if (error != 0) {
                  metaslab_group_activate(mg);
                  ASSERT3P(vd->vdev_log_mg, ==, NULL);
                  return (error);
          }
          ASSERT0(vd->vdev_stat.vs_alloc);
  
          /*
           * The evacuation succeeded.  Remove any remaining MOS metadata
           * associated with this vdev, and wait for these changes to sync.
           */
          vd->vdev_removing = B_TRUE;
  
          vdev_dirty_leaves(vd, VDD_DTL, *txg);
          vdev_config_dirty(vd);
  
          /*
           * When the log space map feature is enabled we look at
           * the vdev's top_zap to find the on-disk flush data of
           * the metaslab we just flushed. Thus, while removing a
           * log vdev we make sure to call vdev_metaslab_fini()
           * first, which removes all metaslabs of this vdev from
           * spa_metaslabs_by_flushed before vdev_remove_empty()
           * destroys the top_zap of this log vdev.
           *
           * This avoids the scenario where we flush a metaslab
           * from the log vdev being removed that doesn't have a
           * top_zap and end up failing to lookup its on-disk flush
           * data.
           *
           * We don't call metaslab_group_destroy() right away
           * though (it will be called in vdev_free() later) as
           * during metaslab_sync() of metaslabs from other vdevs
           * we may touch the metaslab group of this vdev through
           * metaslab_class_histogram_verify()
           */
          vdev_metaslab_fini(vd);
  
          spa_vdev_config_exit(spa, NULL, *txg, 0, FTAG);
          *txg = spa_vdev_config_enter(spa);
  
          sysevent_t *ev = spa_event_create(spa, vd, NULL,
              ESC_ZFS_VDEV_REMOVE_DEV);
          ASSERT(MUTEX_HELD(&spa_namespace_lock));
          ASSERT(spa_config_held(spa, SCL_ALL, RW_WRITER) == SCL_ALL);
  
          /* The top ZAP should have been destroyed by vdev_remove_empty. */
          ASSERT0(vd->vdev_top_zap);
          /* The leaf ZAP should have been destroyed by vdev_dtl_sync. */
          ASSERT0(vd->vdev_leaf_zap);
  
          (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);
  
          ASSERT0(vd->vdev_stat.vs_alloc);
  
          /*
           * Clean up the vdev namespace.
           */
          vdev_remove_make_hole_and_free(vd);
  
          if (ev != NULL)
                  spa_event_post(ev);
  
          return (0);
  }
  
  static int
  spa_vdev_remove_top_check(vdev_t *vd)
  {
          spa_t *spa = vd->vdev_spa;
  
          if (vd != vd->vdev_top)
                  return (SET_ERROR(ENOTSUP));
  
          if (!vdev_is_concrete(vd))
                  return (SET_ERROR(ENOTSUP));
  
          if (!spa_feature_is_enabled(spa, SPA_FEATURE_DEVICE_REMOVAL))
                  return (SET_ERROR(ENOTSUP));
  
          /*
           * This device is already being removed
           */
          if (vd->vdev_removing)
                  return (SET_ERROR(EALREADY));
  
          metaslab_class_t *mc = vd->vdev_mg->mg_class;
          metaslab_class_t *normal = spa_normal_class(spa);
          if (mc != normal) {
                  /*
                   * Space allocated from the special (or dedup) class is
                   * included in the DMU's space usage, but it's not included
                   * in spa_dspace (or dsl_pool_adjustedsize()).  Therefore
                   * there is always at least as much free space in the normal
                   * class, as is allocated from the special (and dedup) class.
                   * As a backup check, we will return ENOSPC if this is
                   * violated. See also spa_update_dspace().
                   */
                  uint64_t available = metaslab_class_get_space(normal) -
                      metaslab_class_get_alloc(normal);
                  ASSERT3U(available, >=, vd->vdev_stat.vs_alloc);
                  if (available < vd->vdev_stat.vs_alloc)
                          return (SET_ERROR(ENOSPC));
          } else if (!vd->vdev_noalloc) {
                  /* available space in the pool's normal class */
                  uint64_t available = dsl_dir_space_available(
                      spa->spa_dsl_pool->dp_root_dir, NULL, 0, B_TRUE);
                  if (available < vd->vdev_stat.vs_dspace)
                          return (SET_ERROR(ENOSPC));
          }
  
          /*
           * There can not be a removal in progress.
           */
          if (spa->spa_removing_phys.sr_state == DSS_SCANNING)
                  return (SET_ERROR(EBUSY));
  
          /*
           * The device must have all its data.
           */
          if (!vdev_dtl_empty(vd, DTL_MISSING) ||
              !vdev_dtl_empty(vd, DTL_OUTAGE))
                  return (SET_ERROR(EBUSY));
  
          /*
           * The device must be healthy.
           */
          if (!vdev_readable(vd))
                  return (SET_ERROR(EIO));
  
          /*
           * All vdevs in normal class must have the same ashift.
           */
          if (spa->spa_max_ashift != spa->spa_min_ashift) {
                  return (SET_ERROR(EINVAL));
          }
  
          /*
           * A removed special/dedup vdev must have same ashift as normal class.
           */
          ASSERT(!vd->vdev_islog);
          if (vd->vdev_alloc_bias != VDEV_BIAS_NONE &&
              vd->vdev_ashift != spa->spa_max_ashift) {
                  return (SET_ERROR(EINVAL));
          }
  
          /*
           * All vdevs in normal class must have the same ashift
           * and not be raidz or draid.
           */
          vdev_t *rvd = spa->spa_root_vdev;
          for (uint64_t id = 0; id < rvd->vdev_children; id++) {
                  vdev_t *cvd = rvd->vdev_child[id];
  
                  /*
                   * A removed special/dedup vdev must have the same ashift
                   * across all vdevs in its class.
                   */
                  if (vd->vdev_alloc_bias != VDEV_BIAS_NONE &&
                      cvd->vdev_alloc_bias == vd->vdev_alloc_bias &&
                      cvd->vdev_ashift != vd->vdev_ashift) {
                          return (SET_ERROR(EINVAL));
                  }
                  if (cvd->vdev_ashift != 0 &&
                      cvd->vdev_alloc_bias == VDEV_BIAS_NONE)
                          ASSERT3U(cvd->vdev_ashift, ==, spa->spa_max_ashift);
                  if (!vdev_is_concrete(cvd))
                          continue;
                  if (vdev_get_nparity(cvd) != 0)
                          return (SET_ERROR(EINVAL));
                  /*
                   * Need the mirror to be mirror of leaf vdevs only
                   */
                  if (cvd->vdev_ops == &vdev_mirror_ops) {
                          for (uint64_t cid = 0;
                              cid < cvd->vdev_children; cid++) {
                                  if (!cvd->vdev_child[cid]->vdev_ops->
                                      vdev_op_leaf)
                                          return (SET_ERROR(EINVAL));
                          }
                  }
          }
  
          return (0);
  }
  
  /*
   * Initiate removal of a top-level vdev, reducing the total space in the pool.
   * The config lock is held for the specified TXG.  Once initiated,
   * evacuation of all allocated space (copying it to other vdevs) happens
   * in the background (see spa_vdev_remove_thread()), and can be canceled
   * (see spa_vdev_remove_cancel()).  If successful, the vdev will
   * be transformed to an indirect vdev (see spa_vdev_remove_complete()).
   */
  static int
  spa_vdev_remove_top(vdev_t *vd, uint64_t *txg)
  {
          spa_t *spa = vd->vdev_spa;
          boolean_t set_noalloc = B_FALSE;
          int error;
  
          /*
           * Check for errors up-front, so that we don't waste time
           * passivating the metaslab group and clearing the ZIL if there
           * are errors.
           */
          error = spa_vdev_remove_top_check(vd);
  
          /*
           * Stop allocating from this vdev.  Note that we must check
           * that this is not the only device in the pool before
           * passivating, otherwise we will not be able to make
           * progress because we can't allocate from any vdevs.
           * The above check for sufficient free space serves this
           * purpose.
           */
          if (error == 0 && !vd->vdev_noalloc) {
                  set_noalloc = B_TRUE;
                  error = vdev_passivate(vd, txg);
          }
  
          if (error != 0)
                  return (error);
  
          /*
           * We stop any initializing and TRIM that is currently in progress
           * but leave the state as "active". This will allow the process to
           * resume if the removal is canceled sometime later.
           */
  
          spa_vdev_config_exit(spa, NULL, *txg, 0, FTAG);
  
          vdev_initialize_stop_all(vd, VDEV_INITIALIZE_ACTIVE);
          vdev_trim_stop_all(vd, VDEV_TRIM_ACTIVE);
          vdev_autotrim_stop_wait(vd);
  
          *txg = spa_vdev_config_enter(spa);
  
          /*
           * Things might have changed while the config lock was dropped
           * (e.g. space usage).  Check for errors again.
           */
          error = spa_vdev_remove_top_check(vd);
  
          if (error != 0) {
                  if (set_noalloc)
                          vdev_activate(vd);
                  spa_async_request(spa, SPA_ASYNC_INITIALIZE_RESTART);
                  spa_async_request(spa, SPA_ASYNC_TRIM_RESTART);
                  spa_async_request(spa, SPA_ASYNC_AUTOTRIM_RESTART);
                  return (error);
          }
  
          vd->vdev_removing = B_TRUE;
  
          vdev_dirty_leaves(vd, VDD_DTL, *txg);
          vdev_config_dirty(vd);
          dmu_tx_t *tx = dmu_tx_create_assigned(spa->spa_dsl_pool, *txg);
          dsl_sync_task_nowait(spa->spa_dsl_pool,
              vdev_remove_initiate_sync, (void *)(uintptr_t)vd->vdev_id, tx);
          dmu_tx_commit(tx);
  
          return (0);
  }
  
  /*
   * 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.
   */
  int
  spa_vdev_remove(spa_t *spa, uint64_t guid, boolean_t unspare)
  {
          vdev_t *vd;
          nvlist_t **spares, **l2cache, *nv;
          uint64_t txg = 0;
          uint_t nspares, nl2cache;
          int error = 0, error_log;
          boolean_t locked = MUTEX_HELD(&spa_namespace_lock);
          sysevent_t *ev = NULL;
          const char *vd_type = NULL;
          char *vd_path = NULL;
  
          ASSERT(spa_writeable(spa));
  
          if (!locked)
                  txg = spa_vdev_enter(spa);
  
          ASSERT(MUTEX_HELD(&spa_namespace_lock));
          if (spa_feature_is_active(spa, SPA_FEATURE_POOL_CHECKPOINT)) {
                  error = (spa_has_checkpoint(spa)) ?
                      ZFS_ERR_CHECKPOINT_EXISTS : ZFS_ERR_DISCARDING_CHECKPOINT;
  
                  if (!locked)
                          return (spa_vdev_exit(spa, NULL, txg, error));
  
                  return (error);
          }
  
          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) {
                          char *type;
                          boolean_t draid_spare = B_FALSE;
  
                          if (nvlist_lookup_string(nv, ZPOOL_CONFIG_TYPE, &type)
                              == 0 && strcmp(type, VDEV_TYPE_DRAID_SPARE) == 0)
                                  draid_spare = B_TRUE;
  
                          if (vd == NULL && draid_spare) {
                                  error = SET_ERROR(ENOTSUP);
                          } else {
                                  if (vd == NULL)
                                          vd = spa_lookup_by_guid(spa,
                                              guid, B_TRUE);
                                  ev = spa_event_create(spa, vd, NULL,
                                      ESC_ZFS_VDEV_REMOVE_AUX);
  
                                  vd_type = VDEV_TYPE_SPARE;
                                  vd_path = spa_strdup(fnvlist_lookup_string(
                                      nv, ZPOOL_CONFIG_PATH));
                                  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) {
                  vd_type = VDEV_TYPE_L2CACHE;
                  vd_path = spa_strdup(fnvlist_lookup_string(
                      nv, ZPOOL_CONFIG_PATH));
                  /*
                   * Cache devices can always be removed.
                   */
                  vd = spa_lookup_by_guid(spa, guid, B_TRUE);
  
                  /*
                   * Stop trimming the cache device. We need to release the
                   * config lock to allow the syncing of TRIM transactions
                   * without releasing the spa_namespace_lock. The same
                   * strategy is employed in spa_vdev_remove_top().
                   */
                  spa_vdev_config_exit(spa, NULL,
                      txg + TXG_CONCURRENT_STATES + TXG_DEFER_SIZE, 0, FTAG);
                  mutex_enter(&vd->vdev_trim_lock);
                  vdev_trim_stop(vd, VDEV_TRIM_CANCELED, NULL);
                  mutex_exit(&vd->vdev_trim_lock);
                  txg = spa_vdev_config_enter(spa);
  
                  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);
                  vd_type = VDEV_TYPE_LOG;
                  vd_path = spa_strdup((vd->vdev_path != NULL) ?
                      vd->vdev_path : "-");
                  error = spa_vdev_remove_log(vd, &txg);
          } else if (vd != NULL) {
                  ASSERT(!locked);
                  error = spa_vdev_remove_top(vd, &txg);
          } else {
                  /*
                   * There is no vdev of any kind with the specified guid.
                   */
                  error = SET_ERROR(ENOENT);
          }
  
          error_log = error;
  
          if (!locked)
                  error = spa_vdev_exit(spa, NULL, txg, error);
  
          /*
           * Logging must be done outside the spa config lock. Otherwise,
           * this code path could end up holding the spa config lock while
           * waiting for a txg_sync so it can write to the internal log.
           * Doing that would prevent the txg sync from actually happening,
           * causing a deadlock.
           */
          if (error_log == 0 && vd_type != NULL && vd_path != NULL) {
                  spa_history_log_internal(spa, "vdev remove", NULL,
                      "%s vdev (%s) %s", spa_name(spa), vd_type, vd_path);
          }
          if (vd_path != NULL)
                  spa_strfree(vd_path);
  
          if (ev != NULL)
                  spa_event_post(ev);
  
          return (error);
  }
  
  int
  spa_removal_get_stats(spa_t *spa, pool_removal_stat_t *prs)
  {
          prs->prs_state = spa->spa_removing_phys.sr_state;
  
          if (prs->prs_state == DSS_NONE)
                  return (SET_ERROR(ENOENT));
  
          prs->prs_removing_vdev = spa->spa_removing_phys.sr_removing_vdev;
          prs->prs_start_time = spa->spa_removing_phys.sr_start_time;
          prs->prs_end_time = spa->spa_removing_phys.sr_end_time;
          prs->prs_to_copy = spa->spa_removing_phys.sr_to_copy;
          prs->prs_copied = spa->spa_removing_phys.sr_copied;
  
          prs->prs_mapping_memory = 0;
          uint64_t indirect_vdev_id =
              spa->spa_removing_phys.sr_prev_indirect_vdev;
          while (indirect_vdev_id != -1) {
                  vdev_t *vd = spa->spa_root_vdev->vdev_child[indirect_vdev_id];
                  vdev_indirect_config_t *vic = &vd->vdev_indirect_config;
                  vdev_indirect_mapping_t *vim = vd->vdev_indirect_mapping;
  
                  ASSERT3P(vd->vdev_ops, ==, &vdev_indirect_ops);
                  prs->prs_mapping_memory += vdev_indirect_mapping_size(vim);
                  indirect_vdev_id = vic->vic_prev_indirect_vdev;
          }
  
          return (0);
  }
  
  ZFS_MODULE_PARAM(zfs_vdev, zfs_, removal_ignore_errors, INT, ZMOD_RW,
          "Ignore hard IO errors when removing device");
  
  ZFS_MODULE_PARAM(zfs_vdev, zfs_, remove_max_segment, UINT, ZMOD_RW,
          "Largest contiguous segment to allocate when removing device");
  
  ZFS_MODULE_PARAM(zfs_vdev, vdev_, removal_max_span, UINT, ZMOD_RW,
          "Largest span of free chunks a remap segment can span");
  
  /* BEGIN CSTYLED */
  ZFS_MODULE_PARAM(zfs_vdev, zfs_, removal_suspend_progress, UINT, ZMOD_RW,
          "Pause device removal after this many bytes are copied "
          "(debug use only - causes removal to hang)");
  /* END CSTYLED */
  
  EXPORT_SYMBOL(free_from_removing_vdev);
  EXPORT_SYMBOL(spa_removal_get_stats);
  EXPORT_SYMBOL(spa_remove_init);
  EXPORT_SYMBOL(spa_restart_removal);
  EXPORT_SYMBOL(spa_vdev_removal_destroy);
  EXPORT_SYMBOL(spa_vdev_remove);
  EXPORT_SYMBOL(spa_vdev_remove_cancel);
  EXPORT_SYMBOL(spa_vdev_remove_suspend);
  EXPORT_SYMBOL(svr_sync);

Cache object: 6eae6541299e9857bc6e3abadf1c6baf