FreeBSD/Linux Kernel Cross Reference
sys/contrib/openzfs/module/zfs/dsl_pool.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) 2013 Steven Hartland. All rights reserved.
     * Copyright (c) 2014 Spectra Logic Corporation, All rights reserved.
     * Copyright 2016 Nexenta Systems, Inc.  All rights reserved.
     */
    
    #include <sys/dsl_pool.h>
    #include <sys/dsl_dataset.h>
    #include <sys/dsl_prop.h>
    #include <sys/dsl_dir.h>
    #include <sys/dsl_synctask.h>
    #include <sys/dsl_scan.h>
    #include <sys/dnode.h>
    #include <sys/dmu_tx.h>
    #include <sys/dmu_objset.h>
    #include <sys/arc.h>
    #include <sys/zap.h>
    #include <sys/zio.h>
    #include <sys/zfs_context.h>
    #include <sys/fs/zfs.h>
    #include <sys/zfs_znode.h>
    #include <sys/spa_impl.h>
    #include <sys/vdev_impl.h>
    #include <sys/metaslab_impl.h>
    #include <sys/bptree.h>
    #include <sys/zfeature.h>
    #include <sys/zil_impl.h>
    #include <sys/dsl_userhold.h>
    #include <sys/trace_zfs.h>
    #include <sys/mmp.h>
    
    /*
     * ZFS Write Throttle
     * ------------------
     *
     * ZFS must limit the rate of incoming writes to the rate at which it is able
     * to sync data modifications to the backend storage. Throttling by too much
     * creates an artificial limit; throttling by too little can only be sustained
     * for short periods and would lead to highly lumpy performance. On a per-pool
     * basis, ZFS tracks the amount of modified (dirty) data. As operations change
     * data, the amount of dirty data increases; as ZFS syncs out data, the amount
     * of dirty data decreases. When the amount of dirty data exceeds a
     * predetermined threshold further modifications are blocked until the amount
     * of dirty data decreases (as data is synced out).
     *
     * The limit on dirty data is tunable, and should be adjusted according to
     * both the IO capacity and available memory of the system. The larger the
     * window, the more ZFS is able to aggregate and amortize metadata (and data)
     * changes. However, memory is a limited resource, and allowing for more dirty
     * data comes at the cost of keeping other useful data in memory (for example
     * ZFS data cached by the ARC).
     *
     * Implementation
     *
     * As buffers are modified dsl_pool_willuse_space() increments both the per-
     * txg (dp_dirty_pertxg[]) and poolwide (dp_dirty_total) accounting of
     * dirty space used; dsl_pool_dirty_space() decrements those values as data
     * is synced out from dsl_pool_sync(). While only the poolwide value is
     * relevant, the per-txg value is useful for debugging. The tunable
     * zfs_dirty_data_max determines the dirty space limit. Once that value is
     * exceeded, new writes are halted until space frees up.
     *
     * The zfs_dirty_data_sync_percent tunable dictates the threshold at which we
     * ensure that there is a txg syncing (see the comment in txg.c for a full
     * description of transaction group stages).
     *
     * The IO scheduler uses both the dirty space limit and current amount of
     * dirty data as inputs. Those values affect the number of concurrent IOs ZFS
     * issues. See the comment in vdev_queue.c for details of the IO scheduler.
     *
     * The delay is also calculated based on the amount of dirty data.  See the
     * comment above dmu_tx_delay() for details.
     */
    
    /*
     * zfs_dirty_data_max will be set to zfs_dirty_data_max_percent% of all memory,
     * capped at zfs_dirty_data_max_max.  It can also be overridden with a module
    * parameter.
    */
   uint64_t zfs_dirty_data_max = 0;
   uint64_t zfs_dirty_data_max_max = 0;
   uint_t zfs_dirty_data_max_percent = 10;
   uint_t zfs_dirty_data_max_max_percent = 25;
   
   /*
    * The upper limit of TX_WRITE log data.  Write operations are throttled
    * when approaching the limit until log data is cleared out after txg sync.
    * It only counts TX_WRITE log with WR_COPIED or WR_NEED_COPY.
    */
   uint64_t zfs_wrlog_data_max = 0;
   
   /*
    * If there's at least this much dirty data (as a percentage of
    * zfs_dirty_data_max), push out a txg.  This should be less than
    * zfs_vdev_async_write_active_min_dirty_percent.
    */
   static uint_t zfs_dirty_data_sync_percent = 20;
   
   /*
    * Once there is this amount of dirty data, the dmu_tx_delay() will kick in
    * and delay each transaction.
    * This value should be >= zfs_vdev_async_write_active_max_dirty_percent.
    */
   uint_t zfs_delay_min_dirty_percent = 60;
   
   /*
    * This controls how quickly the delay approaches infinity.
    * Larger values cause it to delay more for a given amount of dirty data.
    * Therefore larger values will cause there to be less dirty data for a
    * given throughput.
    *
    * For the smoothest delay, this value should be about 1 billion divided
    * by the maximum number of operations per second.  This will smoothly
    * handle between 10x and 1/10th this number.
    *
    * Note: zfs_delay_scale * zfs_dirty_data_max must be < 2^64, due to the
    * multiply in dmu_tx_delay().
    */
   uint64_t zfs_delay_scale = 1000 * 1000 * 1000 / 2000;
   
   /*
    * This determines the number of threads used by the dp_sync_taskq.
    */
   static int zfs_sync_taskq_batch_pct = 75;
   
   /*
    * These tunables determine the behavior of how zil_itxg_clean() is
    * called via zil_clean() in the context of spa_sync(). When an itxg
    * list needs to be cleaned, TQ_NOSLEEP will be used when dispatching.
    * If the dispatch fails, the call to zil_itxg_clean() will occur
    * synchronously in the context of spa_sync(), which can negatively
    * impact the performance of spa_sync() (e.g. in the case of the itxg
    * list having a large number of itxs that needs to be cleaned).
    *
    * Thus, these tunables can be used to manipulate the behavior of the
    * taskq used by zil_clean(); they determine the number of taskq entries
    * that are pre-populated when the taskq is first created (via the
    * "zfs_zil_clean_taskq_minalloc" tunable) and the maximum number of
    * taskq entries that are cached after an on-demand allocation (via the
    * "zfs_zil_clean_taskq_maxalloc").
    *
    * The idea being, we want to try reasonably hard to ensure there will
    * already be a taskq entry pre-allocated by the time that it is needed
    * by zil_clean(). This way, we can avoid the possibility of an
    * on-demand allocation of a new taskq entry from failing, which would
    * result in zil_itxg_clean() being called synchronously from zil_clean()
    * (which can adversely affect performance of spa_sync()).
    *
    * Additionally, the number of threads used by the taskq can be
    * configured via the "zfs_zil_clean_taskq_nthr_pct" tunable.
    */
   static int zfs_zil_clean_taskq_nthr_pct = 100;
   static int zfs_zil_clean_taskq_minalloc = 1024;
   static int zfs_zil_clean_taskq_maxalloc = 1024 * 1024;
   
   int
   dsl_pool_open_special_dir(dsl_pool_t *dp, const char *name, dsl_dir_t **ddp)
   {
           uint64_t obj;
           int err;
   
           err = zap_lookup(dp->dp_meta_objset,
               dsl_dir_phys(dp->dp_root_dir)->dd_child_dir_zapobj,
               name, sizeof (obj), 1, &obj);
           if (err)
                   return (err);
   
           return (dsl_dir_hold_obj(dp, obj, name, dp, ddp));
   }
   
   static dsl_pool_t *
   dsl_pool_open_impl(spa_t *spa, uint64_t txg)
   {
           dsl_pool_t *dp;
           blkptr_t *bp = spa_get_rootblkptr(spa);
   
           dp = kmem_zalloc(sizeof (dsl_pool_t), KM_SLEEP);
           dp->dp_spa = spa;
           dp->dp_meta_rootbp = *bp;
           rrw_init(&dp->dp_config_rwlock, B_TRUE);
           txg_init(dp, txg);
           mmp_init(spa);
   
           txg_list_create(&dp->dp_dirty_datasets, spa,
               offsetof(dsl_dataset_t, ds_dirty_link));
           txg_list_create(&dp->dp_dirty_zilogs, spa,
               offsetof(zilog_t, zl_dirty_link));
           txg_list_create(&dp->dp_dirty_dirs, spa,
               offsetof(dsl_dir_t, dd_dirty_link));
           txg_list_create(&dp->dp_sync_tasks, spa,
               offsetof(dsl_sync_task_t, dst_node));
           txg_list_create(&dp->dp_early_sync_tasks, spa,
               offsetof(dsl_sync_task_t, dst_node));
   
           dp->dp_sync_taskq = taskq_create("dp_sync_taskq",
               zfs_sync_taskq_batch_pct, minclsyspri, 1, INT_MAX,
               TASKQ_THREADS_CPU_PCT);
   
           dp->dp_zil_clean_taskq = taskq_create("dp_zil_clean_taskq",
               zfs_zil_clean_taskq_nthr_pct, minclsyspri,
               zfs_zil_clean_taskq_minalloc,
               zfs_zil_clean_taskq_maxalloc,
               TASKQ_PREPOPULATE | TASKQ_THREADS_CPU_PCT);
   
           mutex_init(&dp->dp_lock, NULL, MUTEX_DEFAULT, NULL);
           cv_init(&dp->dp_spaceavail_cv, NULL, CV_DEFAULT, NULL);
   
           aggsum_init(&dp->dp_wrlog_total, 0);
           for (int i = 0; i < TXG_SIZE; i++) {
                   aggsum_init(&dp->dp_wrlog_pertxg[i], 0);
           }
   
           dp->dp_zrele_taskq = taskq_create("z_zrele", 100, defclsyspri,
               boot_ncpus * 8, INT_MAX, TASKQ_PREPOPULATE | TASKQ_DYNAMIC |
               TASKQ_THREADS_CPU_PCT);
           dp->dp_unlinked_drain_taskq = taskq_create("z_unlinked_drain",
               100, defclsyspri, boot_ncpus, INT_MAX,
               TASKQ_PREPOPULATE | TASKQ_DYNAMIC | TASKQ_THREADS_CPU_PCT);
   
           return (dp);
   }
   
   int
   dsl_pool_init(spa_t *spa, uint64_t txg, dsl_pool_t **dpp)
   {
           int err;
           dsl_pool_t *dp = dsl_pool_open_impl(spa, txg);
   
           /*
            * Initialize the caller's dsl_pool_t structure before we actually open
            * the meta objset.  This is done because a self-healing write zio may
            * be issued as part of dmu_objset_open_impl() and the spa needs its
            * dsl_pool_t initialized in order to handle the write.
            */
           *dpp = dp;
   
           err = dmu_objset_open_impl(spa, NULL, &dp->dp_meta_rootbp,
               &dp->dp_meta_objset);
           if (err != 0) {
                   dsl_pool_close(dp);
                   *dpp = NULL;
           }
   
           return (err);
   }
   
   int
   dsl_pool_open(dsl_pool_t *dp)
   {
           int err;
           dsl_dir_t *dd;
           dsl_dataset_t *ds;
           uint64_t obj;
   
           rrw_enter(&dp->dp_config_rwlock, RW_WRITER, FTAG);
           err = zap_lookup(dp->dp_meta_objset, DMU_POOL_DIRECTORY_OBJECT,
               DMU_POOL_ROOT_DATASET, sizeof (uint64_t), 1,
               &dp->dp_root_dir_obj);
           if (err)
                   goto out;
   
           err = dsl_dir_hold_obj(dp, dp->dp_root_dir_obj,
               NULL, dp, &dp->dp_root_dir);
           if (err)
                   goto out;
   
           err = dsl_pool_open_special_dir(dp, MOS_DIR_NAME, &dp->dp_mos_dir);
           if (err)
                   goto out;
   
           if (spa_version(dp->dp_spa) >= SPA_VERSION_ORIGIN) {
                   err = dsl_pool_open_special_dir(dp, ORIGIN_DIR_NAME, &dd);
                   if (err)
                           goto out;
                   err = dsl_dataset_hold_obj(dp,
                       dsl_dir_phys(dd)->dd_head_dataset_obj, FTAG, &ds);
                   if (err == 0) {
                           err = dsl_dataset_hold_obj(dp,
                               dsl_dataset_phys(ds)->ds_prev_snap_obj, dp,
                               &dp->dp_origin_snap);
                           dsl_dataset_rele(ds, FTAG);
                   }
                   dsl_dir_rele(dd, dp);
                   if (err)
                           goto out;
           }
   
           if (spa_version(dp->dp_spa) >= SPA_VERSION_DEADLISTS) {
                   err = dsl_pool_open_special_dir(dp, FREE_DIR_NAME,
                       &dp->dp_free_dir);
                   if (err)
                           goto out;
   
                   err = zap_lookup(dp->dp_meta_objset, DMU_POOL_DIRECTORY_OBJECT,
                       DMU_POOL_FREE_BPOBJ, sizeof (uint64_t), 1, &obj);
                   if (err)
                           goto out;
                   VERIFY0(bpobj_open(&dp->dp_free_bpobj,
                       dp->dp_meta_objset, obj));
           }
   
           if (spa_feature_is_active(dp->dp_spa, SPA_FEATURE_OBSOLETE_COUNTS)) {
                   err = zap_lookup(dp->dp_meta_objset, DMU_POOL_DIRECTORY_OBJECT,
                       DMU_POOL_OBSOLETE_BPOBJ, sizeof (uint64_t), 1, &obj);
                   if (err == 0) {
                           VERIFY0(bpobj_open(&dp->dp_obsolete_bpobj,
                               dp->dp_meta_objset, obj));
                   } else if (err == ENOENT) {
                           /*
                            * We might not have created the remap bpobj yet.
                            */
                   } else {
                           goto out;
                   }
           }
   
           /*
            * Note: errors ignored, because the these special dirs, used for
            * space accounting, are only created on demand.
            */
           (void) dsl_pool_open_special_dir(dp, LEAK_DIR_NAME,
               &dp->dp_leak_dir);
   
           if (spa_feature_is_active(dp->dp_spa, SPA_FEATURE_ASYNC_DESTROY)) {
                   err = zap_lookup(dp->dp_meta_objset, DMU_POOL_DIRECTORY_OBJECT,
                       DMU_POOL_BPTREE_OBJ, sizeof (uint64_t), 1,
                       &dp->dp_bptree_obj);
                   if (err != 0)
                           goto out;
           }
   
           if (spa_feature_is_active(dp->dp_spa, SPA_FEATURE_EMPTY_BPOBJ)) {
                   err = zap_lookup(dp->dp_meta_objset, DMU_POOL_DIRECTORY_OBJECT,
                       DMU_POOL_EMPTY_BPOBJ, sizeof (uint64_t), 1,
                       &dp->dp_empty_bpobj);
                   if (err != 0)
                           goto out;
           }
   
           err = zap_lookup(dp->dp_meta_objset, DMU_POOL_DIRECTORY_OBJECT,
               DMU_POOL_TMP_USERREFS, sizeof (uint64_t), 1,
               &dp->dp_tmp_userrefs_obj);
           if (err == ENOENT)
                   err = 0;
           if (err)
                   goto out;
   
           err = dsl_scan_init(dp, dp->dp_tx.tx_open_txg);
   
   out:
           rrw_exit(&dp->dp_config_rwlock, FTAG);
           return (err);
   }
   
   void
   dsl_pool_close(dsl_pool_t *dp)
   {
           /*
            * Drop our references from dsl_pool_open().
            *
            * Since we held the origin_snap from "syncing" context (which
            * includes pool-opening context), it actually only got a "ref"
            * and not a hold, so just drop that here.
            */
           if (dp->dp_origin_snap != NULL)
                   dsl_dataset_rele(dp->dp_origin_snap, dp);
           if (dp->dp_mos_dir != NULL)
                   dsl_dir_rele(dp->dp_mos_dir, dp);
           if (dp->dp_free_dir != NULL)
                   dsl_dir_rele(dp->dp_free_dir, dp);
           if (dp->dp_leak_dir != NULL)
                   dsl_dir_rele(dp->dp_leak_dir, dp);
           if (dp->dp_root_dir != NULL)
                   dsl_dir_rele(dp->dp_root_dir, dp);
   
           bpobj_close(&dp->dp_free_bpobj);
           bpobj_close(&dp->dp_obsolete_bpobj);
   
           /* undo the dmu_objset_open_impl(mos) from dsl_pool_open() */
           if (dp->dp_meta_objset != NULL)
                   dmu_objset_evict(dp->dp_meta_objset);
   
           txg_list_destroy(&dp->dp_dirty_datasets);
           txg_list_destroy(&dp->dp_dirty_zilogs);
           txg_list_destroy(&dp->dp_sync_tasks);
           txg_list_destroy(&dp->dp_early_sync_tasks);
           txg_list_destroy(&dp->dp_dirty_dirs);
   
           taskq_destroy(dp->dp_zil_clean_taskq);
           taskq_destroy(dp->dp_sync_taskq);
   
           /*
            * We can't set retry to TRUE since we're explicitly specifying
            * a spa to flush. This is good enough; any missed buffers for
            * this spa won't cause trouble, and they'll eventually fall
            * out of the ARC just like any other unused buffer.
            */
           arc_flush(dp->dp_spa, FALSE);
   
           mmp_fini(dp->dp_spa);
           txg_fini(dp);
           dsl_scan_fini(dp);
           dmu_buf_user_evict_wait();
   
           rrw_destroy(&dp->dp_config_rwlock);
           mutex_destroy(&dp->dp_lock);
           cv_destroy(&dp->dp_spaceavail_cv);
   
           ASSERT0(aggsum_value(&dp->dp_wrlog_total));
           aggsum_fini(&dp->dp_wrlog_total);
           for (int i = 0; i < TXG_SIZE; i++) {
                   ASSERT0(aggsum_value(&dp->dp_wrlog_pertxg[i]));
                   aggsum_fini(&dp->dp_wrlog_pertxg[i]);
           }
   
           taskq_destroy(dp->dp_unlinked_drain_taskq);
           taskq_destroy(dp->dp_zrele_taskq);
           if (dp->dp_blkstats != NULL)
                   vmem_free(dp->dp_blkstats, sizeof (zfs_all_blkstats_t));
           kmem_free(dp, sizeof (dsl_pool_t));
   }
   
   void
   dsl_pool_create_obsolete_bpobj(dsl_pool_t *dp, dmu_tx_t *tx)
   {
           uint64_t obj;
           /*
            * Currently, we only create the obsolete_bpobj where there are
            * indirect vdevs with referenced mappings.
            */
           ASSERT(spa_feature_is_active(dp->dp_spa, SPA_FEATURE_DEVICE_REMOVAL));
           /* create and open the obsolete_bpobj */
           obj = bpobj_alloc(dp->dp_meta_objset, SPA_OLD_MAXBLOCKSIZE, tx);
           VERIFY0(bpobj_open(&dp->dp_obsolete_bpobj, dp->dp_meta_objset, obj));
           VERIFY0(zap_add(dp->dp_meta_objset, DMU_POOL_DIRECTORY_OBJECT,
               DMU_POOL_OBSOLETE_BPOBJ, sizeof (uint64_t), 1, &obj, tx));
           spa_feature_incr(dp->dp_spa, SPA_FEATURE_OBSOLETE_COUNTS, tx);
   }
   
   void
   dsl_pool_destroy_obsolete_bpobj(dsl_pool_t *dp, dmu_tx_t *tx)
   {
           spa_feature_decr(dp->dp_spa, SPA_FEATURE_OBSOLETE_COUNTS, tx);
           VERIFY0(zap_remove(dp->dp_meta_objset,
               DMU_POOL_DIRECTORY_OBJECT,
               DMU_POOL_OBSOLETE_BPOBJ, tx));
           bpobj_free(dp->dp_meta_objset,
               dp->dp_obsolete_bpobj.bpo_object, tx);
           bpobj_close(&dp->dp_obsolete_bpobj);
   }
   
   dsl_pool_t *
   dsl_pool_create(spa_t *spa, nvlist_t *zplprops __attribute__((unused)),
       dsl_crypto_params_t *dcp, uint64_t txg)
   {
           int err;
           dsl_pool_t *dp = dsl_pool_open_impl(spa, txg);
           dmu_tx_t *tx = dmu_tx_create_assigned(dp, txg);
   #ifdef _KERNEL
           objset_t *os;
   #else
           objset_t *os __attribute__((unused));
   #endif
           dsl_dataset_t *ds;
           uint64_t obj;
   
           rrw_enter(&dp->dp_config_rwlock, RW_WRITER, FTAG);
   
           /* create and open the MOS (meta-objset) */
           dp->dp_meta_objset = dmu_objset_create_impl(spa,
               NULL, &dp->dp_meta_rootbp, DMU_OST_META, tx);
           spa->spa_meta_objset = dp->dp_meta_objset;
   
           /* create the pool directory */
           err = zap_create_claim(dp->dp_meta_objset, DMU_POOL_DIRECTORY_OBJECT,
               DMU_OT_OBJECT_DIRECTORY, DMU_OT_NONE, 0, tx);
           ASSERT0(err);
   
           /* Initialize scan structures */
           VERIFY0(dsl_scan_init(dp, txg));
   
           /* create and open the root dir */
           dp->dp_root_dir_obj = dsl_dir_create_sync(dp, NULL, NULL, tx);
           VERIFY0(dsl_dir_hold_obj(dp, dp->dp_root_dir_obj,
               NULL, dp, &dp->dp_root_dir));
   
           /* create and open the meta-objset dir */
           (void) dsl_dir_create_sync(dp, dp->dp_root_dir, MOS_DIR_NAME, tx);
           VERIFY0(dsl_pool_open_special_dir(dp,
               MOS_DIR_NAME, &dp->dp_mos_dir));
   
           if (spa_version(spa) >= SPA_VERSION_DEADLISTS) {
                   /* create and open the free dir */
                   (void) dsl_dir_create_sync(dp, dp->dp_root_dir,
                       FREE_DIR_NAME, tx);
                   VERIFY0(dsl_pool_open_special_dir(dp,
                       FREE_DIR_NAME, &dp->dp_free_dir));
   
                   /* create and open the free_bplist */
                   obj = bpobj_alloc(dp->dp_meta_objset, SPA_OLD_MAXBLOCKSIZE, tx);
                   VERIFY(zap_add(dp->dp_meta_objset, DMU_POOL_DIRECTORY_OBJECT,
                       DMU_POOL_FREE_BPOBJ, sizeof (uint64_t), 1, &obj, tx) == 0);
                   VERIFY0(bpobj_open(&dp->dp_free_bpobj,
                       dp->dp_meta_objset, obj));
           }
   
           if (spa_version(spa) >= SPA_VERSION_DSL_SCRUB)
                   dsl_pool_create_origin(dp, tx);
   
           /*
            * Some features may be needed when creating the root dataset, so we
            * create the feature objects here.
            */
           if (spa_version(spa) >= SPA_VERSION_FEATURES)
                   spa_feature_create_zap_objects(spa, tx);
   
           if (dcp != NULL && dcp->cp_crypt != ZIO_CRYPT_OFF &&
               dcp->cp_crypt != ZIO_CRYPT_INHERIT)
                   spa_feature_enable(spa, SPA_FEATURE_ENCRYPTION, tx);
   
           /* create the root dataset */
           obj = dsl_dataset_create_sync_dd(dp->dp_root_dir, NULL, dcp, 0, tx);
   
           /* create the root objset */
           VERIFY0(dsl_dataset_hold_obj_flags(dp, obj,
               DS_HOLD_FLAG_DECRYPT, FTAG, &ds));
           rrw_enter(&ds->ds_bp_rwlock, RW_READER, FTAG);
           os = dmu_objset_create_impl(dp->dp_spa, ds,
               dsl_dataset_get_blkptr(ds), DMU_OST_ZFS, tx);
           rrw_exit(&ds->ds_bp_rwlock, FTAG);
   #ifdef _KERNEL
           zfs_create_fs(os, kcred, zplprops, tx);
   #endif
           dsl_dataset_rele_flags(ds, DS_HOLD_FLAG_DECRYPT, FTAG);
   
           dmu_tx_commit(tx);
   
           rrw_exit(&dp->dp_config_rwlock, FTAG);
   
           return (dp);
   }
   
   /*
    * Account for the meta-objset space in its placeholder dsl_dir.
    */
   void
   dsl_pool_mos_diduse_space(dsl_pool_t *dp,
       int64_t used, int64_t comp, int64_t uncomp)
   {
           ASSERT3U(comp, ==, uncomp); /* it's all metadata */
           mutex_enter(&dp->dp_lock);
           dp->dp_mos_used_delta += used;
           dp->dp_mos_compressed_delta += comp;
           dp->dp_mos_uncompressed_delta += uncomp;
           mutex_exit(&dp->dp_lock);
   }
   
   static void
   dsl_pool_sync_mos(dsl_pool_t *dp, dmu_tx_t *tx)
   {
           zio_t *zio = zio_root(dp->dp_spa, NULL, NULL, ZIO_FLAG_MUSTSUCCEED);
           dmu_objset_sync(dp->dp_meta_objset, zio, tx);
           VERIFY0(zio_wait(zio));
           dmu_objset_sync_done(dp->dp_meta_objset, tx);
           taskq_wait(dp->dp_sync_taskq);
           multilist_destroy(&dp->dp_meta_objset->os_synced_dnodes);
   
           dprintf_bp(&dp->dp_meta_rootbp, "meta objset rootbp is %s", "");
           spa_set_rootblkptr(dp->dp_spa, &dp->dp_meta_rootbp);
   }
   
   static void
   dsl_pool_dirty_delta(dsl_pool_t *dp, int64_t delta)
   {
           ASSERT(MUTEX_HELD(&dp->dp_lock));
   
           if (delta < 0)
                   ASSERT3U(-delta, <=, dp->dp_dirty_total);
   
           dp->dp_dirty_total += delta;
   
           /*
            * Note: we signal even when increasing dp_dirty_total.
            * This ensures forward progress -- each thread wakes the next waiter.
            */
           if (dp->dp_dirty_total < zfs_dirty_data_max)
                   cv_signal(&dp->dp_spaceavail_cv);
   }
   
   void
   dsl_pool_wrlog_count(dsl_pool_t *dp, int64_t size, uint64_t txg)
   {
           ASSERT3S(size, >=, 0);
   
           aggsum_add(&dp->dp_wrlog_pertxg[txg & TXG_MASK], size);
           aggsum_add(&dp->dp_wrlog_total, size);
   
           /* Choose a value slightly bigger than min dirty sync bytes */
           uint64_t sync_min =
               zfs_wrlog_data_max * (zfs_dirty_data_sync_percent + 10) / 200;
           if (aggsum_compare(&dp->dp_wrlog_pertxg[txg & TXG_MASK], sync_min) > 0)
                   txg_kick(dp, txg);
   }
   
   boolean_t
   dsl_pool_need_wrlog_delay(dsl_pool_t *dp)
   {
           uint64_t delay_min_bytes =
               zfs_wrlog_data_max * zfs_delay_min_dirty_percent / 100;
   
           return (aggsum_compare(&dp->dp_wrlog_total, delay_min_bytes) > 0);
   }
   
   static void
   dsl_pool_wrlog_clear(dsl_pool_t *dp, uint64_t txg)
   {
           int64_t delta;
           delta = -(int64_t)aggsum_value(&dp->dp_wrlog_pertxg[txg & TXG_MASK]);
           aggsum_add(&dp->dp_wrlog_pertxg[txg & TXG_MASK], delta);
           aggsum_add(&dp->dp_wrlog_total, delta);
           /* Compact per-CPU sums after the big change. */
           (void) aggsum_value(&dp->dp_wrlog_pertxg[txg & TXG_MASK]);
           (void) aggsum_value(&dp->dp_wrlog_total);
   }
   
   #ifdef ZFS_DEBUG
   static boolean_t
   dsl_early_sync_task_verify(dsl_pool_t *dp, uint64_t txg)
   {
           spa_t *spa = dp->dp_spa;
           vdev_t *rvd = spa->spa_root_vdev;
   
           for (uint64_t c = 0; c < rvd->vdev_children; c++) {
                   vdev_t *vd = rvd->vdev_child[c];
                   txg_list_t *tl = &vd->vdev_ms_list;
                   metaslab_t *ms;
   
                   for (ms = txg_list_head(tl, TXG_CLEAN(txg)); ms;
                       ms = txg_list_next(tl, ms, TXG_CLEAN(txg))) {
                           VERIFY(range_tree_is_empty(ms->ms_freeing));
                           VERIFY(range_tree_is_empty(ms->ms_checkpointing));
                   }
           }
   
           return (B_TRUE);
   }
   #else
   #define dsl_early_sync_task_verify(dp, txg) \
           ((void) sizeof (dp), (void) sizeof (txg), B_TRUE)
   #endif
   
   void
   dsl_pool_sync(dsl_pool_t *dp, uint64_t txg)
   {
           zio_t *zio;
           dmu_tx_t *tx;
           dsl_dir_t *dd;
           dsl_dataset_t *ds;
           objset_t *mos = dp->dp_meta_objset;
           list_t synced_datasets;
   
           list_create(&synced_datasets, sizeof (dsl_dataset_t),
               offsetof(dsl_dataset_t, ds_synced_link));
   
           tx = dmu_tx_create_assigned(dp, txg);
   
           /*
            * Run all early sync tasks before writing out any dirty blocks.
            * For more info on early sync tasks see block comment in
            * dsl_early_sync_task().
            */
           if (!txg_list_empty(&dp->dp_early_sync_tasks, txg)) {
                   dsl_sync_task_t *dst;
   
                   ASSERT3U(spa_sync_pass(dp->dp_spa), ==, 1);
                   while ((dst =
                       txg_list_remove(&dp->dp_early_sync_tasks, txg)) != NULL) {
                           ASSERT(dsl_early_sync_task_verify(dp, txg));
                           dsl_sync_task_sync(dst, tx);
                   }
                   ASSERT(dsl_early_sync_task_verify(dp, txg));
           }
   
           /*
            * Write out all dirty blocks of dirty datasets.
            */
           zio = zio_root(dp->dp_spa, NULL, NULL, ZIO_FLAG_MUSTSUCCEED);
           while ((ds = txg_list_remove(&dp->dp_dirty_datasets, txg)) != NULL) {
                   /*
                    * We must not sync any non-MOS datasets twice, because
                    * we may have taken a snapshot of them.  However, we
                    * may sync newly-created datasets on pass 2.
                    */
                   ASSERT(!list_link_active(&ds->ds_synced_link));
                   list_insert_tail(&synced_datasets, ds);
                   dsl_dataset_sync(ds, zio, tx);
           }
           VERIFY0(zio_wait(zio));
   
           /*
            * Update the long range free counter after
            * we're done syncing user data
            */
           mutex_enter(&dp->dp_lock);
           ASSERT(spa_sync_pass(dp->dp_spa) == 1 ||
               dp->dp_long_free_dirty_pertxg[txg & TXG_MASK] == 0);
           dp->dp_long_free_dirty_pertxg[txg & TXG_MASK] = 0;
           mutex_exit(&dp->dp_lock);
   
           /*
            * After the data blocks have been written (ensured by the zio_wait()
            * above), update the user/group/project space accounting.  This happens
            * in tasks dispatched to dp_sync_taskq, so wait for them before
            * continuing.
            */
           for (ds = list_head(&synced_datasets); ds != NULL;
               ds = list_next(&synced_datasets, ds)) {
                   dmu_objset_sync_done(ds->ds_objset, tx);
           }
           taskq_wait(dp->dp_sync_taskq);
   
           /*
            * Sync the datasets again to push out the changes due to
            * userspace updates.  This must be done before we process the
            * sync tasks, so that any snapshots will have the correct
            * user accounting information (and we won't get confused
            * about which blocks are part of the snapshot).
            */
           zio = zio_root(dp->dp_spa, NULL, NULL, ZIO_FLAG_MUSTSUCCEED);
           while ((ds = txg_list_remove(&dp->dp_dirty_datasets, txg)) != NULL) {
                   objset_t *os = ds->ds_objset;
   
                   ASSERT(list_link_active(&ds->ds_synced_link));
                   dmu_buf_rele(ds->ds_dbuf, ds);
                   dsl_dataset_sync(ds, zio, tx);
   
                   /*
                    * Release any key mappings created by calls to
                    * dsl_dataset_dirty() from the userquota accounting
                    * code paths.
                    */
                   if (os->os_encrypted && !os->os_raw_receive &&
                       !os->os_next_write_raw[txg & TXG_MASK]) {
                           ASSERT3P(ds->ds_key_mapping, !=, NULL);
                           key_mapping_rele(dp->dp_spa, ds->ds_key_mapping, ds);
                   }
           }
           VERIFY0(zio_wait(zio));
   
           /*
            * Now that the datasets have been completely synced, we can
            * clean up our in-memory structures accumulated while syncing:
            *
            *  - move dead blocks from the pending deadlist and livelists
            *    to the on-disk versions
            *  - release hold from dsl_dataset_dirty()
            *  - release key mapping hold from dsl_dataset_dirty()
            */
           while ((ds = list_remove_head(&synced_datasets)) != NULL) {
                   objset_t *os = ds->ds_objset;
   
                   if (os->os_encrypted && !os->os_raw_receive &&
                       !os->os_next_write_raw[txg & TXG_MASK]) {
                           ASSERT3P(ds->ds_key_mapping, !=, NULL);
                           key_mapping_rele(dp->dp_spa, ds->ds_key_mapping, ds);
                   }
   
                   dsl_dataset_sync_done(ds, tx);
           }
   
           while ((dd = txg_list_remove(&dp->dp_dirty_dirs, txg)) != NULL) {
                   dsl_dir_sync(dd, tx);
           }
   
           /*
            * The MOS's space is accounted for in the pool/$MOS
            * (dp_mos_dir).  We can't modify the mos while we're syncing
            * it, so we remember the deltas and apply them here.
            */
           if (dp->dp_mos_used_delta != 0 || dp->dp_mos_compressed_delta != 0 ||
               dp->dp_mos_uncompressed_delta != 0) {
                   dsl_dir_diduse_space(dp->dp_mos_dir, DD_USED_HEAD,
                       dp->dp_mos_used_delta,
                       dp->dp_mos_compressed_delta,
                       dp->dp_mos_uncompressed_delta, tx);
                   dp->dp_mos_used_delta = 0;
                   dp->dp_mos_compressed_delta = 0;
                   dp->dp_mos_uncompressed_delta = 0;
           }
   
           if (dmu_objset_is_dirty(mos, txg)) {
                   dsl_pool_sync_mos(dp, tx);
           }
   
           /*
            * We have written all of the accounted dirty data, so our
            * dp_space_towrite should now be zero. However, some seldom-used
            * code paths do not adhere to this (e.g. dbuf_undirty()). Shore up
            * the accounting of any dirtied space now.
            *
            * Note that, besides any dirty data from datasets, the amount of
            * dirty data in the MOS is also accounted by the pool. Therefore,
            * we want to do this cleanup after dsl_pool_sync_mos() so we don't
            * attempt to update the accounting for the same dirty data twice.
            * (i.e. at this point we only update the accounting for the space
            * that we know that we "leaked").
            */
           dsl_pool_undirty_space(dp, dp->dp_dirty_pertxg[txg & TXG_MASK], txg);
   
           /*
            * If we modify a dataset in the same txg that we want to destroy it,
            * its dsl_dir's dd_dbuf will be dirty, and thus have a hold on it.
            * dsl_dir_destroy_check() will fail if there are unexpected holds.
            * Therefore, we want to sync the MOS (thus syncing the dd_dbuf
            * and clearing the hold on it) before we process the sync_tasks.
            * The MOS data dirtied by the sync_tasks will be synced on the next
            * pass.
            */
           if (!txg_list_empty(&dp->dp_sync_tasks, txg)) {
                   dsl_sync_task_t *dst;
                   /*
                    * No more sync tasks should have been added while we
                    * were syncing.
                    */
                   ASSERT3U(spa_sync_pass(dp->dp_spa), ==, 1);
                   while ((dst = txg_list_remove(&dp->dp_sync_tasks, txg)) != NULL)
                           dsl_sync_task_sync(dst, tx);
           }
   
           dmu_tx_commit(tx);
   
           DTRACE_PROBE2(dsl_pool_sync__done, dsl_pool_t *dp, dp, uint64_t, txg);
   }
   
   void
   dsl_pool_sync_done(dsl_pool_t *dp, uint64_t txg)
   {
           zilog_t *zilog;
   
           while ((zilog = txg_list_head(&dp->dp_dirty_zilogs, txg))) {
                   dsl_dataset_t *ds = dmu_objset_ds(zilog->zl_os);
                   /*
                    * We don't remove the zilog from the dp_dirty_zilogs
                    * list until after we've cleaned it. This ensures that
                    * callers of zilog_is_dirty() receive an accurate
                    * answer when they are racing with the spa sync thread.
                    */
                   zil_clean(zilog, txg);
                   (void) txg_list_remove_this(&dp->dp_dirty_zilogs, zilog, txg);
                   ASSERT(!dmu_objset_is_dirty(zilog->zl_os, txg));
                   dmu_buf_rele(ds->ds_dbuf, zilog);
           }
   
           dsl_pool_wrlog_clear(dp, txg);
   
           ASSERT(!dmu_objset_is_dirty(dp->dp_meta_objset, txg));
   }
   
   /*
    * TRUE if the current thread is the tx_sync_thread or if we
    * are being called from SPA context during pool initialization.
    */
   int
   dsl_pool_sync_context(dsl_pool_t *dp)
   {
           return (curthread == dp->dp_tx.tx_sync_thread ||
               spa_is_initializing(dp->dp_spa) ||
               taskq_member(dp->dp_sync_taskq, curthread));
   }
   
   /*
    * This function returns the amount of allocatable space in the pool
    * minus whatever space is currently reserved by ZFS for specific
    * purposes. Specifically:
    *
    * 1] Any reserved SLOP space
    * 2] Any space used by the checkpoint
    * 3] Any space used for deferred frees
    *
    * The latter 2 are especially important because they are needed to
    * rectify the SPA's and DMU's different understanding of how much space
    * is used. Now the DMU is aware of that extra space tracked by the SPA
    * without having to maintain a separate special dir (e.g similar to
    * $MOS, $FREEING, and $LEAKED).
    *
    * Note: By deferred frees here, we mean the frees that were deferred
    * in spa_sync() after sync pass 1 (spa_deferred_bpobj), and not the
    * segments placed in ms_defer trees during metaslab_sync_done().
    */
   uint64_t
   dsl_pool_adjustedsize(dsl_pool_t *dp, zfs_space_check_t slop_policy)
   {
           spa_t *spa = dp->dp_spa;
           uint64_t space, resv, adjustedsize;
           uint64_t spa_deferred_frees =
               spa->spa_deferred_bpobj.bpo_phys->bpo_bytes;
   
           space = spa_get_dspace(spa)
               - spa_get_checkpoint_space(spa) - spa_deferred_frees;
           resv = spa_get_slop_space(spa);
   
           switch (slop_policy) {
           case ZFS_SPACE_CHECK_NORMAL:
                   break;
           case ZFS_SPACE_CHECK_RESERVED:
                   resv >>= 1;
                   break;
           case ZFS_SPACE_CHECK_EXTRA_RESERVED:
                   resv >>= 2;
                   break;
           case ZFS_SPACE_CHECK_NONE:
                   resv = 0;
                   break;
           default:
                   panic("invalid slop policy value: %d", slop_policy);
                   break;
           }
           adjustedsize = (space >= resv) ? (space - resv) : 0;
   
           return (adjustedsize);
   }
   
   uint64_t
   dsl_pool_unreserved_space(dsl_pool_t *dp, zfs_space_check_t slop_policy)
   {
           uint64_t poolsize = dsl_pool_adjustedsize(dp, slop_policy);
           uint64_t deferred =
               metaslab_class_get_deferred(spa_normal_class(dp->dp_spa));
           uint64_t quota = (poolsize >= deferred) ? (poolsize - deferred) : 0;
           return (quota);
   }
   
   uint64_t
   dsl_pool_deferred_space(dsl_pool_t *dp)
   {
           return (metaslab_class_get_deferred(spa_normal_class(dp->dp_spa)));
   }
   
   boolean_t
   dsl_pool_need_dirty_delay(dsl_pool_t *dp)
   {
           uint64_t delay_min_bytes =
               zfs_dirty_data_max * zfs_delay_min_dirty_percent / 100;
   
           mutex_enter(&dp->dp_lock);
           uint64_t dirty = dp->dp_dirty_total;
           mutex_exit(&dp->dp_lock);
   
           return (dirty > delay_min_bytes);
   }
   
   static boolean_t
   dsl_pool_need_dirty_sync(dsl_pool_t *dp, uint64_t txg)
   {
           ASSERT(MUTEX_HELD(&dp->dp_lock));
   
           uint64_t dirty_min_bytes =
               zfs_dirty_data_max * zfs_dirty_data_sync_percent / 100;
           uint64_t dirty = dp->dp_dirty_pertxg[txg & TXG_MASK];
   
           return (dirty > dirty_min_bytes);
   }
   
   void
   dsl_pool_dirty_space(dsl_pool_t *dp, int64_t space, dmu_tx_t *tx)
   {
           if (space > 0) {
                   mutex_enter(&dp->dp_lock);
                   dp->dp_dirty_pertxg[tx->tx_txg & TXG_MASK] += space;
                   dsl_pool_dirty_delta(dp, space);
                   boolean_t needsync = !dmu_tx_is_syncing(tx) &&
                       dsl_pool_need_dirty_sync(dp, tx->tx_txg);
                   mutex_exit(&dp->dp_lock);
   
                   if (needsync)
                           txg_kick(dp, tx->tx_txg);
           }
  }
  
  void
  dsl_pool_undirty_space(dsl_pool_t *dp, int64_t space, uint64_t txg)
  {
          ASSERT3S(space, >=, 0);
          if (space == 0)
                  return;
  
          mutex_enter(&dp->dp_lock);
          if (dp->dp_dirty_pertxg[txg & TXG_MASK] < space) {
                  /* XXX writing something we didn't dirty? */
                  space = dp->dp_dirty_pertxg[txg & TXG_MASK];
          }
          ASSERT3U(dp->dp_dirty_pertxg[txg & TXG_MASK], >=, space);
          dp->dp_dirty_pertxg[txg & TXG_MASK] -= space;
          ASSERT3U(dp->dp_dirty_total, >=, space);
          dsl_pool_dirty_delta(dp, -space);
          mutex_exit(&dp->dp_lock);
  }
  
  static int
  upgrade_clones_cb(dsl_pool_t *dp, dsl_dataset_t *hds, void *arg)
  {
          dmu_tx_t *tx = arg;
          dsl_dataset_t *ds, *prev = NULL;
          int err;
  
          err = dsl_dataset_hold_obj(dp, hds->ds_object, FTAG, &ds);
          if (err)
                  return (err);
  
          while (dsl_dataset_phys(ds)->ds_prev_snap_obj != 0) {
                  err = dsl_dataset_hold_obj(dp,
                      dsl_dataset_phys(ds)->ds_prev_snap_obj, FTAG, &prev);
                  if (err) {
                          dsl_dataset_rele(ds, FTAG);
                          return (err);
                  }
  
                  if (dsl_dataset_phys(prev)->ds_next_snap_obj != ds->ds_object)
                          break;
                  dsl_dataset_rele(ds, FTAG);
                  ds = prev;
                  prev = NULL;
          }
  
          if (prev == NULL) {
                  prev = dp->dp_origin_snap;
  
                  /*
                   * The $ORIGIN can't have any data, or the accounting
                   * will be wrong.
                   */
                  rrw_enter(&ds->ds_bp_rwlock, RW_READER, FTAG);
                  ASSERT0(dsl_dataset_phys(prev)->ds_bp.blk_birth);
                  rrw_exit(&ds->ds_bp_rwlock, FTAG);
  
                  /* The origin doesn't get attached to itself */
                  if (ds->ds_object == prev->ds_object) {
                          dsl_dataset_rele(ds, FTAG);
                          return (0);
                  }
  
                  dmu_buf_will_dirty(ds->ds_dbuf, tx);
                  dsl_dataset_phys(ds)->ds_prev_snap_obj = prev->ds_object;
                  dsl_dataset_phys(ds)->ds_prev_snap_txg =
                      dsl_dataset_phys(prev)->ds_creation_txg;
  
                  dmu_buf_will_dirty(ds->ds_dir->dd_dbuf, tx);
                  dsl_dir_phys(ds->ds_dir)->dd_origin_obj = prev->ds_object;
  
                  dmu_buf_will_dirty(prev->ds_dbuf, tx);
                  dsl_dataset_phys(prev)->ds_num_children++;
  
                  if (dsl_dataset_phys(ds)->ds_next_snap_obj == 0) {
                          ASSERT(ds->ds_prev == NULL);
                          VERIFY0(dsl_dataset_hold_obj(dp,
                              dsl_dataset_phys(ds)->ds_prev_snap_obj,
                              ds, &ds->ds_prev));
                  }
          }
  
          ASSERT3U(dsl_dir_phys(ds->ds_dir)->dd_origin_obj, ==, prev->ds_object);
          ASSERT3U(dsl_dataset_phys(ds)->ds_prev_snap_obj, ==, prev->ds_object);
  
          if (dsl_dataset_phys(prev)->ds_next_clones_obj == 0) {
                  dmu_buf_will_dirty(prev->ds_dbuf, tx);
                  dsl_dataset_phys(prev)->ds_next_clones_obj =
                      zap_create(dp->dp_meta_objset,
                      DMU_OT_NEXT_CLONES, DMU_OT_NONE, 0, tx);
          }
          VERIFY0(zap_add_int(dp->dp_meta_objset,
              dsl_dataset_phys(prev)->ds_next_clones_obj, ds->ds_object, tx));
  
          dsl_dataset_rele(ds, FTAG);
          if (prev != dp->dp_origin_snap)
                  dsl_dataset_rele(prev, FTAG);
          return (0);
  }
  
  void
  dsl_pool_upgrade_clones(dsl_pool_t *dp, dmu_tx_t *tx)
  {
          ASSERT(dmu_tx_is_syncing(tx));
          ASSERT(dp->dp_origin_snap != NULL);
  
          VERIFY0(dmu_objset_find_dp(dp, dp->dp_root_dir_obj, upgrade_clones_cb,
              tx, DS_FIND_CHILDREN | DS_FIND_SERIALIZE));
  }
  
  static int
  upgrade_dir_clones_cb(dsl_pool_t *dp, dsl_dataset_t *ds, void *arg)
  {
          dmu_tx_t *tx = arg;
          objset_t *mos = dp->dp_meta_objset;
  
          if (dsl_dir_phys(ds->ds_dir)->dd_origin_obj != 0) {
                  dsl_dataset_t *origin;
  
                  VERIFY0(dsl_dataset_hold_obj(dp,
                      dsl_dir_phys(ds->ds_dir)->dd_origin_obj, FTAG, &origin));
  
                  if (dsl_dir_phys(origin->ds_dir)->dd_clones == 0) {
                          dmu_buf_will_dirty(origin->ds_dir->dd_dbuf, tx);
                          dsl_dir_phys(origin->ds_dir)->dd_clones =
                              zap_create(mos, DMU_OT_DSL_CLONES, DMU_OT_NONE,
                              0, tx);
                  }
  
                  VERIFY0(zap_add_int(dp->dp_meta_objset,
                      dsl_dir_phys(origin->ds_dir)->dd_clones,
                      ds->ds_object, tx));
  
                  dsl_dataset_rele(origin, FTAG);
          }
          return (0);
  }
  
  void
  dsl_pool_upgrade_dir_clones(dsl_pool_t *dp, dmu_tx_t *tx)
  {
          uint64_t obj;
  
          ASSERT(dmu_tx_is_syncing(tx));
  
          (void) dsl_dir_create_sync(dp, dp->dp_root_dir, FREE_DIR_NAME, tx);
          VERIFY0(dsl_pool_open_special_dir(dp,
              FREE_DIR_NAME, &dp->dp_free_dir));
  
          /*
           * We can't use bpobj_alloc(), because spa_version() still
           * returns the old version, and we need a new-version bpobj with
           * subobj support.  So call dmu_object_alloc() directly.
           */
          obj = dmu_object_alloc(dp->dp_meta_objset, DMU_OT_BPOBJ,
              SPA_OLD_MAXBLOCKSIZE, DMU_OT_BPOBJ_HDR, sizeof (bpobj_phys_t), tx);
          VERIFY0(zap_add(dp->dp_meta_objset, DMU_POOL_DIRECTORY_OBJECT,
              DMU_POOL_FREE_BPOBJ, sizeof (uint64_t), 1, &obj, tx));
          VERIFY0(bpobj_open(&dp->dp_free_bpobj, dp->dp_meta_objset, obj));
  
          VERIFY0(dmu_objset_find_dp(dp, dp->dp_root_dir_obj,
              upgrade_dir_clones_cb, tx, DS_FIND_CHILDREN | DS_FIND_SERIALIZE));
  }
  
  void
  dsl_pool_create_origin(dsl_pool_t *dp, dmu_tx_t *tx)
  {
          uint64_t dsobj;
          dsl_dataset_t *ds;
  
          ASSERT(dmu_tx_is_syncing(tx));
          ASSERT(dp->dp_origin_snap == NULL);
          ASSERT(rrw_held(&dp->dp_config_rwlock, RW_WRITER));
  
          /* create the origin dir, ds, & snap-ds */
          dsobj = dsl_dataset_create_sync(dp->dp_root_dir, ORIGIN_DIR_NAME,
              NULL, 0, kcred, NULL, tx);
          VERIFY0(dsl_dataset_hold_obj(dp, dsobj, FTAG, &ds));
          dsl_dataset_snapshot_sync_impl(ds, ORIGIN_DIR_NAME, tx);
          VERIFY0(dsl_dataset_hold_obj(dp, dsl_dataset_phys(ds)->ds_prev_snap_obj,
              dp, &dp->dp_origin_snap));
          dsl_dataset_rele(ds, FTAG);
  }
  
  taskq_t *
  dsl_pool_zrele_taskq(dsl_pool_t *dp)
  {
          return (dp->dp_zrele_taskq);
  }
  
  taskq_t *
  dsl_pool_unlinked_drain_taskq(dsl_pool_t *dp)
  {
          return (dp->dp_unlinked_drain_taskq);
  }
  
  /*
   * Walk through the pool-wide zap object of temporary snapshot user holds
   * and release them.
   */
  void
  dsl_pool_clean_tmp_userrefs(dsl_pool_t *dp)
  {
          zap_attribute_t za;
          zap_cursor_t zc;
          objset_t *mos = dp->dp_meta_objset;
          uint64_t zapobj = dp->dp_tmp_userrefs_obj;
          nvlist_t *holds;
  
          if (zapobj == 0)
                  return;
          ASSERT(spa_version(dp->dp_spa) >= SPA_VERSION_USERREFS);
  
          holds = fnvlist_alloc();
  
          for (zap_cursor_init(&zc, mos, zapobj);
              zap_cursor_retrieve(&zc, &za) == 0;
              zap_cursor_advance(&zc)) {
                  char *htag;
                  nvlist_t *tags;
  
                  htag = strchr(za.za_name, '-');
                  *htag = '\0';
                  ++htag;
                  if (nvlist_lookup_nvlist(holds, za.za_name, &tags) != 0) {
                          tags = fnvlist_alloc();
                          fnvlist_add_boolean(tags, htag);
                          fnvlist_add_nvlist(holds, za.za_name, tags);
                          fnvlist_free(tags);
                  } else {
                          fnvlist_add_boolean(tags, htag);
                  }
          }
          dsl_dataset_user_release_tmp(dp, holds);
          fnvlist_free(holds);
          zap_cursor_fini(&zc);
  }
  
  /*
   * Create the pool-wide zap object for storing temporary snapshot holds.
   */
  static void
  dsl_pool_user_hold_create_obj(dsl_pool_t *dp, dmu_tx_t *tx)
  {
          objset_t *mos = dp->dp_meta_objset;
  
          ASSERT(dp->dp_tmp_userrefs_obj == 0);
          ASSERT(dmu_tx_is_syncing(tx));
  
          dp->dp_tmp_userrefs_obj = zap_create_link(mos, DMU_OT_USERREFS,
              DMU_POOL_DIRECTORY_OBJECT, DMU_POOL_TMP_USERREFS, tx);
  }
  
  static int
  dsl_pool_user_hold_rele_impl(dsl_pool_t *dp, uint64_t dsobj,
      const char *tag, uint64_t now, dmu_tx_t *tx, boolean_t holding)
  {
          objset_t *mos = dp->dp_meta_objset;
          uint64_t zapobj = dp->dp_tmp_userrefs_obj;
          char *name;
          int error;
  
          ASSERT(spa_version(dp->dp_spa) >= SPA_VERSION_USERREFS);
          ASSERT(dmu_tx_is_syncing(tx));
  
          /*
           * If the pool was created prior to SPA_VERSION_USERREFS, the
           * zap object for temporary holds might not exist yet.
           */
          if (zapobj == 0) {
                  if (holding) {
                          dsl_pool_user_hold_create_obj(dp, tx);
                          zapobj = dp->dp_tmp_userrefs_obj;
                  } else {
                          return (SET_ERROR(ENOENT));
                  }
          }
  
          name = kmem_asprintf("%llx-%s", (u_longlong_t)dsobj, tag);
          if (holding)
                  error = zap_add(mos, zapobj, name, 8, 1, &now, tx);
          else
                  error = zap_remove(mos, zapobj, name, tx);
          kmem_strfree(name);
  
          return (error);
  }
  
  /*
   * Add a temporary hold for the given dataset object and tag.
   */
  int
  dsl_pool_user_hold(dsl_pool_t *dp, uint64_t dsobj, const char *tag,
      uint64_t now, dmu_tx_t *tx)
  {
          return (dsl_pool_user_hold_rele_impl(dp, dsobj, tag, now, tx, B_TRUE));
  }
  
  /*
   * Release a temporary hold for the given dataset object and tag.
   */
  int
  dsl_pool_user_release(dsl_pool_t *dp, uint64_t dsobj, const char *tag,
      dmu_tx_t *tx)
  {
          return (dsl_pool_user_hold_rele_impl(dp, dsobj, tag, 0,
              tx, B_FALSE));
  }
  
  /*
   * DSL Pool Configuration Lock
   *
   * The dp_config_rwlock protects against changes to DSL state (e.g. dataset
   * creation / destruction / rename / property setting).  It must be held for
   * read to hold a dataset or dsl_dir.  I.e. you must call
   * dsl_pool_config_enter() or dsl_pool_hold() before calling
   * dsl_{dataset,dir}_hold{_obj}.  In most circumstances, the dp_config_rwlock
   * must be held continuously until all datasets and dsl_dirs are released.
   *
   * The only exception to this rule is that if a "long hold" is placed on
   * a dataset, then the dp_config_rwlock may be dropped while the dataset
   * is still held.  The long hold will prevent the dataset from being
   * destroyed -- the destroy will fail with EBUSY.  A long hold can be
   * obtained by calling dsl_dataset_long_hold(), or by "owning" a dataset
   * (by calling dsl_{dataset,objset}_{try}own{_obj}).
   *
   * Legitimate long-holders (including owners) should be long-running, cancelable
   * tasks that should cause "zfs destroy" to fail.  This includes DMU
   * consumers (i.e. a ZPL filesystem being mounted or ZVOL being open),
   * "zfs send", and "zfs diff".  There are several other long-holders whose
   * uses are suboptimal (e.g. "zfs promote", and zil_suspend()).
   *
   * The usual formula for long-holding would be:
   * dsl_pool_hold()
   * dsl_dataset_hold()
   * ... perform checks ...
   * dsl_dataset_long_hold()
   * dsl_pool_rele()
   * ... perform long-running task ...
   * dsl_dataset_long_rele()
   * dsl_dataset_rele()
   *
   * Note that when the long hold is released, the dataset is still held but
   * the pool is not held.  The dataset may change arbitrarily during this time
   * (e.g. it could be destroyed).  Therefore you shouldn't do anything to the
   * dataset except release it.
   *
   * Operations generally fall somewhere into the following taxonomy:
   *
   *                              Read-Only             Modifying
   *
   *    Dataset Layer / MOS        zfs get             zfs destroy
   *
   *     Individual Dataset         read()                write()
   *
   *
   * Dataset Layer Operations
   *
   * Modifying operations should generally use dsl_sync_task().  The synctask
   * infrastructure enforces proper locking strategy with respect to the
   * dp_config_rwlock.  See the comment above dsl_sync_task() for details.
   *
   * Read-only operations will manually hold the pool, then the dataset, obtain
   * information from the dataset, then release the pool and dataset.
   * dmu_objset_{hold,rele}() are convenience routines that also do the pool
   * hold/rele.
   *
   *
   * Operations On Individual Datasets
   *
   * Objects _within_ an objset should only be modified by the current 'owner'
   * of the objset to prevent incorrect concurrent modification. Thus, use
   * {dmu_objset,dsl_dataset}_own to mark some entity as the current owner,
   * and fail with EBUSY if there is already an owner. The owner can then
   * implement its own locking strategy, independent of the dataset layer's
   * locking infrastructure.
   * (E.g., the ZPL has its own set of locks to control concurrency. A regular
   *  vnop will not reach into the dataset layer).
   *
   * Ideally, objects would also only be read by the objset’s owner, so that we
   * don’t observe state mid-modification.
   * (E.g. the ZPL is creating a new object and linking it into a directory; if
   * you don’t coordinate with the ZPL to hold ZPL-level locks, you could see an
   * intermediate state.  The ioctl level violates this but in pretty benign
   * ways, e.g. reading the zpl props object.)
   */
  
  int
  dsl_pool_hold(const char *name, const void *tag, dsl_pool_t **dp)
  {
          spa_t *spa;
          int error;
  
          error = spa_open(name, &spa, tag);
          if (error == 0) {
                  *dp = spa_get_dsl(spa);
                  dsl_pool_config_enter(*dp, tag);
          }
          return (error);
  }
  
  void
  dsl_pool_rele(dsl_pool_t *dp, const void *tag)
  {
          dsl_pool_config_exit(dp, tag);
          spa_close(dp->dp_spa, tag);
  }
  
  void
  dsl_pool_config_enter(dsl_pool_t *dp, const void *tag)
  {
          /*
           * We use a "reentrant" reader-writer lock, but not reentrantly.
           *
           * The rrwlock can (with the track_all flag) track all reading threads,
           * which is very useful for debugging which code path failed to release
           * the lock, and for verifying that the *current* thread does hold
           * the lock.
           *
           * (Unlike a rwlock, which knows that N threads hold it for
           * read, but not *which* threads, so rw_held(RW_READER) returns TRUE
           * if any thread holds it for read, even if this thread doesn't).
           */
          ASSERT(!rrw_held(&dp->dp_config_rwlock, RW_READER));
          rrw_enter(&dp->dp_config_rwlock, RW_READER, tag);
  }
  
  void
  dsl_pool_config_enter_prio(dsl_pool_t *dp, const void *tag)
  {
          ASSERT(!rrw_held(&dp->dp_config_rwlock, RW_READER));
          rrw_enter_read_prio(&dp->dp_config_rwlock, tag);
  }
  
  void
  dsl_pool_config_exit(dsl_pool_t *dp, const void *tag)
  {
          rrw_exit(&dp->dp_config_rwlock, tag);
  }
  
  boolean_t
  dsl_pool_config_held(dsl_pool_t *dp)
  {
          return (RRW_LOCK_HELD(&dp->dp_config_rwlock));
  }
  
  boolean_t
  dsl_pool_config_held_writer(dsl_pool_t *dp)
  {
          return (RRW_WRITE_HELD(&dp->dp_config_rwlock));
  }
  
  EXPORT_SYMBOL(dsl_pool_config_enter);
  EXPORT_SYMBOL(dsl_pool_config_exit);
  
  /* zfs_dirty_data_max_percent only applied at module load in arc_init(). */
  ZFS_MODULE_PARAM(zfs, zfs_, dirty_data_max_percent, UINT, ZMOD_RD,
          "Max percent of RAM allowed to be dirty");
  
  /* zfs_dirty_data_max_max_percent only applied at module load in arc_init(). */
  ZFS_MODULE_PARAM(zfs, zfs_, dirty_data_max_max_percent, UINT, ZMOD_RD,
          "zfs_dirty_data_max upper bound as % of RAM");
  
  ZFS_MODULE_PARAM(zfs, zfs_, delay_min_dirty_percent, UINT, ZMOD_RW,
          "Transaction delay threshold");
  
  ZFS_MODULE_PARAM(zfs, zfs_, dirty_data_max, U64, ZMOD_RW,
          "Determines the dirty space limit");
  
  ZFS_MODULE_PARAM(zfs, zfs_, wrlog_data_max, U64, ZMOD_RW,
          "The size limit of write-transaction zil log data");
  
  /* zfs_dirty_data_max_max only applied at module load in arc_init(). */
  ZFS_MODULE_PARAM(zfs, zfs_, dirty_data_max_max, U64, ZMOD_RD,
          "zfs_dirty_data_max upper bound in bytes");
  
  ZFS_MODULE_PARAM(zfs, zfs_, dirty_data_sync_percent, UINT, ZMOD_RW,
          "Dirty data txg sync threshold as a percentage of zfs_dirty_data_max");
  
  ZFS_MODULE_PARAM(zfs, zfs_, delay_scale, U64, ZMOD_RW,
          "How quickly delay approaches infinity");
  
  ZFS_MODULE_PARAM(zfs, zfs_, sync_taskq_batch_pct, INT, ZMOD_RW,
          "Max percent of CPUs that are used to sync dirty data");
  
  ZFS_MODULE_PARAM(zfs_zil, zfs_zil_, clean_taskq_nthr_pct, INT, ZMOD_RW,
          "Max percent of CPUs that are used per dp_sync_taskq");
  
  ZFS_MODULE_PARAM(zfs_zil, zfs_zil_, clean_taskq_minalloc, INT, ZMOD_RW,
          "Number of taskq entries that are pre-populated");
  
  ZFS_MODULE_PARAM(zfs_zil, zfs_zil_, clean_taskq_maxalloc, INT, ZMOD_RW,
          "Max number of taskq entries that are cached");

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