]> git.proxmox.com Git - mirror_zfs-debian.git/blobdiff - module/zfs/dsl_pool.c
Update core ZFS code from build 121 to build 141.
[mirror_zfs-debian.git] / module / zfs / dsl_pool.c
index 2c5dfca53b2fbd758f35b353e9b5a5f9bce1cde4..2cd21a102beb10904ae8139993af786167265dcf 100644 (file)
  * CDDL HEADER END
  */
 /*
- * Copyright 2009 Sun Microsystems, Inc.  All rights reserved.
- * Use is subject to license terms.
+ * Copyright (c) 2005, 2010, Oracle and/or its affiliates. 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/fs/zfs.h>
 #include <sys/zfs_znode.h>
 #include <sys/spa_impl.h>
+#include <sys/dsl_deadlist.h>
 
 int zfs_no_write_throttle = 0;
 int zfs_write_limit_shift = 3;                 /* 1/8th of physical memory */
-int zfs_txg_synctime = 5;                      /* target secs to sync a txg */
+int zfs_txg_synctime_ms = 5000;                /* target millisecs to sync a txg */
 
 uint64_t zfs_write_limit_min = 32 << 20;       /* min write limit is 32MB */
 uint64_t zfs_write_limit_max = 0;              /* max data payload per txg */
@@ -50,7 +53,7 @@ kmutex_t zfs_write_limit_lock;
 
 static pgcnt_t old_physmem = 0;
 
-static int
+int
 dsl_pool_open_special_dir(dsl_pool_t *dp, const char *name, dsl_dir_t **ddp)
 {
        uint64_t obj;
@@ -88,7 +91,6 @@ dsl_pool_open_impl(spa_t *spa, uint64_t txg)
            offsetof(dsl_dataset_t, ds_synced_link));
 
        mutex_init(&dp->dp_lock, NULL, MUTEX_DEFAULT, NULL);
-       mutex_init(&dp->dp_scrub_cancel_lock, NULL, MUTEX_DEFAULT, NULL);
 
        dp->dp_vnrele_taskq = taskq_create("zfs_vn_rele_taskq", 1, minclsyspri,
            1, 4, 0);
@@ -103,13 +105,13 @@ dsl_pool_open(spa_t *spa, uint64_t txg, dsl_pool_t **dpp)
        dsl_pool_t *dp = dsl_pool_open_impl(spa, txg);
        dsl_dir_t *dd;
        dsl_dataset_t *ds;
-       objset_impl_t *osi;
+       uint64_t obj;
 
        rw_enter(&dp->dp_config_rwlock, RW_WRITER);
-       err = dmu_objset_open_impl(spa, NULL, &dp->dp_meta_rootbp, &osi);
+       err = dmu_objset_open_impl(spa, NULL, &dp->dp_meta_rootbp,
+           &dp->dp_meta_objset);
        if (err)
                goto out;
-       dp->dp_meta_objset = &osi->os;
 
        err = zap_lookup(dp->dp_meta_objset, DMU_POOL_DIRECTORY_OBJECT,
            DMU_POOL_ROOT_DATASET, sizeof (uint64_t), 1,
@@ -143,53 +145,30 @@ dsl_pool_open(spa_t *spa, uint64_t txg, dsl_pool_t **dpp)
                        goto out;
        }
 
-       /* get scrub status */
-       err = zap_lookup(dp->dp_meta_objset, DMU_POOL_DIRECTORY_OBJECT,
-           DMU_POOL_SCRUB_FUNC, sizeof (uint32_t), 1,
-           &dp->dp_scrub_func);
-       if (err == 0) {
-               err = zap_lookup(dp->dp_meta_objset, DMU_POOL_DIRECTORY_OBJECT,
-                   DMU_POOL_SCRUB_QUEUE, sizeof (uint64_t), 1,
-                   &dp->dp_scrub_queue_obj);
-               if (err)
-                       goto out;
-               err = zap_lookup(dp->dp_meta_objset, DMU_POOL_DIRECTORY_OBJECT,
-                   DMU_POOL_SCRUB_MIN_TXG, sizeof (uint64_t), 1,
-                   &dp->dp_scrub_min_txg);
-               if (err)
-                       goto out;
-               err = zap_lookup(dp->dp_meta_objset, DMU_POOL_DIRECTORY_OBJECT,
-                   DMU_POOL_SCRUB_MAX_TXG, sizeof (uint64_t), 1,
-                   &dp->dp_scrub_max_txg);
-               if (err)
-                       goto out;
-               err = zap_lookup(dp->dp_meta_objset, DMU_POOL_DIRECTORY_OBJECT,
-                   DMU_POOL_SCRUB_BOOKMARK, sizeof (uint64_t), 4,
-                   &dp->dp_scrub_bookmark);
+       if (spa_version(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_SCRUB_ERRORS, sizeof (uint64_t), 1,
-                   &spa->spa_scrub_errors);
+                   DMU_POOL_FREE_BPOBJ, sizeof (uint64_t), 1, &obj);
                if (err)
                        goto out;
-               if (spa_version(spa) < SPA_VERSION_DSL_SCRUB) {
-                       /*
-                        * A new-type scrub was in progress on an old
-                        * pool.  Restart from the beginning, since the
-                        * old software may have changed the pool in the
-                        * meantime.
-                        */
-                       dsl_pool_scrub_restart(dp);
-               }
-       } else {
-               /*
-                * It's OK if there is no scrub in progress (and if
-                * there was an I/O error, ignore it).
-                */
-               err = 0;
+               VERIFY3U(0, ==, bpobj_open(&dp->dp_free_bpobj,
+                   dp->dp_meta_objset, obj));
        }
 
+       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, txg);
+
 out:
        rw_exit(&dp->dp_config_rwlock);
        if (err)
@@ -214,22 +193,27 @@ dsl_pool_close(dsl_pool_t *dp)
                dsl_dataset_drop_ref(dp->dp_origin_snap, dp);
        if (dp->dp_mos_dir)
                dsl_dir_close(dp->dp_mos_dir, dp);
+       if (dp->dp_free_dir)
+               dsl_dir_close(dp->dp_free_dir, dp);
        if (dp->dp_root_dir)
                dsl_dir_close(dp->dp_root_dir, dp);
 
+       bpobj_close(&dp->dp_free_bpobj);
+
        /* undo the dmu_objset_open_impl(mos) from dsl_pool_open() */
        if (dp->dp_meta_objset)
-               dmu_objset_evict(NULL, dp->dp_meta_objset->os);
+               dmu_objset_evict(dp->dp_meta_objset);
 
        txg_list_destroy(&dp->dp_dirty_datasets);
+       txg_list_destroy(&dp->dp_sync_tasks);
        txg_list_destroy(&dp->dp_dirty_dirs);
        list_destroy(&dp->dp_synced_datasets);
 
        arc_flush(dp->dp_spa);
        txg_fini(dp);
+       dsl_scan_fini(dp);
        rw_destroy(&dp->dp_config_rwlock);
        mutex_destroy(&dp->dp_lock);
-       mutex_destroy(&dp->dp_scrub_cancel_lock);
        taskq_destroy(dp->dp_vnrele_taskq);
        if (dp->dp_blkstats)
                kmem_free(dp->dp_blkstats, sizeof (zfs_all_blkstats_t));
@@ -242,19 +226,22 @@ dsl_pool_create(spa_t *spa, nvlist_t *zplprops, 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);
-       objset_impl_t *osip;
+       objset_t *os;
        dsl_dataset_t *ds;
-       uint64_t dsobj;
+       uint64_t obj;
 
        /* 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)->os;
+       dp->dp_meta_objset = dmu_objset_create_impl(spa,
+           NULL, &dp->dp_meta_rootbp, DMU_OST_META, tx);
 
        /* 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);
        ASSERT3U(err, ==, 0);
 
+       /* Initialize scan structures */
+       VERIFY3U(0, ==, dsl_scan_init(dp, txg));
+
        /* create and open the root dir */
        dp->dp_root_dir_obj = dsl_dir_create_sync(dp, NULL, NULL, tx);
        VERIFY(0 == dsl_dir_open_obj(dp, dp->dp_root_dir_obj,
@@ -265,18 +252,33 @@ dsl_pool_create(spa_t *spa, nvlist_t *zplprops, uint64_t txg)
        VERIFY(0 == 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);
+               VERIFY(0 == 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_MAXBLOCKSIZE, tx);
+               VERIFY(zap_add(dp->dp_meta_objset, DMU_POOL_DIRECTORY_OBJECT,
+                   DMU_POOL_FREE_BPOBJ, sizeof (uint64_t), 1, &obj, tx) == 0);
+               VERIFY3U(0, ==, 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);
 
        /* create the root dataset */
-       dsobj = dsl_dataset_create_sync_dd(dp->dp_root_dir, NULL, 0, tx);
+       obj = dsl_dataset_create_sync_dd(dp->dp_root_dir, NULL, 0, tx);
 
        /* create the root objset */
-       VERIFY(0 == dsl_dataset_hold_obj(dp, dsobj, FTAG, &ds));
-       osip = dmu_objset_create_impl(dp->dp_spa, ds,
+       VERIFY(0 == dsl_dataset_hold_obj(dp, obj, FTAG, &ds));
+       os = dmu_objset_create_impl(dp->dp_spa, ds,
            dsl_dataset_get_blkptr(ds), DMU_OST_ZFS, tx);
 #ifdef _KERNEL
-       zfs_create_fs(&osip->os, kcred, zplprops, tx);
+       zfs_create_fs(os, kcred, zplprops, tx);
 #endif
        dsl_dataset_rele(ds, FTAG);
 
@@ -285,6 +287,14 @@ dsl_pool_create(spa_t *spa, nvlist_t *zplprops, uint64_t txg)
        return (dp);
 }
 
+static int
+deadlist_enqueue_cb(void *arg, const blkptr_t *bp, dmu_tx_t *tx)
+{
+       dsl_deadlist_t *dl = arg;
+       dsl_deadlist_insert(dl, bp, tx);
+       return (0);
+}
+
 void
 dsl_pool_sync(dsl_pool_t *dp, uint64_t txg)
 {
@@ -293,11 +303,19 @@ dsl_pool_sync(dsl_pool_t *dp, uint64_t txg)
        dsl_dir_t *dd;
        dsl_dataset_t *ds;
        dsl_sync_task_group_t *dstg;
-       objset_impl_t *mosi = dp->dp_meta_objset->os;
+       objset_t *mos = dp->dp_meta_objset;
        hrtime_t start, write_time;
        uint64_t data_written;
        int err;
 
+       /*
+        * We need to copy dp_space_towrite() before doing
+        * dsl_sync_task_group_sync(), because
+        * dsl_dataset_snapshot_reserve_space() will increase
+        * dp_space_towrite but not actually write anything.
+        */
+       data_written = dp->dp_space_towrite[txg & TXG_MASK];
+
        tx = dmu_tx_create_assigned(dp, txg);
 
        dp->dp_read_overhead = 0;
@@ -323,11 +341,11 @@ dsl_pool_sync(dsl_pool_t *dp, uint64_t txg)
 
        for (ds = list_head(&dp->dp_synced_datasets); ds;
            ds = list_next(&dp->dp_synced_datasets, ds))
-               dmu_objset_do_userquota_callbacks(ds->ds_user_ptr, tx);
+               dmu_objset_do_userquota_updates(ds->ds_objset, tx);
 
        /*
         * Sync the datasets again to push out the changes due to
-        * userquota updates.  This must be done before we process the
+        * userspace updates.  This must be done before we process the
         * sync tasks, because that could cause a snapshot of a dataset
         * whose ds_bp will be rewritten when we do this 2nd sync.
         */
@@ -339,6 +357,16 @@ dsl_pool_sync(dsl_pool_t *dp, uint64_t txg)
        }
        err = zio_wait(zio);
 
+       /*
+        * Move dead blocks from the pending deadlist to the on-disk
+        * deadlist.
+        */
+       for (ds = list_head(&dp->dp_synced_datasets); ds;
+           ds = list_next(&dp->dp_synced_datasets, ds)) {
+               bplist_iterate(&ds->ds_pending_deadlist,
+                   deadlist_enqueue_cb, &ds->ds_deadlist, tx);
+       }
+
        while (dstg = txg_list_remove(&dp->dp_sync_tasks, txg)) {
                /*
                 * No more sync tasks should have been added while we
@@ -354,14 +382,11 @@ dsl_pool_sync(dsl_pool_t *dp, uint64_t txg)
                dsl_dir_sync(dd, tx);
        write_time += gethrtime() - start;
 
-       if (spa_sync_pass(dp->dp_spa) == 1)
-               dsl_pool_scrub_sync(dp, tx);
-
        start = gethrtime();
-       if (list_head(&mosi->os_dirty_dnodes[txg & TXG_MASK]) != NULL ||
-           list_head(&mosi->os_free_dnodes[txg & TXG_MASK]) != NULL) {
+       if (list_head(&mos->os_dirty_dnodes[txg & TXG_MASK]) != NULL ||
+           list_head(&mos->os_free_dnodes[txg & TXG_MASK]) != NULL) {
                zio = zio_root(dp->dp_spa, NULL, NULL, ZIO_FLAG_MUSTSUCCEED);
-               dmu_objset_sync(mosi, zio, tx);
+               dmu_objset_sync(mos, zio, tx);
                err = zio_wait(zio);
                ASSERT(err == 0);
                dprintf_bp(&dp->dp_meta_rootbp, "meta objset rootbp is %s", "");
@@ -374,7 +399,6 @@ dsl_pool_sync(dsl_pool_t *dp, uint64_t txg)
 
        dmu_tx_commit(tx);
 
-       data_written = dp->dp_space_towrite[txg & TXG_MASK];
        dp->dp_space_towrite[txg & TXG_MASK] = 0;
        ASSERT(dp->dp_tempreserved[txg & TXG_MASK] == 0);
 
@@ -399,10 +423,14 @@ dsl_pool_sync(dsl_pool_t *dp, uint64_t txg)
         * amount of write traffic allowed into each transaction group.
         * Weight the throughput calculation towards the current value:
         *      thru = 3/4 old_thru + 1/4 new_thru
+        *
+        * Note: write_time is in nanosecs, so write_time/MICROSEC
+        * yields millisecs
         */
        ASSERT(zfs_write_limit_min > 0);
-       if (data_written > zfs_write_limit_min / 8 && write_time > 0) {
-               uint64_t throughput = (data_written * NANOSEC) / write_time;
+       if (data_written > zfs_write_limit_min / 8 && write_time > MICROSEC) {
+               uint64_t throughput = data_written / (write_time / MICROSEC);
+
                if (dp->dp_throughput)
                        dp->dp_throughput = throughput / 4 +
                            3 * dp->dp_throughput / 4;
@@ -410,21 +438,24 @@ dsl_pool_sync(dsl_pool_t *dp, uint64_t txg)
                        dp->dp_throughput = throughput;
                dp->dp_write_limit = MIN(zfs_write_limit_inflated,
                    MAX(zfs_write_limit_min,
-                   dp->dp_throughput * zfs_txg_synctime));
+                   dp->dp_throughput * zfs_txg_synctime_ms));
        }
 }
 
 void
-dsl_pool_zil_clean(dsl_pool_t *dp)
+dsl_pool_sync_done(dsl_pool_t *dp, uint64_t txg)
 {
        dsl_dataset_t *ds;
+       objset_t *os;
 
        while (ds = list_head(&dp->dp_synced_datasets)) {
                list_remove(&dp->dp_synced_datasets, ds);
-               ASSERT(ds->ds_user_ptr != NULL);
-               zil_clean(((objset_impl_t *)ds->ds_user_ptr)->os_zil);
+               os = ds->ds_objset;
+               zil_clean(os->os_zil);
+               ASSERT(!dmu_objset_is_dirty(os, txg));
                dmu_buf_rele(ds->ds_dbuf, ds);
        }
+       ASSERT(!dmu_objset_is_dirty(dp->dp_meta_objset, txg));
 }
 
 /*
@@ -601,6 +632,7 @@ upgrade_clones_cb(spa_t *spa, uint64_t dsobj, const char *dsname, void *arg)
        ASSERT(ds->ds_phys->ds_prev_snap_obj == prev->ds_object);
 
        if (prev->ds_phys->ds_next_clones_obj == 0) {
+               dmu_buf_will_dirty(prev->ds_dbuf, tx);
                prev->ds_phys->ds_next_clones_obj =
                    zap_create(dp->dp_meta_objset,
                    DMU_OT_NEXT_CLONES, DMU_OT_NONE, 0, tx);
@@ -620,8 +652,67 @@ dsl_pool_upgrade_clones(dsl_pool_t *dp, dmu_tx_t *tx)
        ASSERT(dmu_tx_is_syncing(tx));
        ASSERT(dp->dp_origin_snap != NULL);
 
-       (void) dmu_objset_find_spa(dp->dp_spa, NULL, upgrade_clones_cb,
-           tx, DS_FIND_CHILDREN);
+       VERIFY3U(0, ==, dmu_objset_find_spa(dp->dp_spa, NULL, upgrade_clones_cb,
+           tx, DS_FIND_CHILDREN));
+}
+
+/* ARGSUSED */
+static int
+upgrade_dir_clones_cb(spa_t *spa, uint64_t dsobj, const char *dsname, void *arg)
+{
+       dmu_tx_t *tx = arg;
+       dsl_dataset_t *ds;
+       dsl_pool_t *dp = spa_get_dsl(spa);
+       objset_t *mos = dp->dp_meta_objset;
+
+       VERIFY3U(0, ==, dsl_dataset_hold_obj(dp, dsobj, FTAG, &ds));
+
+       if (ds->ds_dir->dd_phys->dd_origin_obj) {
+               dsl_dataset_t *origin;
+
+               VERIFY3U(0, ==, dsl_dataset_hold_obj(dp,
+                   ds->ds_dir->dd_phys->dd_origin_obj, FTAG, &origin));
+
+               if (origin->ds_dir->dd_phys->dd_clones == 0) {
+                       dmu_buf_will_dirty(origin->ds_dir->dd_dbuf, tx);
+                       origin->ds_dir->dd_phys->dd_clones = zap_create(mos,
+                           DMU_OT_DSL_CLONES, DMU_OT_NONE, 0, tx);
+               }
+
+               VERIFY3U(0, ==, zap_add_int(dp->dp_meta_objset,
+                   origin->ds_dir->dd_phys->dd_clones, dsobj, tx));
+
+               dsl_dataset_rele(origin, FTAG);
+       }
+
+       dsl_dataset_rele(ds, FTAG);
+       return (0);
+}
+
+void
+dsl_pool_upgrade_dir_clones(dsl_pool_t *dp, dmu_tx_t *tx)
+{
+       ASSERT(dmu_tx_is_syncing(tx));
+       uint64_t obj;
+
+       (void) dsl_dir_create_sync(dp, dp->dp_root_dir, FREE_DIR_NAME, tx);
+       VERIFY(0 == 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_MAXBLOCKSIZE, DMU_OT_BPOBJ_HDR, sizeof (bpobj_phys_t), tx);
+       VERIFY3U(0, ==, zap_add(dp->dp_meta_objset, DMU_POOL_DIRECTORY_OBJECT,
+           DMU_POOL_FREE_BPOBJ, sizeof (uint64_t), 1, &obj, tx));
+       VERIFY3U(0, ==, bpobj_open(&dp->dp_free_bpobj,
+           dp->dp_meta_objset, obj));
+
+       VERIFY3U(0, ==, dmu_objset_find_spa(dp->dp_spa, NULL,
+           upgrade_dir_clones_cb, tx, DS_FIND_CHILDREN));
 }
 
 void
@@ -638,7 +729,7 @@ dsl_pool_create_origin(dsl_pool_t *dp, dmu_tx_t *tx)
        dsobj = dsl_dataset_create_sync(dp->dp_root_dir, ORIGIN_DIR_NAME,
            NULL, 0, kcred, tx);
        VERIFY(0 == dsl_dataset_hold_obj(dp, dsobj, FTAG, &ds));
-       dsl_dataset_snapshot_sync(ds, ORIGIN_DIR_NAME, kcred, tx);
+       dsl_dataset_snapshot_sync(ds, ORIGIN_DIR_NAME, tx);
        VERIFY(0 == dsl_dataset_hold_obj(dp, ds->ds_phys->ds_prev_snap_obj,
            dp, &dp->dp_origin_snap));
        dsl_dataset_rele(ds, FTAG);
@@ -650,3 +741,108 @@ dsl_pool_vnrele_taskq(dsl_pool_t *dp)
 {
        return (dp->dp_vnrele_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;
+
+       if (zapobj == 0)
+               return;
+       ASSERT(spa_version(dp->dp_spa) >= SPA_VERSION_USERREFS);
+
+       for (zap_cursor_init(&zc, mos, zapobj);
+           zap_cursor_retrieve(&zc, &za) == 0;
+           zap_cursor_advance(&zc)) {
+               char *htag;
+               uint64_t dsobj;
+
+               htag = strchr(za.za_name, '-');
+               *htag = '\0';
+               ++htag;
+               dsobj = strtonum(za.za_name, NULL);
+               (void) dsl_dataset_user_release_tmp(dp, dsobj, htag);
+       }
+       zap_cursor_fini(&zc);
+}
+
+/*
+ * Create the pool-wide zap object for storing temporary snapshot holds.
+ */
+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(mos, DMU_OT_USERREFS,
+           DMU_OT_NONE, 0, tx);
+
+       VERIFY(zap_add(mos, DMU_POOL_DIRECTORY_OBJECT, DMU_POOL_TMP_USERREFS,
+           sizeof (uint64_t), 1, &dp->dp_tmp_userrefs_obj, tx) == 0);
+}
+
+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 (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);
+       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, NULL,
+           tx, B_FALSE));
+}