1 /*
   2  * CDDL HEADER START
   3  *
   4  * The contents of this file are subject to the terms of the
   5  * Common Development and Distribution License (the "License").
   6  * You may not use this file except in compliance with the License.
   7  *
   8  * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
   9  * or http://www.opensolaris.org/os/licensing.
  10  * See the License for the specific language governing permissions
  11  * and limitations under the License.
  12  *
  13  * When distributing Covered Code, include this CDDL HEADER in each
  14  * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
  15  * If applicable, add the following below this CDDL HEADER, with the
  16  * fields enclosed by brackets "[]" replaced with your own identifying
  17  * information: Portions Copyright [yyyy] [name of copyright owner]
  18  *
  19  * CDDL HEADER END
  20  */
  21 /*
  22  * Copyright (c) 2005, 2010, Oracle and/or its affiliates. All rights reserved.
  23  * Copyright (c) 2013 by Delphix. All rights reserved.
  24  * Copyright (c) 2013 Steven Hartland. All rights reserved.
  25  */
  26 
  27 #include <sys/dsl_pool.h>
  28 #include <sys/dsl_dataset.h>
  29 #include <sys/dsl_prop.h>
  30 #include <sys/dsl_dir.h>
  31 #include <sys/dsl_synctask.h>
  32 #include <sys/dsl_scan.h>
  33 #include <sys/dnode.h>
  34 #include <sys/dmu_tx.h>
  35 #include <sys/dmu_objset.h>
  36 #include <sys/arc.h>
  37 #include <sys/zap.h>
  38 #include <sys/zio.h>
  39 #include <sys/zfs_context.h>
  40 #include <sys/fs/zfs.h>
  41 #include <sys/zfs_znode.h>
  42 #include <sys/spa_impl.h>
  43 #include <sys/dsl_deadlist.h>
  44 #include <sys/bptree.h>
  45 #include <sys/zfeature.h>
  46 #include <sys/zil_impl.h>
  47 #include <sys/dsl_userhold.h>
  48 
  49 /*
  50  * ZFS Write Throttle
  51  * ------------------
  52  *
  53  * ZFS must limit the rate of incoming writes to the rate at which it is able
  54  * to sync data modifications to the backend storage. Throttling by too much
  55  * creates an artificial limit; throttling by too little can only be sustained
  56  * for short periods and would lead to highly lumpy performance. On a per-pool
  57  * basis, ZFS tracks the amount of modified (dirty) data. As operations change
  58  * data, the amount of dirty data increases; as ZFS syncs out data, the amount
  59  * of dirty data decreases. When the amount of dirty data exceeds a
  60  * predetermined threshold further modifications are blocked until the amount
  61  * of dirty data decreases (as data is synced out).
  62  *
  63  * The limit on dirty data is tunable, and should be adjusted according to
  64  * both the IO capacity and available memory of the system. The larger the
  65  * window, the more ZFS is able to aggregate and amortize metadata (and data)
  66  * changes. However, memory is a limited resource, and allowing for more dirty
  67  * data comes at the cost of keeping other useful data in memory (for example
  68  * ZFS data cached by the ARC).
  69  *
  70  * Implementation
  71  *
  72  * As buffers are modified dsl_pool_willuse_space() increments both the per-
  73  * txg (dp_dirty_pertxg[]) and poolwide (dp_dirty_total) accounting of
  74  * dirty space used; dsl_pool_dirty_space() decrements those values as data
  75  * is synced out from dsl_pool_sync(). While only the poolwide value is
  76  * relevant, the per-txg value is useful for debugging. The tunable
  77  * zfs_dirty_data_max determines the dirty space limit. Once that value is
  78  * exceeded, new writes are halted until space frees up.
  79  *
  80  * The zfs_dirty_data_sync tunable dictates the threshold at which we
  81  * ensure that there is a txg syncing (see the comment in txg.c for a full
  82  * description of transaction group stages).
  83  *
  84  * The IO scheduler uses both the dirty space limit and current amount of
  85  * dirty data as inputs. Those values affect the number of concurrent IOs ZFS
  86  * issues. See the comment in vdev_queue.c for details of the IO scheduler.
  87  *
  88  * The delay is also calculated based on the amount of dirty data.  See the
  89  * comment above dmu_tx_delay() for details.
  90  */
  91 
  92 /*
  93  * zfs_dirty_data_max will be set to zfs_dirty_data_max_percent% of all memory,
  94  * capped at zfs_dirty_data_max_max.  It can also be overridden in /etc/system.
  95  */
  96 uint64_t zfs_dirty_data_max;
  97 uint64_t zfs_dirty_data_max_max = 4ULL * 1024 * 1024 * 1024;
  98 int zfs_dirty_data_max_percent = 10;
  99 
 100 /*
 101  * If there is at least this much dirty data, push out a txg.
 102  */
 103 uint64_t zfs_dirty_data_sync = 64 * 1024 * 1024;
 104 
 105 /*
 106  * Once there is this amount of dirty data, the dmu_tx_delay() will kick in
 107  * and delay each transaction.
 108  * This value should be >= zfs_vdev_async_write_active_max_dirty_percent.
 109  */
 110 int zfs_delay_min_dirty_percent = 60;
 111 
 112 /*
 113  * This controls how quickly the delay approaches infinity.
 114  * Larger values cause it to delay less for a given amount of dirty data.
 115  * Therefore larger values will cause there to be more dirty data for a
 116  * given throughput.
 117  *
 118  * For the smoothest delay, this value should be about 1 billion divided
 119  * by the maximum number of operations per second.  This will smoothly
 120  * handle between 10x and 1/10th this number.
 121  *
 122  * Note: zfs_delay_scale * zfs_dirty_data_max must be < 2^64, due to the
 123  * multiply in dmu_tx_delay().
 124  */
 125 uint64_t zfs_delay_scale = 1000 * 1000 * 1000 / 2000;
 126 
 127 
 128 /*
 129  * XXX someday maybe turn these into #defines, and you have to tune it on a
 130  * per-pool basis using zfs.conf.
 131  */
 132 
 133 
 134 hrtime_t zfs_throttle_delay = MSEC2NSEC(10);
 135 hrtime_t zfs_throttle_resolution = MSEC2NSEC(10);
 136 
 137 int
 138 dsl_pool_open_special_dir(dsl_pool_t *dp, const char *name, dsl_dir_t **ddp)
 139 {
 140         uint64_t obj;
 141         int err;
 142 
 143         err = zap_lookup(dp->dp_meta_objset,
 144             dp->dp_root_dir->dd_phys->dd_child_dir_zapobj,
 145             name, sizeof (obj), 1, &obj);
 146         if (err)
 147                 return (err);
 148 
 149         return (dsl_dir_hold_obj(dp, obj, name, dp, ddp));
 150 }
 151 
 152 static dsl_pool_t *
 153 dsl_pool_open_impl(spa_t *spa, uint64_t txg)
 154 {
 155         dsl_pool_t *dp;
 156         blkptr_t *bp = spa_get_rootblkptr(spa);
 157 
 158         dp = kmem_zalloc(sizeof (dsl_pool_t), KM_SLEEP);
 159         dp->dp_spa = spa;
 160         dp->dp_meta_rootbp = *bp;
 161         rrw_init(&dp->dp_config_rwlock, B_TRUE);
 162         txg_init(dp, txg);
 163 
 164         txg_list_create(&dp->dp_dirty_datasets,
 165             offsetof(dsl_dataset_t, ds_dirty_link));
 166         txg_list_create(&dp->dp_dirty_zilogs,
 167             offsetof(zilog_t, zl_dirty_link));
 168         txg_list_create(&dp->dp_dirty_dirs,
 169             offsetof(dsl_dir_t, dd_dirty_link));
 170         txg_list_create(&dp->dp_sync_tasks,
 171             offsetof(dsl_sync_task_t, dst_node));
 172 
 173         mutex_init(&dp->dp_lock, NULL, MUTEX_DEFAULT, NULL);
 174         cv_init(&dp->dp_spaceavail_cv, NULL, CV_DEFAULT, NULL);
 175 
 176         dp->dp_vnrele_taskq = taskq_create("zfs_vn_rele_taskq", 1, minclsyspri,
 177             1, 4, 0);
 178 
 179         return (dp);
 180 }
 181 
 182 int
 183 dsl_pool_init(spa_t *spa, uint64_t txg, dsl_pool_t **dpp)
 184 {
 185         int err;
 186         dsl_pool_t *dp = dsl_pool_open_impl(spa, txg);
 187 
 188         err = dmu_objset_open_impl(spa, NULL, &dp->dp_meta_rootbp,
 189             &dp->dp_meta_objset);
 190         if (err != 0)
 191                 dsl_pool_close(dp);
 192         else
 193                 *dpp = dp;
 194 
 195         return (err);
 196 }
 197 
 198 int
 199 dsl_pool_open(dsl_pool_t *dp)
 200 {
 201         int err;
 202         dsl_dir_t *dd;
 203         dsl_dataset_t *ds;
 204         uint64_t obj;
 205 
 206         rrw_enter(&dp->dp_config_rwlock, RW_WRITER, FTAG);
 207         err = zap_lookup(dp->dp_meta_objset, DMU_POOL_DIRECTORY_OBJECT,
 208             DMU_POOL_ROOT_DATASET, sizeof (uint64_t), 1,
 209             &dp->dp_root_dir_obj);
 210         if (err)
 211                 goto out;
 212 
 213         err = dsl_dir_hold_obj(dp, dp->dp_root_dir_obj,
 214             NULL, dp, &dp->dp_root_dir);
 215         if (err)
 216                 goto out;
 217 
 218         err = dsl_pool_open_special_dir(dp, MOS_DIR_NAME, &dp->dp_mos_dir);
 219         if (err)
 220                 goto out;
 221 
 222         if (spa_version(dp->dp_spa) >= SPA_VERSION_ORIGIN) {
 223                 err = dsl_pool_open_special_dir(dp, ORIGIN_DIR_NAME, &dd);
 224                 if (err)
 225                         goto out;
 226                 err = dsl_dataset_hold_obj(dp, dd->dd_phys->dd_head_dataset_obj,
 227                     FTAG, &ds);
 228                 if (err == 0) {
 229                         err = dsl_dataset_hold_obj(dp,
 230                             ds->ds_phys->ds_prev_snap_obj, dp,
 231                             &dp->dp_origin_snap);
 232                         dsl_dataset_rele(ds, FTAG);
 233                 }
 234                 dsl_dir_rele(dd, dp);
 235                 if (err)
 236                         goto out;
 237         }
 238 
 239         if (spa_version(dp->dp_spa) >= SPA_VERSION_DEADLISTS) {
 240                 err = dsl_pool_open_special_dir(dp, FREE_DIR_NAME,
 241                     &dp->dp_free_dir);
 242                 if (err)
 243                         goto out;
 244 
 245                 err = zap_lookup(dp->dp_meta_objset, DMU_POOL_DIRECTORY_OBJECT,
 246                     DMU_POOL_FREE_BPOBJ, sizeof (uint64_t), 1, &obj);
 247                 if (err)
 248                         goto out;
 249                 VERIFY0(bpobj_open(&dp->dp_free_bpobj,
 250                     dp->dp_meta_objset, obj));
 251         }
 252 
 253         if (spa_feature_is_active(dp->dp_spa,
 254             &spa_feature_table[SPA_FEATURE_ASYNC_DESTROY])) {
 255                 err = zap_lookup(dp->dp_meta_objset, DMU_POOL_DIRECTORY_OBJECT,
 256                     DMU_POOL_BPTREE_OBJ, sizeof (uint64_t), 1,
 257                     &dp->dp_bptree_obj);
 258                 if (err != 0)
 259                         goto out;
 260         }
 261 
 262         if (spa_feature_is_active(dp->dp_spa,
 263             &spa_feature_table[SPA_FEATURE_EMPTY_BPOBJ])) {
 264                 err = zap_lookup(dp->dp_meta_objset, DMU_POOL_DIRECTORY_OBJECT,
 265                     DMU_POOL_EMPTY_BPOBJ, sizeof (uint64_t), 1,
 266                     &dp->dp_empty_bpobj);
 267                 if (err != 0)
 268                         goto out;
 269         }
 270 
 271         err = zap_lookup(dp->dp_meta_objset, DMU_POOL_DIRECTORY_OBJECT,
 272             DMU_POOL_TMP_USERREFS, sizeof (uint64_t), 1,
 273             &dp->dp_tmp_userrefs_obj);
 274         if (err == ENOENT)
 275                 err = 0;
 276         if (err)
 277                 goto out;
 278 
 279         err = dsl_scan_init(dp, dp->dp_tx.tx_open_txg);
 280 
 281 out:
 282         rrw_exit(&dp->dp_config_rwlock, FTAG);
 283         return (err);
 284 }
 285 
 286 void
 287 dsl_pool_close(dsl_pool_t *dp)
 288 {
 289         /*
 290          * Drop our references from dsl_pool_open().
 291          *
 292          * Since we held the origin_snap from "syncing" context (which
 293          * includes pool-opening context), it actually only got a "ref"
 294          * and not a hold, so just drop that here.
 295          */
 296         if (dp->dp_origin_snap)
 297                 dsl_dataset_rele(dp->dp_origin_snap, dp);
 298         if (dp->dp_mos_dir)
 299                 dsl_dir_rele(dp->dp_mos_dir, dp);
 300         if (dp->dp_free_dir)
 301                 dsl_dir_rele(dp->dp_free_dir, dp);
 302         if (dp->dp_root_dir)
 303                 dsl_dir_rele(dp->dp_root_dir, dp);
 304 
 305         bpobj_close(&dp->dp_free_bpobj);
 306 
 307         /* undo the dmu_objset_open_impl(mos) from dsl_pool_open() */
 308         if (dp->dp_meta_objset)
 309                 dmu_objset_evict(dp->dp_meta_objset);
 310 
 311         txg_list_destroy(&dp->dp_dirty_datasets);
 312         txg_list_destroy(&dp->dp_dirty_zilogs);
 313         txg_list_destroy(&dp->dp_sync_tasks);
 314         txg_list_destroy(&dp->dp_dirty_dirs);
 315 
 316         arc_flush(dp->dp_spa);
 317         txg_fini(dp);
 318         dsl_scan_fini(dp);
 319         rrw_destroy(&dp->dp_config_rwlock);
 320         mutex_destroy(&dp->dp_lock);
 321         taskq_destroy(dp->dp_vnrele_taskq);
 322         if (dp->dp_blkstats)
 323                 kmem_free(dp->dp_blkstats, sizeof (zfs_all_blkstats_t));
 324         kmem_free(dp, sizeof (dsl_pool_t));
 325 }
 326 
 327 dsl_pool_t *
 328 dsl_pool_create(spa_t *spa, nvlist_t *zplprops, uint64_t txg)
 329 {
 330         int err;
 331         dsl_pool_t *dp = dsl_pool_open_impl(spa, txg);
 332         dmu_tx_t *tx = dmu_tx_create_assigned(dp, txg);
 333         objset_t *os;
 334         dsl_dataset_t *ds;
 335         uint64_t obj;
 336 
 337         rrw_enter(&dp->dp_config_rwlock, RW_WRITER, FTAG);
 338 
 339         /* create and open the MOS (meta-objset) */
 340         dp->dp_meta_objset = dmu_objset_create_impl(spa,
 341             NULL, &dp->dp_meta_rootbp, DMU_OST_META, tx);
 342 
 343         /* create the pool directory */
 344         err = zap_create_claim(dp->dp_meta_objset, DMU_POOL_DIRECTORY_OBJECT,
 345             DMU_OT_OBJECT_DIRECTORY, DMU_OT_NONE, 0, tx);
 346         ASSERT0(err);
 347 
 348         /* Initialize scan structures */
 349         VERIFY0(dsl_scan_init(dp, txg));
 350 
 351         /* create and open the root dir */
 352         dp->dp_root_dir_obj = dsl_dir_create_sync(dp, NULL, NULL, tx);
 353         VERIFY0(dsl_dir_hold_obj(dp, dp->dp_root_dir_obj,
 354             NULL, dp, &dp->dp_root_dir));
 355 
 356         /* create and open the meta-objset dir */
 357         (void) dsl_dir_create_sync(dp, dp->dp_root_dir, MOS_DIR_NAME, tx);
 358         VERIFY0(dsl_pool_open_special_dir(dp,
 359             MOS_DIR_NAME, &dp->dp_mos_dir));
 360 
 361         if (spa_version(spa) >= SPA_VERSION_DEADLISTS) {
 362                 /* create and open the free dir */
 363                 (void) dsl_dir_create_sync(dp, dp->dp_root_dir,
 364                     FREE_DIR_NAME, tx);
 365                 VERIFY0(dsl_pool_open_special_dir(dp,
 366                     FREE_DIR_NAME, &dp->dp_free_dir));
 367 
 368                 /* create and open the free_bplist */
 369                 obj = bpobj_alloc(dp->dp_meta_objset, SPA_MAXBLOCKSIZE, tx);
 370                 VERIFY(zap_add(dp->dp_meta_objset, DMU_POOL_DIRECTORY_OBJECT,
 371                     DMU_POOL_FREE_BPOBJ, sizeof (uint64_t), 1, &obj, tx) == 0);
 372                 VERIFY0(bpobj_open(&dp->dp_free_bpobj,
 373                     dp->dp_meta_objset, obj));
 374         }
 375 
 376         if (spa_version(spa) >= SPA_VERSION_DSL_SCRUB)
 377                 dsl_pool_create_origin(dp, tx);
 378 
 379         /* create the root dataset */
 380         obj = dsl_dataset_create_sync_dd(dp->dp_root_dir, NULL, 0, tx);
 381 
 382         /* create the root objset */
 383         VERIFY0(dsl_dataset_hold_obj(dp, obj, FTAG, &ds));
 384         os = dmu_objset_create_impl(dp->dp_spa, ds,
 385             dsl_dataset_get_blkptr(ds), DMU_OST_ZFS, tx);
 386 #ifdef _KERNEL
 387         zfs_create_fs(os, kcred, zplprops, tx);
 388 #endif
 389         dsl_dataset_rele(ds, FTAG);
 390 
 391         dmu_tx_commit(tx);
 392 
 393         rrw_exit(&dp->dp_config_rwlock, FTAG);
 394 
 395         return (dp);
 396 }
 397 
 398 /*
 399  * Account for the meta-objset space in its placeholder dsl_dir.
 400  */
 401 void
 402 dsl_pool_mos_diduse_space(dsl_pool_t *dp,
 403     int64_t used, int64_t comp, int64_t uncomp)
 404 {
 405         ASSERT3U(comp, ==, uncomp); /* it's all metadata */
 406         mutex_enter(&dp->dp_lock);
 407         dp->dp_mos_used_delta += used;
 408         dp->dp_mos_compressed_delta += comp;
 409         dp->dp_mos_uncompressed_delta += uncomp;
 410         mutex_exit(&dp->dp_lock);
 411 }
 412 
 413 static int
 414 deadlist_enqueue_cb(void *arg, const blkptr_t *bp, dmu_tx_t *tx)
 415 {
 416         dsl_deadlist_t *dl = arg;
 417         dsl_deadlist_insert(dl, bp, tx);
 418         return (0);
 419 }
 420 
 421 static void
 422 dsl_pool_sync_mos(dsl_pool_t *dp, dmu_tx_t *tx)
 423 {
 424         zio_t *zio = zio_root(dp->dp_spa, NULL, NULL, ZIO_FLAG_MUSTSUCCEED);
 425         dmu_objset_sync(dp->dp_meta_objset, zio, tx);
 426         VERIFY0(zio_wait(zio));
 427         dprintf_bp(&dp->dp_meta_rootbp, "meta objset rootbp is %s", "");
 428         spa_set_rootblkptr(dp->dp_spa, &dp->dp_meta_rootbp);
 429 }
 430 
 431 static void
 432 dsl_pool_dirty_delta(dsl_pool_t *dp, int64_t delta)
 433 {
 434         ASSERT(MUTEX_HELD(&dp->dp_lock));
 435 
 436         if (delta < 0)
 437                 ASSERT3U(-delta, <=, dp->dp_dirty_total);
 438 
 439         dp->dp_dirty_total += delta;
 440 
 441         /*
 442          * Note: we signal even when increasing dp_dirty_total.
 443          * This ensures forward progress -- each thread wakes the next waiter.
 444          */
 445         if (dp->dp_dirty_total <= zfs_dirty_data_max)
 446                 cv_signal(&dp->dp_spaceavail_cv);
 447 }
 448 
 449 void
 450 dsl_pool_sync(dsl_pool_t *dp, uint64_t txg)
 451 {
 452         zio_t *zio;
 453         dmu_tx_t *tx;
 454         dsl_dir_t *dd;
 455         dsl_dataset_t *ds;
 456         objset_t *mos = dp->dp_meta_objset;
 457         list_t synced_datasets;
 458 
 459         list_create(&synced_datasets, sizeof (dsl_dataset_t),
 460             offsetof(dsl_dataset_t, ds_synced_link));
 461 
 462         tx = dmu_tx_create_assigned(dp, txg);
 463 
 464         /*
 465          * Write out all dirty blocks of dirty datasets.
 466          */
 467         zio = zio_root(dp->dp_spa, NULL, NULL, ZIO_FLAG_MUSTSUCCEED);
 468         while ((ds = txg_list_remove(&dp->dp_dirty_datasets, txg)) != NULL) {
 469                 /*
 470                  * We must not sync any non-MOS datasets twice, because
 471                  * we may have taken a snapshot of them.  However, we
 472                  * may sync newly-created datasets on pass 2.
 473                  */
 474                 ASSERT(!list_link_active(&ds->ds_synced_link));
 475                 list_insert_tail(&synced_datasets, ds);
 476                 dsl_dataset_sync(ds, zio, tx);
 477         }
 478         VERIFY0(zio_wait(zio));
 479 
 480         /*
 481          * We have written all of the accounted dirty data, so our
 482          * dp_space_towrite should now be zero.  However, some seldom-used
 483          * code paths do not adhere to this (e.g. dbuf_undirty(), also
 484          * rounding error in dbuf_write_physdone).
 485          * Shore up the accounting of any dirtied space now.
 486          */
 487         dsl_pool_undirty_space(dp, dp->dp_dirty_pertxg[txg & TXG_MASK], txg);
 488 
 489         /*
 490          * After the data blocks have been written (ensured by the zio_wait()
 491          * above), update the user/group space accounting.
 492          */
 493         for (ds = list_head(&synced_datasets); ds != NULL;
 494             ds = list_next(&synced_datasets, ds)) {
 495                 dmu_objset_do_userquota_updates(ds->ds_objset, tx);
 496         }
 497 
 498         /*
 499          * Sync the datasets again to push out the changes due to
 500          * userspace updates.  This must be done before we process the
 501          * sync tasks, so that any snapshots will have the correct
 502          * user accounting information (and we won't get confused
 503          * about which blocks are part of the snapshot).
 504          */
 505         zio = zio_root(dp->dp_spa, NULL, NULL, ZIO_FLAG_MUSTSUCCEED);
 506         while ((ds = txg_list_remove(&dp->dp_dirty_datasets, txg)) != NULL) {
 507                 ASSERT(list_link_active(&ds->ds_synced_link));
 508                 dmu_buf_rele(ds->ds_dbuf, ds);
 509                 dsl_dataset_sync(ds, zio, tx);
 510         }
 511         VERIFY0(zio_wait(zio));
 512 
 513         /*
 514          * Now that the datasets have been completely synced, we can
 515          * clean up our in-memory structures accumulated while syncing:
 516          *
 517          *  - move dead blocks from the pending deadlist to the on-disk deadlist
 518          *  - release hold from dsl_dataset_dirty()
 519          */
 520         while ((ds = list_remove_head(&synced_datasets)) != NULL) {
 521                 objset_t *os = ds->ds_objset;
 522                 bplist_iterate(&ds->ds_pending_deadlist,
 523                     deadlist_enqueue_cb, &ds->ds_deadlist, tx);
 524                 ASSERT(!dmu_objset_is_dirty(os, txg));
 525                 dmu_buf_rele(ds->ds_dbuf, ds);
 526         }
 527         while ((dd = txg_list_remove(&dp->dp_dirty_dirs, txg)) != NULL) {
 528                 dsl_dir_sync(dd, tx);
 529         }
 530 
 531         /*
 532          * The MOS's space is accounted for in the pool/$MOS
 533          * (dp_mos_dir).  We can't modify the mos while we're syncing
 534          * it, so we remember the deltas and apply them here.
 535          */
 536         if (dp->dp_mos_used_delta != 0 || dp->dp_mos_compressed_delta != 0 ||
 537             dp->dp_mos_uncompressed_delta != 0) {
 538                 dsl_dir_diduse_space(dp->dp_mos_dir, DD_USED_HEAD,
 539                     dp->dp_mos_used_delta,
 540                     dp->dp_mos_compressed_delta,
 541                     dp->dp_mos_uncompressed_delta, tx);
 542                 dp->dp_mos_used_delta = 0;
 543                 dp->dp_mos_compressed_delta = 0;
 544                 dp->dp_mos_uncompressed_delta = 0;
 545         }
 546 
 547         if (list_head(&mos->os_dirty_dnodes[txg & TXG_MASK]) != NULL ||
 548             list_head(&mos->os_free_dnodes[txg & TXG_MASK]) != NULL) {
 549                 dsl_pool_sync_mos(dp, tx);
 550         }
 551 
 552         /*
 553          * If we modify a dataset in the same txg that we want to destroy it,
 554          * its dsl_dir's dd_dbuf will be dirty, and thus have a hold on it.
 555          * dsl_dir_destroy_check() will fail if there are unexpected holds.
 556          * Therefore, we want to sync the MOS (thus syncing the dd_dbuf
 557          * and clearing the hold on it) before we process the sync_tasks.
 558          * The MOS data dirtied by the sync_tasks will be synced on the next
 559          * pass.
 560          */
 561         if (!txg_list_empty(&dp->dp_sync_tasks, txg)) {
 562                 dsl_sync_task_t *dst;
 563                 /*
 564                  * No more sync tasks should have been added while we
 565                  * were syncing.
 566                  */
 567                 ASSERT3U(spa_sync_pass(dp->dp_spa), ==, 1);
 568                 while ((dst = txg_list_remove(&dp->dp_sync_tasks, txg)) != NULL)
 569                         dsl_sync_task_sync(dst, tx);
 570         }
 571 
 572         dmu_tx_commit(tx);
 573 
 574         DTRACE_PROBE2(dsl_pool_sync__done, dsl_pool_t *dp, dp, uint64_t, txg);
 575 }
 576 
 577 void
 578 dsl_pool_sync_done(dsl_pool_t *dp, uint64_t txg)
 579 {
 580         zilog_t *zilog;
 581 
 582         while (zilog = txg_list_remove(&dp->dp_dirty_zilogs, txg)) {
 583                 dsl_dataset_t *ds = dmu_objset_ds(zilog->zl_os);
 584                 zil_clean(zilog, txg);
 585                 ASSERT(!dmu_objset_is_dirty(zilog->zl_os, txg));
 586                 dmu_buf_rele(ds->ds_dbuf, zilog);
 587         }
 588         ASSERT(!dmu_objset_is_dirty(dp->dp_meta_objset, txg));
 589 }
 590 
 591 /*
 592  * TRUE if the current thread is the tx_sync_thread or if we
 593  * are being called from SPA context during pool initialization.
 594  */
 595 int
 596 dsl_pool_sync_context(dsl_pool_t *dp)
 597 {
 598         return (curthread == dp->dp_tx.tx_sync_thread ||
 599             spa_is_initializing(dp->dp_spa));
 600 }
 601 
 602 uint64_t
 603 dsl_pool_adjustedsize(dsl_pool_t *dp, boolean_t netfree)
 604 {
 605         uint64_t space, resv;
 606 
 607         /*
 608          * Reserve about 1.6% (1/64), or at least 32MB, for allocation
 609          * efficiency.
 610          * XXX The intent log is not accounted for, so it must fit
 611          * within this slop.
 612          *
 613          * If we're trying to assess whether it's OK to do a free,
 614          * cut the reservation in half to allow forward progress
 615          * (e.g. make it possible to rm(1) files from a full pool).
 616          */
 617         space = spa_get_dspace(dp->dp_spa);
 618         resv = MAX(space >> 6, SPA_MINDEVSIZE >> 1);
 619         if (netfree)
 620                 resv >>= 1;
 621 
 622         return (space - resv);
 623 }
 624 
 625 boolean_t
 626 dsl_pool_need_dirty_delay(dsl_pool_t *dp)
 627 {
 628         uint64_t delay_min_bytes =
 629             zfs_dirty_data_max * zfs_delay_min_dirty_percent / 100;
 630         boolean_t rv;
 631 
 632         mutex_enter(&dp->dp_lock);
 633         if (dp->dp_dirty_total > zfs_dirty_data_sync)
 634                 txg_kick(dp);
 635         rv = (dp->dp_dirty_total > delay_min_bytes);
 636         mutex_exit(&dp->dp_lock);
 637         return (rv);
 638 }
 639 
 640 void
 641 dsl_pool_dirty_space(dsl_pool_t *dp, int64_t space, dmu_tx_t *tx)
 642 {
 643         if (space > 0) {
 644                 mutex_enter(&dp->dp_lock);
 645                 dp->dp_dirty_pertxg[tx->tx_txg & TXG_MASK] += space;
 646                 dsl_pool_dirty_delta(dp, space);
 647                 mutex_exit(&dp->dp_lock);
 648         }
 649 }
 650 
 651 void
 652 dsl_pool_undirty_space(dsl_pool_t *dp, int64_t space, uint64_t txg) {
 653         ASSERT3S(space, >=, 0);
 654         if (space == 0)
 655                 return;
 656         mutex_enter(&dp->dp_lock);
 657         if (dp->dp_dirty_pertxg[txg & TXG_MASK] < space) {
 658                 /* XXX writing something we didn't dirty? */
 659                 space = dp->dp_dirty_pertxg[txg & TXG_MASK];
 660         }
 661         ASSERT3U(dp->dp_dirty_pertxg[txg & TXG_MASK], >=, space);
 662         dp->dp_dirty_pertxg[txg & TXG_MASK] -= space;
 663         ASSERT3U(dp->dp_dirty_total, >=, space);
 664         dsl_pool_dirty_delta(dp, -space);
 665         mutex_exit(&dp->dp_lock);
 666 }
 667 
 668 /* ARGSUSED */
 669 static int
 670 upgrade_clones_cb(dsl_pool_t *dp, dsl_dataset_t *hds, void *arg)
 671 {
 672         dmu_tx_t *tx = arg;
 673         dsl_dataset_t *ds, *prev = NULL;
 674         int err;
 675 
 676         err = dsl_dataset_hold_obj(dp, hds->ds_object, FTAG, &ds);
 677         if (err)
 678                 return (err);
 679 
 680         while (ds->ds_phys->ds_prev_snap_obj != 0) {
 681                 err = dsl_dataset_hold_obj(dp, ds->ds_phys->ds_prev_snap_obj,
 682                     FTAG, &prev);
 683                 if (err) {
 684                         dsl_dataset_rele(ds, FTAG);
 685                         return (err);
 686                 }
 687 
 688                 if (prev->ds_phys->ds_next_snap_obj != ds->ds_object)
 689                         break;
 690                 dsl_dataset_rele(ds, FTAG);
 691                 ds = prev;
 692                 prev = NULL;
 693         }
 694 
 695         if (prev == NULL) {
 696                 prev = dp->dp_origin_snap;
 697 
 698                 /*
 699                  * The $ORIGIN can't have any data, or the accounting
 700                  * will be wrong.
 701                  */
 702                 ASSERT0(prev->ds_phys->ds_bp.blk_birth);
 703 
 704                 /* The origin doesn't get attached to itself */
 705                 if (ds->ds_object == prev->ds_object) {
 706                         dsl_dataset_rele(ds, FTAG);
 707                         return (0);
 708                 }
 709 
 710                 dmu_buf_will_dirty(ds->ds_dbuf, tx);
 711                 ds->ds_phys->ds_prev_snap_obj = prev->ds_object;
 712                 ds->ds_phys->ds_prev_snap_txg = prev->ds_phys->ds_creation_txg;
 713 
 714                 dmu_buf_will_dirty(ds->ds_dir->dd_dbuf, tx);
 715                 ds->ds_dir->dd_phys->dd_origin_obj = prev->ds_object;
 716 
 717                 dmu_buf_will_dirty(prev->ds_dbuf, tx);
 718                 prev->ds_phys->ds_num_children++;
 719 
 720                 if (ds->ds_phys->ds_next_snap_obj == 0) {
 721                         ASSERT(ds->ds_prev == NULL);
 722                         VERIFY0(dsl_dataset_hold_obj(dp,
 723                             ds->ds_phys->ds_prev_snap_obj, ds, &ds->ds_prev));
 724                 }
 725         }
 726 
 727         ASSERT3U(ds->ds_dir->dd_phys->dd_origin_obj, ==, prev->ds_object);
 728         ASSERT3U(ds->ds_phys->ds_prev_snap_obj, ==, prev->ds_object);
 729 
 730         if (prev->ds_phys->ds_next_clones_obj == 0) {
 731                 dmu_buf_will_dirty(prev->ds_dbuf, tx);
 732                 prev->ds_phys->ds_next_clones_obj =
 733                     zap_create(dp->dp_meta_objset,
 734                     DMU_OT_NEXT_CLONES, DMU_OT_NONE, 0, tx);
 735         }
 736         VERIFY0(zap_add_int(dp->dp_meta_objset,
 737             prev->ds_phys->ds_next_clones_obj, ds->ds_object, tx));
 738 
 739         dsl_dataset_rele(ds, FTAG);
 740         if (prev != dp->dp_origin_snap)
 741                 dsl_dataset_rele(prev, FTAG);
 742         return (0);
 743 }
 744 
 745 void
 746 dsl_pool_upgrade_clones(dsl_pool_t *dp, dmu_tx_t *tx)
 747 {
 748         ASSERT(dmu_tx_is_syncing(tx));
 749         ASSERT(dp->dp_origin_snap != NULL);
 750 
 751         VERIFY0(dmu_objset_find_dp(dp, dp->dp_root_dir_obj, upgrade_clones_cb,
 752             tx, DS_FIND_CHILDREN));
 753 }
 754 
 755 /* ARGSUSED */
 756 static int
 757 upgrade_dir_clones_cb(dsl_pool_t *dp, dsl_dataset_t *ds, void *arg)
 758 {
 759         dmu_tx_t *tx = arg;
 760         objset_t *mos = dp->dp_meta_objset;
 761 
 762         if (ds->ds_dir->dd_phys->dd_origin_obj != 0) {
 763                 dsl_dataset_t *origin;
 764 
 765                 VERIFY0(dsl_dataset_hold_obj(dp,
 766                     ds->ds_dir->dd_phys->dd_origin_obj, FTAG, &origin));
 767 
 768                 if (origin->ds_dir->dd_phys->dd_clones == 0) {
 769                         dmu_buf_will_dirty(origin->ds_dir->dd_dbuf, tx);
 770                         origin->ds_dir->dd_phys->dd_clones = zap_create(mos,
 771                             DMU_OT_DSL_CLONES, DMU_OT_NONE, 0, tx);
 772                 }
 773 
 774                 VERIFY0(zap_add_int(dp->dp_meta_objset,
 775                     origin->ds_dir->dd_phys->dd_clones, ds->ds_object, tx));
 776 
 777                 dsl_dataset_rele(origin, FTAG);
 778         }
 779         return (0);
 780 }
 781 
 782 void
 783 dsl_pool_upgrade_dir_clones(dsl_pool_t *dp, dmu_tx_t *tx)
 784 {
 785         ASSERT(dmu_tx_is_syncing(tx));
 786         uint64_t obj;
 787 
 788         (void) dsl_dir_create_sync(dp, dp->dp_root_dir, FREE_DIR_NAME, tx);
 789         VERIFY0(dsl_pool_open_special_dir(dp,
 790             FREE_DIR_NAME, &dp->dp_free_dir));
 791 
 792         /*
 793          * We can't use bpobj_alloc(), because spa_version() still
 794          * returns the old version, and we need a new-version bpobj with
 795          * subobj support.  So call dmu_object_alloc() directly.
 796          */
 797         obj = dmu_object_alloc(dp->dp_meta_objset, DMU_OT_BPOBJ,
 798             SPA_MAXBLOCKSIZE, DMU_OT_BPOBJ_HDR, sizeof (bpobj_phys_t), tx);
 799         VERIFY0(zap_add(dp->dp_meta_objset, DMU_POOL_DIRECTORY_OBJECT,
 800             DMU_POOL_FREE_BPOBJ, sizeof (uint64_t), 1, &obj, tx));
 801         VERIFY0(bpobj_open(&dp->dp_free_bpobj, dp->dp_meta_objset, obj));
 802 
 803         VERIFY0(dmu_objset_find_dp(dp, dp->dp_root_dir_obj,
 804             upgrade_dir_clones_cb, tx, DS_FIND_CHILDREN));
 805 }
 806 
 807 void
 808 dsl_pool_create_origin(dsl_pool_t *dp, dmu_tx_t *tx)
 809 {
 810         uint64_t dsobj;
 811         dsl_dataset_t *ds;
 812 
 813         ASSERT(dmu_tx_is_syncing(tx));
 814         ASSERT(dp->dp_origin_snap == NULL);
 815         ASSERT(rrw_held(&dp->dp_config_rwlock, RW_WRITER));
 816 
 817         /* create the origin dir, ds, & snap-ds */
 818         dsobj = dsl_dataset_create_sync(dp->dp_root_dir, ORIGIN_DIR_NAME,
 819             NULL, 0, kcred, tx);
 820         VERIFY0(dsl_dataset_hold_obj(dp, dsobj, FTAG, &ds));
 821         dsl_dataset_snapshot_sync_impl(ds, ORIGIN_DIR_NAME, tx);
 822         VERIFY0(dsl_dataset_hold_obj(dp, ds->ds_phys->ds_prev_snap_obj,
 823             dp, &dp->dp_origin_snap));
 824         dsl_dataset_rele(ds, FTAG);
 825 }
 826 
 827 taskq_t *
 828 dsl_pool_vnrele_taskq(dsl_pool_t *dp)
 829 {
 830         return (dp->dp_vnrele_taskq);
 831 }
 832 
 833 /*
 834  * Walk through the pool-wide zap object of temporary snapshot user holds
 835  * and release them.
 836  */
 837 void
 838 dsl_pool_clean_tmp_userrefs(dsl_pool_t *dp)
 839 {
 840         zap_attribute_t za;
 841         zap_cursor_t zc;
 842         objset_t *mos = dp->dp_meta_objset;
 843         uint64_t zapobj = dp->dp_tmp_userrefs_obj;
 844         nvlist_t *holds;
 845 
 846         if (zapobj == 0)
 847                 return;
 848         ASSERT(spa_version(dp->dp_spa) >= SPA_VERSION_USERREFS);
 849 
 850         holds = fnvlist_alloc();
 851 
 852         for (zap_cursor_init(&zc, mos, zapobj);
 853             zap_cursor_retrieve(&zc, &za) == 0;
 854             zap_cursor_advance(&zc)) {
 855                 char *htag;
 856                 nvlist_t *tags;
 857 
 858                 htag = strchr(za.za_name, '-');
 859                 *htag = '\0';
 860                 ++htag;
 861                 if (nvlist_lookup_nvlist(holds, za.za_name, &tags) != 0) {
 862                         tags = fnvlist_alloc();
 863                         fnvlist_add_boolean(tags, htag);
 864                         fnvlist_add_nvlist(holds, za.za_name, tags);
 865                         fnvlist_free(tags);
 866                 } else {
 867                         fnvlist_add_boolean(tags, htag);
 868                 }
 869         }
 870         dsl_dataset_user_release_tmp(dp, holds);
 871         fnvlist_free(holds);
 872         zap_cursor_fini(&zc);
 873 }
 874 
 875 /*
 876  * Create the pool-wide zap object for storing temporary snapshot holds.
 877  */
 878 void
 879 dsl_pool_user_hold_create_obj(dsl_pool_t *dp, dmu_tx_t *tx)
 880 {
 881         objset_t *mos = dp->dp_meta_objset;
 882 
 883         ASSERT(dp->dp_tmp_userrefs_obj == 0);
 884         ASSERT(dmu_tx_is_syncing(tx));
 885 
 886         dp->dp_tmp_userrefs_obj = zap_create_link(mos, DMU_OT_USERREFS,
 887             DMU_POOL_DIRECTORY_OBJECT, DMU_POOL_TMP_USERREFS, tx);
 888 }
 889 
 890 static int
 891 dsl_pool_user_hold_rele_impl(dsl_pool_t *dp, uint64_t dsobj,
 892     const char *tag, uint64_t now, dmu_tx_t *tx, boolean_t holding)
 893 {
 894         objset_t *mos = dp->dp_meta_objset;
 895         uint64_t zapobj = dp->dp_tmp_userrefs_obj;
 896         char *name;
 897         int error;
 898 
 899         ASSERT(spa_version(dp->dp_spa) >= SPA_VERSION_USERREFS);
 900         ASSERT(dmu_tx_is_syncing(tx));
 901 
 902         /*
 903          * If the pool was created prior to SPA_VERSION_USERREFS, the
 904          * zap object for temporary holds might not exist yet.
 905          */
 906         if (zapobj == 0) {
 907                 if (holding) {
 908                         dsl_pool_user_hold_create_obj(dp, tx);
 909                         zapobj = dp->dp_tmp_userrefs_obj;
 910                 } else {
 911                         return (SET_ERROR(ENOENT));
 912                 }
 913         }
 914 
 915         name = kmem_asprintf("%llx-%s", (u_longlong_t)dsobj, tag);
 916         if (holding)
 917                 error = zap_add(mos, zapobj, name, 8, 1, &now, tx);
 918         else
 919                 error = zap_remove(mos, zapobj, name, tx);
 920         strfree(name);
 921 
 922         return (error);
 923 }
 924 
 925 /*
 926  * Add a temporary hold for the given dataset object and tag.
 927  */
 928 int
 929 dsl_pool_user_hold(dsl_pool_t *dp, uint64_t dsobj, const char *tag,
 930     uint64_t now, dmu_tx_t *tx)
 931 {
 932         return (dsl_pool_user_hold_rele_impl(dp, dsobj, tag, now, tx, B_TRUE));
 933 }
 934 
 935 /*
 936  * Release a temporary hold for the given dataset object and tag.
 937  */
 938 int
 939 dsl_pool_user_release(dsl_pool_t *dp, uint64_t dsobj, const char *tag,
 940     dmu_tx_t *tx)
 941 {
 942         return (dsl_pool_user_hold_rele_impl(dp, dsobj, tag, NULL,
 943             tx, B_FALSE));
 944 }
 945 
 946 /*
 947  * DSL Pool Configuration Lock
 948  *
 949  * The dp_config_rwlock protects against changes to DSL state (e.g. dataset
 950  * creation / destruction / rename / property setting).  It must be held for
 951  * read to hold a dataset or dsl_dir.  I.e. you must call
 952  * dsl_pool_config_enter() or dsl_pool_hold() before calling
 953  * dsl_{dataset,dir}_hold{_obj}.  In most circumstances, the dp_config_rwlock
 954  * must be held continuously until all datasets and dsl_dirs are released.
 955  *
 956  * The only exception to this rule is that if a "long hold" is placed on
 957  * a dataset, then the dp_config_rwlock may be dropped while the dataset
 958  * is still held.  The long hold will prevent the dataset from being
 959  * destroyed -- the destroy will fail with EBUSY.  A long hold can be
 960  * obtained by calling dsl_dataset_long_hold(), or by "owning" a dataset
 961  * (by calling dsl_{dataset,objset}_{try}own{_obj}).
 962  *
 963  * Legitimate long-holders (including owners) should be long-running, cancelable
 964  * tasks that should cause "zfs destroy" to fail.  This includes DMU
 965  * consumers (i.e. a ZPL filesystem being mounted or ZVOL being open),
 966  * "zfs send", and "zfs diff".  There are several other long-holders whose
 967  * uses are suboptimal (e.g. "zfs promote", and zil_suspend()).
 968  *
 969  * The usual formula for long-holding would be:
 970  * dsl_pool_hold()
 971  * dsl_dataset_hold()
 972  * ... perform checks ...
 973  * dsl_dataset_long_hold()
 974  * dsl_pool_rele()
 975  * ... perform long-running task ...
 976  * dsl_dataset_long_rele()
 977  * dsl_dataset_rele()
 978  *
 979  * Note that when the long hold is released, the dataset is still held but
 980  * the pool is not held.  The dataset may change arbitrarily during this time
 981  * (e.g. it could be destroyed).  Therefore you shouldn't do anything to the
 982  * dataset except release it.
 983  *
 984  * User-initiated operations (e.g. ioctls, zfs_ioc_*()) are either read-only
 985  * or modifying operations.
 986  *
 987  * Modifying operations should generally use dsl_sync_task().  The synctask
 988  * infrastructure enforces proper locking strategy with respect to the
 989  * dp_config_rwlock.  See the comment above dsl_sync_task() for details.
 990  *
 991  * Read-only operations will manually hold the pool, then the dataset, obtain
 992  * information from the dataset, then release the pool and dataset.
 993  * dmu_objset_{hold,rele}() are convenience routines that also do the pool
 994  * hold/rele.
 995  */
 996 
 997 int
 998 dsl_pool_hold(const char *name, void *tag, dsl_pool_t **dp)
 999 {
1000         spa_t *spa;
1001         int error;
1002 
1003         error = spa_open(name, &spa, tag);
1004         if (error == 0) {
1005                 *dp = spa_get_dsl(spa);
1006                 dsl_pool_config_enter(*dp, tag);
1007         }
1008         return (error);
1009 }
1010 
1011 void
1012 dsl_pool_rele(dsl_pool_t *dp, void *tag)
1013 {
1014         dsl_pool_config_exit(dp, tag);
1015         spa_close(dp->dp_spa, tag);
1016 }
1017 
1018 void
1019 dsl_pool_config_enter(dsl_pool_t *dp, void *tag)
1020 {
1021         /*
1022          * We use a "reentrant" reader-writer lock, but not reentrantly.
1023          *
1024          * The rrwlock can (with the track_all flag) track all reading threads,
1025          * which is very useful for debugging which code path failed to release
1026          * the lock, and for verifying that the *current* thread does hold
1027          * the lock.
1028          *
1029          * (Unlike a rwlock, which knows that N threads hold it for
1030          * read, but not *which* threads, so rw_held(RW_READER) returns TRUE
1031          * if any thread holds it for read, even if this thread doesn't).
1032          */
1033         ASSERT(!rrw_held(&dp->dp_config_rwlock, RW_READER));
1034         rrw_enter(&dp->dp_config_rwlock, RW_READER, tag);
1035 }
1036 
1037 void
1038 dsl_pool_config_exit(dsl_pool_t *dp, void *tag)
1039 {
1040         rrw_exit(&dp->dp_config_rwlock, tag);
1041 }
1042 
1043 boolean_t
1044 dsl_pool_config_held(dsl_pool_t *dp)
1045 {
1046         return (RRW_LOCK_HELD(&dp->dp_config_rwlock));
1047 }