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         /*
 254          * Note: errors ignored, because the leak dir will not exist if we
 255          * have not encountered a leak yet.
 256          */
 257         (void) dsl_pool_open_special_dir(dp, LEAK_DIR_NAME,
 258             &dp->dp_leak_dir);
 259 
 260         if (spa_feature_is_active(dp->dp_spa, SPA_FEATURE_ASYNC_DESTROY)) {
 261                 err = zap_lookup(dp->dp_meta_objset, DMU_POOL_DIRECTORY_OBJECT,
 262                     DMU_POOL_BPTREE_OBJ, sizeof (uint64_t), 1,
 263                     &dp->dp_bptree_obj);
 264                 if (err != 0)
 265                         goto out;
 266         }
 267 
 268         if (spa_feature_is_active(dp->dp_spa, SPA_FEATURE_EMPTY_BPOBJ)) {
 269                 err = zap_lookup(dp->dp_meta_objset, DMU_POOL_DIRECTORY_OBJECT,
 270                     DMU_POOL_EMPTY_BPOBJ, sizeof (uint64_t), 1,
 271                     &dp->dp_empty_bpobj);
 272                 if (err != 0)
 273                         goto out;
 274         }
 275 
 276         err = zap_lookup(dp->dp_meta_objset, DMU_POOL_DIRECTORY_OBJECT,
 277             DMU_POOL_TMP_USERREFS, sizeof (uint64_t), 1,
 278             &dp->dp_tmp_userrefs_obj);
 279         if (err == ENOENT)
 280                 err = 0;
 281         if (err)
 282                 goto out;
 283 
 284         err = dsl_scan_init(dp, dp->dp_tx.tx_open_txg);
 285 
 286 out:
 287         rrw_exit(&dp->dp_config_rwlock, FTAG);
 288         return (err);
 289 }
 290 
 291 void
 292 dsl_pool_close(dsl_pool_t *dp)
 293 {
 294         /*
 295          * Drop our references from dsl_pool_open().
 296          *
 297          * Since we held the origin_snap from "syncing" context (which
 298          * includes pool-opening context), it actually only got a "ref"
 299          * and not a hold, so just drop that here.
 300          */
 301         if (dp->dp_origin_snap)
 302                 dsl_dataset_rele(dp->dp_origin_snap, dp);
 303         if (dp->dp_mos_dir)
 304                 dsl_dir_rele(dp->dp_mos_dir, dp);
 305         if (dp->dp_free_dir)
 306                 dsl_dir_rele(dp->dp_free_dir, dp);
 307         if (dp->dp_leak_dir)
 308                 dsl_dir_rele(dp->dp_leak_dir, dp);
 309         if (dp->dp_root_dir)
 310                 dsl_dir_rele(dp->dp_root_dir, dp);
 311 
 312         bpobj_close(&dp->dp_free_bpobj);
 313 
 314         /* undo the dmu_objset_open_impl(mos) from dsl_pool_open() */
 315         if (dp->dp_meta_objset)
 316                 dmu_objset_evict(dp->dp_meta_objset);
 317 
 318         txg_list_destroy(&dp->dp_dirty_datasets);
 319         txg_list_destroy(&dp->dp_dirty_zilogs);
 320         txg_list_destroy(&dp->dp_sync_tasks);
 321         txg_list_destroy(&dp->dp_dirty_dirs);
 322 
 323         arc_flush(dp->dp_spa);
 324         txg_fini(dp);
 325         dsl_scan_fini(dp);
 326         rrw_destroy(&dp->dp_config_rwlock);
 327         mutex_destroy(&dp->dp_lock);
 328         taskq_destroy(dp->dp_vnrele_taskq);
 329         if (dp->dp_blkstats)
 330                 kmem_free(dp->dp_blkstats, sizeof (zfs_all_blkstats_t));
 331         kmem_free(dp, sizeof (dsl_pool_t));
 332 }
 333 
 334 dsl_pool_t *
 335 dsl_pool_create(spa_t *spa, nvlist_t *zplprops, uint64_t txg)
 336 {
 337         int err;
 338         dsl_pool_t *dp = dsl_pool_open_impl(spa, txg);
 339         dmu_tx_t *tx = dmu_tx_create_assigned(dp, txg);
 340         objset_t *os;
 341         dsl_dataset_t *ds;
 342         uint64_t obj;
 343 
 344         rrw_enter(&dp->dp_config_rwlock, RW_WRITER, FTAG);
 345 
 346         /* create and open the MOS (meta-objset) */
 347         dp->dp_meta_objset = dmu_objset_create_impl(spa,
 348             NULL, &dp->dp_meta_rootbp, DMU_OST_META, tx);
 349 
 350         /* create the pool directory */
 351         err = zap_create_claim(dp->dp_meta_objset, DMU_POOL_DIRECTORY_OBJECT,
 352             DMU_OT_OBJECT_DIRECTORY, DMU_OT_NONE, 0, tx);
 353         ASSERT0(err);
 354 
 355         /* Initialize scan structures */
 356         VERIFY0(dsl_scan_init(dp, txg));
 357 
 358         /* create and open the root dir */
 359         dp->dp_root_dir_obj = dsl_dir_create_sync(dp, NULL, NULL, tx);
 360         VERIFY0(dsl_dir_hold_obj(dp, dp->dp_root_dir_obj,
 361             NULL, dp, &dp->dp_root_dir));
 362 
 363         /* create and open the meta-objset dir */
 364         (void) dsl_dir_create_sync(dp, dp->dp_root_dir, MOS_DIR_NAME, tx);
 365         VERIFY0(dsl_pool_open_special_dir(dp,
 366             MOS_DIR_NAME, &dp->dp_mos_dir));
 367 
 368         if (spa_version(spa) >= SPA_VERSION_DEADLISTS) {
 369                 /* create and open the free dir */
 370                 (void) dsl_dir_create_sync(dp, dp->dp_root_dir,
 371                     FREE_DIR_NAME, tx);
 372                 VERIFY0(dsl_pool_open_special_dir(dp,
 373                     FREE_DIR_NAME, &dp->dp_free_dir));
 374 
 375                 /* create and open the free_bplist */
 376                 obj = bpobj_alloc(dp->dp_meta_objset, SPA_MAXBLOCKSIZE, tx);
 377                 VERIFY(zap_add(dp->dp_meta_objset, DMU_POOL_DIRECTORY_OBJECT,
 378                     DMU_POOL_FREE_BPOBJ, sizeof (uint64_t), 1, &obj, tx) == 0);
 379                 VERIFY0(bpobj_open(&dp->dp_free_bpobj,
 380                     dp->dp_meta_objset, obj));
 381         }
 382 
 383         if (spa_version(spa) >= SPA_VERSION_DSL_SCRUB)
 384                 dsl_pool_create_origin(dp, tx);
 385 
 386         /* create the root dataset */
 387         obj = dsl_dataset_create_sync_dd(dp->dp_root_dir, NULL, 0, tx);
 388 
 389         /* create the root objset */
 390         VERIFY0(dsl_dataset_hold_obj(dp, obj, FTAG, &ds));
 391         os = dmu_objset_create_impl(dp->dp_spa, ds,
 392             dsl_dataset_get_blkptr(ds), DMU_OST_ZFS, tx);
 393 #ifdef _KERNEL
 394         zfs_create_fs(os, kcred, zplprops, tx);
 395 #endif
 396         dsl_dataset_rele(ds, FTAG);
 397 
 398         dmu_tx_commit(tx);
 399 
 400         rrw_exit(&dp->dp_config_rwlock, FTAG);
 401 
 402         return (dp);
 403 }
 404 
 405 /*
 406  * Account for the meta-objset space in its placeholder dsl_dir.
 407  */
 408 void
 409 dsl_pool_mos_diduse_space(dsl_pool_t *dp,
 410     int64_t used, int64_t comp, int64_t uncomp)
 411 {
 412         ASSERT3U(comp, ==, uncomp); /* it's all metadata */
 413         mutex_enter(&dp->dp_lock);
 414         dp->dp_mos_used_delta += used;
 415         dp->dp_mos_compressed_delta += comp;
 416         dp->dp_mos_uncompressed_delta += uncomp;
 417         mutex_exit(&dp->dp_lock);
 418 }
 419 
 420 static int
 421 deadlist_enqueue_cb(void *arg, const blkptr_t *bp, dmu_tx_t *tx)
 422 {
 423         dsl_deadlist_t *dl = arg;
 424         dsl_deadlist_insert(dl, bp, tx);
 425         return (0);
 426 }
 427 
 428 static void
 429 dsl_pool_sync_mos(dsl_pool_t *dp, dmu_tx_t *tx)
 430 {
 431         zio_t *zio = zio_root(dp->dp_spa, NULL, NULL, ZIO_FLAG_MUSTSUCCEED);
 432         dmu_objset_sync(dp->dp_meta_objset, zio, tx);
 433         VERIFY0(zio_wait(zio));
 434         dprintf_bp(&dp->dp_meta_rootbp, "meta objset rootbp is %s", "");
 435         spa_set_rootblkptr(dp->dp_spa, &dp->dp_meta_rootbp);
 436 }
 437 
 438 static void
 439 dsl_pool_dirty_delta(dsl_pool_t *dp, int64_t delta)
 440 {
 441         ASSERT(MUTEX_HELD(&dp->dp_lock));
 442 
 443         if (delta < 0)
 444                 ASSERT3U(-delta, <=, dp->dp_dirty_total);
 445 
 446         dp->dp_dirty_total += delta;
 447 
 448         /*
 449          * Note: we signal even when increasing dp_dirty_total.
 450          * This ensures forward progress -- each thread wakes the next waiter.
 451          */
 452         if (dp->dp_dirty_total <= zfs_dirty_data_max)
 453                 cv_signal(&dp->dp_spaceavail_cv);
 454 }
 455 
 456 void
 457 dsl_pool_sync(dsl_pool_t *dp, uint64_t txg)
 458 {
 459         zio_t *zio;
 460         dmu_tx_t *tx;
 461         dsl_dir_t *dd;
 462         dsl_dataset_t *ds;
 463         objset_t *mos = dp->dp_meta_objset;
 464         list_t synced_datasets;
 465 
 466         list_create(&synced_datasets, sizeof (dsl_dataset_t),
 467             offsetof(dsl_dataset_t, ds_synced_link));
 468 
 469         tx = dmu_tx_create_assigned(dp, txg);
 470 
 471         /*
 472          * Write out all dirty blocks of dirty datasets.
 473          */
 474         zio = zio_root(dp->dp_spa, NULL, NULL, ZIO_FLAG_MUSTSUCCEED);
 475         while ((ds = txg_list_remove(&dp->dp_dirty_datasets, txg)) != NULL) {
 476                 /*
 477                  * We must not sync any non-MOS datasets twice, because
 478                  * we may have taken a snapshot of them.  However, we
 479                  * may sync newly-created datasets on pass 2.
 480                  */
 481                 ASSERT(!list_link_active(&ds->ds_synced_link));
 482                 list_insert_tail(&synced_datasets, ds);
 483                 dsl_dataset_sync(ds, zio, tx);
 484         }
 485         VERIFY0(zio_wait(zio));
 486 
 487         /*
 488          * We have written all of the accounted dirty data, so our
 489          * dp_space_towrite should now be zero.  However, some seldom-used
 490          * code paths do not adhere to this (e.g. dbuf_undirty(), also
 491          * rounding error in dbuf_write_physdone).
 492          * Shore up the accounting of any dirtied space now.
 493          */
 494         dsl_pool_undirty_space(dp, dp->dp_dirty_pertxg[txg & TXG_MASK], txg);
 495 
 496         /*
 497          * After the data blocks have been written (ensured by the zio_wait()
 498          * above), update the user/group space accounting.
 499          */
 500         for (ds = list_head(&synced_datasets); ds != NULL;
 501             ds = list_next(&synced_datasets, ds)) {
 502                 dmu_objset_do_userquota_updates(ds->ds_objset, tx);
 503         }
 504 
 505         /*
 506          * Sync the datasets again to push out the changes due to
 507          * userspace updates.  This must be done before we process the
 508          * sync tasks, so that any snapshots will have the correct
 509          * user accounting information (and we won't get confused
 510          * about which blocks are part of the snapshot).
 511          */
 512         zio = zio_root(dp->dp_spa, NULL, NULL, ZIO_FLAG_MUSTSUCCEED);
 513         while ((ds = txg_list_remove(&dp->dp_dirty_datasets, txg)) != NULL) {
 514                 ASSERT(list_link_active(&ds->ds_synced_link));
 515                 dmu_buf_rele(ds->ds_dbuf, ds);
 516                 dsl_dataset_sync(ds, zio, tx);
 517         }
 518         VERIFY0(zio_wait(zio));
 519 
 520         /*
 521          * Now that the datasets have been completely synced, we can
 522          * clean up our in-memory structures accumulated while syncing:
 523          *
 524          *  - move dead blocks from the pending deadlist to the on-disk deadlist
 525          *  - release hold from dsl_dataset_dirty()
 526          */
 527         while ((ds = list_remove_head(&synced_datasets)) != NULL) {
 528                 objset_t *os = ds->ds_objset;
 529                 bplist_iterate(&ds->ds_pending_deadlist,
 530                     deadlist_enqueue_cb, &ds->ds_deadlist, tx);
 531                 ASSERT(!dmu_objset_is_dirty(os, txg));
 532                 dmu_buf_rele(ds->ds_dbuf, ds);
 533         }
 534         while ((dd = txg_list_remove(&dp->dp_dirty_dirs, txg)) != NULL) {
 535                 dsl_dir_sync(dd, tx);
 536         }
 537 
 538         /*
 539          * The MOS's space is accounted for in the pool/$MOS
 540          * (dp_mos_dir).  We can't modify the mos while we're syncing
 541          * it, so we remember the deltas and apply them here.
 542          */
 543         if (dp->dp_mos_used_delta != 0 || dp->dp_mos_compressed_delta != 0 ||
 544             dp->dp_mos_uncompressed_delta != 0) {
 545                 dsl_dir_diduse_space(dp->dp_mos_dir, DD_USED_HEAD,
 546                     dp->dp_mos_used_delta,
 547                     dp->dp_mos_compressed_delta,
 548                     dp->dp_mos_uncompressed_delta, tx);
 549                 dp->dp_mos_used_delta = 0;
 550                 dp->dp_mos_compressed_delta = 0;
 551                 dp->dp_mos_uncompressed_delta = 0;
 552         }
 553 
 554         if (list_head(&mos->os_dirty_dnodes[txg & TXG_MASK]) != NULL ||
 555             list_head(&mos->os_free_dnodes[txg & TXG_MASK]) != NULL) {
 556                 dsl_pool_sync_mos(dp, tx);
 557         }
 558 
 559         /*
 560          * If we modify a dataset in the same txg that we want to destroy it,
 561          * its dsl_dir's dd_dbuf will be dirty, and thus have a hold on it.
 562          * dsl_dir_destroy_check() will fail if there are unexpected holds.
 563          * Therefore, we want to sync the MOS (thus syncing the dd_dbuf
 564          * and clearing the hold on it) before we process the sync_tasks.
 565          * The MOS data dirtied by the sync_tasks will be synced on the next
 566          * pass.
 567          */
 568         if (!txg_list_empty(&dp->dp_sync_tasks, txg)) {
 569                 dsl_sync_task_t *dst;
 570                 /*
 571                  * No more sync tasks should have been added while we
 572                  * were syncing.
 573                  */
 574                 ASSERT3U(spa_sync_pass(dp->dp_spa), ==, 1);
 575                 while ((dst = txg_list_remove(&dp->dp_sync_tasks, txg)) != NULL)
 576                         dsl_sync_task_sync(dst, tx);
 577         }
 578 
 579         dmu_tx_commit(tx);
 580 
 581         DTRACE_PROBE2(dsl_pool_sync__done, dsl_pool_t *dp, dp, uint64_t, txg);
 582 }
 583 
 584 void
 585 dsl_pool_sync_done(dsl_pool_t *dp, uint64_t txg)
 586 {
 587         zilog_t *zilog;
 588 
 589         while (zilog = txg_list_remove(&dp->dp_dirty_zilogs, txg)) {
 590                 dsl_dataset_t *ds = dmu_objset_ds(zilog->zl_os);
 591                 zil_clean(zilog, txg);
 592                 ASSERT(!dmu_objset_is_dirty(zilog->zl_os, txg));
 593                 dmu_buf_rele(ds->ds_dbuf, zilog);
 594         }
 595         ASSERT(!dmu_objset_is_dirty(dp->dp_meta_objset, txg));
 596 }
 597 
 598 /*
 599  * TRUE if the current thread is the tx_sync_thread or if we
 600  * are being called from SPA context during pool initialization.
 601  */
 602 int
 603 dsl_pool_sync_context(dsl_pool_t *dp)
 604 {
 605         return (curthread == dp->dp_tx.tx_sync_thread ||
 606             spa_is_initializing(dp->dp_spa));
 607 }
 608 
 609 uint64_t
 610 dsl_pool_adjustedsize(dsl_pool_t *dp, boolean_t netfree)
 611 {
 612         uint64_t space, resv;
 613 
 614         /*
 615          * Reserve about 1.6% (1/64), or at least 32MB, for allocation
 616          * efficiency.
 617          * XXX The intent log is not accounted for, so it must fit
 618          * within this slop.
 619          *
 620          * If we're trying to assess whether it's OK to do a free,
 621          * cut the reservation in half to allow forward progress
 622          * (e.g. make it possible to rm(1) files from a full pool).
 623          */
 624         space = spa_get_dspace(dp->dp_spa);
 625         resv = MAX(space >> 6, SPA_MINDEVSIZE >> 1);
 626         if (netfree)
 627                 resv >>= 1;
 628 
 629         return (space - resv);
 630 }
 631 
 632 boolean_t
 633 dsl_pool_need_dirty_delay(dsl_pool_t *dp)
 634 {
 635         uint64_t delay_min_bytes =
 636             zfs_dirty_data_max * zfs_delay_min_dirty_percent / 100;
 637         boolean_t rv;
 638 
 639         mutex_enter(&dp->dp_lock);
 640         if (dp->dp_dirty_total > zfs_dirty_data_sync)
 641                 txg_kick(dp);
 642         rv = (dp->dp_dirty_total > delay_min_bytes);
 643         mutex_exit(&dp->dp_lock);
 644         return (rv);
 645 }
 646 
 647 void
 648 dsl_pool_dirty_space(dsl_pool_t *dp, int64_t space, dmu_tx_t *tx)
 649 {
 650         if (space > 0) {
 651                 mutex_enter(&dp->dp_lock);
 652                 dp->dp_dirty_pertxg[tx->tx_txg & TXG_MASK] += space;
 653                 dsl_pool_dirty_delta(dp, space);
 654                 mutex_exit(&dp->dp_lock);
 655         }
 656 }
 657 
 658 void
 659 dsl_pool_undirty_space(dsl_pool_t *dp, int64_t space, uint64_t txg)
 660 {
 661         ASSERT3S(space, >=, 0);
 662         if (space == 0)
 663                 return;
 664         mutex_enter(&dp->dp_lock);
 665         if (dp->dp_dirty_pertxg[txg & TXG_MASK] < space) {
 666                 /* XXX writing something we didn't dirty? */
 667                 space = dp->dp_dirty_pertxg[txg & TXG_MASK];
 668         }
 669         ASSERT3U(dp->dp_dirty_pertxg[txg & TXG_MASK], >=, space);
 670         dp->dp_dirty_pertxg[txg & TXG_MASK] -= space;
 671         ASSERT3U(dp->dp_dirty_total, >=, space);
 672         dsl_pool_dirty_delta(dp, -space);
 673         mutex_exit(&dp->dp_lock);
 674 }
 675 
 676 /* ARGSUSED */
 677 static int
 678 upgrade_clones_cb(dsl_pool_t *dp, dsl_dataset_t *hds, void *arg)
 679 {
 680         dmu_tx_t *tx = arg;
 681         dsl_dataset_t *ds, *prev = NULL;
 682         int err;
 683 
 684         err = dsl_dataset_hold_obj(dp, hds->ds_object, FTAG, &ds);
 685         if (err)
 686                 return (err);
 687 
 688         while (ds->ds_phys->ds_prev_snap_obj != 0) {
 689                 err = dsl_dataset_hold_obj(dp, ds->ds_phys->ds_prev_snap_obj,
 690                     FTAG, &prev);
 691                 if (err) {
 692                         dsl_dataset_rele(ds, FTAG);
 693                         return (err);
 694                 }
 695 
 696                 if (prev->ds_phys->ds_next_snap_obj != ds->ds_object)
 697                         break;
 698                 dsl_dataset_rele(ds, FTAG);
 699                 ds = prev;
 700                 prev = NULL;
 701         }
 702 
 703         if (prev == NULL) {
 704                 prev = dp->dp_origin_snap;
 705 
 706                 /*
 707                  * The $ORIGIN can't have any data, or the accounting
 708                  * will be wrong.
 709                  */
 710                 ASSERT0(prev->ds_phys->ds_bp.blk_birth);
 711 
 712                 /* The origin doesn't get attached to itself */
 713                 if (ds->ds_object == prev->ds_object) {
 714                         dsl_dataset_rele(ds, FTAG);
 715                         return (0);
 716                 }
 717 
 718                 dmu_buf_will_dirty(ds->ds_dbuf, tx);
 719                 ds->ds_phys->ds_prev_snap_obj = prev->ds_object;
 720                 ds->ds_phys->ds_prev_snap_txg = prev->ds_phys->ds_creation_txg;
 721 
 722                 dmu_buf_will_dirty(ds->ds_dir->dd_dbuf, tx);
 723                 ds->ds_dir->dd_phys->dd_origin_obj = prev->ds_object;
 724 
 725                 dmu_buf_will_dirty(prev->ds_dbuf, tx);
 726                 prev->ds_phys->ds_num_children++;
 727 
 728                 if (ds->ds_phys->ds_next_snap_obj == 0) {
 729                         ASSERT(ds->ds_prev == NULL);
 730                         VERIFY0(dsl_dataset_hold_obj(dp,
 731                             ds->ds_phys->ds_prev_snap_obj, ds, &ds->ds_prev));
 732                 }
 733         }
 734 
 735         ASSERT3U(ds->ds_dir->dd_phys->dd_origin_obj, ==, prev->ds_object);
 736         ASSERT3U(ds->ds_phys->ds_prev_snap_obj, ==, prev->ds_object);
 737 
 738         if (prev->ds_phys->ds_next_clones_obj == 0) {
 739                 dmu_buf_will_dirty(prev->ds_dbuf, tx);
 740                 prev->ds_phys->ds_next_clones_obj =
 741                     zap_create(dp->dp_meta_objset,
 742                     DMU_OT_NEXT_CLONES, DMU_OT_NONE, 0, tx);
 743         }
 744         VERIFY0(zap_add_int(dp->dp_meta_objset,
 745             prev->ds_phys->ds_next_clones_obj, ds->ds_object, tx));
 746 
 747         dsl_dataset_rele(ds, FTAG);
 748         if (prev != dp->dp_origin_snap)
 749                 dsl_dataset_rele(prev, FTAG);
 750         return (0);
 751 }
 752 
 753 void
 754 dsl_pool_upgrade_clones(dsl_pool_t *dp, dmu_tx_t *tx)
 755 {
 756         ASSERT(dmu_tx_is_syncing(tx));
 757         ASSERT(dp->dp_origin_snap != NULL);
 758 
 759         VERIFY0(dmu_objset_find_dp(dp, dp->dp_root_dir_obj, upgrade_clones_cb,
 760             tx, DS_FIND_CHILDREN));
 761 }
 762 
 763 /* ARGSUSED */
 764 static int
 765 upgrade_dir_clones_cb(dsl_pool_t *dp, dsl_dataset_t *ds, void *arg)
 766 {
 767         dmu_tx_t *tx = arg;
 768         objset_t *mos = dp->dp_meta_objset;
 769 
 770         if (ds->ds_dir->dd_phys->dd_origin_obj != 0) {
 771                 dsl_dataset_t *origin;
 772 
 773                 VERIFY0(dsl_dataset_hold_obj(dp,
 774                     ds->ds_dir->dd_phys->dd_origin_obj, FTAG, &origin));
 775 
 776                 if (origin->ds_dir->dd_phys->dd_clones == 0) {
 777                         dmu_buf_will_dirty(origin->ds_dir->dd_dbuf, tx);
 778                         origin->ds_dir->dd_phys->dd_clones = zap_create(mos,
 779                             DMU_OT_DSL_CLONES, DMU_OT_NONE, 0, tx);
 780                 }
 781 
 782                 VERIFY0(zap_add_int(dp->dp_meta_objset,
 783                     origin->ds_dir->dd_phys->dd_clones, ds->ds_object, tx));
 784 
 785                 dsl_dataset_rele(origin, FTAG);
 786         }
 787         return (0);
 788 }
 789 
 790 void
 791 dsl_pool_upgrade_dir_clones(dsl_pool_t *dp, dmu_tx_t *tx)
 792 {
 793         ASSERT(dmu_tx_is_syncing(tx));
 794         uint64_t obj;
 795 
 796         (void) dsl_dir_create_sync(dp, dp->dp_root_dir, FREE_DIR_NAME, tx);
 797         VERIFY0(dsl_pool_open_special_dir(dp,
 798             FREE_DIR_NAME, &dp->dp_free_dir));
 799 
 800         /*
 801          * We can't use bpobj_alloc(), because spa_version() still
 802          * returns the old version, and we need a new-version bpobj with
 803          * subobj support.  So call dmu_object_alloc() directly.
 804          */
 805         obj = dmu_object_alloc(dp->dp_meta_objset, DMU_OT_BPOBJ,
 806             SPA_MAXBLOCKSIZE, DMU_OT_BPOBJ_HDR, sizeof (bpobj_phys_t), tx);
 807         VERIFY0(zap_add(dp->dp_meta_objset, DMU_POOL_DIRECTORY_OBJECT,
 808             DMU_POOL_FREE_BPOBJ, sizeof (uint64_t), 1, &obj, tx));
 809         VERIFY0(bpobj_open(&dp->dp_free_bpobj, dp->dp_meta_objset, obj));
 810 
 811         VERIFY0(dmu_objset_find_dp(dp, dp->dp_root_dir_obj,
 812             upgrade_dir_clones_cb, tx, DS_FIND_CHILDREN));
 813 }
 814 
 815 void
 816 dsl_pool_create_origin(dsl_pool_t *dp, dmu_tx_t *tx)
 817 {
 818         uint64_t dsobj;
 819         dsl_dataset_t *ds;
 820 
 821         ASSERT(dmu_tx_is_syncing(tx));
 822         ASSERT(dp->dp_origin_snap == NULL);
 823         ASSERT(rrw_held(&dp->dp_config_rwlock, RW_WRITER));
 824 
 825         /* create the origin dir, ds, & snap-ds */
 826         dsobj = dsl_dataset_create_sync(dp->dp_root_dir, ORIGIN_DIR_NAME,
 827             NULL, 0, kcred, tx);
 828         VERIFY0(dsl_dataset_hold_obj(dp, dsobj, FTAG, &ds));
 829         dsl_dataset_snapshot_sync_impl(ds, ORIGIN_DIR_NAME, tx);
 830         VERIFY0(dsl_dataset_hold_obj(dp, ds->ds_phys->ds_prev_snap_obj,
 831             dp, &dp->dp_origin_snap));
 832         dsl_dataset_rele(ds, FTAG);
 833 }
 834 
 835 taskq_t *
 836 dsl_pool_vnrele_taskq(dsl_pool_t *dp)
 837 {
 838         return (dp->dp_vnrele_taskq);
 839 }
 840 
 841 /*
 842  * Walk through the pool-wide zap object of temporary snapshot user holds
 843  * and release them.
 844  */
 845 void
 846 dsl_pool_clean_tmp_userrefs(dsl_pool_t *dp)
 847 {
 848         zap_attribute_t za;
 849         zap_cursor_t zc;
 850         objset_t *mos = dp->dp_meta_objset;
 851         uint64_t zapobj = dp->dp_tmp_userrefs_obj;
 852         nvlist_t *holds;
 853 
 854         if (zapobj == 0)
 855                 return;
 856         ASSERT(spa_version(dp->dp_spa) >= SPA_VERSION_USERREFS);
 857 
 858         holds = fnvlist_alloc();
 859 
 860         for (zap_cursor_init(&zc, mos, zapobj);
 861             zap_cursor_retrieve(&zc, &za) == 0;
 862             zap_cursor_advance(&zc)) {
 863                 char *htag;
 864                 nvlist_t *tags;
 865 
 866                 htag = strchr(za.za_name, '-');
 867                 *htag = '\0';
 868                 ++htag;
 869                 if (nvlist_lookup_nvlist(holds, za.za_name, &tags) != 0) {
 870                         tags = fnvlist_alloc();
 871                         fnvlist_add_boolean(tags, htag);
 872                         fnvlist_add_nvlist(holds, za.za_name, tags);
 873                         fnvlist_free(tags);
 874                 } else {
 875                         fnvlist_add_boolean(tags, htag);
 876                 }
 877         }
 878         dsl_dataset_user_release_tmp(dp, holds);
 879         fnvlist_free(holds);
 880         zap_cursor_fini(&zc);
 881 }
 882 
 883 /*
 884  * Create the pool-wide zap object for storing temporary snapshot holds.
 885  */
 886 void
 887 dsl_pool_user_hold_create_obj(dsl_pool_t *dp, dmu_tx_t *tx)
 888 {
 889         objset_t *mos = dp->dp_meta_objset;
 890 
 891         ASSERT(dp->dp_tmp_userrefs_obj == 0);
 892         ASSERT(dmu_tx_is_syncing(tx));
 893 
 894         dp->dp_tmp_userrefs_obj = zap_create_link(mos, DMU_OT_USERREFS,
 895             DMU_POOL_DIRECTORY_OBJECT, DMU_POOL_TMP_USERREFS, tx);
 896 }
 897 
 898 static int
 899 dsl_pool_user_hold_rele_impl(dsl_pool_t *dp, uint64_t dsobj,
 900     const char *tag, uint64_t now, dmu_tx_t *tx, boolean_t holding)
 901 {
 902         objset_t *mos = dp->dp_meta_objset;
 903         uint64_t zapobj = dp->dp_tmp_userrefs_obj;
 904         char *name;
 905         int error;
 906 
 907         ASSERT(spa_version(dp->dp_spa) >= SPA_VERSION_USERREFS);
 908         ASSERT(dmu_tx_is_syncing(tx));
 909 
 910         /*
 911          * If the pool was created prior to SPA_VERSION_USERREFS, the
 912          * zap object for temporary holds might not exist yet.
 913          */
 914         if (zapobj == 0) {
 915                 if (holding) {
 916                         dsl_pool_user_hold_create_obj(dp, tx);
 917                         zapobj = dp->dp_tmp_userrefs_obj;
 918                 } else {
 919                         return (SET_ERROR(ENOENT));
 920                 }
 921         }
 922 
 923         name = kmem_asprintf("%llx-%s", (u_longlong_t)dsobj, tag);
 924         if (holding)
 925                 error = zap_add(mos, zapobj, name, 8, 1, &now, tx);
 926         else
 927                 error = zap_remove(mos, zapobj, name, tx);
 928         strfree(name);
 929 
 930         return (error);
 931 }
 932 
 933 /*
 934  * Add a temporary hold for the given dataset object and tag.
 935  */
 936 int
 937 dsl_pool_user_hold(dsl_pool_t *dp, uint64_t dsobj, const char *tag,
 938     uint64_t now, dmu_tx_t *tx)
 939 {
 940         return (dsl_pool_user_hold_rele_impl(dp, dsobj, tag, now, tx, B_TRUE));
 941 }
 942 
 943 /*
 944  * Release a temporary hold for the given dataset object and tag.
 945  */
 946 int
 947 dsl_pool_user_release(dsl_pool_t *dp, uint64_t dsobj, const char *tag,
 948     dmu_tx_t *tx)
 949 {
 950         return (dsl_pool_user_hold_rele_impl(dp, dsobj, tag, NULL,
 951             tx, B_FALSE));
 952 }
 953 
 954 /*
 955  * DSL Pool Configuration Lock
 956  *
 957  * The dp_config_rwlock protects against changes to DSL state (e.g. dataset
 958  * creation / destruction / rename / property setting).  It must be held for
 959  * read to hold a dataset or dsl_dir.  I.e. you must call
 960  * dsl_pool_config_enter() or dsl_pool_hold() before calling
 961  * dsl_{dataset,dir}_hold{_obj}.  In most circumstances, the dp_config_rwlock
 962  * must be held continuously until all datasets and dsl_dirs are released.
 963  *
 964  * The only exception to this rule is that if a "long hold" is placed on
 965  * a dataset, then the dp_config_rwlock may be dropped while the dataset
 966  * is still held.  The long hold will prevent the dataset from being
 967  * destroyed -- the destroy will fail with EBUSY.  A long hold can be
 968  * obtained by calling dsl_dataset_long_hold(), or by "owning" a dataset
 969  * (by calling dsl_{dataset,objset}_{try}own{_obj}).
 970  *
 971  * Legitimate long-holders (including owners) should be long-running, cancelable
 972  * tasks that should cause "zfs destroy" to fail.  This includes DMU
 973  * consumers (i.e. a ZPL filesystem being mounted or ZVOL being open),
 974  * "zfs send", and "zfs diff".  There are several other long-holders whose
 975  * uses are suboptimal (e.g. "zfs promote", and zil_suspend()).
 976  *
 977  * The usual formula for long-holding would be:
 978  * dsl_pool_hold()
 979  * dsl_dataset_hold()
 980  * ... perform checks ...
 981  * dsl_dataset_long_hold()
 982  * dsl_pool_rele()
 983  * ... perform long-running task ...
 984  * dsl_dataset_long_rele()
 985  * dsl_dataset_rele()
 986  *
 987  * Note that when the long hold is released, the dataset is still held but
 988  * the pool is not held.  The dataset may change arbitrarily during this time
 989  * (e.g. it could be destroyed).  Therefore you shouldn't do anything to the
 990  * dataset except release it.
 991  *
 992  * User-initiated operations (e.g. ioctls, zfs_ioc_*()) are either read-only
 993  * or modifying operations.
 994  *
 995  * Modifying operations should generally use dsl_sync_task().  The synctask
 996  * infrastructure enforces proper locking strategy with respect to the
 997  * dp_config_rwlock.  See the comment above dsl_sync_task() for details.
 998  *
 999  * Read-only operations will manually hold the pool, then the dataset, obtain
1000  * information from the dataset, then release the pool and dataset.
1001  * dmu_objset_{hold,rele}() are convenience routines that also do the pool
1002  * hold/rele.
1003  */
1004 
1005 int
1006 dsl_pool_hold(const char *name, void *tag, dsl_pool_t **dp)
1007 {
1008         spa_t *spa;
1009         int error;
1010 
1011         error = spa_open(name, &spa, tag);
1012         if (error == 0) {
1013                 *dp = spa_get_dsl(spa);
1014                 dsl_pool_config_enter(*dp, tag);
1015         }
1016         return (error);
1017 }
1018 
1019 void
1020 dsl_pool_rele(dsl_pool_t *dp, void *tag)
1021 {
1022         dsl_pool_config_exit(dp, tag);
1023         spa_close(dp->dp_spa, tag);
1024 }
1025 
1026 void
1027 dsl_pool_config_enter(dsl_pool_t *dp, void *tag)
1028 {
1029         /*
1030          * We use a "reentrant" reader-writer lock, but not reentrantly.
1031          *
1032          * The rrwlock can (with the track_all flag) track all reading threads,
1033          * which is very useful for debugging which code path failed to release
1034          * the lock, and for verifying that the *current* thread does hold
1035          * the lock.
1036          *
1037          * (Unlike a rwlock, which knows that N threads hold it for
1038          * read, but not *which* threads, so rw_held(RW_READER) returns TRUE
1039          * if any thread holds it for read, even if this thread doesn't).
1040          */
1041         ASSERT(!rrw_held(&dp->dp_config_rwlock, RW_READER));
1042         rrw_enter(&dp->dp_config_rwlock, RW_READER, tag);
1043 }
1044 
1045 void
1046 dsl_pool_config_exit(dsl_pool_t *dp, void *tag)
1047 {
1048         rrw_exit(&dp->dp_config_rwlock, tag);
1049 }
1050 
1051 boolean_t
1052 dsl_pool_config_held(dsl_pool_t *dp)
1053 {
1054         return (RRW_LOCK_HELD(&dp->dp_config_rwlock));
1055 }