xref: /illumos-gate/usr/src/uts/common/fs/zfs/dsl_scan.c (revision 7ed546340881b42865171ddfa1a6167b289faae3)
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) 2008, 2010, Oracle and/or its affiliates. All rights reserved.
23  * Copyright (c) 2011, 2018 by Delphix. All rights reserved.
24  * Copyright 2016 Gary Mills
25  * Copyright (c) 2011, 2017 by Delphix. All rights reserved.
26  * Copyright 2017 Joyent, Inc.
27  * Copyright (c) 2017 Datto Inc.
28  */
29 
30 #include <sys/dsl_scan.h>
31 #include <sys/dsl_pool.h>
32 #include <sys/dsl_dataset.h>
33 #include <sys/dsl_prop.h>
34 #include <sys/dsl_dir.h>
35 #include <sys/dsl_synctask.h>
36 #include <sys/dnode.h>
37 #include <sys/dmu_tx.h>
38 #include <sys/dmu_objset.h>
39 #include <sys/arc.h>
40 #include <sys/zap.h>
41 #include <sys/zio.h>
42 #include <sys/zfs_context.h>
43 #include <sys/fs/zfs.h>
44 #include <sys/zfs_znode.h>
45 #include <sys/spa_impl.h>
46 #include <sys/vdev_impl.h>
47 #include <sys/zil_impl.h>
48 #include <sys/zio_checksum.h>
49 #include <sys/ddt.h>
50 #include <sys/sa.h>
51 #include <sys/sa_impl.h>
52 #include <sys/zfeature.h>
53 #include <sys/abd.h>
54 #ifdef _KERNEL
55 #include <sys/zfs_vfsops.h>
56 #endif
57 
58 typedef int (scan_cb_t)(dsl_pool_t *, const blkptr_t *,
59     const zbookmark_phys_t *);
60 
61 static scan_cb_t dsl_scan_scrub_cb;
62 static void dsl_scan_cancel_sync(void *, dmu_tx_t *);
63 static void dsl_scan_sync_state(dsl_scan_t *, dmu_tx_t *);
64 static boolean_t dsl_scan_restarting(dsl_scan_t *, dmu_tx_t *);
65 
66 int zfs_top_maxinflight = 32;		/* maximum I/Os per top-level */
67 int zfs_resilver_delay = 2;		/* number of ticks to delay resilver */
68 int zfs_scrub_delay = 4;		/* number of ticks to delay scrub */
69 int zfs_scan_idle = 50;			/* idle window in clock ticks */
70 
71 int zfs_scan_min_time_ms = 1000; /* min millisecs to scrub per txg */
72 int zfs_free_min_time_ms = 1000; /* min millisecs to free per txg */
73 int zfs_obsolete_min_time_ms = 500; /* min millisecs to obsolete per txg */
74 int zfs_resilver_min_time_ms = 3000; /* min millisecs to resilver per txg */
75 boolean_t zfs_no_scrub_io = B_FALSE; /* set to disable scrub i/o */
76 boolean_t zfs_no_scrub_prefetch = B_FALSE; /* set to disable scrub prefetch */
77 enum ddt_class zfs_scrub_ddt_class_max = DDT_CLASS_DUPLICATE;
78 int dsl_scan_delay_completion = B_FALSE; /* set to delay scan completion */
79 /* max number of blocks to free in a single TXG */
80 uint64_t zfs_async_block_max_blocks = UINT64_MAX;
81 
82 #define	DSL_SCAN_IS_SCRUB_RESILVER(scn) \
83 	((scn)->scn_phys.scn_func == POOL_SCAN_SCRUB || \
84 	(scn)->scn_phys.scn_func == POOL_SCAN_RESILVER)
85 
86 extern int zfs_txg_timeout;
87 
88 /*
89  * Enable/disable the processing of the free_bpobj object.
90  */
91 boolean_t zfs_free_bpobj_enabled = B_TRUE;
92 
93 /* the order has to match pool_scan_type */
94 static scan_cb_t *scan_funcs[POOL_SCAN_FUNCS] = {
95 	NULL,
96 	dsl_scan_scrub_cb,	/* POOL_SCAN_SCRUB */
97 	dsl_scan_scrub_cb,	/* POOL_SCAN_RESILVER */
98 };
99 
100 int
101 dsl_scan_init(dsl_pool_t *dp, uint64_t txg)
102 {
103 	int err;
104 	dsl_scan_t *scn;
105 	spa_t *spa = dp->dp_spa;
106 	uint64_t f;
107 
108 	scn = dp->dp_scan = kmem_zalloc(sizeof (dsl_scan_t), KM_SLEEP);
109 	scn->scn_dp = dp;
110 
111 	/*
112 	 * It's possible that we're resuming a scan after a reboot so
113 	 * make sure that the scan_async_destroying flag is initialized
114 	 * appropriately.
115 	 */
116 	ASSERT(!scn->scn_async_destroying);
117 	scn->scn_async_destroying = spa_feature_is_active(dp->dp_spa,
118 	    SPA_FEATURE_ASYNC_DESTROY);
119 
120 	err = zap_lookup(dp->dp_meta_objset, DMU_POOL_DIRECTORY_OBJECT,
121 	    "scrub_func", sizeof (uint64_t), 1, &f);
122 	if (err == 0) {
123 		/*
124 		 * There was an old-style scrub in progress.  Restart a
125 		 * new-style scrub from the beginning.
126 		 */
127 		scn->scn_restart_txg = txg;
128 		zfs_dbgmsg("old-style scrub was in progress; "
129 		    "restarting new-style scrub in txg %llu",
130 		    scn->scn_restart_txg);
131 
132 		/*
133 		 * Load the queue obj from the old location so that it
134 		 * can be freed by dsl_scan_done().
135 		 */
136 		(void) zap_lookup(dp->dp_meta_objset, DMU_POOL_DIRECTORY_OBJECT,
137 		    "scrub_queue", sizeof (uint64_t), 1,
138 		    &scn->scn_phys.scn_queue_obj);
139 	} else {
140 		err = zap_lookup(dp->dp_meta_objset, DMU_POOL_DIRECTORY_OBJECT,
141 		    DMU_POOL_SCAN, sizeof (uint64_t), SCAN_PHYS_NUMINTS,
142 		    &scn->scn_phys);
143 		if (err == ENOENT)
144 			return (0);
145 		else if (err)
146 			return (err);
147 
148 		if (scn->scn_phys.scn_state == DSS_SCANNING &&
149 		    spa_prev_software_version(dp->dp_spa) < SPA_VERSION_SCAN) {
150 			/*
151 			 * A new-type scrub was in progress on an old
152 			 * pool, and the pool was accessed by old
153 			 * software.  Restart from the beginning, since
154 			 * the old software may have changed the pool in
155 			 * the meantime.
156 			 */
157 			scn->scn_restart_txg = txg;
158 			zfs_dbgmsg("new-style scrub was modified "
159 			    "by old software; restarting in txg %llu",
160 			    scn->scn_restart_txg);
161 		}
162 	}
163 
164 	spa_scan_stat_init(spa);
165 	return (0);
166 }
167 
168 void
169 dsl_scan_fini(dsl_pool_t *dp)
170 {
171 	if (dp->dp_scan) {
172 		kmem_free(dp->dp_scan, sizeof (dsl_scan_t));
173 		dp->dp_scan = NULL;
174 	}
175 }
176 
177 /* ARGSUSED */
178 static int
179 dsl_scan_setup_check(void *arg, dmu_tx_t *tx)
180 {
181 	dsl_scan_t *scn = dmu_tx_pool(tx)->dp_scan;
182 
183 	if (scn->scn_phys.scn_state == DSS_SCANNING)
184 		return (SET_ERROR(EBUSY));
185 
186 	return (0);
187 }
188 
189 static void
190 dsl_scan_setup_sync(void *arg, dmu_tx_t *tx)
191 {
192 	dsl_scan_t *scn = dmu_tx_pool(tx)->dp_scan;
193 	pool_scan_func_t *funcp = arg;
194 	dmu_object_type_t ot = 0;
195 	dsl_pool_t *dp = scn->scn_dp;
196 	spa_t *spa = dp->dp_spa;
197 
198 	ASSERT(scn->scn_phys.scn_state != DSS_SCANNING);
199 	ASSERT(*funcp > POOL_SCAN_NONE && *funcp < POOL_SCAN_FUNCS);
200 	bzero(&scn->scn_phys, sizeof (scn->scn_phys));
201 	scn->scn_phys.scn_func = *funcp;
202 	scn->scn_phys.scn_state = DSS_SCANNING;
203 	scn->scn_phys.scn_min_txg = 0;
204 	scn->scn_phys.scn_max_txg = tx->tx_txg;
205 	scn->scn_phys.scn_ddt_class_max = DDT_CLASSES - 1; /* the entire DDT */
206 	scn->scn_phys.scn_start_time = gethrestime_sec();
207 	scn->scn_phys.scn_errors = 0;
208 	scn->scn_phys.scn_to_examine = spa->spa_root_vdev->vdev_stat.vs_alloc;
209 	scn->scn_restart_txg = 0;
210 	scn->scn_done_txg = 0;
211 	spa_scan_stat_init(spa);
212 
213 	if (DSL_SCAN_IS_SCRUB_RESILVER(scn)) {
214 		scn->scn_phys.scn_ddt_class_max = zfs_scrub_ddt_class_max;
215 
216 		/* rewrite all disk labels */
217 		vdev_config_dirty(spa->spa_root_vdev);
218 
219 		if (vdev_resilver_needed(spa->spa_root_vdev,
220 		    &scn->scn_phys.scn_min_txg, &scn->scn_phys.scn_max_txg)) {
221 			spa_event_notify(spa, NULL, NULL,
222 			    ESC_ZFS_RESILVER_START);
223 		} else {
224 			spa_event_notify(spa, NULL, NULL, ESC_ZFS_SCRUB_START);
225 		}
226 
227 		spa->spa_scrub_started = B_TRUE;
228 		/*
229 		 * If this is an incremental scrub, limit the DDT scrub phase
230 		 * to just the auto-ditto class (for correctness); the rest
231 		 * of the scrub should go faster using top-down pruning.
232 		 */
233 		if (scn->scn_phys.scn_min_txg > TXG_INITIAL)
234 			scn->scn_phys.scn_ddt_class_max = DDT_CLASS_DITTO;
235 
236 	}
237 
238 	/* back to the generic stuff */
239 
240 	if (dp->dp_blkstats == NULL) {
241 		dp->dp_blkstats =
242 		    kmem_alloc(sizeof (zfs_all_blkstats_t), KM_SLEEP);
243 	}
244 	bzero(dp->dp_blkstats, sizeof (zfs_all_blkstats_t));
245 
246 	if (spa_version(spa) < SPA_VERSION_DSL_SCRUB)
247 		ot = DMU_OT_ZAP_OTHER;
248 
249 	scn->scn_phys.scn_queue_obj = zap_create(dp->dp_meta_objset,
250 	    ot ? ot : DMU_OT_SCAN_QUEUE, DMU_OT_NONE, 0, tx);
251 
252 	dsl_scan_sync_state(scn, tx);
253 
254 	spa_history_log_internal(spa, "scan setup", tx,
255 	    "func=%u mintxg=%llu maxtxg=%llu",
256 	    *funcp, scn->scn_phys.scn_min_txg, scn->scn_phys.scn_max_txg);
257 }
258 
259 /* ARGSUSED */
260 static void
261 dsl_scan_done(dsl_scan_t *scn, boolean_t complete, dmu_tx_t *tx)
262 {
263 	static const char *old_names[] = {
264 		"scrub_bookmark",
265 		"scrub_ddt_bookmark",
266 		"scrub_ddt_class_max",
267 		"scrub_queue",
268 		"scrub_min_txg",
269 		"scrub_max_txg",
270 		"scrub_func",
271 		"scrub_errors",
272 		NULL
273 	};
274 
275 	dsl_pool_t *dp = scn->scn_dp;
276 	spa_t *spa = dp->dp_spa;
277 	int i;
278 
279 	/* Remove any remnants of an old-style scrub. */
280 	for (i = 0; old_names[i]; i++) {
281 		(void) zap_remove(dp->dp_meta_objset,
282 		    DMU_POOL_DIRECTORY_OBJECT, old_names[i], tx);
283 	}
284 
285 	if (scn->scn_phys.scn_queue_obj != 0) {
286 		VERIFY(0 == dmu_object_free(dp->dp_meta_objset,
287 		    scn->scn_phys.scn_queue_obj, tx));
288 		scn->scn_phys.scn_queue_obj = 0;
289 	}
290 
291 	scn->scn_phys.scn_flags &= ~DSF_SCRUB_PAUSED;
292 
293 	/*
294 	 * If we were "restarted" from a stopped state, don't bother
295 	 * with anything else.
296 	 */
297 	if (scn->scn_phys.scn_state != DSS_SCANNING)
298 		return;
299 
300 	if (complete)
301 		scn->scn_phys.scn_state = DSS_FINISHED;
302 	else
303 		scn->scn_phys.scn_state = DSS_CANCELED;
304 
305 	if (dsl_scan_restarting(scn, tx))
306 		spa_history_log_internal(spa, "scan aborted, restarting", tx,
307 		    "errors=%llu", spa_get_errlog_size(spa));
308 	else if (!complete)
309 		spa_history_log_internal(spa, "scan cancelled", tx,
310 		    "errors=%llu", spa_get_errlog_size(spa));
311 	else
312 		spa_history_log_internal(spa, "scan done", tx,
313 		    "errors=%llu", spa_get_errlog_size(spa));
314 
315 	if (DSL_SCAN_IS_SCRUB_RESILVER(scn)) {
316 		mutex_enter(&spa->spa_scrub_lock);
317 		while (spa->spa_scrub_inflight > 0) {
318 			cv_wait(&spa->spa_scrub_io_cv,
319 			    &spa->spa_scrub_lock);
320 		}
321 		mutex_exit(&spa->spa_scrub_lock);
322 		spa->spa_scrub_started = B_FALSE;
323 		spa->spa_scrub_active = B_FALSE;
324 
325 		/*
326 		 * If the scrub/resilver completed, update all DTLs to
327 		 * reflect this.  Whether it succeeded or not, vacate
328 		 * all temporary scrub DTLs.
329 		 *
330 		 * As the scrub does not currently support traversing
331 		 * data that have been freed but are part of a checkpoint,
332 		 * we don't mark the scrub as done in the DTLs as faults
333 		 * may still exist in those vdevs.
334 		 */
335 		if (complete &&
336 		    !spa_feature_is_active(spa, SPA_FEATURE_POOL_CHECKPOINT)) {
337 			vdev_dtl_reassess(spa->spa_root_vdev, tx->tx_txg,
338 			    scn->scn_phys.scn_max_txg, B_TRUE);
339 
340 			spa_event_notify(spa, NULL, NULL,
341 			    scn->scn_phys.scn_min_txg ?
342 			    ESC_ZFS_RESILVER_FINISH : ESC_ZFS_SCRUB_FINISH);
343 		} else {
344 			vdev_dtl_reassess(spa->spa_root_vdev, tx->tx_txg,
345 			    0, B_TRUE);
346 		}
347 		spa_errlog_rotate(spa);
348 
349 		/*
350 		 * We may have finished replacing a device.
351 		 * Let the async thread assess this and handle the detach.
352 		 */
353 		spa_async_request(spa, SPA_ASYNC_RESILVER_DONE);
354 	}
355 
356 	scn->scn_phys.scn_end_time = gethrestime_sec();
357 }
358 
359 /* ARGSUSED */
360 static int
361 dsl_scan_cancel_check(void *arg, dmu_tx_t *tx)
362 {
363 	dsl_scan_t *scn = dmu_tx_pool(tx)->dp_scan;
364 
365 	if (scn->scn_phys.scn_state != DSS_SCANNING)
366 		return (SET_ERROR(ENOENT));
367 	return (0);
368 }
369 
370 /* ARGSUSED */
371 static void
372 dsl_scan_cancel_sync(void *arg, dmu_tx_t *tx)
373 {
374 	dsl_scan_t *scn = dmu_tx_pool(tx)->dp_scan;
375 
376 	dsl_scan_done(scn, B_FALSE, tx);
377 	dsl_scan_sync_state(scn, tx);
378 	spa_event_notify(scn->scn_dp->dp_spa, NULL, NULL, ESC_ZFS_SCRUB_ABORT);
379 }
380 
381 int
382 dsl_scan_cancel(dsl_pool_t *dp)
383 {
384 	return (dsl_sync_task(spa_name(dp->dp_spa), dsl_scan_cancel_check,
385 	    dsl_scan_cancel_sync, NULL, 3, ZFS_SPACE_CHECK_RESERVED));
386 }
387 
388 boolean_t
389 dsl_scan_is_paused_scrub(const dsl_scan_t *scn)
390 {
391 	if (dsl_scan_scrubbing(scn->scn_dp) &&
392 	    scn->scn_phys.scn_flags & DSF_SCRUB_PAUSED)
393 		return (B_TRUE);
394 
395 	return (B_FALSE);
396 }
397 
398 static int
399 dsl_scrub_pause_resume_check(void *arg, dmu_tx_t *tx)
400 {
401 	pool_scrub_cmd_t *cmd = arg;
402 	dsl_pool_t *dp = dmu_tx_pool(tx);
403 	dsl_scan_t *scn = dp->dp_scan;
404 
405 	if (*cmd == POOL_SCRUB_PAUSE) {
406 		/* can't pause a scrub when there is no in-progress scrub */
407 		if (!dsl_scan_scrubbing(dp))
408 			return (SET_ERROR(ENOENT));
409 
410 		/* can't pause a paused scrub */
411 		if (dsl_scan_is_paused_scrub(scn))
412 			return (SET_ERROR(EBUSY));
413 	} else if (*cmd != POOL_SCRUB_NORMAL) {
414 		return (SET_ERROR(ENOTSUP));
415 	}
416 
417 	return (0);
418 }
419 
420 static void
421 dsl_scrub_pause_resume_sync(void *arg, dmu_tx_t *tx)
422 {
423 	pool_scrub_cmd_t *cmd = arg;
424 	dsl_pool_t *dp = dmu_tx_pool(tx);
425 	spa_t *spa = dp->dp_spa;
426 	dsl_scan_t *scn = dp->dp_scan;
427 
428 	if (*cmd == POOL_SCRUB_PAUSE) {
429 		/* can't pause a scrub when there is no in-progress scrub */
430 		spa->spa_scan_pass_scrub_pause = gethrestime_sec();
431 		scn->scn_phys.scn_flags |= DSF_SCRUB_PAUSED;
432 		dsl_scan_sync_state(scn, tx);
433 		spa_event_notify(spa, NULL, NULL, ESC_ZFS_SCRUB_PAUSED);
434 	} else {
435 		ASSERT3U(*cmd, ==, POOL_SCRUB_NORMAL);
436 		if (dsl_scan_is_paused_scrub(scn)) {
437 			/*
438 			 * We need to keep track of how much time we spend
439 			 * paused per pass so that we can adjust the scrub rate
440 			 * shown in the output of 'zpool status'
441 			 */
442 			spa->spa_scan_pass_scrub_spent_paused +=
443 			    gethrestime_sec() - spa->spa_scan_pass_scrub_pause;
444 			spa->spa_scan_pass_scrub_pause = 0;
445 			scn->scn_phys.scn_flags &= ~DSF_SCRUB_PAUSED;
446 			dsl_scan_sync_state(scn, tx);
447 		}
448 	}
449 }
450 
451 /*
452  * Set scrub pause/resume state if it makes sense to do so
453  */
454 int
455 dsl_scrub_set_pause_resume(const dsl_pool_t *dp, pool_scrub_cmd_t cmd)
456 {
457 	return (dsl_sync_task(spa_name(dp->dp_spa),
458 	    dsl_scrub_pause_resume_check, dsl_scrub_pause_resume_sync, &cmd, 3,
459 	    ZFS_SPACE_CHECK_RESERVED));
460 }
461 
462 boolean_t
463 dsl_scan_scrubbing(const dsl_pool_t *dp)
464 {
465 	dsl_scan_t *scn = dp->dp_scan;
466 
467 	if (scn->scn_phys.scn_state == DSS_SCANNING &&
468 	    scn->scn_phys.scn_func == POOL_SCAN_SCRUB)
469 		return (B_TRUE);
470 
471 	return (B_FALSE);
472 }
473 
474 static void dsl_scan_visitbp(blkptr_t *bp, const zbookmark_phys_t *zb,
475     dnode_phys_t *dnp, dsl_dataset_t *ds, dsl_scan_t *scn,
476     dmu_objset_type_t ostype, dmu_tx_t *tx);
477 static void dsl_scan_visitdnode(dsl_scan_t *, dsl_dataset_t *ds,
478     dmu_objset_type_t ostype,
479     dnode_phys_t *dnp, uint64_t object, dmu_tx_t *tx);
480 
481 void
482 dsl_free(dsl_pool_t *dp, uint64_t txg, const blkptr_t *bp)
483 {
484 	zio_free(dp->dp_spa, txg, bp);
485 }
486 
487 void
488 dsl_free_sync(zio_t *pio, dsl_pool_t *dp, uint64_t txg, const blkptr_t *bpp)
489 {
490 	ASSERT(dsl_pool_sync_context(dp));
491 	zio_nowait(zio_free_sync(pio, dp->dp_spa, txg, bpp, pio->io_flags));
492 }
493 
494 static uint64_t
495 dsl_scan_ds_maxtxg(dsl_dataset_t *ds)
496 {
497 	uint64_t smt = ds->ds_dir->dd_pool->dp_scan->scn_phys.scn_max_txg;
498 	if (ds->ds_is_snapshot)
499 		return (MIN(smt, dsl_dataset_phys(ds)->ds_creation_txg));
500 	return (smt);
501 }
502 
503 static void
504 dsl_scan_sync_state(dsl_scan_t *scn, dmu_tx_t *tx)
505 {
506 	VERIFY0(zap_update(scn->scn_dp->dp_meta_objset,
507 	    DMU_POOL_DIRECTORY_OBJECT,
508 	    DMU_POOL_SCAN, sizeof (uint64_t), SCAN_PHYS_NUMINTS,
509 	    &scn->scn_phys, tx));
510 }
511 
512 extern int zfs_vdev_async_write_active_min_dirty_percent;
513 
514 static boolean_t
515 dsl_scan_check_suspend(dsl_scan_t *scn, const zbookmark_phys_t *zb)
516 {
517 	/* we never skip user/group accounting objects */
518 	if (zb && (int64_t)zb->zb_object < 0)
519 		return (B_FALSE);
520 
521 	if (scn->scn_suspending)
522 		return (B_TRUE); /* we're already suspending */
523 
524 	if (!ZB_IS_ZERO(&scn->scn_phys.scn_bookmark))
525 		return (B_FALSE); /* we're resuming */
526 
527 	/* We only know how to resume from level-0 blocks. */
528 	if (zb && zb->zb_level != 0)
529 		return (B_FALSE);
530 
531 	/*
532 	 * We suspend if:
533 	 *  - we have scanned for the maximum time: an entire txg
534 	 *    timeout (default 5 sec)
535 	 *  or
536 	 *  - we have scanned for at least the minimum time (default 1 sec
537 	 *    for scrub, 3 sec for resilver), and either we have sufficient
538 	 *    dirty data that we are starting to write more quickly
539 	 *    (default 30%), or someone is explicitly waiting for this txg
540 	 *    to complete.
541 	 *  or
542 	 *  - the spa is shutting down because this pool is being exported
543 	 *    or the machine is rebooting.
544 	 */
545 	int mintime = (scn->scn_phys.scn_func == POOL_SCAN_RESILVER) ?
546 	    zfs_resilver_min_time_ms : zfs_scan_min_time_ms;
547 	uint64_t elapsed_nanosecs = gethrtime() - scn->scn_sync_start_time;
548 	int dirty_pct = scn->scn_dp->dp_dirty_total * 100 / zfs_dirty_data_max;
549 	if (elapsed_nanosecs / NANOSEC >= zfs_txg_timeout ||
550 	    (NSEC2MSEC(elapsed_nanosecs) > mintime &&
551 	    (txg_sync_waiting(scn->scn_dp) ||
552 	    dirty_pct >= zfs_vdev_async_write_active_min_dirty_percent)) ||
553 	    spa_shutting_down(scn->scn_dp->dp_spa)) {
554 		if (zb) {
555 			dprintf("suspending at bookmark %llx/%llx/%llx/%llx\n",
556 			    (longlong_t)zb->zb_objset,
557 			    (longlong_t)zb->zb_object,
558 			    (longlong_t)zb->zb_level,
559 			    (longlong_t)zb->zb_blkid);
560 			scn->scn_phys.scn_bookmark = *zb;
561 		}
562 		dprintf("suspending at DDT bookmark %llx/%llx/%llx/%llx\n",
563 		    (longlong_t)scn->scn_phys.scn_ddt_bookmark.ddb_class,
564 		    (longlong_t)scn->scn_phys.scn_ddt_bookmark.ddb_type,
565 		    (longlong_t)scn->scn_phys.scn_ddt_bookmark.ddb_checksum,
566 		    (longlong_t)scn->scn_phys.scn_ddt_bookmark.ddb_cursor);
567 		scn->scn_suspending = B_TRUE;
568 		return (B_TRUE);
569 	}
570 	return (B_FALSE);
571 }
572 
573 typedef struct zil_scan_arg {
574 	dsl_pool_t	*zsa_dp;
575 	zil_header_t	*zsa_zh;
576 } zil_scan_arg_t;
577 
578 /* ARGSUSED */
579 static int
580 dsl_scan_zil_block(zilog_t *zilog, blkptr_t *bp, void *arg, uint64_t claim_txg)
581 {
582 	zil_scan_arg_t *zsa = arg;
583 	dsl_pool_t *dp = zsa->zsa_dp;
584 	dsl_scan_t *scn = dp->dp_scan;
585 	zil_header_t *zh = zsa->zsa_zh;
586 	zbookmark_phys_t zb;
587 
588 	if (BP_IS_HOLE(bp) || bp->blk_birth <= scn->scn_phys.scn_cur_min_txg)
589 		return (0);
590 
591 	/*
592 	 * One block ("stubby") can be allocated a long time ago; we
593 	 * want to visit that one because it has been allocated
594 	 * (on-disk) even if it hasn't been claimed (even though for
595 	 * scrub there's nothing to do to it).
596 	 */
597 	if (claim_txg == 0 && bp->blk_birth >= spa_min_claim_txg(dp->dp_spa))
598 		return (0);
599 
600 	SET_BOOKMARK(&zb, zh->zh_log.blk_cksum.zc_word[ZIL_ZC_OBJSET],
601 	    ZB_ZIL_OBJECT, ZB_ZIL_LEVEL, bp->blk_cksum.zc_word[ZIL_ZC_SEQ]);
602 
603 	VERIFY(0 == scan_funcs[scn->scn_phys.scn_func](dp, bp, &zb));
604 	return (0);
605 }
606 
607 /* ARGSUSED */
608 static int
609 dsl_scan_zil_record(zilog_t *zilog, lr_t *lrc, void *arg, uint64_t claim_txg)
610 {
611 	if (lrc->lrc_txtype == TX_WRITE) {
612 		zil_scan_arg_t *zsa = arg;
613 		dsl_pool_t *dp = zsa->zsa_dp;
614 		dsl_scan_t *scn = dp->dp_scan;
615 		zil_header_t *zh = zsa->zsa_zh;
616 		lr_write_t *lr = (lr_write_t *)lrc;
617 		blkptr_t *bp = &lr->lr_blkptr;
618 		zbookmark_phys_t zb;
619 
620 		if (BP_IS_HOLE(bp) ||
621 		    bp->blk_birth <= scn->scn_phys.scn_cur_min_txg)
622 			return (0);
623 
624 		/*
625 		 * birth can be < claim_txg if this record's txg is
626 		 * already txg sync'ed (but this log block contains
627 		 * other records that are not synced)
628 		 */
629 		if (claim_txg == 0 || bp->blk_birth < claim_txg)
630 			return (0);
631 
632 		SET_BOOKMARK(&zb, zh->zh_log.blk_cksum.zc_word[ZIL_ZC_OBJSET],
633 		    lr->lr_foid, ZB_ZIL_LEVEL,
634 		    lr->lr_offset / BP_GET_LSIZE(bp));
635 
636 		VERIFY(0 == scan_funcs[scn->scn_phys.scn_func](dp, bp, &zb));
637 	}
638 	return (0);
639 }
640 
641 static void
642 dsl_scan_zil(dsl_pool_t *dp, zil_header_t *zh)
643 {
644 	uint64_t claim_txg = zh->zh_claim_txg;
645 	zil_scan_arg_t zsa = { dp, zh };
646 	zilog_t *zilog;
647 
648 	ASSERT(spa_writeable(dp->dp_spa));
649 
650 	/*
651 	 * We only want to visit blocks that have been claimed
652 	 * but not yet replayed.
653 	 */
654 	if (claim_txg == 0)
655 		return;
656 
657 	zilog = zil_alloc(dp->dp_meta_objset, zh);
658 
659 	(void) zil_parse(zilog, dsl_scan_zil_block, dsl_scan_zil_record, &zsa,
660 	    claim_txg);
661 
662 	zil_free(zilog);
663 }
664 
665 /* ARGSUSED */
666 static void
667 dsl_scan_prefetch(dsl_scan_t *scn, arc_buf_t *buf, blkptr_t *bp,
668     uint64_t objset, uint64_t object, uint64_t blkid)
669 {
670 	zbookmark_phys_t czb;
671 	arc_flags_t flags = ARC_FLAG_NOWAIT | ARC_FLAG_PREFETCH;
672 
673 	if (zfs_no_scrub_prefetch)
674 		return;
675 
676 	if (BP_IS_HOLE(bp) || bp->blk_birth <= scn->scn_phys.scn_min_txg ||
677 	    (BP_GET_LEVEL(bp) == 0 && BP_GET_TYPE(bp) != DMU_OT_DNODE))
678 		return;
679 
680 	SET_BOOKMARK(&czb, objset, object, BP_GET_LEVEL(bp), blkid);
681 
682 	(void) arc_read(scn->scn_zio_root, scn->scn_dp->dp_spa, bp,
683 	    NULL, NULL, ZIO_PRIORITY_ASYNC_READ,
684 	    ZIO_FLAG_CANFAIL | ZIO_FLAG_SCAN_THREAD, &flags, &czb);
685 }
686 
687 static boolean_t
688 dsl_scan_check_resume(dsl_scan_t *scn, const dnode_phys_t *dnp,
689     const zbookmark_phys_t *zb)
690 {
691 	/*
692 	 * We never skip over user/group accounting objects (obj<0)
693 	 */
694 	if (!ZB_IS_ZERO(&scn->scn_phys.scn_bookmark) &&
695 	    (int64_t)zb->zb_object >= 0) {
696 		/*
697 		 * If we already visited this bp & everything below (in
698 		 * a prior txg sync), don't bother doing it again.
699 		 */
700 		if (zbookmark_subtree_completed(dnp, zb,
701 		    &scn->scn_phys.scn_bookmark))
702 			return (B_TRUE);
703 
704 		/*
705 		 * If we found the block we're trying to resume from, or
706 		 * we went past it to a different object, zero it out to
707 		 * indicate that it's OK to start checking for suspending
708 		 * again.
709 		 */
710 		if (bcmp(zb, &scn->scn_phys.scn_bookmark, sizeof (*zb)) == 0 ||
711 		    zb->zb_object > scn->scn_phys.scn_bookmark.zb_object) {
712 			dprintf("resuming at %llx/%llx/%llx/%llx\n",
713 			    (longlong_t)zb->zb_objset,
714 			    (longlong_t)zb->zb_object,
715 			    (longlong_t)zb->zb_level,
716 			    (longlong_t)zb->zb_blkid);
717 			bzero(&scn->scn_phys.scn_bookmark, sizeof (*zb));
718 		}
719 	}
720 	return (B_FALSE);
721 }
722 
723 /*
724  * Return nonzero on i/o error.
725  * Return new buf to write out in *bufp.
726  */
727 static int
728 dsl_scan_recurse(dsl_scan_t *scn, dsl_dataset_t *ds, dmu_objset_type_t ostype,
729     dnode_phys_t *dnp, const blkptr_t *bp,
730     const zbookmark_phys_t *zb, dmu_tx_t *tx)
731 {
732 	dsl_pool_t *dp = scn->scn_dp;
733 	int zio_flags = ZIO_FLAG_CANFAIL | ZIO_FLAG_SCAN_THREAD;
734 	int err;
735 
736 	if (BP_GET_LEVEL(bp) > 0) {
737 		arc_flags_t flags = ARC_FLAG_WAIT;
738 		int i;
739 		blkptr_t *cbp;
740 		int epb = BP_GET_LSIZE(bp) >> SPA_BLKPTRSHIFT;
741 		arc_buf_t *buf;
742 
743 		err = arc_read(NULL, dp->dp_spa, bp, arc_getbuf_func, &buf,
744 		    ZIO_PRIORITY_ASYNC_READ, zio_flags, &flags, zb);
745 		if (err) {
746 			scn->scn_phys.scn_errors++;
747 			return (err);
748 		}
749 		for (i = 0, cbp = buf->b_data; i < epb; i++, cbp++) {
750 			dsl_scan_prefetch(scn, buf, cbp, zb->zb_objset,
751 			    zb->zb_object, zb->zb_blkid * epb + i);
752 		}
753 		for (i = 0, cbp = buf->b_data; i < epb; i++, cbp++) {
754 			zbookmark_phys_t czb;
755 
756 			SET_BOOKMARK(&czb, zb->zb_objset, zb->zb_object,
757 			    zb->zb_level - 1,
758 			    zb->zb_blkid * epb + i);
759 			dsl_scan_visitbp(cbp, &czb, dnp,
760 			    ds, scn, ostype, tx);
761 		}
762 		arc_buf_destroy(buf, &buf);
763 	} else if (BP_GET_TYPE(bp) == DMU_OT_DNODE) {
764 		arc_flags_t flags = ARC_FLAG_WAIT;
765 		dnode_phys_t *cdnp;
766 		int i, j;
767 		int epb = BP_GET_LSIZE(bp) >> DNODE_SHIFT;
768 		arc_buf_t *buf;
769 
770 		err = arc_read(NULL, dp->dp_spa, bp, arc_getbuf_func, &buf,
771 		    ZIO_PRIORITY_ASYNC_READ, zio_flags, &flags, zb);
772 		if (err) {
773 			scn->scn_phys.scn_errors++;
774 			return (err);
775 		}
776 		for (i = 0, cdnp = buf->b_data; i < epb; i++, cdnp++) {
777 			for (j = 0; j < cdnp->dn_nblkptr; j++) {
778 				blkptr_t *cbp = &cdnp->dn_blkptr[j];
779 				dsl_scan_prefetch(scn, buf, cbp,
780 				    zb->zb_objset, zb->zb_blkid * epb + i, j);
781 			}
782 		}
783 		for (i = 0, cdnp = buf->b_data; i < epb; i++, cdnp++) {
784 			dsl_scan_visitdnode(scn, ds, ostype,
785 			    cdnp, zb->zb_blkid * epb + i, tx);
786 		}
787 
788 		arc_buf_destroy(buf, &buf);
789 	} else if (BP_GET_TYPE(bp) == DMU_OT_OBJSET) {
790 		arc_flags_t flags = ARC_FLAG_WAIT;
791 		objset_phys_t *osp;
792 		arc_buf_t *buf;
793 
794 		err = arc_read(NULL, dp->dp_spa, bp, arc_getbuf_func, &buf,
795 		    ZIO_PRIORITY_ASYNC_READ, zio_flags, &flags, zb);
796 		if (err) {
797 			scn->scn_phys.scn_errors++;
798 			return (err);
799 		}
800 
801 		osp = buf->b_data;
802 
803 		dsl_scan_visitdnode(scn, ds, osp->os_type,
804 		    &osp->os_meta_dnode, DMU_META_DNODE_OBJECT, tx);
805 
806 		if (OBJSET_BUF_HAS_USERUSED(buf)) {
807 			/*
808 			 * We also always visit user/group accounting
809 			 * objects, and never skip them, even if we are
810 			 * suspending.  This is necessary so that the space
811 			 * deltas from this txg get integrated.
812 			 */
813 			dsl_scan_visitdnode(scn, ds, osp->os_type,
814 			    &osp->os_groupused_dnode,
815 			    DMU_GROUPUSED_OBJECT, tx);
816 			dsl_scan_visitdnode(scn, ds, osp->os_type,
817 			    &osp->os_userused_dnode,
818 			    DMU_USERUSED_OBJECT, tx);
819 		}
820 		arc_buf_destroy(buf, &buf);
821 	}
822 
823 	return (0);
824 }
825 
826 static void
827 dsl_scan_visitdnode(dsl_scan_t *scn, dsl_dataset_t *ds,
828     dmu_objset_type_t ostype, dnode_phys_t *dnp,
829     uint64_t object, dmu_tx_t *tx)
830 {
831 	int j;
832 
833 	for (j = 0; j < dnp->dn_nblkptr; j++) {
834 		zbookmark_phys_t czb;
835 
836 		SET_BOOKMARK(&czb, ds ? ds->ds_object : 0, object,
837 		    dnp->dn_nlevels - 1, j);
838 		dsl_scan_visitbp(&dnp->dn_blkptr[j],
839 		    &czb, dnp, ds, scn, ostype, tx);
840 	}
841 
842 	if (dnp->dn_flags & DNODE_FLAG_SPILL_BLKPTR) {
843 		zbookmark_phys_t czb;
844 		SET_BOOKMARK(&czb, ds ? ds->ds_object : 0, object,
845 		    0, DMU_SPILL_BLKID);
846 		dsl_scan_visitbp(&dnp->dn_spill,
847 		    &czb, dnp, ds, scn, ostype, tx);
848 	}
849 }
850 
851 /*
852  * The arguments are in this order because mdb can only print the
853  * first 5; we want them to be useful.
854  */
855 static void
856 dsl_scan_visitbp(blkptr_t *bp, const zbookmark_phys_t *zb,
857     dnode_phys_t *dnp, dsl_dataset_t *ds, dsl_scan_t *scn,
858     dmu_objset_type_t ostype, dmu_tx_t *tx)
859 {
860 	dsl_pool_t *dp = scn->scn_dp;
861 	arc_buf_t *buf = NULL;
862 	blkptr_t bp_toread = *bp;
863 
864 	/* ASSERT(pbuf == NULL || arc_released(pbuf)); */
865 
866 	if (dsl_scan_check_suspend(scn, zb))
867 		return;
868 
869 	if (dsl_scan_check_resume(scn, dnp, zb))
870 		return;
871 
872 	if (BP_IS_HOLE(bp))
873 		return;
874 
875 	scn->scn_visited_this_txg++;
876 
877 	dprintf_bp(bp,
878 	    "visiting ds=%p/%llu zb=%llx/%llx/%llx/%llx bp=%p",
879 	    ds, ds ? ds->ds_object : 0,
880 	    zb->zb_objset, zb->zb_object, zb->zb_level, zb->zb_blkid,
881 	    bp);
882 
883 	if (bp->blk_birth <= scn->scn_phys.scn_cur_min_txg)
884 		return;
885 
886 	if (dsl_scan_recurse(scn, ds, ostype, dnp, &bp_toread, zb, tx) != 0)
887 		return;
888 
889 	/*
890 	 * If dsl_scan_ddt() has already visited this block, it will have
891 	 * already done any translations or scrubbing, so don't call the
892 	 * callback again.
893 	 */
894 	if (ddt_class_contains(dp->dp_spa,
895 	    scn->scn_phys.scn_ddt_class_max, bp)) {
896 		ASSERT(buf == NULL);
897 		return;
898 	}
899 
900 	/*
901 	 * If this block is from the future (after cur_max_txg), then we
902 	 * are doing this on behalf of a deleted snapshot, and we will
903 	 * revisit the future block on the next pass of this dataset.
904 	 * Don't scan it now unless we need to because something
905 	 * under it was modified.
906 	 */
907 	if (BP_PHYSICAL_BIRTH(bp) <= scn->scn_phys.scn_cur_max_txg) {
908 		scan_funcs[scn->scn_phys.scn_func](dp, bp, zb);
909 	}
910 }
911 
912 static void
913 dsl_scan_visit_rootbp(dsl_scan_t *scn, dsl_dataset_t *ds, blkptr_t *bp,
914     dmu_tx_t *tx)
915 {
916 	zbookmark_phys_t zb;
917 
918 	SET_BOOKMARK(&zb, ds ? ds->ds_object : DMU_META_OBJSET,
919 	    ZB_ROOT_OBJECT, ZB_ROOT_LEVEL, ZB_ROOT_BLKID);
920 	dsl_scan_visitbp(bp, &zb, NULL,
921 	    ds, scn, DMU_OST_NONE, tx);
922 
923 	dprintf_ds(ds, "finished scan%s", "");
924 }
925 
926 void
927 dsl_scan_ds_destroyed(dsl_dataset_t *ds, dmu_tx_t *tx)
928 {
929 	dsl_pool_t *dp = ds->ds_dir->dd_pool;
930 	dsl_scan_t *scn = dp->dp_scan;
931 	uint64_t mintxg;
932 
933 	if (scn->scn_phys.scn_state != DSS_SCANNING)
934 		return;
935 
936 	if (scn->scn_phys.scn_bookmark.zb_objset == ds->ds_object) {
937 		if (ds->ds_is_snapshot) {
938 			/*
939 			 * Note:
940 			 *  - scn_cur_{min,max}_txg stays the same.
941 			 *  - Setting the flag is not really necessary if
942 			 *    scn_cur_max_txg == scn_max_txg, because there
943 			 *    is nothing after this snapshot that we care
944 			 *    about.  However, we set it anyway and then
945 			 *    ignore it when we retraverse it in
946 			 *    dsl_scan_visitds().
947 			 */
948 			scn->scn_phys.scn_bookmark.zb_objset =
949 			    dsl_dataset_phys(ds)->ds_next_snap_obj;
950 			zfs_dbgmsg("destroying ds %llu; currently traversing; "
951 			    "reset zb_objset to %llu",
952 			    (u_longlong_t)ds->ds_object,
953 			    (u_longlong_t)dsl_dataset_phys(ds)->
954 			    ds_next_snap_obj);
955 			scn->scn_phys.scn_flags |= DSF_VISIT_DS_AGAIN;
956 		} else {
957 			SET_BOOKMARK(&scn->scn_phys.scn_bookmark,
958 			    ZB_DESTROYED_OBJSET, 0, 0, 0);
959 			zfs_dbgmsg("destroying ds %llu; currently traversing; "
960 			    "reset bookmark to -1,0,0,0",
961 			    (u_longlong_t)ds->ds_object);
962 		}
963 	} else if (zap_lookup_int_key(dp->dp_meta_objset,
964 	    scn->scn_phys.scn_queue_obj, ds->ds_object, &mintxg) == 0) {
965 		ASSERT3U(dsl_dataset_phys(ds)->ds_num_children, <=, 1);
966 		VERIFY3U(0, ==, zap_remove_int(dp->dp_meta_objset,
967 		    scn->scn_phys.scn_queue_obj, ds->ds_object, tx));
968 		if (ds->ds_is_snapshot) {
969 			/*
970 			 * We keep the same mintxg; it could be >
971 			 * ds_creation_txg if the previous snapshot was
972 			 * deleted too.
973 			 */
974 			VERIFY(zap_add_int_key(dp->dp_meta_objset,
975 			    scn->scn_phys.scn_queue_obj,
976 			    dsl_dataset_phys(ds)->ds_next_snap_obj,
977 			    mintxg, tx) == 0);
978 			zfs_dbgmsg("destroying ds %llu; in queue; "
979 			    "replacing with %llu",
980 			    (u_longlong_t)ds->ds_object,
981 			    (u_longlong_t)dsl_dataset_phys(ds)->
982 			    ds_next_snap_obj);
983 		} else {
984 			zfs_dbgmsg("destroying ds %llu; in queue; removing",
985 			    (u_longlong_t)ds->ds_object);
986 		}
987 	}
988 
989 	/*
990 	 * dsl_scan_sync() should be called after this, and should sync
991 	 * out our changed state, but just to be safe, do it here.
992 	 */
993 	dsl_scan_sync_state(scn, tx);
994 }
995 
996 void
997 dsl_scan_ds_snapshotted(dsl_dataset_t *ds, dmu_tx_t *tx)
998 {
999 	dsl_pool_t *dp = ds->ds_dir->dd_pool;
1000 	dsl_scan_t *scn = dp->dp_scan;
1001 	uint64_t mintxg;
1002 
1003 	if (scn->scn_phys.scn_state != DSS_SCANNING)
1004 		return;
1005 
1006 	ASSERT(dsl_dataset_phys(ds)->ds_prev_snap_obj != 0);
1007 
1008 	if (scn->scn_phys.scn_bookmark.zb_objset == ds->ds_object) {
1009 		scn->scn_phys.scn_bookmark.zb_objset =
1010 		    dsl_dataset_phys(ds)->ds_prev_snap_obj;
1011 		zfs_dbgmsg("snapshotting ds %llu; currently traversing; "
1012 		    "reset zb_objset to %llu",
1013 		    (u_longlong_t)ds->ds_object,
1014 		    (u_longlong_t)dsl_dataset_phys(ds)->ds_prev_snap_obj);
1015 	} else if (zap_lookup_int_key(dp->dp_meta_objset,
1016 	    scn->scn_phys.scn_queue_obj, ds->ds_object, &mintxg) == 0) {
1017 		VERIFY3U(0, ==, zap_remove_int(dp->dp_meta_objset,
1018 		    scn->scn_phys.scn_queue_obj, ds->ds_object, tx));
1019 		VERIFY(zap_add_int_key(dp->dp_meta_objset,
1020 		    scn->scn_phys.scn_queue_obj,
1021 		    dsl_dataset_phys(ds)->ds_prev_snap_obj, mintxg, tx) == 0);
1022 		zfs_dbgmsg("snapshotting ds %llu; in queue; "
1023 		    "replacing with %llu",
1024 		    (u_longlong_t)ds->ds_object,
1025 		    (u_longlong_t)dsl_dataset_phys(ds)->ds_prev_snap_obj);
1026 	}
1027 	dsl_scan_sync_state(scn, tx);
1028 }
1029 
1030 void
1031 dsl_scan_ds_clone_swapped(dsl_dataset_t *ds1, dsl_dataset_t *ds2, dmu_tx_t *tx)
1032 {
1033 	dsl_pool_t *dp = ds1->ds_dir->dd_pool;
1034 	dsl_scan_t *scn = dp->dp_scan;
1035 	uint64_t mintxg;
1036 
1037 	if (scn->scn_phys.scn_state != DSS_SCANNING)
1038 		return;
1039 
1040 	if (scn->scn_phys.scn_bookmark.zb_objset == ds1->ds_object) {
1041 		scn->scn_phys.scn_bookmark.zb_objset = ds2->ds_object;
1042 		zfs_dbgmsg("clone_swap ds %llu; currently traversing; "
1043 		    "reset zb_objset to %llu",
1044 		    (u_longlong_t)ds1->ds_object,
1045 		    (u_longlong_t)ds2->ds_object);
1046 	} else if (scn->scn_phys.scn_bookmark.zb_objset == ds2->ds_object) {
1047 		scn->scn_phys.scn_bookmark.zb_objset = ds1->ds_object;
1048 		zfs_dbgmsg("clone_swap ds %llu; currently traversing; "
1049 		    "reset zb_objset to %llu",
1050 		    (u_longlong_t)ds2->ds_object,
1051 		    (u_longlong_t)ds1->ds_object);
1052 	}
1053 
1054 	if (zap_lookup_int_key(dp->dp_meta_objset, scn->scn_phys.scn_queue_obj,
1055 	    ds1->ds_object, &mintxg) == 0) {
1056 		int err;
1057 
1058 		ASSERT3U(mintxg, ==, dsl_dataset_phys(ds1)->ds_prev_snap_txg);
1059 		ASSERT3U(mintxg, ==, dsl_dataset_phys(ds2)->ds_prev_snap_txg);
1060 		VERIFY3U(0, ==, zap_remove_int(dp->dp_meta_objset,
1061 		    scn->scn_phys.scn_queue_obj, ds1->ds_object, tx));
1062 		err = zap_add_int_key(dp->dp_meta_objset,
1063 		    scn->scn_phys.scn_queue_obj, ds2->ds_object, mintxg, tx);
1064 		VERIFY(err == 0 || err == EEXIST);
1065 		if (err == EEXIST) {
1066 			/* Both were there to begin with */
1067 			VERIFY(0 == zap_add_int_key(dp->dp_meta_objset,
1068 			    scn->scn_phys.scn_queue_obj,
1069 			    ds1->ds_object, mintxg, tx));
1070 		}
1071 		zfs_dbgmsg("clone_swap ds %llu; in queue; "
1072 		    "replacing with %llu",
1073 		    (u_longlong_t)ds1->ds_object,
1074 		    (u_longlong_t)ds2->ds_object);
1075 	} else if (zap_lookup_int_key(dp->dp_meta_objset,
1076 	    scn->scn_phys.scn_queue_obj, ds2->ds_object, &mintxg) == 0) {
1077 		ASSERT3U(mintxg, ==, dsl_dataset_phys(ds1)->ds_prev_snap_txg);
1078 		ASSERT3U(mintxg, ==, dsl_dataset_phys(ds2)->ds_prev_snap_txg);
1079 		VERIFY3U(0, ==, zap_remove_int(dp->dp_meta_objset,
1080 		    scn->scn_phys.scn_queue_obj, ds2->ds_object, tx));
1081 		VERIFY(0 == zap_add_int_key(dp->dp_meta_objset,
1082 		    scn->scn_phys.scn_queue_obj, ds1->ds_object, mintxg, tx));
1083 		zfs_dbgmsg("clone_swap ds %llu; in queue; "
1084 		    "replacing with %llu",
1085 		    (u_longlong_t)ds2->ds_object,
1086 		    (u_longlong_t)ds1->ds_object);
1087 	}
1088 
1089 	dsl_scan_sync_state(scn, tx);
1090 }
1091 
1092 struct enqueue_clones_arg {
1093 	dmu_tx_t *tx;
1094 	uint64_t originobj;
1095 };
1096 
1097 /* ARGSUSED */
1098 static int
1099 enqueue_clones_cb(dsl_pool_t *dp, dsl_dataset_t *hds, void *arg)
1100 {
1101 	struct enqueue_clones_arg *eca = arg;
1102 	dsl_dataset_t *ds;
1103 	int err;
1104 	dsl_scan_t *scn = dp->dp_scan;
1105 
1106 	if (dsl_dir_phys(hds->ds_dir)->dd_origin_obj != eca->originobj)
1107 		return (0);
1108 
1109 	err = dsl_dataset_hold_obj(dp, hds->ds_object, FTAG, &ds);
1110 	if (err)
1111 		return (err);
1112 
1113 	while (dsl_dataset_phys(ds)->ds_prev_snap_obj != eca->originobj) {
1114 		dsl_dataset_t *prev;
1115 		err = dsl_dataset_hold_obj(dp,
1116 		    dsl_dataset_phys(ds)->ds_prev_snap_obj, FTAG, &prev);
1117 
1118 		dsl_dataset_rele(ds, FTAG);
1119 		if (err)
1120 			return (err);
1121 		ds = prev;
1122 	}
1123 	VERIFY(zap_add_int_key(dp->dp_meta_objset,
1124 	    scn->scn_phys.scn_queue_obj, ds->ds_object,
1125 	    dsl_dataset_phys(ds)->ds_prev_snap_txg, eca->tx) == 0);
1126 	dsl_dataset_rele(ds, FTAG);
1127 	return (0);
1128 }
1129 
1130 static void
1131 dsl_scan_visitds(dsl_scan_t *scn, uint64_t dsobj, dmu_tx_t *tx)
1132 {
1133 	dsl_pool_t *dp = scn->scn_dp;
1134 	dsl_dataset_t *ds;
1135 
1136 	VERIFY3U(0, ==, dsl_dataset_hold_obj(dp, dsobj, FTAG, &ds));
1137 
1138 	if (scn->scn_phys.scn_cur_min_txg >=
1139 	    scn->scn_phys.scn_max_txg) {
1140 		/*
1141 		 * This can happen if this snapshot was created after the
1142 		 * scan started, and we already completed a previous snapshot
1143 		 * that was created after the scan started.  This snapshot
1144 		 * only references blocks with:
1145 		 *
1146 		 *	birth < our ds_creation_txg
1147 		 *	cur_min_txg is no less than ds_creation_txg.
1148 		 *	We have already visited these blocks.
1149 		 * or
1150 		 *	birth > scn_max_txg
1151 		 *	The scan requested not to visit these blocks.
1152 		 *
1153 		 * Subsequent snapshots (and clones) can reference our
1154 		 * blocks, or blocks with even higher birth times.
1155 		 * Therefore we do not need to visit them either,
1156 		 * so we do not add them to the work queue.
1157 		 *
1158 		 * Note that checking for cur_min_txg >= cur_max_txg
1159 		 * is not sufficient, because in that case we may need to
1160 		 * visit subsequent snapshots.  This happens when min_txg > 0,
1161 		 * which raises cur_min_txg.  In this case we will visit
1162 		 * this dataset but skip all of its blocks, because the
1163 		 * rootbp's birth time is < cur_min_txg.  Then we will
1164 		 * add the next snapshots/clones to the work queue.
1165 		 */
1166 		char *dsname = kmem_alloc(MAXNAMELEN, KM_SLEEP);
1167 		dsl_dataset_name(ds, dsname);
1168 		zfs_dbgmsg("scanning dataset %llu (%s) is unnecessary because "
1169 		    "cur_min_txg (%llu) >= max_txg (%llu)",
1170 		    dsobj, dsname,
1171 		    scn->scn_phys.scn_cur_min_txg,
1172 		    scn->scn_phys.scn_max_txg);
1173 		kmem_free(dsname, MAXNAMELEN);
1174 
1175 		goto out;
1176 	}
1177 
1178 	/*
1179 	 * Only the ZIL in the head (non-snapshot) is valid. Even though
1180 	 * snapshots can have ZIL block pointers (which may be the same
1181 	 * BP as in the head), they must be ignored. In addition, $ORIGIN
1182 	 * doesn't have a objset (i.e. its ds_bp is a hole) so we don't
1183 	 * need to look for a ZIL in it either. So we traverse the ZIL here,
1184 	 * rather than in scan_recurse(), because the regular snapshot
1185 	 * block-sharing rules don't apply to it.
1186 	 */
1187 	if (DSL_SCAN_IS_SCRUB_RESILVER(scn) && !dsl_dataset_is_snapshot(ds) &&
1188 	    (dp->dp_origin_snap == NULL ||
1189 	    ds->ds_dir != dp->dp_origin_snap->ds_dir)) {
1190 		objset_t *os;
1191 		if (dmu_objset_from_ds(ds, &os) != 0) {
1192 			goto out;
1193 		}
1194 		dsl_scan_zil(dp, &os->os_zil_header);
1195 	}
1196 
1197 	/*
1198 	 * Iterate over the bps in this ds.
1199 	 */
1200 	dmu_buf_will_dirty(ds->ds_dbuf, tx);
1201 	rrw_enter(&ds->ds_bp_rwlock, RW_READER, FTAG);
1202 	dsl_scan_visit_rootbp(scn, ds, &dsl_dataset_phys(ds)->ds_bp, tx);
1203 	rrw_exit(&ds->ds_bp_rwlock, FTAG);
1204 
1205 	char *dsname = kmem_alloc(ZFS_MAX_DATASET_NAME_LEN, KM_SLEEP);
1206 	dsl_dataset_name(ds, dsname);
1207 	zfs_dbgmsg("scanned dataset %llu (%s) with min=%llu max=%llu; "
1208 	    "suspending=%u",
1209 	    (longlong_t)dsobj, dsname,
1210 	    (longlong_t)scn->scn_phys.scn_cur_min_txg,
1211 	    (longlong_t)scn->scn_phys.scn_cur_max_txg,
1212 	    (int)scn->scn_suspending);
1213 	kmem_free(dsname, ZFS_MAX_DATASET_NAME_LEN);
1214 
1215 	if (scn->scn_suspending)
1216 		goto out;
1217 
1218 	/*
1219 	 * We've finished this pass over this dataset.
1220 	 */
1221 
1222 	/*
1223 	 * If we did not completely visit this dataset, do another pass.
1224 	 */
1225 	if (scn->scn_phys.scn_flags & DSF_VISIT_DS_AGAIN) {
1226 		zfs_dbgmsg("incomplete pass; visiting again");
1227 		scn->scn_phys.scn_flags &= ~DSF_VISIT_DS_AGAIN;
1228 		VERIFY(zap_add_int_key(dp->dp_meta_objset,
1229 		    scn->scn_phys.scn_queue_obj, ds->ds_object,
1230 		    scn->scn_phys.scn_cur_max_txg, tx) == 0);
1231 		goto out;
1232 	}
1233 
1234 	/*
1235 	 * Add descendent datasets to work queue.
1236 	 */
1237 	if (dsl_dataset_phys(ds)->ds_next_snap_obj != 0) {
1238 		VERIFY(zap_add_int_key(dp->dp_meta_objset,
1239 		    scn->scn_phys.scn_queue_obj,
1240 		    dsl_dataset_phys(ds)->ds_next_snap_obj,
1241 		    dsl_dataset_phys(ds)->ds_creation_txg, tx) == 0);
1242 	}
1243 	if (dsl_dataset_phys(ds)->ds_num_children > 1) {
1244 		boolean_t usenext = B_FALSE;
1245 		if (dsl_dataset_phys(ds)->ds_next_clones_obj != 0) {
1246 			uint64_t count;
1247 			/*
1248 			 * A bug in a previous version of the code could
1249 			 * cause upgrade_clones_cb() to not set
1250 			 * ds_next_snap_obj when it should, leading to a
1251 			 * missing entry.  Therefore we can only use the
1252 			 * next_clones_obj when its count is correct.
1253 			 */
1254 			int err = zap_count(dp->dp_meta_objset,
1255 			    dsl_dataset_phys(ds)->ds_next_clones_obj, &count);
1256 			if (err == 0 &&
1257 			    count == dsl_dataset_phys(ds)->ds_num_children - 1)
1258 				usenext = B_TRUE;
1259 		}
1260 
1261 		if (usenext) {
1262 			VERIFY0(zap_join_key(dp->dp_meta_objset,
1263 			    dsl_dataset_phys(ds)->ds_next_clones_obj,
1264 			    scn->scn_phys.scn_queue_obj,
1265 			    dsl_dataset_phys(ds)->ds_creation_txg, tx));
1266 		} else {
1267 			struct enqueue_clones_arg eca;
1268 			eca.tx = tx;
1269 			eca.originobj = ds->ds_object;
1270 
1271 			VERIFY0(dmu_objset_find_dp(dp, dp->dp_root_dir_obj,
1272 			    enqueue_clones_cb, &eca, DS_FIND_CHILDREN));
1273 		}
1274 	}
1275 
1276 out:
1277 	dsl_dataset_rele(ds, FTAG);
1278 }
1279 
1280 /* ARGSUSED */
1281 static int
1282 enqueue_cb(dsl_pool_t *dp, dsl_dataset_t *hds, void *arg)
1283 {
1284 	dmu_tx_t *tx = arg;
1285 	dsl_dataset_t *ds;
1286 	int err;
1287 	dsl_scan_t *scn = dp->dp_scan;
1288 
1289 	err = dsl_dataset_hold_obj(dp, hds->ds_object, FTAG, &ds);
1290 	if (err)
1291 		return (err);
1292 
1293 	while (dsl_dataset_phys(ds)->ds_prev_snap_obj != 0) {
1294 		dsl_dataset_t *prev;
1295 		err = dsl_dataset_hold_obj(dp,
1296 		    dsl_dataset_phys(ds)->ds_prev_snap_obj, FTAG, &prev);
1297 		if (err) {
1298 			dsl_dataset_rele(ds, FTAG);
1299 			return (err);
1300 		}
1301 
1302 		/*
1303 		 * If this is a clone, we don't need to worry about it for now.
1304 		 */
1305 		if (dsl_dataset_phys(prev)->ds_next_snap_obj != ds->ds_object) {
1306 			dsl_dataset_rele(ds, FTAG);
1307 			dsl_dataset_rele(prev, FTAG);
1308 			return (0);
1309 		}
1310 		dsl_dataset_rele(ds, FTAG);
1311 		ds = prev;
1312 	}
1313 
1314 	VERIFY(zap_add_int_key(dp->dp_meta_objset, scn->scn_phys.scn_queue_obj,
1315 	    ds->ds_object, dsl_dataset_phys(ds)->ds_prev_snap_txg, tx) == 0);
1316 	dsl_dataset_rele(ds, FTAG);
1317 	return (0);
1318 }
1319 
1320 /*
1321  * Scrub/dedup interaction.
1322  *
1323  * If there are N references to a deduped block, we don't want to scrub it
1324  * N times -- ideally, we should scrub it exactly once.
1325  *
1326  * We leverage the fact that the dde's replication class (enum ddt_class)
1327  * is ordered from highest replication class (DDT_CLASS_DITTO) to lowest
1328  * (DDT_CLASS_UNIQUE) so that we may walk the DDT in that order.
1329  *
1330  * To prevent excess scrubbing, the scrub begins by walking the DDT
1331  * to find all blocks with refcnt > 1, and scrubs each of these once.
1332  * Since there are two replication classes which contain blocks with
1333  * refcnt > 1, we scrub the highest replication class (DDT_CLASS_DITTO) first.
1334  * Finally the top-down scrub begins, only visiting blocks with refcnt == 1.
1335  *
1336  * There would be nothing more to say if a block's refcnt couldn't change
1337  * during a scrub, but of course it can so we must account for changes
1338  * in a block's replication class.
1339  *
1340  * Here's an example of what can occur:
1341  *
1342  * If a block has refcnt > 1 during the DDT scrub phase, but has refcnt == 1
1343  * when visited during the top-down scrub phase, it will be scrubbed twice.
1344  * This negates our scrub optimization, but is otherwise harmless.
1345  *
1346  * If a block has refcnt == 1 during the DDT scrub phase, but has refcnt > 1
1347  * on each visit during the top-down scrub phase, it will never be scrubbed.
1348  * To catch this, ddt_sync_entry() notifies the scrub code whenever a block's
1349  * reference class transitions to a higher level (i.e DDT_CLASS_UNIQUE to
1350  * DDT_CLASS_DUPLICATE); if it transitions from refcnt == 1 to refcnt > 1
1351  * while a scrub is in progress, it scrubs the block right then.
1352  */
1353 static void
1354 dsl_scan_ddt(dsl_scan_t *scn, dmu_tx_t *tx)
1355 {
1356 	ddt_bookmark_t *ddb = &scn->scn_phys.scn_ddt_bookmark;
1357 	ddt_entry_t dde = { 0 };
1358 	int error;
1359 	uint64_t n = 0;
1360 
1361 	while ((error = ddt_walk(scn->scn_dp->dp_spa, ddb, &dde)) == 0) {
1362 		ddt_t *ddt;
1363 
1364 		if (ddb->ddb_class > scn->scn_phys.scn_ddt_class_max)
1365 			break;
1366 		dprintf("visiting ddb=%llu/%llu/%llu/%llx\n",
1367 		    (longlong_t)ddb->ddb_class,
1368 		    (longlong_t)ddb->ddb_type,
1369 		    (longlong_t)ddb->ddb_checksum,
1370 		    (longlong_t)ddb->ddb_cursor);
1371 
1372 		/* There should be no pending changes to the dedup table */
1373 		ddt = scn->scn_dp->dp_spa->spa_ddt[ddb->ddb_checksum];
1374 		ASSERT(avl_first(&ddt->ddt_tree) == NULL);
1375 
1376 		dsl_scan_ddt_entry(scn, ddb->ddb_checksum, &dde, tx);
1377 		n++;
1378 
1379 		if (dsl_scan_check_suspend(scn, NULL))
1380 			break;
1381 	}
1382 
1383 	zfs_dbgmsg("scanned %llu ddt entries with class_max = %u; "
1384 	    "suspending=%u", (longlong_t)n,
1385 	    (int)scn->scn_phys.scn_ddt_class_max, (int)scn->scn_suspending);
1386 
1387 	ASSERT(error == 0 || error == ENOENT);
1388 	ASSERT(error != ENOENT ||
1389 	    ddb->ddb_class > scn->scn_phys.scn_ddt_class_max);
1390 }
1391 
1392 /* ARGSUSED */
1393 void
1394 dsl_scan_ddt_entry(dsl_scan_t *scn, enum zio_checksum checksum,
1395     ddt_entry_t *dde, dmu_tx_t *tx)
1396 {
1397 	const ddt_key_t *ddk = &dde->dde_key;
1398 	ddt_phys_t *ddp = dde->dde_phys;
1399 	blkptr_t bp;
1400 	zbookmark_phys_t zb = { 0 };
1401 
1402 	if (scn->scn_phys.scn_state != DSS_SCANNING)
1403 		return;
1404 
1405 	for (int p = 0; p < DDT_PHYS_TYPES; p++, ddp++) {
1406 		if (ddp->ddp_phys_birth == 0 ||
1407 		    ddp->ddp_phys_birth > scn->scn_phys.scn_max_txg)
1408 			continue;
1409 		ddt_bp_create(checksum, ddk, ddp, &bp);
1410 
1411 		scn->scn_visited_this_txg++;
1412 		scan_funcs[scn->scn_phys.scn_func](scn->scn_dp, &bp, &zb);
1413 	}
1414 }
1415 
1416 static void
1417 dsl_scan_visit(dsl_scan_t *scn, dmu_tx_t *tx)
1418 {
1419 	dsl_pool_t *dp = scn->scn_dp;
1420 	zap_cursor_t zc;
1421 	zap_attribute_t za;
1422 
1423 	if (scn->scn_phys.scn_ddt_bookmark.ddb_class <=
1424 	    scn->scn_phys.scn_ddt_class_max) {
1425 		scn->scn_phys.scn_cur_min_txg = scn->scn_phys.scn_min_txg;
1426 		scn->scn_phys.scn_cur_max_txg = scn->scn_phys.scn_max_txg;
1427 		dsl_scan_ddt(scn, tx);
1428 		if (scn->scn_suspending)
1429 			return;
1430 	}
1431 
1432 	if (scn->scn_phys.scn_bookmark.zb_objset == DMU_META_OBJSET) {
1433 		/* First do the MOS & ORIGIN */
1434 
1435 		scn->scn_phys.scn_cur_min_txg = scn->scn_phys.scn_min_txg;
1436 		scn->scn_phys.scn_cur_max_txg = scn->scn_phys.scn_max_txg;
1437 		dsl_scan_visit_rootbp(scn, NULL,
1438 		    &dp->dp_meta_rootbp, tx);
1439 		spa_set_rootblkptr(dp->dp_spa, &dp->dp_meta_rootbp);
1440 		if (scn->scn_suspending)
1441 			return;
1442 
1443 		if (spa_version(dp->dp_spa) < SPA_VERSION_DSL_SCRUB) {
1444 			VERIFY0(dmu_objset_find_dp(dp, dp->dp_root_dir_obj,
1445 			    enqueue_cb, tx, DS_FIND_CHILDREN));
1446 		} else {
1447 			dsl_scan_visitds(scn,
1448 			    dp->dp_origin_snap->ds_object, tx);
1449 		}
1450 		ASSERT(!scn->scn_suspending);
1451 	} else if (scn->scn_phys.scn_bookmark.zb_objset !=
1452 	    ZB_DESTROYED_OBJSET) {
1453 		/*
1454 		 * If we were suspended, continue from here.  Note if the
1455 		 * ds we were suspended on was deleted, the zb_objset may
1456 		 * be -1, so we will skip this and find a new objset
1457 		 * below.
1458 		 */
1459 		dsl_scan_visitds(scn, scn->scn_phys.scn_bookmark.zb_objset, tx);
1460 		if (scn->scn_suspending)
1461 			return;
1462 	}
1463 
1464 	/*
1465 	 * In case we were suspended right at the end of the ds, zero the
1466 	 * bookmark so we don't think that we're still trying to resume.
1467 	 */
1468 	bzero(&scn->scn_phys.scn_bookmark, sizeof (zbookmark_phys_t));
1469 
1470 	/* keep pulling things out of the zap-object-as-queue */
1471 	while (zap_cursor_init(&zc, dp->dp_meta_objset,
1472 	    scn->scn_phys.scn_queue_obj),
1473 	    zap_cursor_retrieve(&zc, &za) == 0) {
1474 		dsl_dataset_t *ds;
1475 		uint64_t dsobj;
1476 
1477 		dsobj = zfs_strtonum(za.za_name, NULL);
1478 		VERIFY3U(0, ==, zap_remove_int(dp->dp_meta_objset,
1479 		    scn->scn_phys.scn_queue_obj, dsobj, tx));
1480 
1481 		/* Set up min/max txg */
1482 		VERIFY3U(0, ==, dsl_dataset_hold_obj(dp, dsobj, FTAG, &ds));
1483 		if (za.za_first_integer != 0) {
1484 			scn->scn_phys.scn_cur_min_txg =
1485 			    MAX(scn->scn_phys.scn_min_txg,
1486 			    za.za_first_integer);
1487 		} else {
1488 			scn->scn_phys.scn_cur_min_txg =
1489 			    MAX(scn->scn_phys.scn_min_txg,
1490 			    dsl_dataset_phys(ds)->ds_prev_snap_txg);
1491 		}
1492 		scn->scn_phys.scn_cur_max_txg = dsl_scan_ds_maxtxg(ds);
1493 		dsl_dataset_rele(ds, FTAG);
1494 
1495 		dsl_scan_visitds(scn, dsobj, tx);
1496 		zap_cursor_fini(&zc);
1497 		if (scn->scn_suspending)
1498 			return;
1499 	}
1500 	zap_cursor_fini(&zc);
1501 }
1502 
1503 static boolean_t
1504 dsl_scan_async_block_should_pause(dsl_scan_t *scn)
1505 {
1506 	uint64_t elapsed_nanosecs;
1507 
1508 	if (zfs_recover)
1509 		return (B_FALSE);
1510 
1511 	if (scn->scn_visited_this_txg >= zfs_async_block_max_blocks)
1512 		return (B_TRUE);
1513 
1514 	elapsed_nanosecs = gethrtime() - scn->scn_sync_start_time;
1515 	return (elapsed_nanosecs / NANOSEC > zfs_txg_timeout ||
1516 	    (NSEC2MSEC(elapsed_nanosecs) > scn->scn_async_block_min_time_ms &&
1517 	    txg_sync_waiting(scn->scn_dp)) ||
1518 	    spa_shutting_down(scn->scn_dp->dp_spa));
1519 }
1520 
1521 static int
1522 dsl_scan_free_block_cb(void *arg, const blkptr_t *bp, dmu_tx_t *tx)
1523 {
1524 	dsl_scan_t *scn = arg;
1525 
1526 	if (!scn->scn_is_bptree ||
1527 	    (BP_GET_LEVEL(bp) == 0 && BP_GET_TYPE(bp) != DMU_OT_OBJSET)) {
1528 		if (dsl_scan_async_block_should_pause(scn))
1529 			return (SET_ERROR(ERESTART));
1530 	}
1531 
1532 	zio_nowait(zio_free_sync(scn->scn_zio_root, scn->scn_dp->dp_spa,
1533 	    dmu_tx_get_txg(tx), bp, 0));
1534 	dsl_dir_diduse_space(tx->tx_pool->dp_free_dir, DD_USED_HEAD,
1535 	    -bp_get_dsize_sync(scn->scn_dp->dp_spa, bp),
1536 	    -BP_GET_PSIZE(bp), -BP_GET_UCSIZE(bp), tx);
1537 	scn->scn_visited_this_txg++;
1538 	return (0);
1539 }
1540 
1541 static int
1542 dsl_scan_obsolete_block_cb(void *arg, const blkptr_t *bp, dmu_tx_t *tx)
1543 {
1544 	dsl_scan_t *scn = arg;
1545 	const dva_t *dva = &bp->blk_dva[0];
1546 
1547 	if (dsl_scan_async_block_should_pause(scn))
1548 		return (SET_ERROR(ERESTART));
1549 
1550 	spa_vdev_indirect_mark_obsolete(scn->scn_dp->dp_spa,
1551 	    DVA_GET_VDEV(dva), DVA_GET_OFFSET(dva),
1552 	    DVA_GET_ASIZE(dva), tx);
1553 	scn->scn_visited_this_txg++;
1554 	return (0);
1555 }
1556 
1557 boolean_t
1558 dsl_scan_active(dsl_scan_t *scn)
1559 {
1560 	spa_t *spa = scn->scn_dp->dp_spa;
1561 	uint64_t used = 0, comp, uncomp;
1562 
1563 	if (spa->spa_load_state != SPA_LOAD_NONE)
1564 		return (B_FALSE);
1565 	if (spa_shutting_down(spa))
1566 		return (B_FALSE);
1567 	if ((scn->scn_phys.scn_state == DSS_SCANNING &&
1568 	    !dsl_scan_is_paused_scrub(scn)) ||
1569 	    (scn->scn_async_destroying && !scn->scn_async_stalled))
1570 		return (B_TRUE);
1571 
1572 	if (spa_version(scn->scn_dp->dp_spa) >= SPA_VERSION_DEADLISTS) {
1573 		(void) bpobj_space(&scn->scn_dp->dp_free_bpobj,
1574 		    &used, &comp, &uncomp);
1575 	}
1576 	return (used != 0);
1577 }
1578 
1579 static int
1580 dsl_process_async_destroys(dsl_pool_t *dp, dmu_tx_t *tx)
1581 {
1582 	dsl_scan_t *scn = dp->dp_scan;
1583 	spa_t *spa = dp->dp_spa;
1584 	int err = 0;
1585 
1586 	if (spa_suspend_async_destroy(spa))
1587 		return (0);
1588 
1589 	if (zfs_free_bpobj_enabled &&
1590 	    spa_version(dp->dp_spa) >= SPA_VERSION_DEADLISTS) {
1591 		scn->scn_is_bptree = B_FALSE;
1592 		scn->scn_async_block_min_time_ms = zfs_free_min_time_ms;
1593 		scn->scn_zio_root = zio_root(dp->dp_spa, NULL,
1594 		    NULL, ZIO_FLAG_MUSTSUCCEED);
1595 		err = bpobj_iterate(&dp->dp_free_bpobj,
1596 		    dsl_scan_free_block_cb, scn, tx);
1597 		VERIFY3U(0, ==, zio_wait(scn->scn_zio_root));
1598 
1599 		if (err != 0 && err != ERESTART)
1600 			zfs_panic_recover("error %u from bpobj_iterate()", err);
1601 	}
1602 
1603 	if (err == 0 && spa_feature_is_active(spa, SPA_FEATURE_ASYNC_DESTROY)) {
1604 		ASSERT(scn->scn_async_destroying);
1605 		scn->scn_is_bptree = B_TRUE;
1606 		scn->scn_zio_root = zio_root(dp->dp_spa, NULL,
1607 		    NULL, ZIO_FLAG_MUSTSUCCEED);
1608 		err = bptree_iterate(dp->dp_meta_objset,
1609 		    dp->dp_bptree_obj, B_TRUE, dsl_scan_free_block_cb, scn, tx);
1610 		VERIFY0(zio_wait(scn->scn_zio_root));
1611 
1612 		if (err == EIO || err == ECKSUM) {
1613 			err = 0;
1614 		} else if (err != 0 && err != ERESTART) {
1615 			zfs_panic_recover("error %u from "
1616 			    "traverse_dataset_destroyed()", err);
1617 		}
1618 
1619 		if (bptree_is_empty(dp->dp_meta_objset, dp->dp_bptree_obj)) {
1620 			/* finished; deactivate async destroy feature */
1621 			spa_feature_decr(spa, SPA_FEATURE_ASYNC_DESTROY, tx);
1622 			ASSERT(!spa_feature_is_active(spa,
1623 			    SPA_FEATURE_ASYNC_DESTROY));
1624 			VERIFY0(zap_remove(dp->dp_meta_objset,
1625 			    DMU_POOL_DIRECTORY_OBJECT,
1626 			    DMU_POOL_BPTREE_OBJ, tx));
1627 			VERIFY0(bptree_free(dp->dp_meta_objset,
1628 			    dp->dp_bptree_obj, tx));
1629 			dp->dp_bptree_obj = 0;
1630 			scn->scn_async_destroying = B_FALSE;
1631 			scn->scn_async_stalled = B_FALSE;
1632 		} else {
1633 			/*
1634 			 * If we didn't make progress, mark the async
1635 			 * destroy as stalled, so that we will not initiate
1636 			 * a spa_sync() on its behalf.  Note that we only
1637 			 * check this if we are not finished, because if the
1638 			 * bptree had no blocks for us to visit, we can
1639 			 * finish without "making progress".
1640 			 */
1641 			scn->scn_async_stalled =
1642 			    (scn->scn_visited_this_txg == 0);
1643 		}
1644 	}
1645 	if (scn->scn_visited_this_txg) {
1646 		zfs_dbgmsg("freed %llu blocks in %llums from "
1647 		    "free_bpobj/bptree txg %llu; err=%u",
1648 		    (longlong_t)scn->scn_visited_this_txg,
1649 		    (longlong_t)
1650 		    NSEC2MSEC(gethrtime() - scn->scn_sync_start_time),
1651 		    (longlong_t)tx->tx_txg, err);
1652 		scn->scn_visited_this_txg = 0;
1653 
1654 		/*
1655 		 * Write out changes to the DDT that may be required as a
1656 		 * result of the blocks freed.  This ensures that the DDT
1657 		 * is clean when a scrub/resilver runs.
1658 		 */
1659 		ddt_sync(spa, tx->tx_txg);
1660 	}
1661 	if (err != 0)
1662 		return (err);
1663 	if (dp->dp_free_dir != NULL && !scn->scn_async_destroying &&
1664 	    zfs_free_leak_on_eio &&
1665 	    (dsl_dir_phys(dp->dp_free_dir)->dd_used_bytes != 0 ||
1666 	    dsl_dir_phys(dp->dp_free_dir)->dd_compressed_bytes != 0 ||
1667 	    dsl_dir_phys(dp->dp_free_dir)->dd_uncompressed_bytes != 0)) {
1668 		/*
1669 		 * We have finished background destroying, but there is still
1670 		 * some space left in the dp_free_dir. Transfer this leaked
1671 		 * space to the dp_leak_dir.
1672 		 */
1673 		if (dp->dp_leak_dir == NULL) {
1674 			rrw_enter(&dp->dp_config_rwlock, RW_WRITER, FTAG);
1675 			(void) dsl_dir_create_sync(dp, dp->dp_root_dir,
1676 			    LEAK_DIR_NAME, tx);
1677 			VERIFY0(dsl_pool_open_special_dir(dp,
1678 			    LEAK_DIR_NAME, &dp->dp_leak_dir));
1679 			rrw_exit(&dp->dp_config_rwlock, FTAG);
1680 		}
1681 		dsl_dir_diduse_space(dp->dp_leak_dir, DD_USED_HEAD,
1682 		    dsl_dir_phys(dp->dp_free_dir)->dd_used_bytes,
1683 		    dsl_dir_phys(dp->dp_free_dir)->dd_compressed_bytes,
1684 		    dsl_dir_phys(dp->dp_free_dir)->dd_uncompressed_bytes, tx);
1685 		dsl_dir_diduse_space(dp->dp_free_dir, DD_USED_HEAD,
1686 		    -dsl_dir_phys(dp->dp_free_dir)->dd_used_bytes,
1687 		    -dsl_dir_phys(dp->dp_free_dir)->dd_compressed_bytes,
1688 		    -dsl_dir_phys(dp->dp_free_dir)->dd_uncompressed_bytes, tx);
1689 	}
1690 
1691 	if (dp->dp_free_dir != NULL && !scn->scn_async_destroying) {
1692 		/* finished; verify that space accounting went to zero */
1693 		ASSERT0(dsl_dir_phys(dp->dp_free_dir)->dd_used_bytes);
1694 		ASSERT0(dsl_dir_phys(dp->dp_free_dir)->dd_compressed_bytes);
1695 		ASSERT0(dsl_dir_phys(dp->dp_free_dir)->dd_uncompressed_bytes);
1696 	}
1697 
1698 	EQUIV(bpobj_is_open(&dp->dp_obsolete_bpobj),
1699 	    0 == zap_contains(dp->dp_meta_objset, DMU_POOL_DIRECTORY_OBJECT,
1700 	    DMU_POOL_OBSOLETE_BPOBJ));
1701 	if (err == 0 && bpobj_is_open(&dp->dp_obsolete_bpobj)) {
1702 		ASSERT(spa_feature_is_active(dp->dp_spa,
1703 		    SPA_FEATURE_OBSOLETE_COUNTS));
1704 
1705 		scn->scn_is_bptree = B_FALSE;
1706 		scn->scn_async_block_min_time_ms = zfs_obsolete_min_time_ms;
1707 		err = bpobj_iterate(&dp->dp_obsolete_bpobj,
1708 		    dsl_scan_obsolete_block_cb, scn, tx);
1709 		if (err != 0 && err != ERESTART)
1710 			zfs_panic_recover("error %u from bpobj_iterate()", err);
1711 
1712 		if (bpobj_is_empty(&dp->dp_obsolete_bpobj))
1713 			dsl_pool_destroy_obsolete_bpobj(dp, tx);
1714 	}
1715 
1716 	return (0);
1717 }
1718 
1719 void
1720 dsl_scan_sync(dsl_pool_t *dp, dmu_tx_t *tx)
1721 {
1722 	dsl_scan_t *scn = dp->dp_scan;
1723 	spa_t *spa = dp->dp_spa;
1724 	int err = 0;
1725 
1726 	/*
1727 	 * Check for scn_restart_txg before checking spa_load_state, so
1728 	 * that we can restart an old-style scan while the pool is being
1729 	 * imported (see dsl_scan_init).
1730 	 */
1731 	if (dsl_scan_restarting(scn, tx)) {
1732 		pool_scan_func_t func = POOL_SCAN_SCRUB;
1733 		dsl_scan_done(scn, B_FALSE, tx);
1734 		if (vdev_resilver_needed(spa->spa_root_vdev, NULL, NULL))
1735 			func = POOL_SCAN_RESILVER;
1736 		zfs_dbgmsg("restarting scan func=%u txg=%llu",
1737 		    func, tx->tx_txg);
1738 		dsl_scan_setup_sync(&func, tx);
1739 	}
1740 
1741 	/*
1742 	 * Only process scans in sync pass 1.
1743 	 */
1744 	if (spa_sync_pass(dp->dp_spa) > 1)
1745 		return;
1746 
1747 	/*
1748 	 * If the spa is shutting down, then stop scanning. This will
1749 	 * ensure that the scan does not dirty any new data during the
1750 	 * shutdown phase.
1751 	 */
1752 	if (spa_shutting_down(spa))
1753 		return;
1754 
1755 	/*
1756 	 * If the scan is inactive due to a stalled async destroy, try again.
1757 	 */
1758 	if (!scn->scn_async_stalled && !dsl_scan_active(scn))
1759 		return;
1760 
1761 	scn->scn_visited_this_txg = 0;
1762 	scn->scn_suspending = B_FALSE;
1763 	scn->scn_sync_start_time = gethrtime();
1764 	spa->spa_scrub_active = B_TRUE;
1765 
1766 	/*
1767 	 * First process the async destroys.  If we pause, don't do
1768 	 * any scrubbing or resilvering.  This ensures that there are no
1769 	 * async destroys while we are scanning, so the scan code doesn't
1770 	 * have to worry about traversing it.  It is also faster to free the
1771 	 * blocks than to scrub them.
1772 	 */
1773 	err = dsl_process_async_destroys(dp, tx);
1774 	if (err != 0)
1775 		return;
1776 
1777 	if (scn->scn_phys.scn_state != DSS_SCANNING)
1778 		return;
1779 
1780 	if (scn->scn_done_txg == tx->tx_txg) {
1781 		ASSERT(!scn->scn_suspending);
1782 		/* finished with scan. */
1783 		zfs_dbgmsg("txg %llu scan complete", tx->tx_txg);
1784 		dsl_scan_done(scn, B_TRUE, tx);
1785 		ASSERT3U(spa->spa_scrub_inflight, ==, 0);
1786 		dsl_scan_sync_state(scn, tx);
1787 		return;
1788 	}
1789 
1790 	if (dsl_scan_is_paused_scrub(scn))
1791 		return;
1792 
1793 	if (scn->scn_phys.scn_ddt_bookmark.ddb_class <=
1794 	    scn->scn_phys.scn_ddt_class_max) {
1795 		zfs_dbgmsg("doing scan sync txg %llu; "
1796 		    "ddt bm=%llu/%llu/%llu/%llx",
1797 		    (longlong_t)tx->tx_txg,
1798 		    (longlong_t)scn->scn_phys.scn_ddt_bookmark.ddb_class,
1799 		    (longlong_t)scn->scn_phys.scn_ddt_bookmark.ddb_type,
1800 		    (longlong_t)scn->scn_phys.scn_ddt_bookmark.ddb_checksum,
1801 		    (longlong_t)scn->scn_phys.scn_ddt_bookmark.ddb_cursor);
1802 		ASSERT(scn->scn_phys.scn_bookmark.zb_objset == 0);
1803 		ASSERT(scn->scn_phys.scn_bookmark.zb_object == 0);
1804 		ASSERT(scn->scn_phys.scn_bookmark.zb_level == 0);
1805 		ASSERT(scn->scn_phys.scn_bookmark.zb_blkid == 0);
1806 	} else {
1807 		zfs_dbgmsg("doing scan sync txg %llu; bm=%llu/%llu/%llu/%llu",
1808 		    (longlong_t)tx->tx_txg,
1809 		    (longlong_t)scn->scn_phys.scn_bookmark.zb_objset,
1810 		    (longlong_t)scn->scn_phys.scn_bookmark.zb_object,
1811 		    (longlong_t)scn->scn_phys.scn_bookmark.zb_level,
1812 		    (longlong_t)scn->scn_phys.scn_bookmark.zb_blkid);
1813 	}
1814 
1815 	scn->scn_zio_root = zio_root(dp->dp_spa, NULL,
1816 	    NULL, ZIO_FLAG_CANFAIL);
1817 	dsl_pool_config_enter(dp, FTAG);
1818 	dsl_scan_visit(scn, tx);
1819 	dsl_pool_config_exit(dp, FTAG);
1820 	(void) zio_wait(scn->scn_zio_root);
1821 	scn->scn_zio_root = NULL;
1822 
1823 	zfs_dbgmsg("visited %llu blocks in %llums",
1824 	    (longlong_t)scn->scn_visited_this_txg,
1825 	    (longlong_t)NSEC2MSEC(gethrtime() - scn->scn_sync_start_time));
1826 
1827 	if (!scn->scn_suspending) {
1828 		scn->scn_done_txg = tx->tx_txg + 1;
1829 		zfs_dbgmsg("txg %llu traversal complete, waiting till txg %llu",
1830 		    tx->tx_txg, scn->scn_done_txg);
1831 	}
1832 
1833 	if (DSL_SCAN_IS_SCRUB_RESILVER(scn)) {
1834 		mutex_enter(&spa->spa_scrub_lock);
1835 		while (spa->spa_scrub_inflight > 0) {
1836 			cv_wait(&spa->spa_scrub_io_cv,
1837 			    &spa->spa_scrub_lock);
1838 		}
1839 		mutex_exit(&spa->spa_scrub_lock);
1840 	}
1841 
1842 	dsl_scan_sync_state(scn, tx);
1843 }
1844 
1845 /*
1846  * This will start a new scan, or restart an existing one.
1847  */
1848 void
1849 dsl_resilver_restart(dsl_pool_t *dp, uint64_t txg)
1850 {
1851 	if (txg == 0) {
1852 		dmu_tx_t *tx;
1853 		tx = dmu_tx_create_dd(dp->dp_mos_dir);
1854 		VERIFY(0 == dmu_tx_assign(tx, TXG_WAIT));
1855 
1856 		txg = dmu_tx_get_txg(tx);
1857 		dp->dp_scan->scn_restart_txg = txg;
1858 		dmu_tx_commit(tx);
1859 	} else {
1860 		dp->dp_scan->scn_restart_txg = txg;
1861 	}
1862 	zfs_dbgmsg("restarting resilver txg=%llu", txg);
1863 }
1864 
1865 boolean_t
1866 dsl_scan_resilvering(dsl_pool_t *dp)
1867 {
1868 	return (dp->dp_scan->scn_phys.scn_state == DSS_SCANNING &&
1869 	    dp->dp_scan->scn_phys.scn_func == POOL_SCAN_RESILVER);
1870 }
1871 
1872 /*
1873  * scrub consumers
1874  */
1875 
1876 static void
1877 count_block(zfs_all_blkstats_t *zab, const blkptr_t *bp)
1878 {
1879 	int i;
1880 
1881 	/*
1882 	 * If we resume after a reboot, zab will be NULL; don't record
1883 	 * incomplete stats in that case.
1884 	 */
1885 	if (zab == NULL)
1886 		return;
1887 
1888 	for (i = 0; i < 4; i++) {
1889 		int l = (i < 2) ? BP_GET_LEVEL(bp) : DN_MAX_LEVELS;
1890 		int t = (i & 1) ? BP_GET_TYPE(bp) : DMU_OT_TOTAL;
1891 		if (t & DMU_OT_NEWTYPE)
1892 			t = DMU_OT_OTHER;
1893 		zfs_blkstat_t *zb = &zab->zab_type[l][t];
1894 		int equal;
1895 
1896 		zb->zb_count++;
1897 		zb->zb_asize += BP_GET_ASIZE(bp);
1898 		zb->zb_lsize += BP_GET_LSIZE(bp);
1899 		zb->zb_psize += BP_GET_PSIZE(bp);
1900 		zb->zb_gangs += BP_COUNT_GANG(bp);
1901 
1902 		switch (BP_GET_NDVAS(bp)) {
1903 		case 2:
1904 			if (DVA_GET_VDEV(&bp->blk_dva[0]) ==
1905 			    DVA_GET_VDEV(&bp->blk_dva[1]))
1906 				zb->zb_ditto_2_of_2_samevdev++;
1907 			break;
1908 		case 3:
1909 			equal = (DVA_GET_VDEV(&bp->blk_dva[0]) ==
1910 			    DVA_GET_VDEV(&bp->blk_dva[1])) +
1911 			    (DVA_GET_VDEV(&bp->blk_dva[0]) ==
1912 			    DVA_GET_VDEV(&bp->blk_dva[2])) +
1913 			    (DVA_GET_VDEV(&bp->blk_dva[1]) ==
1914 			    DVA_GET_VDEV(&bp->blk_dva[2]));
1915 			if (equal == 1)
1916 				zb->zb_ditto_2_of_3_samevdev++;
1917 			else if (equal == 3)
1918 				zb->zb_ditto_3_of_3_samevdev++;
1919 			break;
1920 		}
1921 	}
1922 }
1923 
1924 static void
1925 dsl_scan_scrub_done(zio_t *zio)
1926 {
1927 	spa_t *spa = zio->io_spa;
1928 
1929 	abd_free(zio->io_abd);
1930 
1931 	mutex_enter(&spa->spa_scrub_lock);
1932 	spa->spa_scrub_inflight--;
1933 	cv_broadcast(&spa->spa_scrub_io_cv);
1934 
1935 	if (zio->io_error && (zio->io_error != ECKSUM ||
1936 	    !(zio->io_flags & ZIO_FLAG_SPECULATIVE))) {
1937 		spa->spa_dsl_pool->dp_scan->scn_phys.scn_errors++;
1938 	}
1939 	mutex_exit(&spa->spa_scrub_lock);
1940 }
1941 
1942 static int
1943 dsl_scan_scrub_cb(dsl_pool_t *dp,
1944     const blkptr_t *bp, const zbookmark_phys_t *zb)
1945 {
1946 	dsl_scan_t *scn = dp->dp_scan;
1947 	size_t size = BP_GET_PSIZE(bp);
1948 	spa_t *spa = dp->dp_spa;
1949 	uint64_t phys_birth = BP_PHYSICAL_BIRTH(bp);
1950 	boolean_t needs_io;
1951 	int zio_flags = ZIO_FLAG_SCAN_THREAD | ZIO_FLAG_RAW | ZIO_FLAG_CANFAIL;
1952 	int scan_delay = 0;
1953 
1954 	count_block(dp->dp_blkstats, bp);
1955 
1956 	if (phys_birth <= scn->scn_phys.scn_min_txg ||
1957 	    phys_birth >= scn->scn_phys.scn_max_txg)
1958 		return (0);
1959 
1960 	/* Embedded BP's have phys_birth==0, so we reject them above. */
1961 	ASSERT(!BP_IS_EMBEDDED(bp));
1962 
1963 	ASSERT(DSL_SCAN_IS_SCRUB_RESILVER(scn));
1964 	if (scn->scn_phys.scn_func == POOL_SCAN_SCRUB) {
1965 		zio_flags |= ZIO_FLAG_SCRUB;
1966 		needs_io = B_TRUE;
1967 		scan_delay = zfs_scrub_delay;
1968 	} else {
1969 		ASSERT3U(scn->scn_phys.scn_func, ==, POOL_SCAN_RESILVER);
1970 		zio_flags |= ZIO_FLAG_RESILVER;
1971 		needs_io = B_FALSE;
1972 		scan_delay = zfs_resilver_delay;
1973 	}
1974 
1975 	/* If it's an intent log block, failure is expected. */
1976 	if (zb->zb_level == ZB_ZIL_LEVEL)
1977 		zio_flags |= ZIO_FLAG_SPECULATIVE;
1978 
1979 	for (int d = 0; d < BP_GET_NDVAS(bp); d++) {
1980 		vdev_t *vd = vdev_lookup_top(spa,
1981 		    DVA_GET_VDEV(&bp->blk_dva[d]));
1982 
1983 		/*
1984 		 * Keep track of how much data we've examined so that
1985 		 * zpool(1M) status can make useful progress reports.
1986 		 */
1987 		scn->scn_phys.scn_examined += DVA_GET_ASIZE(&bp->blk_dva[d]);
1988 		spa->spa_scan_pass_exam += DVA_GET_ASIZE(&bp->blk_dva[d]);
1989 
1990 		/* if it's a resilver, this may not be in the target range */
1991 		if (!needs_io) {
1992 			if (vd->vdev_ops == &vdev_indirect_ops) {
1993 				/*
1994 				 * The indirect vdev can point to multiple
1995 				 * vdevs.  For simplicity, always create
1996 				 * the resilver zio_t. zio_vdev_io_start()
1997 				 * will bypass the child resilver i/o's if
1998 				 * they are on vdevs that don't have DTL's.
1999 				 */
2000 				needs_io = B_TRUE;
2001 			} else if (DVA_GET_GANG(&bp->blk_dva[d])) {
2002 				/*
2003 				 * Gang members may be spread across multiple
2004 				 * vdevs, so the best estimate we have is the
2005 				 * scrub range, which has already been checked.
2006 				 * XXX -- it would be better to change our
2007 				 * allocation policy to ensure that all
2008 				 * gang members reside on the same vdev.
2009 				 */
2010 				needs_io = B_TRUE;
2011 			} else {
2012 				needs_io = vdev_dtl_contains(vd, DTL_PARTIAL,
2013 				    phys_birth, 1);
2014 			}
2015 		}
2016 	}
2017 
2018 	if (needs_io && !zfs_no_scrub_io) {
2019 		vdev_t *rvd = spa->spa_root_vdev;
2020 		uint64_t maxinflight = rvd->vdev_children * zfs_top_maxinflight;
2021 
2022 		mutex_enter(&spa->spa_scrub_lock);
2023 		while (spa->spa_scrub_inflight >= maxinflight)
2024 			cv_wait(&spa->spa_scrub_io_cv, &spa->spa_scrub_lock);
2025 		spa->spa_scrub_inflight++;
2026 		mutex_exit(&spa->spa_scrub_lock);
2027 
2028 		/*
2029 		 * If we're seeing recent (zfs_scan_idle) "important" I/Os
2030 		 * then throttle our workload to limit the impact of a scan.
2031 		 */
2032 		if (ddi_get_lbolt64() - spa->spa_last_io <= zfs_scan_idle)
2033 			delay(scan_delay);
2034 
2035 		zio_nowait(zio_read(NULL, spa, bp,
2036 		    abd_alloc_for_io(size, B_FALSE), size, dsl_scan_scrub_done,
2037 		    NULL, ZIO_PRIORITY_SCRUB, zio_flags, zb));
2038 	}
2039 
2040 	/* do not relocate this block */
2041 	return (0);
2042 }
2043 
2044 /*
2045  * Called by the ZFS_IOC_POOL_SCAN ioctl to start a scrub or resilver.
2046  * Can also be called to resume a paused scrub.
2047  */
2048 int
2049 dsl_scan(dsl_pool_t *dp, pool_scan_func_t func)
2050 {
2051 	spa_t *spa = dp->dp_spa;
2052 	dsl_scan_t *scn = dp->dp_scan;
2053 
2054 	/*
2055 	 * Purge all vdev caches and probe all devices.  We do this here
2056 	 * rather than in sync context because this requires a writer lock
2057 	 * on the spa_config lock, which we can't do from sync context.  The
2058 	 * spa_scrub_reopen flag indicates that vdev_open() should not
2059 	 * attempt to start another scrub.
2060 	 */
2061 	spa_vdev_state_enter(spa, SCL_NONE);
2062 	spa->spa_scrub_reopen = B_TRUE;
2063 	vdev_reopen(spa->spa_root_vdev);
2064 	spa->spa_scrub_reopen = B_FALSE;
2065 	(void) spa_vdev_state_exit(spa, NULL, 0);
2066 
2067 	if (func == POOL_SCAN_SCRUB && dsl_scan_is_paused_scrub(scn)) {
2068 		/* got scrub start cmd, resume paused scrub */
2069 		int err = dsl_scrub_set_pause_resume(scn->scn_dp,
2070 		    POOL_SCRUB_NORMAL);
2071 		if (err == 0) {
2072 			spa_event_notify(spa, NULL, NULL, ESC_ZFS_SCRUB_RESUME);
2073 			return (ECANCELED);
2074 		}
2075 
2076 		return (SET_ERROR(err));
2077 	}
2078 
2079 	return (dsl_sync_task(spa_name(spa), dsl_scan_setup_check,
2080 	    dsl_scan_setup_sync, &func, 0, ZFS_SPACE_CHECK_EXTRA_RESERVED));
2081 }
2082 
2083 static boolean_t
2084 dsl_scan_restarting(dsl_scan_t *scn, dmu_tx_t *tx)
2085 {
2086 	return (scn->scn_restart_txg != 0 &&
2087 	    scn->scn_restart_txg <= tx->tx_txg);
2088 }
2089