vdev_indirect.c revision ac04831df9010f533275633d3bb9829b86c171d3
1/*
2 * CDDL HEADER START
3 *
4 * This file and its contents are supplied under the terms of the
5 * Common Development and Distribution License ("CDDL"), version 1.0.
6 * You may only use this file in accordance with the terms of version
7 * 1.0 of the CDDL.
8 *
9 * A full copy of the text of the CDDL should have accompanied this
10 * source.  A copy of the CDDL is also available via the Internet at
11 * http://www.illumos.org/license/CDDL.
12 *
13 * CDDL HEADER END
14 */
15
16/*
17 * Copyright (c) 2014, 2019 by Delphix. All rights reserved.
18 * Copyright 2019 Joyent, Inc.
19 */
20
21#include <sys/zfs_context.h>
22#include <sys/spa.h>
23#include <sys/spa_impl.h>
24#include <sys/vdev_impl.h>
25#include <sys/fs/zfs.h>
26#include <sys/zio.h>
27#include <sys/zio_checksum.h>
28#include <sys/metaslab.h>
29#include <sys/refcount.h>
30#include <sys/dmu.h>
31#include <sys/vdev_indirect_mapping.h>
32#include <sys/dmu_tx.h>
33#include <sys/dsl_synctask.h>
34#include <sys/zap.h>
35#include <sys/abd.h>
36#include <sys/zthr.h>
37
38/*
39 * An indirect vdev corresponds to a vdev that has been removed.  Since
40 * we cannot rewrite block pointers of snapshots, etc., we keep a
41 * mapping from old location on the removed device to the new location
42 * on another device in the pool and use this mapping whenever we need
43 * to access the DVA.  Unfortunately, this mapping did not respect
44 * logical block boundaries when it was first created, and so a DVA on
45 * this indirect vdev may be "split" into multiple sections that each
46 * map to a different location.  As a consequence, not all DVAs can be
47 * translated to an equivalent new DVA.  Instead we must provide a
48 * "vdev_remap" operation that executes a callback on each contiguous
49 * segment of the new location.  This function is used in multiple ways:
50 *
51 *  - i/os to this vdev use the callback to determine where the
52 *    data is now located, and issue child i/os for each segment's new
53 *    location.
54 *
55 *  - frees and claims to this vdev use the callback to free or claim
56 *    each mapped segment.  (Note that we don't actually need to claim
57 *    log blocks on indirect vdevs, because we don't allocate to
58 *    removing vdevs.  However, zdb uses zio_claim() for its leak
59 *    detection.)
60 */
61
62/*
63 * "Big theory statement" for how we mark blocks obsolete.
64 *
65 * When a block on an indirect vdev is freed or remapped, a section of
66 * that vdev's mapping may no longer be referenced (aka "obsolete").  We
67 * keep track of how much of each mapping entry is obsolete.  When
68 * an entry becomes completely obsolete, we can remove it, thus reducing
69 * the memory used by the mapping.  The complete picture of obsolescence
70 * is given by the following data structures, described below:
71 *  - the entry-specific obsolete count
72 *  - the vdev-specific obsolete spacemap
73 *  - the pool-specific obsolete bpobj
74 *
75 * == On disk data structures used ==
76 *
77 * We track the obsolete space for the pool using several objects.  Each
78 * of these objects is created on demand and freed when no longer
79 * needed, and is assumed to be empty if it does not exist.
80 * SPA_FEATURE_OBSOLETE_COUNTS includes the count of these objects.
81 *
82 *  - Each vic_mapping_object (associated with an indirect vdev) can
83 *    have a vimp_counts_object.  This is an array of uint32_t's
84 *    with the same number of entries as the vic_mapping_object.  When
85 *    the mapping is condensed, entries from the vic_obsolete_sm_object
86 *    (see below) are folded into the counts.  Therefore, each
87 *    obsolete_counts entry tells us the number of bytes in the
88 *    corresponding mapping entry that were not referenced when the
89 *    mapping was last condensed.
90 *
91 *  - Each indirect or removing vdev can have a vic_obsolete_sm_object.
92 *    This is a space map containing an alloc entry for every DVA that
93 *    has been obsoleted since the last time this indirect vdev was
94 *    condensed.  We use this object in order to improve performance
95 *    when marking a DVA as obsolete.  Instead of modifying an arbitrary
96 *    offset of the vimp_counts_object, we only need to append an entry
97 *    to the end of this object.  When a DVA becomes obsolete, it is
98 *    added to the obsolete space map.  This happens when the DVA is
99 *    freed, remapped and not referenced by a snapshot, or the last
100 *    snapshot referencing it is destroyed.
101 *
102 *  - Each dataset can have a ds_remap_deadlist object.  This is a
103 *    deadlist object containing all blocks that were remapped in this
104 *    dataset but referenced in a previous snapshot.  Blocks can *only*
105 *    appear on this list if they were remapped (dsl_dataset_block_remapped);
106 *    blocks that were killed in a head dataset are put on the normal
107 *    ds_deadlist and marked obsolete when they are freed.
108 *
109 *  - The pool can have a dp_obsolete_bpobj.  This is a list of blocks
110 *    in the pool that need to be marked obsolete.  When a snapshot is
111 *    destroyed, we move some of the ds_remap_deadlist to the obsolete
112 *    bpobj (see dsl_destroy_snapshot_handle_remaps()).  We then
113 *    asynchronously process the obsolete bpobj, moving its entries to
114 *    the specific vdevs' obsolete space maps.
115 *
116 * == Summary of how we mark blocks as obsolete ==
117 *
118 * - When freeing a block: if any DVA is on an indirect vdev, append to
119 *   vic_obsolete_sm_object.
120 * - When remapping a block, add dva to ds_remap_deadlist (if prev snap
121 *   references; otherwise append to vic_obsolete_sm_object).
122 * - When freeing a snapshot: move parts of ds_remap_deadlist to
123 *   dp_obsolete_bpobj (same algorithm as ds_deadlist).
124 * - When syncing the spa: process dp_obsolete_bpobj, moving ranges to
125 *   individual vdev's vic_obsolete_sm_object.
126 */
127
128/*
129 * "Big theory statement" for how we condense indirect vdevs.
130 *
131 * Condensing an indirect vdev's mapping is the process of determining
132 * the precise counts of obsolete space for each mapping entry (by
133 * integrating the obsolete spacemap into the obsolete counts) and
134 * writing out a new mapping that contains only referenced entries.
135 *
136 * We condense a vdev when we expect the mapping to shrink (see
137 * vdev_indirect_should_condense()), but only perform one condense at a
138 * time to limit the memory usage.  In addition, we use a separate
139 * open-context thread (spa_condense_indirect_thread) to incrementally
140 * create the new mapping object in a way that minimizes the impact on
141 * the rest of the system.
142 *
143 * == Generating a new mapping ==
144 *
145 * To generate a new mapping, we follow these steps:
146 *
147 * 1. Save the old obsolete space map and create a new mapping object
148 *    (see spa_condense_indirect_start_sync()).  This initializes the
149 *    spa_condensing_indirect_phys with the "previous obsolete space map",
150 *    which is now read only.  Newly obsolete DVAs will be added to a
151 *    new (initially empty) obsolete space map, and will not be
152 *    considered as part of this condense operation.
153 *
154 * 2. Construct in memory the precise counts of obsolete space for each
155 *    mapping entry, by incorporating the obsolete space map into the
156 *    counts.  (See vdev_indirect_mapping_load_obsolete_{counts,spacemap}().)
157 *
158 * 3. Iterate through each mapping entry, writing to the new mapping any
159 *    entries that are not completely obsolete (i.e. which don't have
160 *    obsolete count == mapping length).  (See
161 *    spa_condense_indirect_generate_new_mapping().)
162 *
163 * 4. Destroy the old mapping object and switch over to the new one
164 *    (spa_condense_indirect_complete_sync).
165 *
166 * == Restarting from failure ==
167 *
168 * To restart the condense when we import/open the pool, we must start
169 * at the 2nd step above: reconstruct the precise counts in memory,
170 * based on the space map + counts.  Then in the 3rd step, we start
171 * iterating where we left off: at vimp_max_offset of the new mapping
172 * object.
173 */
174
175boolean_t zfs_condense_indirect_vdevs_enable = B_TRUE;
176
177/*
178 * Condense if at least this percent of the bytes in the mapping is
179 * obsolete.  With the default of 25%, the amount of space mapped
180 * will be reduced to 1% of its original size after at most 16
181 * condenses.  Higher values will condense less often (causing less
182 * i/o); lower values will reduce the mapping size more quickly.
183 */
184int zfs_indirect_condense_obsolete_pct = 25;
185
186/*
187 * Condense if the obsolete space map takes up more than this amount of
188 * space on disk (logically).  This limits the amount of disk space
189 * consumed by the obsolete space map; the default of 1GB is small enough
190 * that we typically don't mind "wasting" it.
191 */
192uint64_t zfs_condense_max_obsolete_bytes = 1024 * 1024 * 1024;
193
194/*
195 * Don't bother condensing if the mapping uses less than this amount of
196 * memory.  The default of 128KB is considered a "trivial" amount of
197 * memory and not worth reducing.
198 */
199uint64_t zfs_condense_min_mapping_bytes = 128 * 1024;
200
201/*
202 * This is used by the test suite so that it can ensure that certain
203 * actions happen while in the middle of a condense (which might otherwise
204 * complete too quickly).  If used to reduce the performance impact of
205 * condensing in production, a maximum value of 1 should be sufficient.
206 */
207int zfs_condense_indirect_commit_entry_delay_ticks = 0;
208
209/*
210 * If an indirect split block contains more than this many possible unique
211 * combinations when being reconstructed, consider it too computationally
212 * expensive to check them all. Instead, try at most 100 randomly-selected
213 * combinations each time the block is accessed.  This allows all segment
214 * copies to participate fairly in the reconstruction when all combinations
215 * cannot be checked and prevents repeated use of one bad copy.
216 */
217int zfs_reconstruct_indirect_combinations_max = 256;
218
219
220/*
221 * Enable to simulate damaged segments and validate reconstruction.
222 * Used by ztest
223 */
224unsigned long zfs_reconstruct_indirect_damage_fraction = 0;
225
226/*
227 * The indirect_child_t represents the vdev that we will read from, when we
228 * need to read all copies of the data (e.g. for scrub or reconstruction).
229 * For plain (non-mirror) top-level vdevs (i.e. is_vdev is not a mirror),
230 * ic_vdev is the same as is_vdev.  However, for mirror top-level vdevs,
231 * ic_vdev is a child of the mirror.
232 */
233typedef struct indirect_child {
234	abd_t *ic_data;
235	vdev_t *ic_vdev;
236
237	/*
238	 * ic_duplicate is NULL when the ic_data contents are unique, when it
239	 * is determined to be a duplicate it references the primary child.
240	 */
241	struct indirect_child *ic_duplicate;
242	list_node_t ic_node; /* node on is_unique_child */
243} indirect_child_t;
244
245/*
246 * The indirect_split_t represents one mapped segment of an i/o to the
247 * indirect vdev. For non-split (contiguously-mapped) blocks, there will be
248 * only one indirect_split_t, with is_split_offset==0 and is_size==io_size.
249 * For split blocks, there will be several of these.
250 */
251typedef struct indirect_split {
252	list_node_t is_node; /* link on iv_splits */
253
254	/*
255	 * is_split_offset is the offset into the i/o.
256	 * This is the sum of the previous splits' is_size's.
257	 */
258	uint64_t is_split_offset;
259
260	vdev_t *is_vdev; /* top-level vdev */
261	uint64_t is_target_offset; /* offset on is_vdev */
262	uint64_t is_size;
263	int is_children; /* number of entries in is_child[] */
264	int is_unique_children; /* number of entries in is_unique_child */
265	list_t is_unique_child;
266
267	/*
268	 * is_good_child is the child that we are currently using to
269	 * attempt reconstruction.
270	 */
271	indirect_child_t *is_good_child;
272
273	indirect_child_t is_child[1]; /* variable-length */
274} indirect_split_t;
275
276/*
277 * The indirect_vsd_t is associated with each i/o to the indirect vdev.
278 * It is the "Vdev-Specific Data" in the zio_t's io_vsd.
279 */
280typedef struct indirect_vsd {
281	boolean_t iv_split_block;
282	boolean_t iv_reconstruct;
283	uint64_t iv_unique_combinations;
284	uint64_t iv_attempts;
285	uint64_t iv_attempts_max;
286
287	list_t iv_splits; /* list of indirect_split_t's */
288} indirect_vsd_t;
289
290static void
291vdev_indirect_map_free(zio_t *zio)
292{
293	indirect_vsd_t *iv = zio->io_vsd;
294
295	indirect_split_t *is;
296	while ((is = list_head(&iv->iv_splits)) != NULL) {
297		for (int c = 0; c < is->is_children; c++) {
298			indirect_child_t *ic = &is->is_child[c];
299			if (ic->ic_data != NULL)
300				abd_free(ic->ic_data);
301		}
302		list_remove(&iv->iv_splits, is);
303
304		indirect_child_t *ic;
305		while ((ic = list_head(&is->is_unique_child)) != NULL)
306			list_remove(&is->is_unique_child, ic);
307
308		list_destroy(&is->is_unique_child);
309
310		kmem_free(is,
311		    offsetof(indirect_split_t, is_child[is->is_children]));
312	}
313	kmem_free(iv, sizeof (*iv));
314}
315
316static const zio_vsd_ops_t vdev_indirect_vsd_ops = {
317	vdev_indirect_map_free,
318	zio_vsd_default_cksum_report
319};
320/*
321 * Mark the given offset and size as being obsolete.
322 */
323void
324vdev_indirect_mark_obsolete(vdev_t *vd, uint64_t offset, uint64_t size)
325{
326	spa_t *spa = vd->vdev_spa;
327
328	ASSERT3U(vd->vdev_indirect_config.vic_mapping_object, !=, 0);
329	ASSERT(vd->vdev_removing || vd->vdev_ops == &vdev_indirect_ops);
330	ASSERT(size > 0);
331	VERIFY(vdev_indirect_mapping_entry_for_offset(
332	    vd->vdev_indirect_mapping, offset) != NULL);
333
334	if (spa_feature_is_enabled(spa, SPA_FEATURE_OBSOLETE_COUNTS)) {
335		mutex_enter(&vd->vdev_obsolete_lock);
336		range_tree_add(vd->vdev_obsolete_segments, offset, size);
337		mutex_exit(&vd->vdev_obsolete_lock);
338		vdev_dirty(vd, 0, NULL, spa_syncing_txg(spa));
339	}
340}
341
342/*
343 * Mark the DVA vdev_id:offset:size as being obsolete in the given tx. This
344 * wrapper is provided because the DMU does not know about vdev_t's and
345 * cannot directly call vdev_indirect_mark_obsolete.
346 */
347void
348spa_vdev_indirect_mark_obsolete(spa_t *spa, uint64_t vdev_id, uint64_t offset,
349    uint64_t size, dmu_tx_t *tx)
350{
351	vdev_t *vd = vdev_lookup_top(spa, vdev_id);
352	ASSERT(dmu_tx_is_syncing(tx));
353
354	/* The DMU can only remap indirect vdevs. */
355	ASSERT3P(vd->vdev_ops, ==, &vdev_indirect_ops);
356	vdev_indirect_mark_obsolete(vd, offset, size);
357}
358
359static spa_condensing_indirect_t *
360spa_condensing_indirect_create(spa_t *spa)
361{
362	spa_condensing_indirect_phys_t *scip =
363	    &spa->spa_condensing_indirect_phys;
364	spa_condensing_indirect_t *sci = kmem_zalloc(sizeof (*sci), KM_SLEEP);
365	objset_t *mos = spa->spa_meta_objset;
366
367	for (int i = 0; i < TXG_SIZE; i++) {
368		list_create(&sci->sci_new_mapping_entries[i],
369		    sizeof (vdev_indirect_mapping_entry_t),
370		    offsetof(vdev_indirect_mapping_entry_t, vime_node));
371	}
372
373	sci->sci_new_mapping =
374	    vdev_indirect_mapping_open(mos, scip->scip_next_mapping_object);
375
376	return (sci);
377}
378
379static void
380spa_condensing_indirect_destroy(spa_condensing_indirect_t *sci)
381{
382	for (int i = 0; i < TXG_SIZE; i++)
383		list_destroy(&sci->sci_new_mapping_entries[i]);
384
385	if (sci->sci_new_mapping != NULL)
386		vdev_indirect_mapping_close(sci->sci_new_mapping);
387
388	kmem_free(sci, sizeof (*sci));
389}
390
391boolean_t
392vdev_indirect_should_condense(vdev_t *vd)
393{
394	vdev_indirect_mapping_t *vim = vd->vdev_indirect_mapping;
395	spa_t *spa = vd->vdev_spa;
396
397	ASSERT(dsl_pool_sync_context(spa->spa_dsl_pool));
398
399	if (!zfs_condense_indirect_vdevs_enable)
400		return (B_FALSE);
401
402	/*
403	 * We can only condense one indirect vdev at a time.
404	 */
405	if (spa->spa_condensing_indirect != NULL)
406		return (B_FALSE);
407
408	if (spa_shutting_down(spa))
409		return (B_FALSE);
410
411	/*
412	 * The mapping object size must not change while we are
413	 * condensing, so we can only condense indirect vdevs
414	 * (not vdevs that are still in the middle of being removed).
415	 */
416	if (vd->vdev_ops != &vdev_indirect_ops)
417		return (B_FALSE);
418
419	/*
420	 * If nothing new has been marked obsolete, there is no
421	 * point in condensing.
422	 */
423	if (vd->vdev_obsolete_sm == NULL) {
424		ASSERT0(vdev_obsolete_sm_object(vd));
425		return (B_FALSE);
426	}
427
428	ASSERT(vd->vdev_obsolete_sm != NULL);
429
430	ASSERT3U(vdev_obsolete_sm_object(vd), ==,
431	    space_map_object(vd->vdev_obsolete_sm));
432
433	uint64_t bytes_mapped = vdev_indirect_mapping_bytes_mapped(vim);
434	uint64_t bytes_obsolete = space_map_allocated(vd->vdev_obsolete_sm);
435	uint64_t mapping_size = vdev_indirect_mapping_size(vim);
436	uint64_t obsolete_sm_size = space_map_length(vd->vdev_obsolete_sm);
437
438	ASSERT3U(bytes_obsolete, <=, bytes_mapped);
439
440	/*
441	 * If a high percentage of the bytes that are mapped have become
442	 * obsolete, condense (unless the mapping is already small enough).
443	 * This has a good chance of reducing the amount of memory used
444	 * by the mapping.
445	 */
446	if (bytes_obsolete * 100 / bytes_mapped >=
447	    zfs_indirect_condense_obsolete_pct &&
448	    mapping_size > zfs_condense_min_mapping_bytes) {
449		zfs_dbgmsg("should condense vdev %llu because obsolete "
450		    "spacemap covers %d%% of %lluMB mapping",
451		    (u_longlong_t)vd->vdev_id,
452		    (int)(bytes_obsolete * 100 / bytes_mapped),
453		    (u_longlong_t)bytes_mapped / 1024 / 1024);
454		return (B_TRUE);
455	}
456
457	/*
458	 * If the obsolete space map takes up too much space on disk,
459	 * condense in order to free up this disk space.
460	 */
461	if (obsolete_sm_size >= zfs_condense_max_obsolete_bytes) {
462		zfs_dbgmsg("should condense vdev %llu because obsolete sm "
463		    "length %lluMB >= max size %lluMB",
464		    (u_longlong_t)vd->vdev_id,
465		    (u_longlong_t)obsolete_sm_size / 1024 / 1024,
466		    (u_longlong_t)zfs_condense_max_obsolete_bytes /
467		    1024 / 1024);
468		return (B_TRUE);
469	}
470
471	return (B_FALSE);
472}
473
474/*
475 * This sync task completes (finishes) a condense, deleting the old
476 * mapping and replacing it with the new one.
477 */
478static void
479spa_condense_indirect_complete_sync(void *arg, dmu_tx_t *tx)
480{
481	spa_condensing_indirect_t *sci = arg;
482	spa_t *spa = dmu_tx_pool(tx)->dp_spa;
483	spa_condensing_indirect_phys_t *scip =
484	    &spa->spa_condensing_indirect_phys;
485	vdev_t *vd = vdev_lookup_top(spa, scip->scip_vdev);
486	vdev_indirect_config_t *vic = &vd->vdev_indirect_config;
487	objset_t *mos = spa->spa_meta_objset;
488	vdev_indirect_mapping_t *old_mapping = vd->vdev_indirect_mapping;
489	uint64_t old_count = vdev_indirect_mapping_num_entries(old_mapping);
490	uint64_t new_count =
491	    vdev_indirect_mapping_num_entries(sci->sci_new_mapping);
492
493	ASSERT(dmu_tx_is_syncing(tx));
494	ASSERT3P(vd->vdev_ops, ==, &vdev_indirect_ops);
495	ASSERT3P(sci, ==, spa->spa_condensing_indirect);
496	for (int i = 0; i < TXG_SIZE; i++) {
497		ASSERT(list_is_empty(&sci->sci_new_mapping_entries[i]));
498	}
499	ASSERT(vic->vic_mapping_object != 0);
500	ASSERT3U(vd->vdev_id, ==, scip->scip_vdev);
501	ASSERT(scip->scip_next_mapping_object != 0);
502	ASSERT(scip->scip_prev_obsolete_sm_object != 0);
503
504	/*
505	 * Reset vdev_indirect_mapping to refer to the new object.
506	 */
507	rw_enter(&vd->vdev_indirect_rwlock, RW_WRITER);
508	vdev_indirect_mapping_close(vd->vdev_indirect_mapping);
509	vd->vdev_indirect_mapping = sci->sci_new_mapping;
510	rw_exit(&vd->vdev_indirect_rwlock);
511
512	sci->sci_new_mapping = NULL;
513	vdev_indirect_mapping_free(mos, vic->vic_mapping_object, tx);
514	vic->vic_mapping_object = scip->scip_next_mapping_object;
515	scip->scip_next_mapping_object = 0;
516
517	space_map_free_obj(mos, scip->scip_prev_obsolete_sm_object, tx);
518	spa_feature_decr(spa, SPA_FEATURE_OBSOLETE_COUNTS, tx);
519	scip->scip_prev_obsolete_sm_object = 0;
520
521	scip->scip_vdev = 0;
522
523	VERIFY0(zap_remove(mos, DMU_POOL_DIRECTORY_OBJECT,
524	    DMU_POOL_CONDENSING_INDIRECT, tx));
525	spa_condensing_indirect_destroy(spa->spa_condensing_indirect);
526	spa->spa_condensing_indirect = NULL;
527
528	zfs_dbgmsg("finished condense of vdev %llu in txg %llu: "
529	    "new mapping object %llu has %llu entries "
530	    "(was %llu entries)",
531	    vd->vdev_id, dmu_tx_get_txg(tx), vic->vic_mapping_object,
532	    new_count, old_count);
533
534	vdev_config_dirty(spa->spa_root_vdev);
535}
536
537/*
538 * This sync task appends entries to the new mapping object.
539 */
540static void
541spa_condense_indirect_commit_sync(void *arg, dmu_tx_t *tx)
542{
543	spa_condensing_indirect_t *sci = arg;
544	uint64_t txg = dmu_tx_get_txg(tx);
545	spa_t *spa = dmu_tx_pool(tx)->dp_spa;
546
547	ASSERT(dmu_tx_is_syncing(tx));
548	ASSERT3P(sci, ==, spa->spa_condensing_indirect);
549
550	vdev_indirect_mapping_add_entries(sci->sci_new_mapping,
551	    &sci->sci_new_mapping_entries[txg & TXG_MASK], tx);
552	ASSERT(list_is_empty(&sci->sci_new_mapping_entries[txg & TXG_MASK]));
553}
554
555/*
556 * Open-context function to add one entry to the new mapping.  The new
557 * entry will be remembered and written from syncing context.
558 */
559static void
560spa_condense_indirect_commit_entry(spa_t *spa,
561    vdev_indirect_mapping_entry_phys_t *vimep, uint32_t count)
562{
563	spa_condensing_indirect_t *sci = spa->spa_condensing_indirect;
564
565	ASSERT3U(count, <, DVA_GET_ASIZE(&vimep->vimep_dst));
566
567	dmu_tx_t *tx = dmu_tx_create_dd(spa_get_dsl(spa)->dp_mos_dir);
568	dmu_tx_hold_space(tx, sizeof (*vimep) + sizeof (count));
569	VERIFY0(dmu_tx_assign(tx, TXG_WAIT));
570	int txgoff = dmu_tx_get_txg(tx) & TXG_MASK;
571
572	/*
573	 * If we are the first entry committed this txg, kick off the sync
574	 * task to write to the MOS on our behalf.
575	 */
576	if (list_is_empty(&sci->sci_new_mapping_entries[txgoff])) {
577		dsl_sync_task_nowait(dmu_tx_pool(tx),
578		    spa_condense_indirect_commit_sync, sci,
579		    0, ZFS_SPACE_CHECK_NONE, tx);
580	}
581
582	vdev_indirect_mapping_entry_t *vime =
583	    kmem_alloc(sizeof (*vime), KM_SLEEP);
584	vime->vime_mapping = *vimep;
585	vime->vime_obsolete_count = count;
586	list_insert_tail(&sci->sci_new_mapping_entries[txgoff], vime);
587
588	dmu_tx_commit(tx);
589}
590
591static void
592spa_condense_indirect_generate_new_mapping(vdev_t *vd,
593    uint32_t *obsolete_counts, uint64_t start_index, zthr_t *zthr)
594{
595	spa_t *spa = vd->vdev_spa;
596	uint64_t mapi = start_index;
597	vdev_indirect_mapping_t *old_mapping = vd->vdev_indirect_mapping;
598	uint64_t old_num_entries =
599	    vdev_indirect_mapping_num_entries(old_mapping);
600
601	ASSERT3P(vd->vdev_ops, ==, &vdev_indirect_ops);
602	ASSERT3U(vd->vdev_id, ==, spa->spa_condensing_indirect_phys.scip_vdev);
603
604	zfs_dbgmsg("starting condense of vdev %llu from index %llu",
605	    (u_longlong_t)vd->vdev_id,
606	    (u_longlong_t)mapi);
607
608	while (mapi < old_num_entries) {
609
610		if (zthr_iscancelled(zthr)) {
611			zfs_dbgmsg("pausing condense of vdev %llu "
612			    "at index %llu", (u_longlong_t)vd->vdev_id,
613			    (u_longlong_t)mapi);
614			break;
615		}
616
617		vdev_indirect_mapping_entry_phys_t *entry =
618		    &old_mapping->vim_entries[mapi];
619		uint64_t entry_size = DVA_GET_ASIZE(&entry->vimep_dst);
620		ASSERT3U(obsolete_counts[mapi], <=, entry_size);
621		if (obsolete_counts[mapi] < entry_size) {
622			spa_condense_indirect_commit_entry(spa, entry,
623			    obsolete_counts[mapi]);
624
625			/*
626			 * This delay may be requested for testing, debugging,
627			 * or performance reasons.
628			 */
629			delay(zfs_condense_indirect_commit_entry_delay_ticks);
630		}
631
632		mapi++;
633	}
634}
635
636/* ARGSUSED */
637static boolean_t
638spa_condense_indirect_thread_check(void *arg, zthr_t *zthr)
639{
640	spa_t *spa = arg;
641
642	return (spa->spa_condensing_indirect != NULL);
643}
644
645/* ARGSUSED */
646static void
647spa_condense_indirect_thread(void *arg, zthr_t *zthr)
648{
649	spa_t *spa = arg;
650	vdev_t *vd;
651
652	ASSERT3P(spa->spa_condensing_indirect, !=, NULL);
653	spa_config_enter(spa, SCL_VDEV, FTAG, RW_READER);
654	vd = vdev_lookup_top(spa, spa->spa_condensing_indirect_phys.scip_vdev);
655	ASSERT3P(vd, !=, NULL);
656	spa_config_exit(spa, SCL_VDEV, FTAG);
657
658	spa_condensing_indirect_t *sci = spa->spa_condensing_indirect;
659	spa_condensing_indirect_phys_t *scip =
660	    &spa->spa_condensing_indirect_phys;
661	uint32_t *counts;
662	uint64_t start_index;
663	vdev_indirect_mapping_t *old_mapping = vd->vdev_indirect_mapping;
664	space_map_t *prev_obsolete_sm = NULL;
665
666	ASSERT3U(vd->vdev_id, ==, scip->scip_vdev);
667	ASSERT(scip->scip_next_mapping_object != 0);
668	ASSERT(scip->scip_prev_obsolete_sm_object != 0);
669	ASSERT3P(vd->vdev_ops, ==, &vdev_indirect_ops);
670
671	for (int i = 0; i < TXG_SIZE; i++) {
672		/*
673		 * The list must start out empty in order for the
674		 * _commit_sync() sync task to be properly registered
675		 * on the first call to _commit_entry(); so it's wise
676		 * to double check and ensure we actually are starting
677		 * with empty lists.
678		 */
679		ASSERT(list_is_empty(&sci->sci_new_mapping_entries[i]));
680	}
681
682	VERIFY0(space_map_open(&prev_obsolete_sm, spa->spa_meta_objset,
683	    scip->scip_prev_obsolete_sm_object, 0, vd->vdev_asize, 0));
684	counts = vdev_indirect_mapping_load_obsolete_counts(old_mapping);
685	if (prev_obsolete_sm != NULL) {
686		vdev_indirect_mapping_load_obsolete_spacemap(old_mapping,
687		    counts, prev_obsolete_sm);
688	}
689	space_map_close(prev_obsolete_sm);
690
691	/*
692	 * Generate new mapping.  Determine what index to continue from
693	 * based on the max offset that we've already written in the
694	 * new mapping.
695	 */
696	uint64_t max_offset =
697	    vdev_indirect_mapping_max_offset(sci->sci_new_mapping);
698	if (max_offset == 0) {
699		/* We haven't written anything to the new mapping yet. */
700		start_index = 0;
701	} else {
702		/*
703		 * Pick up from where we left off. _entry_for_offset()
704		 * returns a pointer into the vim_entries array. If
705		 * max_offset is greater than any of the mappings
706		 * contained in the table  NULL will be returned and
707		 * that indicates we've exhausted our iteration of the
708		 * old_mapping.
709		 */
710
711		vdev_indirect_mapping_entry_phys_t *entry =
712		    vdev_indirect_mapping_entry_for_offset_or_next(old_mapping,
713		    max_offset);
714
715		if (entry == NULL) {
716			/*
717			 * We've already written the whole new mapping.
718			 * This special value will cause us to skip the
719			 * generate_new_mapping step and just do the sync
720			 * task to complete the condense.
721			 */
722			start_index = UINT64_MAX;
723		} else {
724			start_index = entry - old_mapping->vim_entries;
725			ASSERT3U(start_index, <,
726			    vdev_indirect_mapping_num_entries(old_mapping));
727		}
728	}
729
730	spa_condense_indirect_generate_new_mapping(vd, counts,
731	    start_index, zthr);
732
733	vdev_indirect_mapping_free_obsolete_counts(old_mapping, counts);
734
735	/*
736	 * If the zthr has received a cancellation signal while running
737	 * in generate_new_mapping() or at any point after that, then bail
738	 * early. We don't want to complete the condense if the spa is
739	 * shutting down.
740	 */
741	if (zthr_iscancelled(zthr))
742		return;
743
744	VERIFY0(dsl_sync_task(spa_name(spa), NULL,
745	    spa_condense_indirect_complete_sync, sci, 0,
746	    ZFS_SPACE_CHECK_EXTRA_RESERVED));
747}
748
749/*
750 * Sync task to begin the condensing process.
751 */
752void
753spa_condense_indirect_start_sync(vdev_t *vd, dmu_tx_t *tx)
754{
755	spa_t *spa = vd->vdev_spa;
756	spa_condensing_indirect_phys_t *scip =
757	    &spa->spa_condensing_indirect_phys;
758
759	ASSERT0(scip->scip_next_mapping_object);
760	ASSERT0(scip->scip_prev_obsolete_sm_object);
761	ASSERT0(scip->scip_vdev);
762	ASSERT(dmu_tx_is_syncing(tx));
763	ASSERT3P(vd->vdev_ops, ==, &vdev_indirect_ops);
764	ASSERT(spa_feature_is_active(spa, SPA_FEATURE_OBSOLETE_COUNTS));
765	ASSERT(vdev_indirect_mapping_num_entries(vd->vdev_indirect_mapping));
766
767	uint64_t obsolete_sm_obj = vdev_obsolete_sm_object(vd);
768	ASSERT(obsolete_sm_obj != 0);
769
770	scip->scip_vdev = vd->vdev_id;
771	scip->scip_next_mapping_object =
772	    vdev_indirect_mapping_alloc(spa->spa_meta_objset, tx);
773
774	scip->scip_prev_obsolete_sm_object = obsolete_sm_obj;
775
776	/*
777	 * We don't need to allocate a new space map object, since
778	 * vdev_indirect_sync_obsolete will allocate one when needed.
779	 */
780	space_map_close(vd->vdev_obsolete_sm);
781	vd->vdev_obsolete_sm = NULL;
782	VERIFY0(zap_remove(spa->spa_meta_objset, vd->vdev_top_zap,
783	    VDEV_TOP_ZAP_INDIRECT_OBSOLETE_SM, tx));
784
785	VERIFY0(zap_add(spa->spa_dsl_pool->dp_meta_objset,
786	    DMU_POOL_DIRECTORY_OBJECT,
787	    DMU_POOL_CONDENSING_INDIRECT, sizeof (uint64_t),
788	    sizeof (*scip) / sizeof (uint64_t), scip, tx));
789
790	ASSERT3P(spa->spa_condensing_indirect, ==, NULL);
791	spa->spa_condensing_indirect = spa_condensing_indirect_create(spa);
792
793	zfs_dbgmsg("starting condense of vdev %llu in txg %llu: "
794	    "posm=%llu nm=%llu",
795	    vd->vdev_id, dmu_tx_get_txg(tx),
796	    (u_longlong_t)scip->scip_prev_obsolete_sm_object,
797	    (u_longlong_t)scip->scip_next_mapping_object);
798
799	zthr_wakeup(spa->spa_condense_zthr);
800}
801
802/*
803 * Sync to the given vdev's obsolete space map any segments that are no longer
804 * referenced as of the given txg.
805 *
806 * If the obsolete space map doesn't exist yet, create and open it.
807 */
808void
809vdev_indirect_sync_obsolete(vdev_t *vd, dmu_tx_t *tx)
810{
811	spa_t *spa = vd->vdev_spa;
812	vdev_indirect_config_t *vic = &vd->vdev_indirect_config;
813
814	ASSERT3U(vic->vic_mapping_object, !=, 0);
815	ASSERT(range_tree_space(vd->vdev_obsolete_segments) > 0);
816	ASSERT(vd->vdev_removing || vd->vdev_ops == &vdev_indirect_ops);
817	ASSERT(spa_feature_is_enabled(spa, SPA_FEATURE_OBSOLETE_COUNTS));
818
819	if (vdev_obsolete_sm_object(vd) == 0) {
820		uint64_t obsolete_sm_object =
821		    space_map_alloc(spa->spa_meta_objset,
822		    zfs_vdev_standard_sm_blksz, tx);
823
824		ASSERT(vd->vdev_top_zap != 0);
825		VERIFY0(zap_add(vd->vdev_spa->spa_meta_objset, vd->vdev_top_zap,
826		    VDEV_TOP_ZAP_INDIRECT_OBSOLETE_SM,
827		    sizeof (obsolete_sm_object), 1, &obsolete_sm_object, tx));
828		ASSERT3U(vdev_obsolete_sm_object(vd), !=, 0);
829
830		spa_feature_incr(spa, SPA_FEATURE_OBSOLETE_COUNTS, tx);
831		VERIFY0(space_map_open(&vd->vdev_obsolete_sm,
832		    spa->spa_meta_objset, obsolete_sm_object,
833		    0, vd->vdev_asize, 0));
834	}
835
836	ASSERT(vd->vdev_obsolete_sm != NULL);
837	ASSERT3U(vdev_obsolete_sm_object(vd), ==,
838	    space_map_object(vd->vdev_obsolete_sm));
839
840	space_map_write(vd->vdev_obsolete_sm,
841	    vd->vdev_obsolete_segments, SM_ALLOC, SM_NO_VDEVID, tx);
842	range_tree_vacate(vd->vdev_obsolete_segments, NULL, NULL);
843}
844
845int
846spa_condense_init(spa_t *spa)
847{
848	int error = zap_lookup(spa->spa_meta_objset,
849	    DMU_POOL_DIRECTORY_OBJECT,
850	    DMU_POOL_CONDENSING_INDIRECT, sizeof (uint64_t),
851	    sizeof (spa->spa_condensing_indirect_phys) / sizeof (uint64_t),
852	    &spa->spa_condensing_indirect_phys);
853	if (error == 0) {
854		if (spa_writeable(spa)) {
855			spa->spa_condensing_indirect =
856			    spa_condensing_indirect_create(spa);
857		}
858		return (0);
859	} else if (error == ENOENT) {
860		return (0);
861	} else {
862		return (error);
863	}
864}
865
866void
867spa_condense_fini(spa_t *spa)
868{
869	if (spa->spa_condensing_indirect != NULL) {
870		spa_condensing_indirect_destroy(spa->spa_condensing_indirect);
871		spa->spa_condensing_indirect = NULL;
872	}
873}
874
875void
876spa_start_indirect_condensing_thread(spa_t *spa)
877{
878	ASSERT3P(spa->spa_condense_zthr, ==, NULL);
879	spa->spa_condense_zthr = zthr_create(spa_condense_indirect_thread_check,
880	    spa_condense_indirect_thread, spa);
881}
882
883/*
884 * Gets the obsolete spacemap object from the vdev's ZAP.
885 * Returns the spacemap object, or 0 if it wasn't in the ZAP or the ZAP doesn't
886 * exist yet.
887 */
888int
889vdev_obsolete_sm_object(vdev_t *vd)
890{
891	ASSERT0(spa_config_held(vd->vdev_spa, SCL_ALL, RW_WRITER));
892	if (vd->vdev_top_zap == 0) {
893		return (0);
894	}
895
896	uint64_t sm_obj = 0;
897	int err = zap_lookup(vd->vdev_spa->spa_meta_objset, vd->vdev_top_zap,
898	    VDEV_TOP_ZAP_INDIRECT_OBSOLETE_SM, sizeof (sm_obj), 1, &sm_obj);
899
900	ASSERT(err == 0 || err == ENOENT);
901
902	return (sm_obj);
903}
904
905boolean_t
906vdev_obsolete_counts_are_precise(vdev_t *vd)
907{
908	ASSERT0(spa_config_held(vd->vdev_spa, SCL_ALL, RW_WRITER));
909	if (vd->vdev_top_zap == 0) {
910		return (B_FALSE);
911	}
912
913	uint64_t val = 0;
914	int err = zap_lookup(vd->vdev_spa->spa_meta_objset, vd->vdev_top_zap,
915	    VDEV_TOP_ZAP_OBSOLETE_COUNTS_ARE_PRECISE, sizeof (val), 1, &val);
916
917	ASSERT(err == 0 || err == ENOENT);
918
919	return (val != 0);
920}
921
922/* ARGSUSED */
923static void
924vdev_indirect_close(vdev_t *vd)
925{
926}
927
928/* ARGSUSED */
929static int
930vdev_indirect_open(vdev_t *vd, uint64_t *psize, uint64_t *max_psize,
931    uint64_t *ashift)
932{
933	*psize = *max_psize = vd->vdev_asize +
934	    VDEV_LABEL_START_SIZE + VDEV_LABEL_END_SIZE;
935	*ashift = vd->vdev_ashift;
936	return (0);
937}
938
939typedef struct remap_segment {
940	vdev_t *rs_vd;
941	uint64_t rs_offset;
942	uint64_t rs_asize;
943	uint64_t rs_split_offset;
944	list_node_t rs_node;
945} remap_segment_t;
946
947remap_segment_t *
948rs_alloc(vdev_t *vd, uint64_t offset, uint64_t asize, uint64_t split_offset)
949{
950	remap_segment_t *rs = kmem_alloc(sizeof (remap_segment_t), KM_SLEEP);
951	rs->rs_vd = vd;
952	rs->rs_offset = offset;
953	rs->rs_asize = asize;
954	rs->rs_split_offset = split_offset;
955	return (rs);
956}
957
958/*
959 * Given an indirect vdev and an extent on that vdev, it duplicates the
960 * physical entries of the indirect mapping that correspond to the extent
961 * to a new array and returns a pointer to it. In addition, copied_entries
962 * is populated with the number of mapping entries that were duplicated.
963 *
964 * Note that the function assumes that the caller holds vdev_indirect_rwlock.
965 * This ensures that the mapping won't change due to condensing as we
966 * copy over its contents.
967 *
968 * Finally, since we are doing an allocation, it is up to the caller to
969 * free the array allocated in this function.
970 */
971vdev_indirect_mapping_entry_phys_t *
972vdev_indirect_mapping_duplicate_adjacent_entries(vdev_t *vd, uint64_t offset,
973    uint64_t asize, uint64_t *copied_entries)
974{
975	vdev_indirect_mapping_entry_phys_t *duplicate_mappings = NULL;
976	vdev_indirect_mapping_t *vim = vd->vdev_indirect_mapping;
977	uint64_t entries = 0;
978
979	ASSERT(RW_READ_HELD(&vd->vdev_indirect_rwlock));
980
981	vdev_indirect_mapping_entry_phys_t *first_mapping =
982	    vdev_indirect_mapping_entry_for_offset(vim, offset);
983	ASSERT3P(first_mapping, !=, NULL);
984
985	vdev_indirect_mapping_entry_phys_t *m = first_mapping;
986	while (asize > 0) {
987		uint64_t size = DVA_GET_ASIZE(&m->vimep_dst);
988
989		ASSERT3U(offset, >=, DVA_MAPPING_GET_SRC_OFFSET(m));
990		ASSERT3U(offset, <, DVA_MAPPING_GET_SRC_OFFSET(m) + size);
991
992		uint64_t inner_offset = offset - DVA_MAPPING_GET_SRC_OFFSET(m);
993		uint64_t inner_size = MIN(asize, size - inner_offset);
994
995		offset += inner_size;
996		asize -= inner_size;
997		entries++;
998		m++;
999	}
1000
1001	size_t copy_length = entries * sizeof (*first_mapping);
1002	duplicate_mappings = kmem_alloc(copy_length, KM_SLEEP);
1003	bcopy(first_mapping, duplicate_mappings, copy_length);
1004	*copied_entries = entries;
1005
1006	return (duplicate_mappings);
1007}
1008
1009/*
1010 * Goes through the relevant indirect mappings until it hits a concrete vdev
1011 * and issues the callback. On the way to the concrete vdev, if any other
1012 * indirect vdevs are encountered, then the callback will also be called on
1013 * each of those indirect vdevs. For example, if the segment is mapped to
1014 * segment A on indirect vdev 1, and then segment A on indirect vdev 1 is
1015 * mapped to segment B on concrete vdev 2, then the callback will be called on
1016 * both vdev 1 and vdev 2.
1017 *
1018 * While the callback passed to vdev_indirect_remap() is called on every vdev
1019 * the function encounters, certain callbacks only care about concrete vdevs.
1020 * These types of callbacks should return immediately and explicitly when they
1021 * are called on an indirect vdev.
1022 *
1023 * Because there is a possibility that a DVA section in the indirect device
1024 * has been split into multiple sections in our mapping, we keep track
1025 * of the relevant contiguous segments of the new location (remap_segment_t)
1026 * in a stack. This way we can call the callback for each of the new sections
1027 * created by a single section of the indirect device. Note though, that in
1028 * this scenario the callbacks in each split block won't occur in-order in
1029 * terms of offset, so callers should not make any assumptions about that.
1030 *
1031 * For callbacks that don't handle split blocks and immediately return when
1032 * they encounter them (as is the case for remap_blkptr_cb), the caller can
1033 * assume that its callback will be applied from the first indirect vdev
1034 * encountered to the last one and then the concrete vdev, in that order.
1035 */
1036static void
1037vdev_indirect_remap(vdev_t *vd, uint64_t offset, uint64_t asize,
1038    void (*func)(uint64_t, vdev_t *, uint64_t, uint64_t, void *), void *arg)
1039{
1040	list_t stack;
1041	spa_t *spa = vd->vdev_spa;
1042
1043	list_create(&stack, sizeof (remap_segment_t),
1044	    offsetof(remap_segment_t, rs_node));
1045
1046	for (remap_segment_t *rs = rs_alloc(vd, offset, asize, 0);
1047	    rs != NULL; rs = list_remove_head(&stack)) {
1048		vdev_t *v = rs->rs_vd;
1049		uint64_t num_entries = 0;
1050
1051		ASSERT(spa_config_held(spa, SCL_ALL, RW_READER) != 0);
1052		ASSERT(rs->rs_asize > 0);
1053
1054		/*
1055		 * Note: As this function can be called from open context
1056		 * (e.g. zio_read()), we need the following rwlock to
1057		 * prevent the mapping from being changed by condensing.
1058		 *
1059		 * So we grab the lock and we make a copy of the entries
1060		 * that are relevant to the extent that we are working on.
1061		 * Once that is done, we drop the lock and iterate over
1062		 * our copy of the mapping. Once we are done with the with
1063		 * the remap segment and we free it, we also free our copy
1064		 * of the indirect mapping entries that are relevant to it.
1065		 *
1066		 * This way we don't need to wait until the function is
1067		 * finished with a segment, to condense it. In addition, we
1068		 * don't need a recursive rwlock for the case that a call to
1069		 * vdev_indirect_remap() needs to call itself (through the
1070		 * codepath of its callback) for the same vdev in the middle
1071		 * of its execution.
1072		 */
1073		rw_enter(&v->vdev_indirect_rwlock, RW_READER);
1074		vdev_indirect_mapping_t *vim = v->vdev_indirect_mapping;
1075		ASSERT3P(vim, !=, NULL);
1076
1077		vdev_indirect_mapping_entry_phys_t *mapping =
1078		    vdev_indirect_mapping_duplicate_adjacent_entries(v,
1079		    rs->rs_offset, rs->rs_asize, &num_entries);
1080		ASSERT3P(mapping, !=, NULL);
1081		ASSERT3U(num_entries, >, 0);
1082		rw_exit(&v->vdev_indirect_rwlock);
1083
1084		for (uint64_t i = 0; i < num_entries; i++) {
1085			/*
1086			 * Note: the vdev_indirect_mapping can not change
1087			 * while we are running.  It only changes while the
1088			 * removal is in progress, and then only from syncing
1089			 * context. While a removal is in progress, this
1090			 * function is only called for frees, which also only
1091			 * happen from syncing context.
1092			 */
1093			vdev_indirect_mapping_entry_phys_t *m = &mapping[i];
1094
1095			ASSERT3P(m, !=, NULL);
1096			ASSERT3U(rs->rs_asize, >, 0);
1097
1098			uint64_t size = DVA_GET_ASIZE(&m->vimep_dst);
1099			uint64_t dst_offset = DVA_GET_OFFSET(&m->vimep_dst);
1100			uint64_t dst_vdev = DVA_GET_VDEV(&m->vimep_dst);
1101
1102			ASSERT3U(rs->rs_offset, >=,
1103			    DVA_MAPPING_GET_SRC_OFFSET(m));
1104			ASSERT3U(rs->rs_offset, <,
1105			    DVA_MAPPING_GET_SRC_OFFSET(m) + size);
1106			ASSERT3U(dst_vdev, !=, v->vdev_id);
1107
1108			uint64_t inner_offset = rs->rs_offset -
1109			    DVA_MAPPING_GET_SRC_OFFSET(m);
1110			uint64_t inner_size =
1111			    MIN(rs->rs_asize, size - inner_offset);
1112
1113			vdev_t *dst_v = vdev_lookup_top(spa, dst_vdev);
1114			ASSERT3P(dst_v, !=, NULL);
1115
1116			if (dst_v->vdev_ops == &vdev_indirect_ops) {
1117				list_insert_head(&stack,
1118				    rs_alloc(dst_v, dst_offset + inner_offset,
1119				    inner_size, rs->rs_split_offset));
1120
1121			}
1122
1123			if ((zfs_flags & ZFS_DEBUG_INDIRECT_REMAP) &&
1124			    IS_P2ALIGNED(inner_size, 2 * SPA_MINBLOCKSIZE)) {
1125				/*
1126				 * Note: This clause exists only solely for
1127				 * testing purposes. We use it to ensure that
1128				 * split blocks work and that the callbacks
1129				 * using them yield the same result if issued
1130				 * in reverse order.
1131				 */
1132				uint64_t inner_half = inner_size / 2;
1133
1134				func(rs->rs_split_offset + inner_half, dst_v,
1135				    dst_offset + inner_offset + inner_half,
1136				    inner_half, arg);
1137
1138				func(rs->rs_split_offset, dst_v,
1139				    dst_offset + inner_offset,
1140				    inner_half, arg);
1141			} else {
1142				func(rs->rs_split_offset, dst_v,
1143				    dst_offset + inner_offset,
1144				    inner_size, arg);
1145			}
1146
1147			rs->rs_offset += inner_size;
1148			rs->rs_asize -= inner_size;
1149			rs->rs_split_offset += inner_size;
1150		}
1151		VERIFY0(rs->rs_asize);
1152
1153		kmem_free(mapping, num_entries * sizeof (*mapping));
1154		kmem_free(rs, sizeof (remap_segment_t));
1155	}
1156	list_destroy(&stack);
1157}
1158
1159static void
1160vdev_indirect_child_io_done(zio_t *zio)
1161{
1162	zio_t *pio = zio->io_private;
1163
1164	mutex_enter(&pio->io_lock);
1165	pio->io_error = zio_worst_error(pio->io_error, zio->io_error);
1166	mutex_exit(&pio->io_lock);
1167
1168	abd_put(zio->io_abd);
1169}
1170
1171/*
1172 * This is a callback for vdev_indirect_remap() which allocates an
1173 * indirect_split_t for each split segment and adds it to iv_splits.
1174 */
1175static void
1176vdev_indirect_gather_splits(uint64_t split_offset, vdev_t *vd, uint64_t offset,
1177    uint64_t size, void *arg)
1178{
1179	zio_t *zio = arg;
1180	indirect_vsd_t *iv = zio->io_vsd;
1181
1182	ASSERT3P(vd, !=, NULL);
1183
1184	if (vd->vdev_ops == &vdev_indirect_ops)
1185		return;
1186
1187	int n = 1;
1188	if (vd->vdev_ops == &vdev_mirror_ops)
1189		n = vd->vdev_children;
1190
1191	indirect_split_t *is =
1192	    kmem_zalloc(offsetof(indirect_split_t, is_child[n]), KM_SLEEP);
1193
1194	is->is_children = n;
1195	is->is_size = size;
1196	is->is_split_offset = split_offset;
1197	is->is_target_offset = offset;
1198	is->is_vdev = vd;
1199	list_create(&is->is_unique_child, sizeof (indirect_child_t),
1200	    offsetof(indirect_child_t, ic_node));
1201
1202	/*
1203	 * Note that we only consider multiple copies of the data for
1204	 * *mirror* vdevs.  We don't for "replacing" or "spare" vdevs, even
1205	 * though they use the same ops as mirror, because there's only one
1206	 * "good" copy under the replacing/spare.
1207	 */
1208	if (vd->vdev_ops == &vdev_mirror_ops) {
1209		for (int i = 0; i < n; i++) {
1210			is->is_child[i].ic_vdev = vd->vdev_child[i];
1211			list_link_init(&is->is_child[i].ic_node);
1212		}
1213	} else {
1214		is->is_child[0].ic_vdev = vd;
1215	}
1216
1217	list_insert_tail(&iv->iv_splits, is);
1218}
1219
1220static void
1221vdev_indirect_read_split_done(zio_t *zio)
1222{
1223	indirect_child_t *ic = zio->io_private;
1224
1225	if (zio->io_error != 0) {
1226		/*
1227		 * Clear ic_data to indicate that we do not have data for this
1228		 * child.
1229		 */
1230		abd_free(ic->ic_data);
1231		ic->ic_data = NULL;
1232	}
1233}
1234
1235/*
1236 * Issue reads for all copies (mirror children) of all splits.
1237 */
1238static void
1239vdev_indirect_read_all(zio_t *zio)
1240{
1241	indirect_vsd_t *iv = zio->io_vsd;
1242
1243	ASSERT3U(zio->io_type, ==, ZIO_TYPE_READ);
1244
1245	for (indirect_split_t *is = list_head(&iv->iv_splits);
1246	    is != NULL; is = list_next(&iv->iv_splits, is)) {
1247		for (int i = 0; i < is->is_children; i++) {
1248			indirect_child_t *ic = &is->is_child[i];
1249
1250			if (!vdev_readable(ic->ic_vdev))
1251				continue;
1252
1253			/*
1254			 * Note, we may read from a child whose DTL
1255			 * indicates that the data may not be present here.
1256			 * While this might result in a few i/os that will
1257			 * likely return incorrect data, it simplifies the
1258			 * code since we can treat scrub and resilver
1259			 * identically.  (The incorrect data will be
1260			 * detected and ignored when we verify the
1261			 * checksum.)
1262			 */
1263
1264			ic->ic_data = abd_alloc_sametype(zio->io_abd,
1265			    is->is_size);
1266			ic->ic_duplicate = NULL;
1267
1268			zio_nowait(zio_vdev_child_io(zio, NULL,
1269			    ic->ic_vdev, is->is_target_offset, ic->ic_data,
1270			    is->is_size, zio->io_type, zio->io_priority, 0,
1271			    vdev_indirect_read_split_done, ic));
1272		}
1273	}
1274	iv->iv_reconstruct = B_TRUE;
1275}
1276
1277static void
1278vdev_indirect_io_start(zio_t *zio)
1279{
1280	spa_t *spa = zio->io_spa;
1281	indirect_vsd_t *iv = kmem_zalloc(sizeof (*iv), KM_SLEEP);
1282	list_create(&iv->iv_splits,
1283	    sizeof (indirect_split_t), offsetof(indirect_split_t, is_node));
1284
1285	zio->io_vsd = iv;
1286	zio->io_vsd_ops = &vdev_indirect_vsd_ops;
1287
1288	ASSERT(spa_config_held(spa, SCL_ALL, RW_READER) != 0);
1289	if (zio->io_type != ZIO_TYPE_READ) {
1290		ASSERT3U(zio->io_type, ==, ZIO_TYPE_WRITE);
1291		/*
1292		 * Note: this code can handle other kinds of writes,
1293		 * but we don't expect them.
1294		 */
1295		ASSERT((zio->io_flags & (ZIO_FLAG_SELF_HEAL |
1296		    ZIO_FLAG_RESILVER | ZIO_FLAG_INDUCE_DAMAGE)) != 0);
1297	}
1298
1299	vdev_indirect_remap(zio->io_vd, zio->io_offset, zio->io_size,
1300	    vdev_indirect_gather_splits, zio);
1301
1302	indirect_split_t *first = list_head(&iv->iv_splits);
1303	if (first->is_size == zio->io_size) {
1304		/*
1305		 * This is not a split block; we are pointing to the entire
1306		 * data, which will checksum the same as the original data.
1307		 * Pass the BP down so that the child i/o can verify the
1308		 * checksum, and try a different location if available
1309		 * (e.g. on a mirror).
1310		 *
1311		 * While this special case could be handled the same as the
1312		 * general (split block) case, doing it this way ensures
1313		 * that the vast majority of blocks on indirect vdevs
1314		 * (which are not split) are handled identically to blocks
1315		 * on non-indirect vdevs.  This allows us to be less strict
1316		 * about performance in the general (but rare) case.
1317		 */
1318		ASSERT0(first->is_split_offset);
1319		ASSERT3P(list_next(&iv->iv_splits, first), ==, NULL);
1320		zio_nowait(zio_vdev_child_io(zio, zio->io_bp,
1321		    first->is_vdev, first->is_target_offset,
1322		    abd_get_offset(zio->io_abd, 0),
1323		    zio->io_size, zio->io_type, zio->io_priority, 0,
1324		    vdev_indirect_child_io_done, zio));
1325	} else {
1326		iv->iv_split_block = B_TRUE;
1327		if (zio->io_type == ZIO_TYPE_READ &&
1328		    zio->io_flags & (ZIO_FLAG_SCRUB | ZIO_FLAG_RESILVER)) {
1329			/*
1330			 * Read all copies.  Note that for simplicity,
1331			 * we don't bother consulting the DTL in the
1332			 * resilver case.
1333			 */
1334			vdev_indirect_read_all(zio);
1335		} else {
1336			/*
1337			 * If this is a read zio, we read one copy of each
1338			 * split segment, from the top-level vdev.  Since
1339			 * we don't know the checksum of each split
1340			 * individually, the child zio can't ensure that
1341			 * we get the right data. E.g. if it's a mirror,
1342			 * it will just read from a random (healthy) leaf
1343			 * vdev. We have to verify the checksum in
1344			 * vdev_indirect_io_done().
1345			 *
1346			 * For write zios, the vdev code will ensure we write
1347			 * to all children.
1348			 */
1349			for (indirect_split_t *is = list_head(&iv->iv_splits);
1350			    is != NULL; is = list_next(&iv->iv_splits, is)) {
1351				zio_nowait(zio_vdev_child_io(zio, NULL,
1352				    is->is_vdev, is->is_target_offset,
1353				    abd_get_offset(zio->io_abd,
1354				    is->is_split_offset),
1355				    is->is_size, zio->io_type,
1356				    zio->io_priority, 0,
1357				    vdev_indirect_child_io_done, zio));
1358			}
1359		}
1360	}
1361
1362	zio_execute(zio);
1363}
1364
1365/*
1366 * Report a checksum error for a child.
1367 */
1368static void
1369vdev_indirect_checksum_error(zio_t *zio,
1370    indirect_split_t *is, indirect_child_t *ic)
1371{
1372	vdev_t *vd = ic->ic_vdev;
1373
1374	if (zio->io_flags & ZIO_FLAG_SPECULATIVE)
1375		return;
1376
1377	mutex_enter(&vd->vdev_stat_lock);
1378	vd->vdev_stat.vs_checksum_errors++;
1379	mutex_exit(&vd->vdev_stat_lock);
1380
1381	zio_bad_cksum_t zbc = { 0 };
1382	void *bad_buf = abd_borrow_buf_copy(ic->ic_data, is->is_size);
1383	abd_t *good_abd = is->is_good_child->ic_data;
1384	void *good_buf = abd_borrow_buf_copy(good_abd, is->is_size);
1385	zfs_ereport_post_checksum(zio->io_spa, vd, &zio->io_bookmark, zio,
1386	    is->is_target_offset, is->is_size, good_buf, bad_buf, &zbc);
1387	abd_return_buf(ic->ic_data, bad_buf, is->is_size);
1388	abd_return_buf(good_abd, good_buf, is->is_size);
1389}
1390
1391/*
1392 * Issue repair i/os for any incorrect copies.  We do this by comparing
1393 * each split segment's correct data (is_good_child's ic_data) with each
1394 * other copy of the data.  If they differ, then we overwrite the bad data
1395 * with the good copy.  Note that we do this without regard for the DTL's,
1396 * which simplifies this code and also issues the optimal number of writes
1397 * (based on which copies actually read bad data, as opposed to which we
1398 * think might be wrong).  For the same reason, we always use
1399 * ZIO_FLAG_SELF_HEAL, to bypass the DTL check in zio_vdev_io_start().
1400 */
1401static void
1402vdev_indirect_repair(zio_t *zio)
1403{
1404	indirect_vsd_t *iv = zio->io_vsd;
1405
1406	enum zio_flag flags = ZIO_FLAG_IO_REPAIR;
1407
1408	if (!(zio->io_flags & (ZIO_FLAG_SCRUB | ZIO_FLAG_RESILVER)))
1409		flags |= ZIO_FLAG_SELF_HEAL;
1410
1411	if (!spa_writeable(zio->io_spa))
1412		return;
1413
1414	for (indirect_split_t *is = list_head(&iv->iv_splits);
1415	    is != NULL; is = list_next(&iv->iv_splits, is)) {
1416		for (int c = 0; c < is->is_children; c++) {
1417			indirect_child_t *ic = &is->is_child[c];
1418			if (ic == is->is_good_child)
1419				continue;
1420			if (ic->ic_data == NULL)
1421				continue;
1422			if (ic->ic_duplicate == is->is_good_child)
1423				continue;
1424
1425			zio_nowait(zio_vdev_child_io(zio, NULL,
1426			    ic->ic_vdev, is->is_target_offset,
1427			    is->is_good_child->ic_data, is->is_size,
1428			    ZIO_TYPE_WRITE, ZIO_PRIORITY_ASYNC_WRITE,
1429			    ZIO_FLAG_IO_REPAIR | ZIO_FLAG_SELF_HEAL,
1430			    NULL, NULL));
1431
1432			vdev_indirect_checksum_error(zio, is, ic);
1433		}
1434	}
1435}
1436
1437/*
1438 * Report checksum errors on all children that we read from.
1439 */
1440static void
1441vdev_indirect_all_checksum_errors(zio_t *zio)
1442{
1443	indirect_vsd_t *iv = zio->io_vsd;
1444
1445	if (zio->io_flags & ZIO_FLAG_SPECULATIVE)
1446		return;
1447
1448	for (indirect_split_t *is = list_head(&iv->iv_splits);
1449	    is != NULL; is = list_next(&iv->iv_splits, is)) {
1450		for (int c = 0; c < is->is_children; c++) {
1451			indirect_child_t *ic = &is->is_child[c];
1452
1453			if (ic->ic_data == NULL)
1454				continue;
1455
1456			vdev_t *vd = ic->ic_vdev;
1457
1458			mutex_enter(&vd->vdev_stat_lock);
1459			vd->vdev_stat.vs_checksum_errors++;
1460			mutex_exit(&vd->vdev_stat_lock);
1461
1462			zfs_ereport_post_checksum(zio->io_spa, vd,
1463			    &zio->io_bookmark, zio, is->is_target_offset,
1464			    is->is_size, NULL, NULL, NULL);
1465		}
1466	}
1467}
1468
1469/*
1470 * Copy data from all the splits to a main zio then validate the checksum.
1471 * If then checksum is successfully validated return success.
1472 */
1473static int
1474vdev_indirect_splits_checksum_validate(indirect_vsd_t *iv, zio_t *zio)
1475{
1476	zio_bad_cksum_t zbc;
1477
1478	for (indirect_split_t *is = list_head(&iv->iv_splits);
1479	    is != NULL; is = list_next(&iv->iv_splits, is)) {
1480
1481		ASSERT3P(is->is_good_child->ic_data, !=, NULL);
1482		ASSERT3P(is->is_good_child->ic_duplicate, ==, NULL);
1483
1484		abd_copy_off(zio->io_abd, is->is_good_child->ic_data,
1485		    is->is_split_offset, 0, is->is_size);
1486	}
1487
1488	return (zio_checksum_error(zio, &zbc));
1489}
1490
1491/*
1492 * There are relatively few possible combinations making it feasible to
1493 * deterministically check them all.  We do this by setting the good_child
1494 * to the next unique split version.  If we reach the end of the list then
1495 * "carry over" to the next unique split version (like counting in base
1496 * is_unique_children, but each digit can have a different base).
1497 */
1498static int
1499vdev_indirect_splits_enumerate_all(indirect_vsd_t *iv, zio_t *zio)
1500{
1501	boolean_t more = B_TRUE;
1502
1503	iv->iv_attempts = 0;
1504
1505	for (indirect_split_t *is = list_head(&iv->iv_splits);
1506	    is != NULL; is = list_next(&iv->iv_splits, is))
1507		is->is_good_child = list_head(&is->is_unique_child);
1508
1509	while (more == B_TRUE) {
1510		iv->iv_attempts++;
1511		more = B_FALSE;
1512
1513		if (vdev_indirect_splits_checksum_validate(iv, zio) == 0)
1514			return (0);
1515
1516		for (indirect_split_t *is = list_head(&iv->iv_splits);
1517		    is != NULL; is = list_next(&iv->iv_splits, is)) {
1518			is->is_good_child = list_next(&is->is_unique_child,
1519			    is->is_good_child);
1520			if (is->is_good_child != NULL) {
1521				more = B_TRUE;
1522				break;
1523			}
1524
1525			is->is_good_child = list_head(&is->is_unique_child);
1526		}
1527	}
1528
1529	ASSERT3S(iv->iv_attempts, <=, iv->iv_unique_combinations);
1530
1531	return (SET_ERROR(ECKSUM));
1532}
1533
1534/*
1535 * There are too many combinations to try all of them in a reasonable amount
1536 * of time.  So try a fixed number of random combinations from the unique
1537 * split versions, after which we'll consider the block unrecoverable.
1538 */
1539static int
1540vdev_indirect_splits_enumerate_randomly(indirect_vsd_t *iv, zio_t *zio)
1541{
1542	iv->iv_attempts = 0;
1543
1544	while (iv->iv_attempts < iv->iv_attempts_max) {
1545		iv->iv_attempts++;
1546
1547		for (indirect_split_t *is = list_head(&iv->iv_splits);
1548		    is != NULL; is = list_next(&iv->iv_splits, is)) {
1549			indirect_child_t *ic = list_head(&is->is_unique_child);
1550			int children = is->is_unique_children;
1551
1552			for (int i = spa_get_random(children); i > 0; i--)
1553				ic = list_next(&is->is_unique_child, ic);
1554
1555			ASSERT3P(ic, !=, NULL);
1556			is->is_good_child = ic;
1557		}
1558
1559		if (vdev_indirect_splits_checksum_validate(iv, zio) == 0)
1560			return (0);
1561	}
1562
1563	return (SET_ERROR(ECKSUM));
1564}
1565
1566/*
1567 * This is a validation function for reconstruction.  It randomly selects
1568 * a good combination, if one can be found, and then it intentionally
1569 * damages all other segment copes by zeroing them.  This forces the
1570 * reconstruction algorithm to locate the one remaining known good copy.
1571 */
1572static int
1573vdev_indirect_splits_damage(indirect_vsd_t *iv, zio_t *zio)
1574{
1575	/* Presume all the copies are unique for initial selection. */
1576	for (indirect_split_t *is = list_head(&iv->iv_splits);
1577	    is != NULL; is = list_next(&iv->iv_splits, is)) {
1578		is->is_unique_children = 0;
1579
1580		for (int i = 0; i < is->is_children; i++) {
1581			indirect_child_t *ic = &is->is_child[i];
1582			if (ic->ic_data != NULL) {
1583				is->is_unique_children++;
1584				list_insert_tail(&is->is_unique_child, ic);
1585			}
1586		}
1587	}
1588
1589	/*
1590	 * Set each is_good_child to a randomly-selected child which
1591	 * is known to contain validated data.
1592	 */
1593	int error = vdev_indirect_splits_enumerate_randomly(iv, zio);
1594	if (error)
1595		goto out;
1596
1597	/*
1598	 * Damage all but the known good copy by zeroing it.  This will
1599	 * result in two or less unique copies per indirect_child_t.
1600	 * Both may need to be checked in order to reconstruct the block.
1601	 * Set iv->iv_attempts_max such that all unique combinations will
1602	 * enumerated, but limit the damage to at most 16 indirect splits.
1603	 */
1604	iv->iv_attempts_max = 1;
1605
1606	for (indirect_split_t *is = list_head(&iv->iv_splits);
1607	    is != NULL; is = list_next(&iv->iv_splits, is)) {
1608		for (int c = 0; c < is->is_children; c++) {
1609			indirect_child_t *ic = &is->is_child[c];
1610
1611			if (ic == is->is_good_child)
1612				continue;
1613			if (ic->ic_data == NULL)
1614				continue;
1615
1616			abd_zero(ic->ic_data, ic->ic_data->abd_size);
1617		}
1618
1619		iv->iv_attempts_max *= 2;
1620		if (iv->iv_attempts_max > (1ULL << 16)) {
1621			iv->iv_attempts_max = UINT64_MAX;
1622			break;
1623		}
1624	}
1625
1626out:
1627	/* Empty the unique children lists so they can be reconstructed. */
1628	for (indirect_split_t *is = list_head(&iv->iv_splits);
1629	    is != NULL; is = list_next(&iv->iv_splits, is)) {
1630		indirect_child_t *ic;
1631		while ((ic = list_head(&is->is_unique_child)) != NULL)
1632			list_remove(&is->is_unique_child, ic);
1633
1634		is->is_unique_children = 0;
1635	}
1636
1637	return (error);
1638}
1639
1640/*
1641 * This function is called when we have read all copies of the data and need
1642 * to try to find a combination of copies that gives us the right checksum.
1643 *
1644 * If we pointed to any mirror vdevs, this effectively does the job of the
1645 * mirror.  The mirror vdev code can't do its own job because we don't know
1646 * the checksum of each split segment individually.
1647 *
1648 * We have to try every unique combination of copies of split segments, until
1649 * we find one that checksums correctly.  Duplicate segment copies are first
1650 * identified and latter skipped during reconstruction.  This optimization
1651 * reduces the search space and ensures that of the remaining combinations
1652 * at most one is correct.
1653 *
1654 * When the total number of combinations is small they can all be checked.
1655 * For example, if we have 3 segments in the split, and each points to a
1656 * 2-way mirror with unique copies, we will have the following pieces of data:
1657 *
1658 *       |     mirror child
1659 * split |     [0]        [1]
1660 * ======|=====================
1661 *   A   |  data_A_0   data_A_1
1662 *   B   |  data_B_0   data_B_1
1663 *   C   |  data_C_0   data_C_1
1664 *
1665 * We will try the following (mirror children)^(number of splits) (2^3=8)
1666 * combinations, which is similar to bitwise-little-endian counting in
1667 * binary.  In general each "digit" corresponds to a split segment, and the
1668 * base of each digit is is_children, which can be different for each
1669 * digit.
1670 *
1671 * "low bit"        "high bit"
1672 *        v                 v
1673 * data_A_0 data_B_0 data_C_0
1674 * data_A_1 data_B_0 data_C_0
1675 * data_A_0 data_B_1 data_C_0
1676 * data_A_1 data_B_1 data_C_0
1677 * data_A_0 data_B_0 data_C_1
1678 * data_A_1 data_B_0 data_C_1
1679 * data_A_0 data_B_1 data_C_1
1680 * data_A_1 data_B_1 data_C_1
1681 *
1682 * Note that the split segments may be on the same or different top-level
1683 * vdevs. In either case, we may need to try lots of combinations (see
1684 * zfs_reconstruct_indirect_combinations_max).  This ensures that if a mirror
1685 * has small silent errors on all of its children, we can still reconstruct
1686 * the correct data, as long as those errors are at sufficiently-separated
1687 * offsets (specifically, separated by the largest block size - default of
1688 * 128KB, but up to 16MB).
1689 */
1690static void
1691vdev_indirect_reconstruct_io_done(zio_t *zio)
1692{
1693	indirect_vsd_t *iv = zio->io_vsd;
1694	boolean_t known_good = B_FALSE;
1695	int error;
1696
1697	iv->iv_unique_combinations = 1;
1698	iv->iv_attempts_max = UINT64_MAX;
1699
1700	if (zfs_reconstruct_indirect_combinations_max > 0)
1701		iv->iv_attempts_max = zfs_reconstruct_indirect_combinations_max;
1702
1703	/*
1704	 * If nonzero, every 1/x blocks will be damaged, in order to validate
1705	 * reconstruction when there are split segments with damaged copies.
1706	 * Known_good will TRUE when reconstruction is known to be possible.
1707	 */
1708	if (zfs_reconstruct_indirect_damage_fraction != 0 &&
1709	    spa_get_random(zfs_reconstruct_indirect_damage_fraction) == 0)
1710		known_good = (vdev_indirect_splits_damage(iv, zio) == 0);
1711
1712	/*
1713	 * Determine the unique children for a split segment and add them
1714	 * to the is_unique_child list.  By restricting reconstruction
1715	 * to these children, only unique combinations will be considered.
1716	 * This can vastly reduce the search space when there are a large
1717	 * number of indirect splits.
1718	 */
1719	for (indirect_split_t *is = list_head(&iv->iv_splits);
1720	    is != NULL; is = list_next(&iv->iv_splits, is)) {
1721		is->is_unique_children = 0;
1722
1723		for (int i = 0; i < is->is_children; i++) {
1724			indirect_child_t *ic_i = &is->is_child[i];
1725
1726			if (ic_i->ic_data == NULL ||
1727			    ic_i->ic_duplicate != NULL)
1728				continue;
1729
1730			for (int j = i + 1; j < is->is_children; j++) {
1731				indirect_child_t *ic_j = &is->is_child[j];
1732
1733				if (ic_j->ic_data == NULL ||
1734				    ic_j->ic_duplicate != NULL)
1735					continue;
1736
1737				if (abd_cmp(ic_i->ic_data, ic_j->ic_data,
1738				    is->is_size) == 0) {
1739					ic_j->ic_duplicate = ic_i;
1740				}
1741			}
1742
1743			is->is_unique_children++;
1744			list_insert_tail(&is->is_unique_child, ic_i);
1745		}
1746
1747		/* Reconstruction is impossible, no valid children */
1748		EQUIV(list_is_empty(&is->is_unique_child),
1749		    is->is_unique_children == 0);
1750		if (list_is_empty(&is->is_unique_child)) {
1751			zio->io_error = EIO;
1752			vdev_indirect_all_checksum_errors(zio);
1753			zio_checksum_verified(zio);
1754			return;
1755		}
1756
1757		iv->iv_unique_combinations *= is->is_unique_children;
1758	}
1759
1760	if (iv->iv_unique_combinations <= iv->iv_attempts_max)
1761		error = vdev_indirect_splits_enumerate_all(iv, zio);
1762	else
1763		error = vdev_indirect_splits_enumerate_randomly(iv, zio);
1764
1765	if (error != 0) {
1766		/* All attempted combinations failed. */
1767		ASSERT3B(known_good, ==, B_FALSE);
1768		zio->io_error = error;
1769		vdev_indirect_all_checksum_errors(zio);
1770	} else {
1771		/*
1772		 * The checksum has been successfully validated.  Issue
1773		 * repair I/Os to any copies of splits which don't match
1774		 * the validated version.
1775		 */
1776		ASSERT0(vdev_indirect_splits_checksum_validate(iv, zio));
1777		vdev_indirect_repair(zio);
1778		zio_checksum_verified(zio);
1779	}
1780}
1781
1782static void
1783vdev_indirect_io_done(zio_t *zio)
1784{
1785	indirect_vsd_t *iv = zio->io_vsd;
1786
1787	if (iv->iv_reconstruct) {
1788		/*
1789		 * We have read all copies of the data (e.g. from mirrors),
1790		 * either because this was a scrub/resilver, or because the
1791		 * one-copy read didn't checksum correctly.
1792		 */
1793		vdev_indirect_reconstruct_io_done(zio);
1794		return;
1795	}
1796
1797	if (!iv->iv_split_block) {
1798		/*
1799		 * This was not a split block, so we passed the BP down,
1800		 * and the checksum was handled by the (one) child zio.
1801		 */
1802		return;
1803	}
1804
1805	zio_bad_cksum_t zbc;
1806	int ret = zio_checksum_error(zio, &zbc);
1807	if (ret == 0) {
1808		zio_checksum_verified(zio);
1809		return;
1810	}
1811
1812	/*
1813	 * The checksum didn't match.  Read all copies of all splits, and
1814	 * then we will try to reconstruct.  The next time
1815	 * vdev_indirect_io_done() is called, iv_reconstruct will be set.
1816	 */
1817	vdev_indirect_read_all(zio);
1818
1819	zio_vdev_io_redone(zio);
1820}
1821
1822vdev_ops_t vdev_indirect_ops = {
1823	.vdev_op_open = vdev_indirect_open,
1824	.vdev_op_close = vdev_indirect_close,
1825	.vdev_op_asize = vdev_default_asize,
1826	.vdev_op_io_start = vdev_indirect_io_start,
1827	.vdev_op_io_done = vdev_indirect_io_done,
1828	.vdev_op_state_change = NULL,
1829	.vdev_op_need_resilver = NULL,
1830	.vdev_op_hold = NULL,
1831	.vdev_op_rele = NULL,
1832	.vdev_op_remap = vdev_indirect_remap,
1833	.vdev_op_xlate = NULL,
1834	.vdev_op_dumpio = NULL,
1835	.vdev_op_type = VDEV_TYPE_INDIRECT,	/* name of this vdev type */
1836	.vdev_op_leaf = B_FALSE			/* leaf vdev */
1837};
1838