vdev_indirect.c revision 6a316e1f6d32750bb8fcf2558dcb17b90ca580fd
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, 2017 by Delphix. All rights reserved.
18 */
19
20#include <sys/zfs_context.h>
21#include <sys/spa.h>
22#include <sys/spa_impl.h>
23#include <sys/vdev_impl.h>
24#include <sys/fs/zfs.h>
25#include <sys/zio.h>
26#include <sys/zio_checksum.h>
27#include <sys/metaslab.h>
28#include <sys/refcount.h>
29#include <sys/dmu.h>
30#include <sys/vdev_indirect_mapping.h>
31#include <sys/dmu_tx.h>
32#include <sys/dsl_synctask.h>
33#include <sys/zap.h>
34#include <sys/abd.h>
35#include <sys/zthr.h>
36
37/*
38 * An indirect vdev corresponds to a vdev that has been removed.  Since
39 * we cannot rewrite block pointers of snapshots, etc., we keep a
40 * mapping from old location on the removed device to the new location
41 * on another device in the pool and use this mapping whenever we need
42 * to access the DVA.  Unfortunately, this mapping did not respect
43 * logical block boundaries when it was first created, and so a DVA on
44 * this indirect vdev may be "split" into multiple sections that each
45 * map to a different location.  As a consequence, not all DVAs can be
46 * translated to an equivalent new DVA.  Instead we must provide a
47 * "vdev_remap" operation that executes a callback on each contiguous
48 * segment of the new location.  This function is used in multiple ways:
49 *
50 *  - i/os to this vdev use the callback to determine where the
51 *    data is now located, and issue child i/os for each segment's new
52 *    location.
53 *
54 *  - frees and claims to this vdev use the callback to free or claim
55 *    each mapped segment.  (Note that we don't actually need to claim
56 *    log blocks on indirect vdevs, because we don't allocate to
57 *    removing vdevs.  However, zdb uses zio_claim() for its leak
58 *    detection.)
59 */
60
61/*
62 * "Big theory statement" for how we mark blocks obsolete.
63 *
64 * When a block on an indirect vdev is freed or remapped, a section of
65 * that vdev's mapping may no longer be referenced (aka "obsolete").  We
66 * keep track of how much of each mapping entry is obsolete.  When
67 * an entry becomes completely obsolete, we can remove it, thus reducing
68 * the memory used by the mapping.  The complete picture of obsolescence
69 * is given by the following data structures, described below:
70 *  - the entry-specific obsolete count
71 *  - the vdev-specific obsolete spacemap
72 *  - the pool-specific obsolete bpobj
73 *
74 * == On disk data structures used ==
75 *
76 * We track the obsolete space for the pool using several objects.  Each
77 * of these objects is created on demand and freed when no longer
78 * needed, and is assumed to be empty if it does not exist.
79 * SPA_FEATURE_OBSOLETE_COUNTS includes the count of these objects.
80 *
81 *  - Each vic_mapping_object (associated with an indirect vdev) can
82 *    have a vimp_counts_object.  This is an array of uint32_t's
83 *    with the same number of entries as the vic_mapping_object.  When
84 *    the mapping is condensed, entries from the vic_obsolete_sm_object
85 *    (see below) are folded into the counts.  Therefore, each
86 *    obsolete_counts entry tells us the number of bytes in the
87 *    corresponding mapping entry that were not referenced when the
88 *    mapping was last condensed.
89 *
90 *  - Each indirect or removing vdev can have a vic_obsolete_sm_object.
91 *    This is a space map containing an alloc entry for every DVA that
92 *    has been obsoleted since the last time this indirect vdev was
93 *    condensed.  We use this object in order to improve performance
94 *    when marking a DVA as obsolete.  Instead of modifying an arbitrary
95 *    offset of the vimp_counts_object, we only need to append an entry
96 *    to the end of this object.  When a DVA becomes obsolete, it is
97 *    added to the obsolete space map.  This happens when the DVA is
98 *    freed, remapped and not referenced by a snapshot, or the last
99 *    snapshot referencing it is destroyed.
100 *
101 *  - Each dataset can have a ds_remap_deadlist object.  This is a
102 *    deadlist object containing all blocks that were remapped in this
103 *    dataset but referenced in a previous snapshot.  Blocks can *only*
104 *    appear on this list if they were remapped (dsl_dataset_block_remapped);
105 *    blocks that were killed in a head dataset are put on the normal
106 *    ds_deadlist and marked obsolete when they are freed.
107 *
108 *  - The pool can have a dp_obsolete_bpobj.  This is a list of blocks
109 *    in the pool that need to be marked obsolete.  When a snapshot is
110 *    destroyed, we move some of the ds_remap_deadlist to the obsolete
111 *    bpobj (see dsl_destroy_snapshot_handle_remaps()).  We then
112 *    asynchronously process the obsolete bpobj, moving its entries to
113 *    the specific vdevs' obsolete space maps.
114 *
115 * == Summary of how we mark blocks as obsolete ==
116 *
117 * - When freeing a block: if any DVA is on an indirect vdev, append to
118 *   vic_obsolete_sm_object.
119 * - When remapping a block, add dva to ds_remap_deadlist (if prev snap
120 *   references; otherwise append to vic_obsolete_sm_object).
121 * - When freeing a snapshot: move parts of ds_remap_deadlist to
122 *   dp_obsolete_bpobj (same algorithm as ds_deadlist).
123 * - When syncing the spa: process dp_obsolete_bpobj, moving ranges to
124 *   individual vdev's vic_obsolete_sm_object.
125 */
126
127/*
128 * "Big theory statement" for how we condense indirect vdevs.
129 *
130 * Condensing an indirect vdev's mapping is the process of determining
131 * the precise counts of obsolete space for each mapping entry (by
132 * integrating the obsolete spacemap into the obsolete counts) and
133 * writing out a new mapping that contains only referenced entries.
134 *
135 * We condense a vdev when we expect the mapping to shrink (see
136 * vdev_indirect_should_condense()), but only perform one condense at a
137 * time to limit the memory usage.  In addition, we use a separate
138 * open-context thread (spa_condense_indirect_thread) to incrementally
139 * create the new mapping object in a way that minimizes the impact on
140 * the rest of the system.
141 *
142 * == Generating a new mapping ==
143 *
144 * To generate a new mapping, we follow these steps:
145 *
146 * 1. Save the old obsolete space map and create a new mapping object
147 *    (see spa_condense_indirect_start_sync()).  This initializes the
148 *    spa_condensing_indirect_phys with the "previous obsolete space map",
149 *    which is now read only.  Newly obsolete DVAs will be added to a
150 *    new (initially empty) obsolete space map, and will not be
151 *    considered as part of this condense operation.
152 *
153 * 2. Construct in memory the precise counts of obsolete space for each
154 *    mapping entry, by incorporating the obsolete space map into the
155 *    counts.  (See vdev_indirect_mapping_load_obsolete_{counts,spacemap}().)
156 *
157 * 3. Iterate through each mapping entry, writing to the new mapping any
158 *    entries that are not completely obsolete (i.e. which don't have
159 *    obsolete count == mapping length).  (See
160 *    spa_condense_indirect_generate_new_mapping().)
161 *
162 * 4. Destroy the old mapping object and switch over to the new one
163 *    (spa_condense_indirect_complete_sync).
164 *
165 * == Restarting from failure ==
166 *
167 * To restart the condense when we import/open the pool, we must start
168 * at the 2nd step above: reconstruct the precise counts in memory,
169 * based on the space map + counts.  Then in the 3rd step, we start
170 * iterating where we left off: at vimp_max_offset of the new mapping
171 * object.
172 */
173
174boolean_t zfs_condense_indirect_vdevs_enable = B_TRUE;
175
176/*
177 * Condense if at least this percent of the bytes in the mapping is
178 * obsolete.  With the default of 25%, the amount of space mapped
179 * will be reduced to 1% of its original size after at most 16
180 * condenses.  Higher values will condense less often (causing less
181 * i/o); lower values will reduce the mapping size more quickly.
182 */
183int zfs_indirect_condense_obsolete_pct = 25;
184
185/*
186 * Condense if the obsolete space map takes up more than this amount of
187 * space on disk (logically).  This limits the amount of disk space
188 * consumed by the obsolete space map; the default of 1GB is small enough
189 * that we typically don't mind "wasting" it.
190 */
191uint64_t zfs_condense_max_obsolete_bytes = 1024 * 1024 * 1024;
192
193/*
194 * Don't bother condensing if the mapping uses less than this amount of
195 * memory.  The default of 128KB is considered a "trivial" amount of
196 * memory and not worth reducing.
197 */
198uint64_t zfs_condense_min_mapping_bytes = 128 * 1024;
199
200/*
201 * This is used by the test suite so that it can ensure that certain
202 * actions happen while in the middle of a condense (which might otherwise
203 * complete too quickly).  If used to reduce the performance impact of
204 * condensing in production, a maximum value of 1 should be sufficient.
205 */
206int zfs_condense_indirect_commit_entry_delay_ticks = 0;
207
208/*
209 * If an indirect split block contains more than this many possible unique
210 * combinations when being reconstructed, consider it too computationally
211 * expensive to check them all. Instead, try at most 100 randomly-selected
212 * combinations each time the block is accessed.  This allows all segment
213 * copies to participate fairly in the reconstruction when all combinations
214 * cannot be checked and prevents repeated use of one bad copy.
215 */
216int zfs_reconstruct_indirect_combinations_max = 256;
217
218
219/*
220 * Enable to simulate damaged segments and validate reconstruction.
221 * Used by ztest
222 */
223unsigned long zfs_reconstruct_indirect_damage_fraction = 0;
224
225/*
226 * The indirect_child_t represents the vdev that we will read from, when we
227 * need to read all copies of the data (e.g. for scrub or reconstruction).
228 * For plain (non-mirror) top-level vdevs (i.e. is_vdev is not a mirror),
229 * ic_vdev is the same as is_vdev.  However, for mirror top-level vdevs,
230 * ic_vdev is a child of the mirror.
231 */
232typedef struct indirect_child {
233	abd_t *ic_data;
234	vdev_t *ic_vdev;
235
236	/*
237	 * ic_duplicate is NULL when the ic_data contents are unique, when it
238	 * is determined to be a duplicate it references the primary child.
239	 */
240	struct indirect_child *ic_duplicate;
241	list_node_t ic_node; /* node on is_unique_child */
242} indirect_child_t;
243
244/*
245 * The indirect_split_t represents one mapped segment of an i/o to the
246 * indirect vdev. For non-split (contiguously-mapped) blocks, there will be
247 * only one indirect_split_t, with is_split_offset==0 and is_size==io_size.
248 * For split blocks, there will be several of these.
249 */
250typedef struct indirect_split {
251	list_node_t is_node; /* link on iv_splits */
252
253	/*
254	 * is_split_offset is the offset into the i/o.
255	 * This is the sum of the previous splits' is_size's.
256	 */
257	uint64_t is_split_offset;
258
259	vdev_t *is_vdev; /* top-level vdev */
260	uint64_t is_target_offset; /* offset on is_vdev */
261	uint64_t is_size;
262	int is_children; /* number of entries in is_child[] */
263	int is_unique_children; /* number of entries in is_unique_child */
264	list_t is_unique_child;
265
266	/*
267	 * is_good_child is the child that we are currently using to
268	 * attempt reconstruction.
269	 */
270	indirect_child_t *is_good_child;
271
272	indirect_child_t is_child[1]; /* variable-length */
273} indirect_split_t;
274
275/*
276 * The indirect_vsd_t is associated with each i/o to the indirect vdev.
277 * It is the "Vdev-Specific Data" in the zio_t's io_vsd.
278 */
279typedef struct indirect_vsd {
280	boolean_t iv_split_block;
281	boolean_t iv_reconstruct;
282	uint64_t iv_unique_combinations;
283	uint64_t iv_attempts;
284	uint64_t iv_attempts_max;
285
286	list_t iv_splits; /* list of indirect_split_t's */
287} indirect_vsd_t;
288
289static void
290vdev_indirect_map_free(zio_t *zio)
291{
292	indirect_vsd_t *iv = zio->io_vsd;
293
294	indirect_split_t *is;
295	while ((is = list_head(&iv->iv_splits)) != NULL) {
296		for (int c = 0; c < is->is_children; c++) {
297			indirect_child_t *ic = &is->is_child[c];
298			if (ic->ic_data != NULL)
299				abd_free(ic->ic_data);
300		}
301		list_remove(&iv->iv_splits, is);
302
303		indirect_child_t *ic;
304		while ((ic = list_head(&is->is_unique_child)) != NULL)
305			list_remove(&is->is_unique_child, ic);
306
307		list_destroy(&is->is_unique_child);
308
309		kmem_free(is,
310		    offsetof(indirect_split_t, is_child[is->is_children]));
311	}
312	kmem_free(iv, sizeof (*iv));
313}
314
315static const zio_vsd_ops_t vdev_indirect_vsd_ops = {
316	vdev_indirect_map_free,
317	zio_vsd_default_cksum_report
318};
319/*
320 * Mark the given offset and size as being obsolete.
321 */
322void
323vdev_indirect_mark_obsolete(vdev_t *vd, uint64_t offset, uint64_t size)
324{
325	spa_t *spa = vd->vdev_spa;
326
327	ASSERT3U(vd->vdev_indirect_config.vic_mapping_object, !=, 0);
328	ASSERT(vd->vdev_removing || vd->vdev_ops == &vdev_indirect_ops);
329	ASSERT(size > 0);
330	VERIFY(vdev_indirect_mapping_entry_for_offset(
331	    vd->vdev_indirect_mapping, offset) != NULL);
332
333	if (spa_feature_is_enabled(spa, SPA_FEATURE_OBSOLETE_COUNTS)) {
334		mutex_enter(&vd->vdev_obsolete_lock);
335		range_tree_add(vd->vdev_obsolete_segments, offset, size);
336		mutex_exit(&vd->vdev_obsolete_lock);
337		vdev_dirty(vd, 0, NULL, spa_syncing_txg(spa));
338	}
339}
340
341/*
342 * Mark the DVA vdev_id:offset:size as being obsolete in the given tx. This
343 * wrapper is provided because the DMU does not know about vdev_t's and
344 * cannot directly call vdev_indirect_mark_obsolete.
345 */
346void
347spa_vdev_indirect_mark_obsolete(spa_t *spa, uint64_t vdev_id, uint64_t offset,
348    uint64_t size, dmu_tx_t *tx)
349{
350	vdev_t *vd = vdev_lookup_top(spa, vdev_id);
351	ASSERT(dmu_tx_is_syncing(tx));
352
353	/* The DMU can only remap indirect vdevs. */
354	ASSERT3P(vd->vdev_ops, ==, &vdev_indirect_ops);
355	vdev_indirect_mark_obsolete(vd, offset, size);
356}
357
358static spa_condensing_indirect_t *
359spa_condensing_indirect_create(spa_t *spa)
360{
361	spa_condensing_indirect_phys_t *scip =
362	    &spa->spa_condensing_indirect_phys;
363	spa_condensing_indirect_t *sci = kmem_zalloc(sizeof (*sci), KM_SLEEP);
364	objset_t *mos = spa->spa_meta_objset;
365
366	for (int i = 0; i < TXG_SIZE; i++) {
367		list_create(&sci->sci_new_mapping_entries[i],
368		    sizeof (vdev_indirect_mapping_entry_t),
369		    offsetof(vdev_indirect_mapping_entry_t, vime_node));
370	}
371
372	sci->sci_new_mapping =
373	    vdev_indirect_mapping_open(mos, scip->scip_next_mapping_object);
374
375	return (sci);
376}
377
378static void
379spa_condensing_indirect_destroy(spa_condensing_indirect_t *sci)
380{
381	for (int i = 0; i < TXG_SIZE; i++)
382		list_destroy(&sci->sci_new_mapping_entries[i]);
383
384	if (sci->sci_new_mapping != NULL)
385		vdev_indirect_mapping_close(sci->sci_new_mapping);
386
387	kmem_free(sci, sizeof (*sci));
388}
389
390boolean_t
391vdev_indirect_should_condense(vdev_t *vd)
392{
393	vdev_indirect_mapping_t *vim = vd->vdev_indirect_mapping;
394	spa_t *spa = vd->vdev_spa;
395
396	ASSERT(dsl_pool_sync_context(spa->spa_dsl_pool));
397
398	if (!zfs_condense_indirect_vdevs_enable)
399		return (B_FALSE);
400
401	/*
402	 * We can only condense one indirect vdev at a time.
403	 */
404	if (spa->spa_condensing_indirect != NULL)
405		return (B_FALSE);
406
407	if (spa_shutting_down(spa))
408		return (B_FALSE);
409
410	/*
411	 * The mapping object size must not change while we are
412	 * condensing, so we can only condense indirect vdevs
413	 * (not vdevs that are still in the middle of being removed).
414	 */
415	if (vd->vdev_ops != &vdev_indirect_ops)
416		return (B_FALSE);
417
418	/*
419	 * If nothing new has been marked obsolete, there is no
420	 * point in condensing.
421	 */
422	if (vd->vdev_obsolete_sm == NULL) {
423		ASSERT0(vdev_obsolete_sm_object(vd));
424		return (B_FALSE);
425	}
426
427	ASSERT(vd->vdev_obsolete_sm != NULL);
428
429	ASSERT3U(vdev_obsolete_sm_object(vd), ==,
430	    space_map_object(vd->vdev_obsolete_sm));
431
432	uint64_t bytes_mapped = vdev_indirect_mapping_bytes_mapped(vim);
433	uint64_t bytes_obsolete = space_map_allocated(vd->vdev_obsolete_sm);
434	uint64_t mapping_size = vdev_indirect_mapping_size(vim);
435	uint64_t obsolete_sm_size = space_map_length(vd->vdev_obsolete_sm);
436
437	ASSERT3U(bytes_obsolete, <=, bytes_mapped);
438
439	/*
440	 * If a high percentage of the bytes that are mapped have become
441	 * obsolete, condense (unless the mapping is already small enough).
442	 * This has a good chance of reducing the amount of memory used
443	 * by the mapping.
444	 */
445	if (bytes_obsolete * 100 / bytes_mapped >=
446	    zfs_indirect_condense_obsolete_pct &&
447	    mapping_size > zfs_condense_min_mapping_bytes) {
448		zfs_dbgmsg("should condense vdev %llu because obsolete "
449		    "spacemap covers %d%% of %lluMB mapping",
450		    (u_longlong_t)vd->vdev_id,
451		    (int)(bytes_obsolete * 100 / bytes_mapped),
452		    (u_longlong_t)bytes_mapped / 1024 / 1024);
453		return (B_TRUE);
454	}
455
456	/*
457	 * If the obsolete space map takes up too much space on disk,
458	 * condense in order to free up this disk space.
459	 */
460	if (obsolete_sm_size >= zfs_condense_max_obsolete_bytes) {
461		zfs_dbgmsg("should condense vdev %llu because obsolete sm "
462		    "length %lluMB >= max size %lluMB",
463		    (u_longlong_t)vd->vdev_id,
464		    (u_longlong_t)obsolete_sm_size / 1024 / 1024,
465		    (u_longlong_t)zfs_condense_max_obsolete_bytes /
466		    1024 / 1024);
467		return (B_TRUE);
468	}
469
470	return (B_FALSE);
471}
472
473/*
474 * This sync task completes (finishes) a condense, deleting the old
475 * mapping and replacing it with the new one.
476 */
477static void
478spa_condense_indirect_complete_sync(void *arg, dmu_tx_t *tx)
479{
480	spa_condensing_indirect_t *sci = arg;
481	spa_t *spa = dmu_tx_pool(tx)->dp_spa;
482	spa_condensing_indirect_phys_t *scip =
483	    &spa->spa_condensing_indirect_phys;
484	vdev_t *vd = vdev_lookup_top(spa, scip->scip_vdev);
485	vdev_indirect_config_t *vic = &vd->vdev_indirect_config;
486	objset_t *mos = spa->spa_meta_objset;
487	vdev_indirect_mapping_t *old_mapping = vd->vdev_indirect_mapping;
488	uint64_t old_count = vdev_indirect_mapping_num_entries(old_mapping);
489	uint64_t new_count =
490	    vdev_indirect_mapping_num_entries(sci->sci_new_mapping);
491
492	ASSERT(dmu_tx_is_syncing(tx));
493	ASSERT3P(vd->vdev_ops, ==, &vdev_indirect_ops);
494	ASSERT3P(sci, ==, spa->spa_condensing_indirect);
495	for (int i = 0; i < TXG_SIZE; i++) {
496		ASSERT(list_is_empty(&sci->sci_new_mapping_entries[i]));
497	}
498	ASSERT(vic->vic_mapping_object != 0);
499	ASSERT3U(vd->vdev_id, ==, scip->scip_vdev);
500	ASSERT(scip->scip_next_mapping_object != 0);
501	ASSERT(scip->scip_prev_obsolete_sm_object != 0);
502
503	/*
504	 * Reset vdev_indirect_mapping to refer to the new object.
505	 */
506	rw_enter(&vd->vdev_indirect_rwlock, RW_WRITER);
507	vdev_indirect_mapping_close(vd->vdev_indirect_mapping);
508	vd->vdev_indirect_mapping = sci->sci_new_mapping;
509	rw_exit(&vd->vdev_indirect_rwlock);
510
511	sci->sci_new_mapping = NULL;
512	vdev_indirect_mapping_free(mos, vic->vic_mapping_object, tx);
513	vic->vic_mapping_object = scip->scip_next_mapping_object;
514	scip->scip_next_mapping_object = 0;
515
516	space_map_free_obj(mos, scip->scip_prev_obsolete_sm_object, tx);
517	spa_feature_decr(spa, SPA_FEATURE_OBSOLETE_COUNTS, tx);
518	scip->scip_prev_obsolete_sm_object = 0;
519
520	scip->scip_vdev = 0;
521
522	VERIFY0(zap_remove(mos, DMU_POOL_DIRECTORY_OBJECT,
523	    DMU_POOL_CONDENSING_INDIRECT, tx));
524	spa_condensing_indirect_destroy(spa->spa_condensing_indirect);
525	spa->spa_condensing_indirect = NULL;
526
527	zfs_dbgmsg("finished condense of vdev %llu in txg %llu: "
528	    "new mapping object %llu has %llu entries "
529	    "(was %llu entries)",
530	    vd->vdev_id, dmu_tx_get_txg(tx), vic->vic_mapping_object,
531	    new_count, old_count);
532
533	vdev_config_dirty(spa->spa_root_vdev);
534}
535
536/*
537 * This sync task appends entries to the new mapping object.
538 */
539static void
540spa_condense_indirect_commit_sync(void *arg, dmu_tx_t *tx)
541{
542	spa_condensing_indirect_t *sci = arg;
543	uint64_t txg = dmu_tx_get_txg(tx);
544	spa_t *spa = dmu_tx_pool(tx)->dp_spa;
545
546	ASSERT(dmu_tx_is_syncing(tx));
547	ASSERT3P(sci, ==, spa->spa_condensing_indirect);
548
549	vdev_indirect_mapping_add_entries(sci->sci_new_mapping,
550	    &sci->sci_new_mapping_entries[txg & TXG_MASK], tx);
551	ASSERT(list_is_empty(&sci->sci_new_mapping_entries[txg & TXG_MASK]));
552}
553
554/*
555 * Open-context function to add one entry to the new mapping.  The new
556 * entry will be remembered and written from syncing context.
557 */
558static void
559spa_condense_indirect_commit_entry(spa_t *spa,
560    vdev_indirect_mapping_entry_phys_t *vimep, uint32_t count)
561{
562	spa_condensing_indirect_t *sci = spa->spa_condensing_indirect;
563
564	ASSERT3U(count, <, DVA_GET_ASIZE(&vimep->vimep_dst));
565
566	dmu_tx_t *tx = dmu_tx_create_dd(spa_get_dsl(spa)->dp_mos_dir);
567	dmu_tx_hold_space(tx, sizeof (*vimep) + sizeof (count));
568	VERIFY0(dmu_tx_assign(tx, TXG_WAIT));
569	int txgoff = dmu_tx_get_txg(tx) & TXG_MASK;
570
571	/*
572	 * If we are the first entry committed this txg, kick off the sync
573	 * task to write to the MOS on our behalf.
574	 */
575	if (list_is_empty(&sci->sci_new_mapping_entries[txgoff])) {
576		dsl_sync_task_nowait(dmu_tx_pool(tx),
577		    spa_condense_indirect_commit_sync, sci,
578		    0, ZFS_SPACE_CHECK_NONE, tx);
579	}
580
581	vdev_indirect_mapping_entry_t *vime =
582	    kmem_alloc(sizeof (*vime), KM_SLEEP);
583	vime->vime_mapping = *vimep;
584	vime->vime_obsolete_count = count;
585	list_insert_tail(&sci->sci_new_mapping_entries[txgoff], vime);
586
587	dmu_tx_commit(tx);
588}
589
590static void
591spa_condense_indirect_generate_new_mapping(vdev_t *vd,
592    uint32_t *obsolete_counts, uint64_t start_index, zthr_t *zthr)
593{
594	spa_t *spa = vd->vdev_spa;
595	uint64_t mapi = start_index;
596	vdev_indirect_mapping_t *old_mapping = vd->vdev_indirect_mapping;
597	uint64_t old_num_entries =
598	    vdev_indirect_mapping_num_entries(old_mapping);
599
600	ASSERT3P(vd->vdev_ops, ==, &vdev_indirect_ops);
601	ASSERT3U(vd->vdev_id, ==, spa->spa_condensing_indirect_phys.scip_vdev);
602
603	zfs_dbgmsg("starting condense of vdev %llu from index %llu",
604	    (u_longlong_t)vd->vdev_id,
605	    (u_longlong_t)mapi);
606
607	while (mapi < old_num_entries) {
608
609		if (zthr_iscancelled(zthr)) {
610			zfs_dbgmsg("pausing condense of vdev %llu "
611			    "at index %llu", (u_longlong_t)vd->vdev_id,
612			    (u_longlong_t)mapi);
613			break;
614		}
615
616		vdev_indirect_mapping_entry_phys_t *entry =
617		    &old_mapping->vim_entries[mapi];
618		uint64_t entry_size = DVA_GET_ASIZE(&entry->vimep_dst);
619		ASSERT3U(obsolete_counts[mapi], <=, entry_size);
620		if (obsolete_counts[mapi] < entry_size) {
621			spa_condense_indirect_commit_entry(spa, entry,
622			    obsolete_counts[mapi]);
623
624			/*
625			 * This delay may be requested for testing, debugging,
626			 * or performance reasons.
627			 */
628			delay(zfs_condense_indirect_commit_entry_delay_ticks);
629		}
630
631		mapi++;
632	}
633}
634
635/* ARGSUSED */
636static boolean_t
637spa_condense_indirect_thread_check(void *arg, zthr_t *zthr)
638{
639	spa_t *spa = arg;
640
641	return (spa->spa_condensing_indirect != NULL);
642}
643
644/* ARGSUSED */
645static void
646spa_condense_indirect_thread(void *arg, zthr_t *zthr)
647{
648	spa_t *spa = arg;
649	vdev_t *vd;
650
651	ASSERT3P(spa->spa_condensing_indirect, !=, NULL);
652	spa_config_enter(spa, SCL_VDEV, FTAG, RW_READER);
653	vd = vdev_lookup_top(spa, spa->spa_condensing_indirect_phys.scip_vdev);
654	ASSERT3P(vd, !=, NULL);
655	spa_config_exit(spa, SCL_VDEV, FTAG);
656
657	spa_condensing_indirect_t *sci = spa->spa_condensing_indirect;
658	spa_condensing_indirect_phys_t *scip =
659	    &spa->spa_condensing_indirect_phys;
660	uint32_t *counts;
661	uint64_t start_index;
662	vdev_indirect_mapping_t *old_mapping = vd->vdev_indirect_mapping;
663	space_map_t *prev_obsolete_sm = NULL;
664
665	ASSERT3U(vd->vdev_id, ==, scip->scip_vdev);
666	ASSERT(scip->scip_next_mapping_object != 0);
667	ASSERT(scip->scip_prev_obsolete_sm_object != 0);
668	ASSERT3P(vd->vdev_ops, ==, &vdev_indirect_ops);
669
670	for (int i = 0; i < TXG_SIZE; i++) {
671		/*
672		 * The list must start out empty in order for the
673		 * _commit_sync() sync task to be properly registered
674		 * on the first call to _commit_entry(); so it's wise
675		 * to double check and ensure we actually are starting
676		 * with empty lists.
677		 */
678		ASSERT(list_is_empty(&sci->sci_new_mapping_entries[i]));
679	}
680
681	VERIFY0(space_map_open(&prev_obsolete_sm, spa->spa_meta_objset,
682	    scip->scip_prev_obsolete_sm_object, 0, vd->vdev_asize, 0));
683	counts = vdev_indirect_mapping_load_obsolete_counts(old_mapping);
684	if (prev_obsolete_sm != NULL) {
685		vdev_indirect_mapping_load_obsolete_spacemap(old_mapping,
686		    counts, prev_obsolete_sm);
687	}
688	space_map_close(prev_obsolete_sm);
689
690	/*
691	 * Generate new mapping.  Determine what index to continue from
692	 * based on the max offset that we've already written in the
693	 * new mapping.
694	 */
695	uint64_t max_offset =
696	    vdev_indirect_mapping_max_offset(sci->sci_new_mapping);
697	if (max_offset == 0) {
698		/* We haven't written anything to the new mapping yet. */
699		start_index = 0;
700	} else {
701		/*
702		 * Pick up from where we left off. _entry_for_offset()
703		 * returns a pointer into the vim_entries array. If
704		 * max_offset is greater than any of the mappings
705		 * contained in the table  NULL will be returned and
706		 * that indicates we've exhausted our iteration of the
707		 * old_mapping.
708		 */
709
710		vdev_indirect_mapping_entry_phys_t *entry =
711		    vdev_indirect_mapping_entry_for_offset_or_next(old_mapping,
712		    max_offset);
713
714		if (entry == NULL) {
715			/*
716			 * We've already written the whole new mapping.
717			 * This special value will cause us to skip the
718			 * generate_new_mapping step and just do the sync
719			 * task to complete the condense.
720			 */
721			start_index = UINT64_MAX;
722		} else {
723			start_index = entry - old_mapping->vim_entries;
724			ASSERT3U(start_index, <,
725			    vdev_indirect_mapping_num_entries(old_mapping));
726		}
727	}
728
729	spa_condense_indirect_generate_new_mapping(vd, counts,
730	    start_index, zthr);
731
732	vdev_indirect_mapping_free_obsolete_counts(old_mapping, counts);
733
734	/*
735	 * If the zthr has received a cancellation signal while running
736	 * in generate_new_mapping() or at any point after that, then bail
737	 * early. We don't want to complete the condense if the spa is
738	 * shutting down.
739	 */
740	if (zthr_iscancelled(zthr))
741		return;
742
743	VERIFY0(dsl_sync_task(spa_name(spa), NULL,
744	    spa_condense_indirect_complete_sync, sci, 0,
745	    ZFS_SPACE_CHECK_EXTRA_RESERVED));
746}
747
748/*
749 * Sync task to begin the condensing process.
750 */
751void
752spa_condense_indirect_start_sync(vdev_t *vd, dmu_tx_t *tx)
753{
754	spa_t *spa = vd->vdev_spa;
755	spa_condensing_indirect_phys_t *scip =
756	    &spa->spa_condensing_indirect_phys;
757
758	ASSERT0(scip->scip_next_mapping_object);
759	ASSERT0(scip->scip_prev_obsolete_sm_object);
760	ASSERT0(scip->scip_vdev);
761	ASSERT(dmu_tx_is_syncing(tx));
762	ASSERT3P(vd->vdev_ops, ==, &vdev_indirect_ops);
763	ASSERT(spa_feature_is_active(spa, SPA_FEATURE_OBSOLETE_COUNTS));
764	ASSERT(vdev_indirect_mapping_num_entries(vd->vdev_indirect_mapping));
765
766	uint64_t obsolete_sm_obj = vdev_obsolete_sm_object(vd);
767	ASSERT(obsolete_sm_obj != 0);
768
769	scip->scip_vdev = vd->vdev_id;
770	scip->scip_next_mapping_object =
771	    vdev_indirect_mapping_alloc(spa->spa_meta_objset, tx);
772
773	scip->scip_prev_obsolete_sm_object = obsolete_sm_obj;
774
775	/*
776	 * We don't need to allocate a new space map object, since
777	 * vdev_indirect_sync_obsolete will allocate one when needed.
778	 */
779	space_map_close(vd->vdev_obsolete_sm);
780	vd->vdev_obsolete_sm = NULL;
781	VERIFY0(zap_remove(spa->spa_meta_objset, vd->vdev_top_zap,
782	    VDEV_TOP_ZAP_INDIRECT_OBSOLETE_SM, tx));
783
784	VERIFY0(zap_add(spa->spa_dsl_pool->dp_meta_objset,
785	    DMU_POOL_DIRECTORY_OBJECT,
786	    DMU_POOL_CONDENSING_INDIRECT, sizeof (uint64_t),
787	    sizeof (*scip) / sizeof (uint64_t), scip, tx));
788
789	ASSERT3P(spa->spa_condensing_indirect, ==, NULL);
790	spa->spa_condensing_indirect = spa_condensing_indirect_create(spa);
791
792	zfs_dbgmsg("starting condense of vdev %llu in txg %llu: "
793	    "posm=%llu nm=%llu",
794	    vd->vdev_id, dmu_tx_get_txg(tx),
795	    (u_longlong_t)scip->scip_prev_obsolete_sm_object,
796	    (u_longlong_t)scip->scip_next_mapping_object);
797
798	zthr_wakeup(spa->spa_condense_zthr);
799}
800
801/*
802 * Sync to the given vdev's obsolete space map any segments that are no longer
803 * referenced as of the given txg.
804 *
805 * If the obsolete space map doesn't exist yet, create and open it.
806 */
807void
808vdev_indirect_sync_obsolete(vdev_t *vd, dmu_tx_t *tx)
809{
810	spa_t *spa = vd->vdev_spa;
811	vdev_indirect_config_t *vic = &vd->vdev_indirect_config;
812
813	ASSERT3U(vic->vic_mapping_object, !=, 0);
814	ASSERT(range_tree_space(vd->vdev_obsolete_segments) > 0);
815	ASSERT(vd->vdev_removing || vd->vdev_ops == &vdev_indirect_ops);
816	ASSERT(spa_feature_is_enabled(spa, SPA_FEATURE_OBSOLETE_COUNTS));
817
818	if (vdev_obsolete_sm_object(vd) == 0) {
819		uint64_t obsolete_sm_object =
820		    space_map_alloc(spa->spa_meta_objset,
821		    vdev_standard_sm_blksz, tx);
822
823		ASSERT(vd->vdev_top_zap != 0);
824		VERIFY0(zap_add(vd->vdev_spa->spa_meta_objset, vd->vdev_top_zap,
825		    VDEV_TOP_ZAP_INDIRECT_OBSOLETE_SM,
826		    sizeof (obsolete_sm_object), 1, &obsolete_sm_object, tx));
827		ASSERT3U(vdev_obsolete_sm_object(vd), !=, 0);
828
829		spa_feature_incr(spa, SPA_FEATURE_OBSOLETE_COUNTS, tx);
830		VERIFY0(space_map_open(&vd->vdev_obsolete_sm,
831		    spa->spa_meta_objset, obsolete_sm_object,
832		    0, vd->vdev_asize, 0));
833	}
834
835	ASSERT(vd->vdev_obsolete_sm != NULL);
836	ASSERT3U(vdev_obsolete_sm_object(vd), ==,
837	    space_map_object(vd->vdev_obsolete_sm));
838
839	space_map_write(vd->vdev_obsolete_sm,
840	    vd->vdev_obsolete_segments, SM_ALLOC, SM_NO_VDEVID, tx);
841	range_tree_vacate(vd->vdev_obsolete_segments, NULL, NULL);
842}
843
844int
845spa_condense_init(spa_t *spa)
846{
847	int error = zap_lookup(spa->spa_meta_objset,
848	    DMU_POOL_DIRECTORY_OBJECT,
849	    DMU_POOL_CONDENSING_INDIRECT, sizeof (uint64_t),
850	    sizeof (spa->spa_condensing_indirect_phys) / sizeof (uint64_t),
851	    &spa->spa_condensing_indirect_phys);
852	if (error == 0) {
853		if (spa_writeable(spa)) {
854			spa->spa_condensing_indirect =
855			    spa_condensing_indirect_create(spa);
856		}
857		return (0);
858	} else if (error == ENOENT) {
859		return (0);
860	} else {
861		return (error);
862	}
863}
864
865void
866spa_condense_fini(spa_t *spa)
867{
868	if (spa->spa_condensing_indirect != NULL) {
869		spa_condensing_indirect_destroy(spa->spa_condensing_indirect);
870		spa->spa_condensing_indirect = NULL;
871	}
872}
873
874void
875spa_start_indirect_condensing_thread(spa_t *spa)
876{
877	ASSERT3P(spa->spa_condense_zthr, ==, NULL);
878	spa->spa_condense_zthr = zthr_create(spa_condense_indirect_thread_check,
879	    spa_condense_indirect_thread, spa);
880}
881
882/*
883 * Gets the obsolete spacemap object from the vdev's ZAP.
884 * Returns the spacemap object, or 0 if it wasn't in the ZAP or the ZAP doesn't
885 * exist yet.
886 */
887int
888vdev_obsolete_sm_object(vdev_t *vd)
889{
890	ASSERT0(spa_config_held(vd->vdev_spa, SCL_ALL, RW_WRITER));
891	if (vd->vdev_top_zap == 0) {
892		return (0);
893	}
894
895	uint64_t sm_obj = 0;
896	int err = zap_lookup(vd->vdev_spa->spa_meta_objset, vd->vdev_top_zap,
897	    VDEV_TOP_ZAP_INDIRECT_OBSOLETE_SM, sizeof (sm_obj), 1, &sm_obj);
898
899	ASSERT(err == 0 || err == ENOENT);
900
901	return (sm_obj);
902}
903
904boolean_t
905vdev_obsolete_counts_are_precise(vdev_t *vd)
906{
907	ASSERT0(spa_config_held(vd->vdev_spa, SCL_ALL, RW_WRITER));
908	if (vd->vdev_top_zap == 0) {
909		return (B_FALSE);
910	}
911
912	uint64_t val = 0;
913	int err = zap_lookup(vd->vdev_spa->spa_meta_objset, vd->vdev_top_zap,
914	    VDEV_TOP_ZAP_OBSOLETE_COUNTS_ARE_PRECISE, sizeof (val), 1, &val);
915
916	ASSERT(err == 0 || err == ENOENT);
917
918	return (val != 0);
919}
920
921/* ARGSUSED */
922static void
923vdev_indirect_close(vdev_t *vd)
924{
925}
926
927/* ARGSUSED */
928static int
929vdev_indirect_open(vdev_t *vd, uint64_t *psize, uint64_t *max_psize,
930    uint64_t *ashift)
931{
932	*psize = *max_psize = vd->vdev_asize +
933	    VDEV_LABEL_START_SIZE + VDEV_LABEL_END_SIZE;
934	*ashift = vd->vdev_ashift;
935	return (0);
936}
937
938typedef struct remap_segment {
939	vdev_t *rs_vd;
940	uint64_t rs_offset;
941	uint64_t rs_asize;
942	uint64_t rs_split_offset;
943	list_node_t rs_node;
944} remap_segment_t;
945
946remap_segment_t *
947rs_alloc(vdev_t *vd, uint64_t offset, uint64_t asize, uint64_t split_offset)
948{
949	remap_segment_t *rs = kmem_alloc(sizeof (remap_segment_t), KM_SLEEP);
950	rs->rs_vd = vd;
951	rs->rs_offset = offset;
952	rs->rs_asize = asize;
953	rs->rs_split_offset = split_offset;
954	return (rs);
955}
956
957/*
958 * Given an indirect vdev and an extent on that vdev, it duplicates the
959 * physical entries of the indirect mapping that correspond to the extent
960 * to a new array and returns a pointer to it. In addition, copied_entries
961 * is populated with the number of mapping entries that were duplicated.
962 *
963 * Note that the function assumes that the caller holds vdev_indirect_rwlock.
964 * This ensures that the mapping won't change due to condensing as we
965 * copy over its contents.
966 *
967 * Finally, since we are doing an allocation, it is up to the caller to
968 * free the array allocated in this function.
969 */
970vdev_indirect_mapping_entry_phys_t *
971vdev_indirect_mapping_duplicate_adjacent_entries(vdev_t *vd, uint64_t offset,
972    uint64_t asize, uint64_t *copied_entries)
973{
974	vdev_indirect_mapping_entry_phys_t *duplicate_mappings = NULL;
975	vdev_indirect_mapping_t *vim = vd->vdev_indirect_mapping;
976	uint64_t entries = 0;
977
978	ASSERT(RW_READ_HELD(&vd->vdev_indirect_rwlock));
979
980	vdev_indirect_mapping_entry_phys_t *first_mapping =
981	    vdev_indirect_mapping_entry_for_offset(vim, offset);
982	ASSERT3P(first_mapping, !=, NULL);
983
984	vdev_indirect_mapping_entry_phys_t *m = first_mapping;
985	while (asize > 0) {
986		uint64_t size = DVA_GET_ASIZE(&m->vimep_dst);
987
988		ASSERT3U(offset, >=, DVA_MAPPING_GET_SRC_OFFSET(m));
989		ASSERT3U(offset, <, DVA_MAPPING_GET_SRC_OFFSET(m) + size);
990
991		uint64_t inner_offset = offset - DVA_MAPPING_GET_SRC_OFFSET(m);
992		uint64_t inner_size = MIN(asize, size - inner_offset);
993
994		offset += inner_size;
995		asize -= inner_size;
996		entries++;
997		m++;
998	}
999
1000	size_t copy_length = entries * sizeof (*first_mapping);
1001	duplicate_mappings = kmem_alloc(copy_length, KM_SLEEP);
1002	bcopy(first_mapping, duplicate_mappings, copy_length);
1003	*copied_entries = entries;
1004
1005	return (duplicate_mappings);
1006}
1007
1008/*
1009 * Goes through the relevant indirect mappings until it hits a concrete vdev
1010 * and issues the callback. On the way to the concrete vdev, if any other
1011 * indirect vdevs are encountered, then the callback will also be called on
1012 * each of those indirect vdevs. For example, if the segment is mapped to
1013 * segment A on indirect vdev 1, and then segment A on indirect vdev 1 is
1014 * mapped to segment B on concrete vdev 2, then the callback will be called on
1015 * both vdev 1 and vdev 2.
1016 *
1017 * While the callback passed to vdev_indirect_remap() is called on every vdev
1018 * the function encounters, certain callbacks only care about concrete vdevs.
1019 * These types of callbacks should return immediately and explicitly when they
1020 * are called on an indirect vdev.
1021 *
1022 * Because there is a possibility that a DVA section in the indirect device
1023 * has been split into multiple sections in our mapping, we keep track
1024 * of the relevant contiguous segments of the new location (remap_segment_t)
1025 * in a stack. This way we can call the callback for each of the new sections
1026 * created by a single section of the indirect device. Note though, that in
1027 * this scenario the callbacks in each split block won't occur in-order in
1028 * terms of offset, so callers should not make any assumptions about that.
1029 *
1030 * For callbacks that don't handle split blocks and immediately return when
1031 * they encounter them (as is the case for remap_blkptr_cb), the caller can
1032 * assume that its callback will be applied from the first indirect vdev
1033 * encountered to the last one and then the concrete vdev, in that order.
1034 */
1035static void
1036vdev_indirect_remap(vdev_t *vd, uint64_t offset, uint64_t asize,
1037    void (*func)(uint64_t, vdev_t *, uint64_t, uint64_t, void *), void *arg)
1038{
1039	list_t stack;
1040	spa_t *spa = vd->vdev_spa;
1041
1042	list_create(&stack, sizeof (remap_segment_t),
1043	    offsetof(remap_segment_t, rs_node));
1044
1045	for (remap_segment_t *rs = rs_alloc(vd, offset, asize, 0);
1046	    rs != NULL; rs = list_remove_head(&stack)) {
1047		vdev_t *v = rs->rs_vd;
1048		uint64_t num_entries = 0;
1049
1050		ASSERT(spa_config_held(spa, SCL_ALL, RW_READER) != 0);
1051		ASSERT(rs->rs_asize > 0);
1052
1053		/*
1054		 * Note: As this function can be called from open context
1055		 * (e.g. zio_read()), we need the following rwlock to
1056		 * prevent the mapping from being changed by condensing.
1057		 *
1058		 * So we grab the lock and we make a copy of the entries
1059		 * that are relevant to the extent that we are working on.
1060		 * Once that is done, we drop the lock and iterate over
1061		 * our copy of the mapping. Once we are done with the with
1062		 * the remap segment and we free it, we also free our copy
1063		 * of the indirect mapping entries that are relevant to it.
1064		 *
1065		 * This way we don't need to wait until the function is
1066		 * finished with a segment, to condense it. In addition, we
1067		 * don't need a recursive rwlock for the case that a call to
1068		 * vdev_indirect_remap() needs to call itself (through the
1069		 * codepath of its callback) for the same vdev in the middle
1070		 * of its execution.
1071		 */
1072		rw_enter(&v->vdev_indirect_rwlock, RW_READER);
1073		vdev_indirect_mapping_t *vim = v->vdev_indirect_mapping;
1074		ASSERT3P(vim, !=, NULL);
1075
1076		vdev_indirect_mapping_entry_phys_t *mapping =
1077		    vdev_indirect_mapping_duplicate_adjacent_entries(v,
1078		    rs->rs_offset, rs->rs_asize, &num_entries);
1079		ASSERT3P(mapping, !=, NULL);
1080		ASSERT3U(num_entries, >, 0);
1081		rw_exit(&v->vdev_indirect_rwlock);
1082
1083		for (uint64_t i = 0; i < num_entries; i++) {
1084			/*
1085			 * Note: the vdev_indirect_mapping can not change
1086			 * while we are running.  It only changes while the
1087			 * removal is in progress, and then only from syncing
1088			 * context. While a removal is in progress, this
1089			 * function is only called for frees, which also only
1090			 * happen from syncing context.
1091			 */
1092			vdev_indirect_mapping_entry_phys_t *m = &mapping[i];
1093
1094			ASSERT3P(m, !=, NULL);
1095			ASSERT3U(rs->rs_asize, >, 0);
1096
1097			uint64_t size = DVA_GET_ASIZE(&m->vimep_dst);
1098			uint64_t dst_offset = DVA_GET_OFFSET(&m->vimep_dst);
1099			uint64_t dst_vdev = DVA_GET_VDEV(&m->vimep_dst);
1100
1101			ASSERT3U(rs->rs_offset, >=,
1102			    DVA_MAPPING_GET_SRC_OFFSET(m));
1103			ASSERT3U(rs->rs_offset, <,
1104			    DVA_MAPPING_GET_SRC_OFFSET(m) + size);
1105			ASSERT3U(dst_vdev, !=, v->vdev_id);
1106
1107			uint64_t inner_offset = rs->rs_offset -
1108			    DVA_MAPPING_GET_SRC_OFFSET(m);
1109			uint64_t inner_size =
1110			    MIN(rs->rs_asize, size - inner_offset);
1111
1112			vdev_t *dst_v = vdev_lookup_top(spa, dst_vdev);
1113			ASSERT3P(dst_v, !=, NULL);
1114
1115			if (dst_v->vdev_ops == &vdev_indirect_ops) {
1116				list_insert_head(&stack,
1117				    rs_alloc(dst_v, dst_offset + inner_offset,
1118				    inner_size, rs->rs_split_offset));
1119
1120			}
1121
1122			if ((zfs_flags & ZFS_DEBUG_INDIRECT_REMAP) &&
1123			    IS_P2ALIGNED(inner_size, 2 * SPA_MINBLOCKSIZE)) {
1124				/*
1125				 * Note: This clause exists only solely for
1126				 * testing purposes. We use it to ensure that
1127				 * split blocks work and that the callbacks
1128				 * using them yield the same result if issued
1129				 * in reverse order.
1130				 */
1131				uint64_t inner_half = inner_size / 2;
1132
1133				func(rs->rs_split_offset + inner_half, dst_v,
1134				    dst_offset + inner_offset + inner_half,
1135				    inner_half, arg);
1136
1137				func(rs->rs_split_offset, dst_v,
1138				    dst_offset + inner_offset,
1139				    inner_half, arg);
1140			} else {
1141				func(rs->rs_split_offset, dst_v,
1142				    dst_offset + inner_offset,
1143				    inner_size, arg);
1144			}
1145
1146			rs->rs_offset += inner_size;
1147			rs->rs_asize -= inner_size;
1148			rs->rs_split_offset += inner_size;
1149		}
1150		VERIFY0(rs->rs_asize);
1151
1152		kmem_free(mapping, num_entries * sizeof (*mapping));
1153		kmem_free(rs, sizeof (remap_segment_t));
1154	}
1155	list_destroy(&stack);
1156}
1157
1158static void
1159vdev_indirect_child_io_done(zio_t *zio)
1160{
1161	zio_t *pio = zio->io_private;
1162
1163	mutex_enter(&pio->io_lock);
1164	pio->io_error = zio_worst_error(pio->io_error, zio->io_error);
1165	mutex_exit(&pio->io_lock);
1166
1167	abd_put(zio->io_abd);
1168}
1169
1170/*
1171 * This is a callback for vdev_indirect_remap() which allocates an
1172 * indirect_split_t for each split segment and adds it to iv_splits.
1173 */
1174static void
1175vdev_indirect_gather_splits(uint64_t split_offset, vdev_t *vd, uint64_t offset,
1176    uint64_t size, void *arg)
1177{
1178	zio_t *zio = arg;
1179	indirect_vsd_t *iv = zio->io_vsd;
1180
1181	ASSERT3P(vd, !=, NULL);
1182
1183	if (vd->vdev_ops == &vdev_indirect_ops)
1184		return;
1185
1186	int n = 1;
1187	if (vd->vdev_ops == &vdev_mirror_ops)
1188		n = vd->vdev_children;
1189
1190	indirect_split_t *is =
1191	    kmem_zalloc(offsetof(indirect_split_t, is_child[n]), KM_SLEEP);
1192
1193	is->is_children = n;
1194	is->is_size = size;
1195	is->is_split_offset = split_offset;
1196	is->is_target_offset = offset;
1197	is->is_vdev = vd;
1198	list_create(&is->is_unique_child, sizeof (indirect_child_t),
1199	    offsetof(indirect_child_t, ic_node));
1200
1201	/*
1202	 * Note that we only consider multiple copies of the data for
1203	 * *mirror* vdevs.  We don't for "replacing" or "spare" vdevs, even
1204	 * though they use the same ops as mirror, because there's only one
1205	 * "good" copy under the replacing/spare.
1206	 */
1207	if (vd->vdev_ops == &vdev_mirror_ops) {
1208		for (int i = 0; i < n; i++) {
1209			is->is_child[i].ic_vdev = vd->vdev_child[i];
1210			list_link_init(&is->is_child[i].ic_node);
1211		}
1212	} else {
1213		is->is_child[0].ic_vdev = vd;
1214	}
1215
1216	list_insert_tail(&iv->iv_splits, is);
1217}
1218
1219static void
1220vdev_indirect_read_split_done(zio_t *zio)
1221{
1222	indirect_child_t *ic = zio->io_private;
1223
1224	if (zio->io_error != 0) {
1225		/*
1226		 * Clear ic_data to indicate that we do not have data for this
1227		 * child.
1228		 */
1229		abd_free(ic->ic_data);
1230		ic->ic_data = NULL;
1231	}
1232}
1233
1234/*
1235 * Issue reads for all copies (mirror children) of all splits.
1236 */
1237static void
1238vdev_indirect_read_all(zio_t *zio)
1239{
1240	indirect_vsd_t *iv = zio->io_vsd;
1241
1242	for (indirect_split_t *is = list_head(&iv->iv_splits);
1243	    is != NULL; is = list_next(&iv->iv_splits, is)) {
1244		for (int i = 0; i < is->is_children; i++) {
1245			indirect_child_t *ic = &is->is_child[i];
1246
1247			if (!vdev_readable(ic->ic_vdev))
1248				continue;
1249
1250			/*
1251			 * Note, we may read from a child whose DTL
1252			 * indicates that the data may not be present here.
1253			 * While this might result in a few i/os that will
1254			 * likely return incorrect data, it simplifies the
1255			 * code since we can treat scrub and resilver
1256			 * identically.  (The incorrect data will be
1257			 * detected and ignored when we verify the
1258			 * checksum.)
1259			 */
1260
1261			ic->ic_data = abd_alloc_sametype(zio->io_abd,
1262			    is->is_size);
1263			ic->ic_duplicate = NULL;
1264
1265			zio_nowait(zio_vdev_child_io(zio, NULL,
1266			    ic->ic_vdev, is->is_target_offset, ic->ic_data,
1267			    is->is_size, zio->io_type, zio->io_priority, 0,
1268			    vdev_indirect_read_split_done, ic));
1269		}
1270	}
1271	iv->iv_reconstruct = B_TRUE;
1272}
1273
1274static void
1275vdev_indirect_io_start(zio_t *zio)
1276{
1277	spa_t *spa = zio->io_spa;
1278	indirect_vsd_t *iv = kmem_zalloc(sizeof (*iv), KM_SLEEP);
1279	list_create(&iv->iv_splits,
1280	    sizeof (indirect_split_t), offsetof(indirect_split_t, is_node));
1281
1282	zio->io_vsd = iv;
1283	zio->io_vsd_ops = &vdev_indirect_vsd_ops;
1284
1285	ASSERT(spa_config_held(spa, SCL_ALL, RW_READER) != 0);
1286	if (zio->io_type != ZIO_TYPE_READ) {
1287		ASSERT3U(zio->io_type, ==, ZIO_TYPE_WRITE);
1288		/*
1289		 * Note: this code can handle other kinds of writes,
1290		 * but we don't expect them.
1291		 */
1292		ASSERT((zio->io_flags & (ZIO_FLAG_SELF_HEAL |
1293		    ZIO_FLAG_RESILVER | ZIO_FLAG_INDUCE_DAMAGE)) != 0);
1294	}
1295
1296	vdev_indirect_remap(zio->io_vd, zio->io_offset, zio->io_size,
1297	    vdev_indirect_gather_splits, zio);
1298
1299	indirect_split_t *first = list_head(&iv->iv_splits);
1300	if (first->is_size == zio->io_size) {
1301		/*
1302		 * This is not a split block; we are pointing to the entire
1303		 * data, which will checksum the same as the original data.
1304		 * Pass the BP down so that the child i/o can verify the
1305		 * checksum, and try a different location if available
1306		 * (e.g. on a mirror).
1307		 *
1308		 * While this special case could be handled the same as the
1309		 * general (split block) case, doing it this way ensures
1310		 * that the vast majority of blocks on indirect vdevs
1311		 * (which are not split) are handled identically to blocks
1312		 * on non-indirect vdevs.  This allows us to be less strict
1313		 * about performance in the general (but rare) case.
1314		 */
1315		ASSERT0(first->is_split_offset);
1316		ASSERT3P(list_next(&iv->iv_splits, first), ==, NULL);
1317		zio_nowait(zio_vdev_child_io(zio, zio->io_bp,
1318		    first->is_vdev, first->is_target_offset,
1319		    abd_get_offset(zio->io_abd, 0),
1320		    zio->io_size, zio->io_type, zio->io_priority, 0,
1321		    vdev_indirect_child_io_done, zio));
1322	} else {
1323		iv->iv_split_block = B_TRUE;
1324		if (zio->io_flags & (ZIO_FLAG_SCRUB | ZIO_FLAG_RESILVER)) {
1325			/*
1326			 * Read all copies.  Note that for simplicity,
1327			 * we don't bother consulting the DTL in the
1328			 * resilver case.
1329			 */
1330			vdev_indirect_read_all(zio);
1331		} else {
1332			/*
1333			 * Read one copy of each split segment, from the
1334			 * top-level vdev.  Since we don't know the
1335			 * checksum of each split individually, the child
1336			 * zio can't ensure that we get the right data.
1337			 * E.g. if it's a mirror, it will just read from a
1338			 * random (healthy) leaf vdev.  We have to verify
1339			 * the checksum in vdev_indirect_io_done().
1340			 */
1341			for (indirect_split_t *is = list_head(&iv->iv_splits);
1342			    is != NULL; is = list_next(&iv->iv_splits, is)) {
1343				zio_nowait(zio_vdev_child_io(zio, NULL,
1344				    is->is_vdev, is->is_target_offset,
1345				    abd_get_offset(zio->io_abd,
1346				    is->is_split_offset),
1347				    is->is_size, zio->io_type,
1348				    zio->io_priority, 0,
1349				    vdev_indirect_child_io_done, zio));
1350			}
1351		}
1352	}
1353
1354	zio_execute(zio);
1355}
1356
1357/*
1358 * Report a checksum error for a child.
1359 */
1360static void
1361vdev_indirect_checksum_error(zio_t *zio,
1362    indirect_split_t *is, indirect_child_t *ic)
1363{
1364	vdev_t *vd = ic->ic_vdev;
1365
1366	if (zio->io_flags & ZIO_FLAG_SPECULATIVE)
1367		return;
1368
1369	mutex_enter(&vd->vdev_stat_lock);
1370	vd->vdev_stat.vs_checksum_errors++;
1371	mutex_exit(&vd->vdev_stat_lock);
1372
1373	zio_bad_cksum_t zbc = { 0 };
1374	void *bad_buf = abd_borrow_buf_copy(ic->ic_data, is->is_size);
1375	abd_t *good_abd = is->is_good_child->ic_data;
1376	void *good_buf = abd_borrow_buf_copy(good_abd, is->is_size);
1377	zfs_ereport_post_checksum(zio->io_spa, vd, zio,
1378	    is->is_target_offset, is->is_size, good_buf, bad_buf, &zbc);
1379	abd_return_buf(ic->ic_data, bad_buf, is->is_size);
1380	abd_return_buf(good_abd, good_buf, is->is_size);
1381}
1382
1383/*
1384 * Issue repair i/os for any incorrect copies.  We do this by comparing
1385 * each split segment's correct data (is_good_child's ic_data) with each
1386 * other copy of the data.  If they differ, then we overwrite the bad data
1387 * with the good copy.  Note that we do this without regard for the DTL's,
1388 * which simplifies this code and also issues the optimal number of writes
1389 * (based on which copies actually read bad data, as opposed to which we
1390 * think might be wrong).  For the same reason, we always use
1391 * ZIO_FLAG_SELF_HEAL, to bypass the DTL check in zio_vdev_io_start().
1392 */
1393static void
1394vdev_indirect_repair(zio_t *zio)
1395{
1396	indirect_vsd_t *iv = zio->io_vsd;
1397
1398	enum zio_flag flags = ZIO_FLAG_IO_REPAIR;
1399
1400	if (!(zio->io_flags & (ZIO_FLAG_SCRUB | ZIO_FLAG_RESILVER)))
1401		flags |= ZIO_FLAG_SELF_HEAL;
1402
1403	if (!spa_writeable(zio->io_spa))
1404		return;
1405
1406	for (indirect_split_t *is = list_head(&iv->iv_splits);
1407	    is != NULL; is = list_next(&iv->iv_splits, is)) {
1408		for (int c = 0; c < is->is_children; c++) {
1409			indirect_child_t *ic = &is->is_child[c];
1410			if (ic == is->is_good_child)
1411				continue;
1412			if (ic->ic_data == NULL)
1413				continue;
1414			if (ic->ic_duplicate == is->is_good_child)
1415				continue;
1416
1417			zio_nowait(zio_vdev_child_io(zio, NULL,
1418			    ic->ic_vdev, is->is_target_offset,
1419			    is->is_good_child->ic_data, is->is_size,
1420			    ZIO_TYPE_WRITE, ZIO_PRIORITY_ASYNC_WRITE,
1421			    ZIO_FLAG_IO_REPAIR | ZIO_FLAG_SELF_HEAL,
1422			    NULL, NULL));
1423
1424			vdev_indirect_checksum_error(zio, is, ic);
1425		}
1426	}
1427}
1428
1429/*
1430 * Report checksum errors on all children that we read from.
1431 */
1432static void
1433vdev_indirect_all_checksum_errors(zio_t *zio)
1434{
1435	indirect_vsd_t *iv = zio->io_vsd;
1436
1437	if (zio->io_flags & ZIO_FLAG_SPECULATIVE)
1438		return;
1439
1440	for (indirect_split_t *is = list_head(&iv->iv_splits);
1441	    is != NULL; is = list_next(&iv->iv_splits, is)) {
1442		for (int c = 0; c < is->is_children; c++) {
1443			indirect_child_t *ic = &is->is_child[c];
1444
1445			if (ic->ic_data == NULL)
1446				continue;
1447
1448			vdev_t *vd = ic->ic_vdev;
1449
1450			mutex_enter(&vd->vdev_stat_lock);
1451			vd->vdev_stat.vs_checksum_errors++;
1452			mutex_exit(&vd->vdev_stat_lock);
1453
1454			zfs_ereport_post_checksum(zio->io_spa, vd, zio,
1455			    is->is_target_offset, is->is_size,
1456			    NULL, NULL, NULL);
1457		}
1458	}
1459}
1460
1461/*
1462 * Copy data from all the splits to a main zio then validate the checksum.
1463 * If then checksum is successfully validated return success.
1464 */
1465static int
1466vdev_indirect_splits_checksum_validate(indirect_vsd_t *iv, zio_t *zio)
1467{
1468	zio_bad_cksum_t zbc;
1469
1470	for (indirect_split_t *is = list_head(&iv->iv_splits);
1471	    is != NULL; is = list_next(&iv->iv_splits, is)) {
1472
1473		ASSERT3P(is->is_good_child->ic_data, !=, NULL);
1474		ASSERT3P(is->is_good_child->ic_duplicate, ==, NULL);
1475
1476		abd_copy_off(zio->io_abd, is->is_good_child->ic_data,
1477		    is->is_split_offset, 0, is->is_size);
1478	}
1479
1480	return (zio_checksum_error(zio, &zbc));
1481}
1482
1483/*
1484 * There are relatively few possible combinations making it feasible to
1485 * deterministically check them all.  We do this by setting the good_child
1486 * to the next unique split version.  If we reach the end of the list then
1487 * "carry over" to the next unique split version (like counting in base
1488 * is_unique_children, but each digit can have a different base).
1489 */
1490static int
1491vdev_indirect_splits_enumerate_all(indirect_vsd_t *iv, zio_t *zio)
1492{
1493	boolean_t more = B_TRUE;
1494
1495	iv->iv_attempts = 0;
1496
1497	for (indirect_split_t *is = list_head(&iv->iv_splits);
1498	    is != NULL; is = list_next(&iv->iv_splits, is))
1499		is->is_good_child = list_head(&is->is_unique_child);
1500
1501	while (more == B_TRUE) {
1502		iv->iv_attempts++;
1503		more = B_FALSE;
1504
1505		if (vdev_indirect_splits_checksum_validate(iv, zio) == 0)
1506			return (0);
1507
1508		for (indirect_split_t *is = list_head(&iv->iv_splits);
1509		    is != NULL; is = list_next(&iv->iv_splits, is)) {
1510			is->is_good_child = list_next(&is->is_unique_child,
1511			    is->is_good_child);
1512			if (is->is_good_child != NULL) {
1513				more = B_TRUE;
1514				break;
1515			}
1516
1517			is->is_good_child = list_head(&is->is_unique_child);
1518		}
1519	}
1520
1521	ASSERT3S(iv->iv_attempts, <=, iv->iv_unique_combinations);
1522
1523	return (SET_ERROR(ECKSUM));
1524}
1525
1526/*
1527 * There are too many combinations to try all of them in a reasonable amount
1528 * of time.  So try a fixed number of random combinations from the unique
1529 * split versions, after which we'll consider the block unrecoverable.
1530 */
1531static int
1532vdev_indirect_splits_enumerate_randomly(indirect_vsd_t *iv, zio_t *zio)
1533{
1534	iv->iv_attempts = 0;
1535
1536	while (iv->iv_attempts < iv->iv_attempts_max) {
1537		iv->iv_attempts++;
1538
1539		for (indirect_split_t *is = list_head(&iv->iv_splits);
1540		    is != NULL; is = list_next(&iv->iv_splits, is)) {
1541			indirect_child_t *ic = list_head(&is->is_unique_child);
1542			int children = is->is_unique_children;
1543
1544			for (int i = spa_get_random(children); i > 0; i--)
1545				ic = list_next(&is->is_unique_child, ic);
1546
1547			ASSERT3P(ic, !=, NULL);
1548			is->is_good_child = ic;
1549		}
1550
1551		if (vdev_indirect_splits_checksum_validate(iv, zio) == 0)
1552			return (0);
1553	}
1554
1555	return (SET_ERROR(ECKSUM));
1556}
1557
1558/*
1559 * This is a validation function for reconstruction.  It randomly selects
1560 * a good combination, if one can be found, and then it intentionally
1561 * damages all other segment copes by zeroing them.  This forces the
1562 * reconstruction algorithm to locate the one remaining known good copy.
1563 */
1564static int
1565vdev_indirect_splits_damage(indirect_vsd_t *iv, zio_t *zio)
1566{
1567	/* Presume all the copies are unique for initial selection. */
1568	for (indirect_split_t *is = list_head(&iv->iv_splits);
1569	    is != NULL; is = list_next(&iv->iv_splits, is)) {
1570		is->is_unique_children = 0;
1571
1572		for (int i = 0; i < is->is_children; i++) {
1573			indirect_child_t *ic = &is->is_child[i];
1574			if (ic->ic_data != NULL) {
1575				is->is_unique_children++;
1576				list_insert_tail(&is->is_unique_child, ic);
1577			}
1578		}
1579	}
1580
1581	/*
1582	 * Set each is_good_child to a randomly-selected child which
1583	 * is known to contain validated data.
1584	 */
1585	int error = vdev_indirect_splits_enumerate_randomly(iv, zio);
1586	if (error)
1587		goto out;
1588
1589	/*
1590	 * Damage all but the known good copy by zeroing it.  This will
1591	 * result in two or less unique copies per indirect_child_t.
1592	 * Both may need to be checked in order to reconstruct the block.
1593	 * Set iv->iv_attempts_max such that all unique combinations will
1594	 * enumerated, but limit the damage to at most 16 indirect splits.
1595	 */
1596	iv->iv_attempts_max = 1;
1597
1598	for (indirect_split_t *is = list_head(&iv->iv_splits);
1599	    is != NULL; is = list_next(&iv->iv_splits, is)) {
1600		for (int c = 0; c < is->is_children; c++) {
1601			indirect_child_t *ic = &is->is_child[c];
1602
1603			if (ic == is->is_good_child)
1604				continue;
1605			if (ic->ic_data == NULL)
1606				continue;
1607
1608			abd_zero(ic->ic_data, ic->ic_data->abd_size);
1609		}
1610
1611		iv->iv_attempts_max *= 2;
1612		if (iv->iv_attempts_max > (1ULL << 16)) {
1613			iv->iv_attempts_max = UINT64_MAX;
1614			break;
1615		}
1616	}
1617
1618out:
1619	/* Empty the unique children lists so they can be reconstructed. */
1620	for (indirect_split_t *is = list_head(&iv->iv_splits);
1621	    is != NULL; is = list_next(&iv->iv_splits, is)) {
1622		indirect_child_t *ic;
1623		while ((ic = list_head(&is->is_unique_child)) != NULL)
1624			list_remove(&is->is_unique_child, ic);
1625
1626		is->is_unique_children = 0;
1627	}
1628
1629	return (error);
1630}
1631
1632/*
1633 * This function is called when we have read all copies of the data and need
1634 * to try to find a combination of copies that gives us the right checksum.
1635 *
1636 * If we pointed to any mirror vdevs, this effectively does the job of the
1637 * mirror.  The mirror vdev code can't do its own job because we don't know
1638 * the checksum of each split segment individually.
1639 *
1640 * We have to try every unique combination of copies of split segments, until
1641 * we find one that checksums correctly.  Duplicate segment copies are first
1642 * identified and latter skipped during reconstruction.  This optimization
1643 * reduces the search space and ensures that of the remaining combinations
1644 * at most one is correct.
1645 *
1646 * When the total number of combinations is small they can all be checked.
1647 * For example, if we have 3 segments in the split, and each points to a
1648 * 2-way mirror with unique copies, we will have the following pieces of data:
1649 *
1650 *       |     mirror child
1651 * split |     [0]        [1]
1652 * ======|=====================
1653 *   A   |  data_A_0   data_A_1
1654 *   B   |  data_B_0   data_B_1
1655 *   C   |  data_C_0   data_C_1
1656 *
1657 * We will try the following (mirror children)^(number of splits) (2^3=8)
1658 * combinations, which is similar to bitwise-little-endian counting in
1659 * binary.  In general each "digit" corresponds to a split segment, and the
1660 * base of each digit is is_children, which can be different for each
1661 * digit.
1662 *
1663 * "low bit"        "high bit"
1664 *        v                 v
1665 * data_A_0 data_B_0 data_C_0
1666 * data_A_1 data_B_0 data_C_0
1667 * data_A_0 data_B_1 data_C_0
1668 * data_A_1 data_B_1 data_C_0
1669 * data_A_0 data_B_0 data_C_1
1670 * data_A_1 data_B_0 data_C_1
1671 * data_A_0 data_B_1 data_C_1
1672 * data_A_1 data_B_1 data_C_1
1673 *
1674 * Note that the split segments may be on the same or different top-level
1675 * vdevs. In either case, we may need to try lots of combinations (see
1676 * zfs_reconstruct_indirect_combinations_max).  This ensures that if a mirror
1677 * has small silent errors on all of its children, we can still reconstruct
1678 * the correct data, as long as those errors are at sufficiently-separated
1679 * offsets (specifically, separated by the largest block size - default of
1680 * 128KB, but up to 16MB).
1681 */
1682static void
1683vdev_indirect_reconstruct_io_done(zio_t *zio)
1684{
1685	indirect_vsd_t *iv = zio->io_vsd;
1686	boolean_t known_good = B_FALSE;
1687	int error;
1688
1689	iv->iv_unique_combinations = 1;
1690	iv->iv_attempts_max = UINT64_MAX;
1691
1692	if (zfs_reconstruct_indirect_combinations_max > 0)
1693		iv->iv_attempts_max = zfs_reconstruct_indirect_combinations_max;
1694
1695	/*
1696	 * If nonzero, every 1/x blocks will be damaged, in order to validate
1697	 * reconstruction when there are split segments with damaged copies.
1698	 * Known_good will TRUE when reconstruction is known to be possible.
1699	 */
1700	if (zfs_reconstruct_indirect_damage_fraction != 0 &&
1701	    spa_get_random(zfs_reconstruct_indirect_damage_fraction) == 0)
1702		known_good = (vdev_indirect_splits_damage(iv, zio) == 0);
1703
1704	/*
1705	 * Determine the unique children for a split segment and add them
1706	 * to the is_unique_child list.  By restricting reconstruction
1707	 * to these children, only unique combinations will be considered.
1708	 * This can vastly reduce the search space when there are a large
1709	 * number of indirect splits.
1710	 */
1711	for (indirect_split_t *is = list_head(&iv->iv_splits);
1712	    is != NULL; is = list_next(&iv->iv_splits, is)) {
1713		is->is_unique_children = 0;
1714
1715		for (int i = 0; i < is->is_children; i++) {
1716			indirect_child_t *ic_i = &is->is_child[i];
1717
1718			if (ic_i->ic_data == NULL ||
1719			    ic_i->ic_duplicate != NULL)
1720				continue;
1721
1722			for (int j = i + 1; j < is->is_children; j++) {
1723				indirect_child_t *ic_j = &is->is_child[j];
1724
1725				if (ic_j->ic_data == NULL ||
1726				    ic_j->ic_duplicate != NULL)
1727					continue;
1728
1729				if (abd_cmp(ic_i->ic_data, ic_j->ic_data,
1730				    is->is_size) == 0) {
1731					ic_j->ic_duplicate = ic_i;
1732				}
1733			}
1734
1735			is->is_unique_children++;
1736			list_insert_tail(&is->is_unique_child, ic_i);
1737		}
1738
1739		/* Reconstruction is impossible, no valid children */
1740		EQUIV(list_is_empty(&is->is_unique_child),
1741		    is->is_unique_children == 0);
1742		if (list_is_empty(&is->is_unique_child)) {
1743			zio->io_error = EIO;
1744			vdev_indirect_all_checksum_errors(zio);
1745			zio_checksum_verified(zio);
1746			return;
1747		}
1748
1749		iv->iv_unique_combinations *= is->is_unique_children;
1750	}
1751
1752	if (iv->iv_unique_combinations <= iv->iv_attempts_max)
1753		error = vdev_indirect_splits_enumerate_all(iv, zio);
1754	else
1755		error = vdev_indirect_splits_enumerate_randomly(iv, zio);
1756
1757	if (error != 0) {
1758		/* All attempted combinations failed. */
1759		ASSERT3B(known_good, ==, B_FALSE);
1760		zio->io_error = error;
1761		vdev_indirect_all_checksum_errors(zio);
1762	} else {
1763		/*
1764		 * The checksum has been successfully validated.  Issue
1765		 * repair I/Os to any copies of splits which don't match
1766		 * the validated version.
1767		 */
1768		ASSERT0(vdev_indirect_splits_checksum_validate(iv, zio));
1769		vdev_indirect_repair(zio);
1770		zio_checksum_verified(zio);
1771	}
1772}
1773
1774static void
1775vdev_indirect_io_done(zio_t *zio)
1776{
1777	indirect_vsd_t *iv = zio->io_vsd;
1778
1779	if (iv->iv_reconstruct) {
1780		/*
1781		 * We have read all copies of the data (e.g. from mirrors),
1782		 * either because this was a scrub/resilver, or because the
1783		 * one-copy read didn't checksum correctly.
1784		 */
1785		vdev_indirect_reconstruct_io_done(zio);
1786		return;
1787	}
1788
1789	if (!iv->iv_split_block) {
1790		/*
1791		 * This was not a split block, so we passed the BP down,
1792		 * and the checksum was handled by the (one) child zio.
1793		 */
1794		return;
1795	}
1796
1797	zio_bad_cksum_t zbc;
1798	int ret = zio_checksum_error(zio, &zbc);
1799	if (ret == 0) {
1800		zio_checksum_verified(zio);
1801		return;
1802	}
1803
1804	/*
1805	 * The checksum didn't match.  Read all copies of all splits, and
1806	 * then we will try to reconstruct.  The next time
1807	 * vdev_indirect_io_done() is called, iv_reconstruct will be set.
1808	 */
1809	vdev_indirect_read_all(zio);
1810
1811	zio_vdev_io_redone(zio);
1812}
1813
1814vdev_ops_t vdev_indirect_ops = {
1815	vdev_indirect_open,
1816	vdev_indirect_close,
1817	vdev_default_asize,
1818	vdev_indirect_io_start,
1819	vdev_indirect_io_done,
1820	NULL,
1821	NULL,
1822	NULL,
1823	vdev_indirect_remap,
1824	NULL,
1825	VDEV_TYPE_INDIRECT,	/* name of this vdev type */
1826	B_FALSE			/* leaf vdev */
1827};
1828