xref: /illumos-gate/usr/src/uts/common/fs/zfs/zio.c (revision 22fe2c8844be88ebae6478ca1b0b92c8ec2aef54)
1 /*
2  * CDDL HEADER START
3  *
4  * The contents of this file are subject to the terms of the
5  * Common Development and Distribution License (the "License").
6  * You may not use this file except in compliance with the License.
7  *
8  * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
9  * or http://www.opensolaris.org/os/licensing.
10  * See the License for the specific language governing permissions
11  * and limitations under the License.
12  *
13  * When distributing Covered Code, include this CDDL HEADER in each
14  * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
15  * If applicable, add the following below this CDDL HEADER, with the
16  * fields enclosed by brackets "[]" replaced with your own identifying
17  * information: Portions Copyright [yyyy] [name of copyright owner]
18  *
19  * CDDL HEADER END
20  */
21 /*
22  * Copyright 2009 Sun Microsystems, Inc.  All rights reserved.
23  * Use is subject to license terms.
24  */
25 
26 #include <sys/zfs_context.h>
27 #include <sys/fm/fs/zfs.h>
28 #include <sys/spa.h>
29 #include <sys/txg.h>
30 #include <sys/spa_impl.h>
31 #include <sys/vdev_impl.h>
32 #include <sys/zio_impl.h>
33 #include <sys/zio_compress.h>
34 #include <sys/zio_checksum.h>
35 
36 /*
37  * ==========================================================================
38  * I/O priority table
39  * ==========================================================================
40  */
41 uint8_t zio_priority_table[ZIO_PRIORITY_TABLE_SIZE] = {
42 	0,	/* ZIO_PRIORITY_NOW		*/
43 	0,	/* ZIO_PRIORITY_SYNC_READ	*/
44 	0,	/* ZIO_PRIORITY_SYNC_WRITE	*/
45 	6,	/* ZIO_PRIORITY_ASYNC_READ	*/
46 	4,	/* ZIO_PRIORITY_ASYNC_WRITE	*/
47 	4,	/* ZIO_PRIORITY_FREE		*/
48 	0,	/* ZIO_PRIORITY_CACHE_FILL	*/
49 	0,	/* ZIO_PRIORITY_LOG_WRITE	*/
50 	10,	/* ZIO_PRIORITY_RESILVER	*/
51 	20,	/* ZIO_PRIORITY_SCRUB		*/
52 };
53 
54 /*
55  * ==========================================================================
56  * I/O type descriptions
57  * ==========================================================================
58  */
59 char *zio_type_name[ZIO_TYPES] = {
60 	"null", "read", "write", "free", "claim", "ioctl" };
61 
62 #define	SYNC_PASS_DEFERRED_FREE	1	/* defer frees after this pass */
63 #define	SYNC_PASS_DONT_COMPRESS	4	/* don't compress after this pass */
64 #define	SYNC_PASS_REWRITE	1	/* rewrite new bps after this pass */
65 
66 /*
67  * ==========================================================================
68  * I/O kmem caches
69  * ==========================================================================
70  */
71 kmem_cache_t *zio_cache;
72 kmem_cache_t *zio_link_cache;
73 kmem_cache_t *zio_buf_cache[SPA_MAXBLOCKSIZE >> SPA_MINBLOCKSHIFT];
74 kmem_cache_t *zio_data_buf_cache[SPA_MAXBLOCKSIZE >> SPA_MINBLOCKSHIFT];
75 
76 #ifdef _KERNEL
77 extern vmem_t *zio_alloc_arena;
78 #endif
79 
80 /*
81  * An allocating zio is one that either currently has the DVA allocate
82  * stage set or will have it later in its lifetime.
83  */
84 #define	IO_IS_ALLOCATING(zio) \
85 	((zio)->io_orig_pipeline & (1U << ZIO_STAGE_DVA_ALLOCATE))
86 
87 void
88 zio_init(void)
89 {
90 	size_t c;
91 	vmem_t *data_alloc_arena = NULL;
92 
93 #ifdef _KERNEL
94 	data_alloc_arena = zio_alloc_arena;
95 #endif
96 	zio_cache = kmem_cache_create("zio_cache",
97 	    sizeof (zio_t), 0, NULL, NULL, NULL, NULL, NULL, 0);
98 	zio_link_cache = kmem_cache_create("zio_link_cache",
99 	    sizeof (zio_link_t), 0, NULL, NULL, NULL, NULL, NULL, 0);
100 
101 	/*
102 	 * For small buffers, we want a cache for each multiple of
103 	 * SPA_MINBLOCKSIZE.  For medium-size buffers, we want a cache
104 	 * for each quarter-power of 2.  For large buffers, we want
105 	 * a cache for each multiple of PAGESIZE.
106 	 */
107 	for (c = 0; c < SPA_MAXBLOCKSIZE >> SPA_MINBLOCKSHIFT; c++) {
108 		size_t size = (c + 1) << SPA_MINBLOCKSHIFT;
109 		size_t p2 = size;
110 		size_t align = 0;
111 
112 		while (p2 & (p2 - 1))
113 			p2 &= p2 - 1;
114 
115 		if (size <= 4 * SPA_MINBLOCKSIZE) {
116 			align = SPA_MINBLOCKSIZE;
117 		} else if (P2PHASE(size, PAGESIZE) == 0) {
118 			align = PAGESIZE;
119 		} else if (P2PHASE(size, p2 >> 2) == 0) {
120 			align = p2 >> 2;
121 		}
122 
123 		if (align != 0) {
124 			char name[36];
125 			(void) sprintf(name, "zio_buf_%lu", (ulong_t)size);
126 			zio_buf_cache[c] = kmem_cache_create(name, size,
127 			    align, NULL, NULL, NULL, NULL, NULL, KMC_NODEBUG);
128 
129 			(void) sprintf(name, "zio_data_buf_%lu", (ulong_t)size);
130 			zio_data_buf_cache[c] = kmem_cache_create(name, size,
131 			    align, NULL, NULL, NULL, NULL, data_alloc_arena,
132 			    KMC_NODEBUG);
133 		}
134 	}
135 
136 	while (--c != 0) {
137 		ASSERT(zio_buf_cache[c] != NULL);
138 		if (zio_buf_cache[c - 1] == NULL)
139 			zio_buf_cache[c - 1] = zio_buf_cache[c];
140 
141 		ASSERT(zio_data_buf_cache[c] != NULL);
142 		if (zio_data_buf_cache[c - 1] == NULL)
143 			zio_data_buf_cache[c - 1] = zio_data_buf_cache[c];
144 	}
145 
146 	zio_inject_init();
147 }
148 
149 void
150 zio_fini(void)
151 {
152 	size_t c;
153 	kmem_cache_t *last_cache = NULL;
154 	kmem_cache_t *last_data_cache = NULL;
155 
156 	for (c = 0; c < SPA_MAXBLOCKSIZE >> SPA_MINBLOCKSHIFT; c++) {
157 		if (zio_buf_cache[c] != last_cache) {
158 			last_cache = zio_buf_cache[c];
159 			kmem_cache_destroy(zio_buf_cache[c]);
160 		}
161 		zio_buf_cache[c] = NULL;
162 
163 		if (zio_data_buf_cache[c] != last_data_cache) {
164 			last_data_cache = zio_data_buf_cache[c];
165 			kmem_cache_destroy(zio_data_buf_cache[c]);
166 		}
167 		zio_data_buf_cache[c] = NULL;
168 	}
169 
170 	kmem_cache_destroy(zio_link_cache);
171 	kmem_cache_destroy(zio_cache);
172 
173 	zio_inject_fini();
174 }
175 
176 /*
177  * ==========================================================================
178  * Allocate and free I/O buffers
179  * ==========================================================================
180  */
181 
182 /*
183  * Use zio_buf_alloc to allocate ZFS metadata.  This data will appear in a
184  * crashdump if the kernel panics, so use it judiciously.  Obviously, it's
185  * useful to inspect ZFS metadata, but if possible, we should avoid keeping
186  * excess / transient data in-core during a crashdump.
187  */
188 void *
189 zio_buf_alloc(size_t size)
190 {
191 	size_t c = (size - 1) >> SPA_MINBLOCKSHIFT;
192 
193 	ASSERT(c < SPA_MAXBLOCKSIZE >> SPA_MINBLOCKSHIFT);
194 
195 	return (kmem_cache_alloc(zio_buf_cache[c], KM_PUSHPAGE));
196 }
197 
198 /*
199  * Use zio_data_buf_alloc to allocate data.  The data will not appear in a
200  * crashdump if the kernel panics.  This exists so that we will limit the amount
201  * of ZFS data that shows up in a kernel crashdump.  (Thus reducing the amount
202  * of kernel heap dumped to disk when the kernel panics)
203  */
204 void *
205 zio_data_buf_alloc(size_t size)
206 {
207 	size_t c = (size - 1) >> SPA_MINBLOCKSHIFT;
208 
209 	ASSERT(c < SPA_MAXBLOCKSIZE >> SPA_MINBLOCKSHIFT);
210 
211 	return (kmem_cache_alloc(zio_data_buf_cache[c], KM_PUSHPAGE));
212 }
213 
214 void
215 zio_buf_free(void *buf, size_t size)
216 {
217 	size_t c = (size - 1) >> SPA_MINBLOCKSHIFT;
218 
219 	ASSERT(c < SPA_MAXBLOCKSIZE >> SPA_MINBLOCKSHIFT);
220 
221 	kmem_cache_free(zio_buf_cache[c], buf);
222 }
223 
224 void
225 zio_data_buf_free(void *buf, size_t size)
226 {
227 	size_t c = (size - 1) >> SPA_MINBLOCKSHIFT;
228 
229 	ASSERT(c < SPA_MAXBLOCKSIZE >> SPA_MINBLOCKSHIFT);
230 
231 	kmem_cache_free(zio_data_buf_cache[c], buf);
232 }
233 
234 /*
235  * ==========================================================================
236  * Push and pop I/O transform buffers
237  * ==========================================================================
238  */
239 static void
240 zio_push_transform(zio_t *zio, void *data, uint64_t size, uint64_t bufsize,
241 	zio_transform_func_t *transform)
242 {
243 	zio_transform_t *zt = kmem_alloc(sizeof (zio_transform_t), KM_SLEEP);
244 
245 	zt->zt_orig_data = zio->io_data;
246 	zt->zt_orig_size = zio->io_size;
247 	zt->zt_bufsize = bufsize;
248 	zt->zt_transform = transform;
249 
250 	zt->zt_next = zio->io_transform_stack;
251 	zio->io_transform_stack = zt;
252 
253 	zio->io_data = data;
254 	zio->io_size = size;
255 }
256 
257 static void
258 zio_pop_transforms(zio_t *zio)
259 {
260 	zio_transform_t *zt;
261 
262 	while ((zt = zio->io_transform_stack) != NULL) {
263 		if (zt->zt_transform != NULL)
264 			zt->zt_transform(zio,
265 			    zt->zt_orig_data, zt->zt_orig_size);
266 
267 		zio_buf_free(zio->io_data, zt->zt_bufsize);
268 
269 		zio->io_data = zt->zt_orig_data;
270 		zio->io_size = zt->zt_orig_size;
271 		zio->io_transform_stack = zt->zt_next;
272 
273 		kmem_free(zt, sizeof (zio_transform_t));
274 	}
275 }
276 
277 /*
278  * ==========================================================================
279  * I/O transform callbacks for subblocks and decompression
280  * ==========================================================================
281  */
282 static void
283 zio_subblock(zio_t *zio, void *data, uint64_t size)
284 {
285 	ASSERT(zio->io_size > size);
286 
287 	if (zio->io_type == ZIO_TYPE_READ)
288 		bcopy(zio->io_data, data, size);
289 }
290 
291 static void
292 zio_decompress(zio_t *zio, void *data, uint64_t size)
293 {
294 	if (zio->io_error == 0 &&
295 	    zio_decompress_data(BP_GET_COMPRESS(zio->io_bp),
296 	    zio->io_data, zio->io_size, data, size) != 0)
297 		zio->io_error = EIO;
298 }
299 
300 /*
301  * ==========================================================================
302  * I/O parent/child relationships and pipeline interlocks
303  * ==========================================================================
304  */
305 /*
306  * NOTE - Callers to zio_walk_parents() and zio_walk_children must
307  *        continue calling these functions until they return NULL.
308  *        Otherwise, the next caller will pick up the list walk in
309  *        some indeterminate state.  (Otherwise every caller would
310  *        have to pass in a cookie to keep the state represented by
311  *        io_walk_link, which gets annoying.)
312  */
313 zio_t *
314 zio_walk_parents(zio_t *cio)
315 {
316 	zio_link_t *zl = cio->io_walk_link;
317 	list_t *pl = &cio->io_parent_list;
318 
319 	zl = (zl == NULL) ? list_head(pl) : list_next(pl, zl);
320 	cio->io_walk_link = zl;
321 
322 	if (zl == NULL)
323 		return (NULL);
324 
325 	ASSERT(zl->zl_child == cio);
326 	return (zl->zl_parent);
327 }
328 
329 zio_t *
330 zio_walk_children(zio_t *pio)
331 {
332 	zio_link_t *zl = pio->io_walk_link;
333 	list_t *cl = &pio->io_child_list;
334 
335 	zl = (zl == NULL) ? list_head(cl) : list_next(cl, zl);
336 	pio->io_walk_link = zl;
337 
338 	if (zl == NULL)
339 		return (NULL);
340 
341 	ASSERT(zl->zl_parent == pio);
342 	return (zl->zl_child);
343 }
344 
345 zio_t *
346 zio_unique_parent(zio_t *cio)
347 {
348 	zio_t *pio = zio_walk_parents(cio);
349 
350 	VERIFY(zio_walk_parents(cio) == NULL);
351 	return (pio);
352 }
353 
354 void
355 zio_add_child(zio_t *pio, zio_t *cio)
356 {
357 	zio_link_t *zl = kmem_cache_alloc(zio_link_cache, KM_SLEEP);
358 
359 	/*
360 	 * Logical I/Os can have logical, gang, or vdev children.
361 	 * Gang I/Os can have gang or vdev children.
362 	 * Vdev I/Os can only have vdev children.
363 	 * The following ASSERT captures all of these constraints.
364 	 */
365 	ASSERT(cio->io_child_type <= pio->io_child_type);
366 
367 	zl->zl_parent = pio;
368 	zl->zl_child = cio;
369 
370 	mutex_enter(&cio->io_lock);
371 	mutex_enter(&pio->io_lock);
372 
373 	ASSERT(pio->io_state[ZIO_WAIT_DONE] == 0);
374 
375 	for (int w = 0; w < ZIO_WAIT_TYPES; w++)
376 		pio->io_children[cio->io_child_type][w] += !cio->io_state[w];
377 
378 	list_insert_head(&pio->io_child_list, zl);
379 	list_insert_head(&cio->io_parent_list, zl);
380 
381 	mutex_exit(&pio->io_lock);
382 	mutex_exit(&cio->io_lock);
383 }
384 
385 static void
386 zio_remove_child(zio_t *pio, zio_t *cio, zio_link_t *zl)
387 {
388 	ASSERT(zl->zl_parent == pio);
389 	ASSERT(zl->zl_child == cio);
390 
391 	mutex_enter(&cio->io_lock);
392 	mutex_enter(&pio->io_lock);
393 
394 	list_remove(&pio->io_child_list, zl);
395 	list_remove(&cio->io_parent_list, zl);
396 
397 	mutex_exit(&pio->io_lock);
398 	mutex_exit(&cio->io_lock);
399 
400 	kmem_cache_free(zio_link_cache, zl);
401 }
402 
403 static boolean_t
404 zio_wait_for_children(zio_t *zio, enum zio_child child, enum zio_wait_type wait)
405 {
406 	uint64_t *countp = &zio->io_children[child][wait];
407 	boolean_t waiting = B_FALSE;
408 
409 	mutex_enter(&zio->io_lock);
410 	ASSERT(zio->io_stall == NULL);
411 	if (*countp != 0) {
412 		zio->io_stage--;
413 		zio->io_stall = countp;
414 		waiting = B_TRUE;
415 	}
416 	mutex_exit(&zio->io_lock);
417 
418 	return (waiting);
419 }
420 
421 static void
422 zio_notify_parent(zio_t *pio, zio_t *zio, enum zio_wait_type wait)
423 {
424 	uint64_t *countp = &pio->io_children[zio->io_child_type][wait];
425 	int *errorp = &pio->io_child_error[zio->io_child_type];
426 
427 	mutex_enter(&pio->io_lock);
428 	if (zio->io_error && !(zio->io_flags & ZIO_FLAG_DONT_PROPAGATE))
429 		*errorp = zio_worst_error(*errorp, zio->io_error);
430 	pio->io_reexecute |= zio->io_reexecute;
431 	ASSERT3U(*countp, >, 0);
432 	if (--*countp == 0 && pio->io_stall == countp) {
433 		pio->io_stall = NULL;
434 		mutex_exit(&pio->io_lock);
435 		zio_execute(pio);
436 	} else {
437 		mutex_exit(&pio->io_lock);
438 	}
439 }
440 
441 static void
442 zio_inherit_child_errors(zio_t *zio, enum zio_child c)
443 {
444 	if (zio->io_child_error[c] != 0 && zio->io_error == 0)
445 		zio->io_error = zio->io_child_error[c];
446 }
447 
448 /*
449  * ==========================================================================
450  * Create the various types of I/O (read, write, free, etc)
451  * ==========================================================================
452  */
453 static zio_t *
454 zio_create(zio_t *pio, spa_t *spa, uint64_t txg, blkptr_t *bp,
455     void *data, uint64_t size, zio_done_func_t *done, void *private,
456     zio_type_t type, int priority, int flags, vdev_t *vd, uint64_t offset,
457     const zbookmark_t *zb, uint8_t stage, uint32_t pipeline)
458 {
459 	zio_t *zio;
460 
461 	ASSERT3U(size, <=, SPA_MAXBLOCKSIZE);
462 	ASSERT(P2PHASE(size, SPA_MINBLOCKSIZE) == 0);
463 	ASSERT(P2PHASE(offset, SPA_MINBLOCKSIZE) == 0);
464 
465 	ASSERT(!vd || spa_config_held(spa, SCL_STATE_ALL, RW_READER));
466 	ASSERT(!bp || !(flags & ZIO_FLAG_CONFIG_WRITER));
467 	ASSERT(vd || stage == ZIO_STAGE_OPEN);
468 
469 	zio = kmem_cache_alloc(zio_cache, KM_SLEEP);
470 	bzero(zio, sizeof (zio_t));
471 
472 	mutex_init(&zio->io_lock, NULL, MUTEX_DEFAULT, NULL);
473 	cv_init(&zio->io_cv, NULL, CV_DEFAULT, NULL);
474 
475 	list_create(&zio->io_parent_list, sizeof (zio_link_t),
476 	    offsetof(zio_link_t, zl_parent_node));
477 	list_create(&zio->io_child_list, sizeof (zio_link_t),
478 	    offsetof(zio_link_t, zl_child_node));
479 
480 	if (vd != NULL)
481 		zio->io_child_type = ZIO_CHILD_VDEV;
482 	else if (flags & ZIO_FLAG_GANG_CHILD)
483 		zio->io_child_type = ZIO_CHILD_GANG;
484 	else
485 		zio->io_child_type = ZIO_CHILD_LOGICAL;
486 
487 	if (bp != NULL) {
488 		zio->io_bp = bp;
489 		zio->io_bp_copy = *bp;
490 		zio->io_bp_orig = *bp;
491 		if (type != ZIO_TYPE_WRITE)
492 			zio->io_bp = &zio->io_bp_copy;	/* so caller can free */
493 		if (zio->io_child_type == ZIO_CHILD_LOGICAL)
494 			zio->io_logical = zio;
495 		if (zio->io_child_type > ZIO_CHILD_GANG && BP_IS_GANG(bp))
496 			pipeline |= ZIO_GANG_STAGES;
497 	}
498 
499 	zio->io_spa = spa;
500 	zio->io_txg = txg;
501 	zio->io_data = data;
502 	zio->io_size = size;
503 	zio->io_done = done;
504 	zio->io_private = private;
505 	zio->io_type = type;
506 	zio->io_priority = priority;
507 	zio->io_vd = vd;
508 	zio->io_offset = offset;
509 	zio->io_orig_flags = zio->io_flags = flags;
510 	zio->io_orig_stage = zio->io_stage = stage;
511 	zio->io_orig_pipeline = zio->io_pipeline = pipeline;
512 
513 	zio->io_state[ZIO_WAIT_READY] = (stage >= ZIO_STAGE_READY);
514 	zio->io_state[ZIO_WAIT_DONE] = (stage >= ZIO_STAGE_DONE);
515 
516 	if (zb != NULL)
517 		zio->io_bookmark = *zb;
518 
519 	if (pio != NULL) {
520 		if (zio->io_logical == NULL)
521 			zio->io_logical = pio->io_logical;
522 		if (zio->io_child_type == ZIO_CHILD_GANG)
523 			zio->io_gang_leader = pio->io_gang_leader;
524 		zio_add_child(pio, zio);
525 	}
526 
527 	return (zio);
528 }
529 
530 static void
531 zio_destroy(zio_t *zio)
532 {
533 	list_destroy(&zio->io_parent_list);
534 	list_destroy(&zio->io_child_list);
535 	mutex_destroy(&zio->io_lock);
536 	cv_destroy(&zio->io_cv);
537 	kmem_cache_free(zio_cache, zio);
538 }
539 
540 zio_t *
541 zio_null(zio_t *pio, spa_t *spa, vdev_t *vd, zio_done_func_t *done,
542     void *private, int flags)
543 {
544 	zio_t *zio;
545 
546 	zio = zio_create(pio, spa, 0, NULL, NULL, 0, done, private,
547 	    ZIO_TYPE_NULL, ZIO_PRIORITY_NOW, flags, vd, 0, NULL,
548 	    ZIO_STAGE_OPEN, ZIO_INTERLOCK_PIPELINE);
549 
550 	return (zio);
551 }
552 
553 zio_t *
554 zio_root(spa_t *spa, zio_done_func_t *done, void *private, int flags)
555 {
556 	return (zio_null(NULL, spa, NULL, done, private, flags));
557 }
558 
559 zio_t *
560 zio_read(zio_t *pio, spa_t *spa, const blkptr_t *bp,
561     void *data, uint64_t size, zio_done_func_t *done, void *private,
562     int priority, int flags, const zbookmark_t *zb)
563 {
564 	zio_t *zio;
565 
566 	zio = zio_create(pio, spa, bp->blk_birth, (blkptr_t *)bp,
567 	    data, size, done, private,
568 	    ZIO_TYPE_READ, priority, flags, NULL, 0, zb,
569 	    ZIO_STAGE_OPEN, ZIO_READ_PIPELINE);
570 
571 	return (zio);
572 }
573 
574 void
575 zio_skip_write(zio_t *zio)
576 {
577 	ASSERT(zio->io_type == ZIO_TYPE_WRITE);
578 	ASSERT(zio->io_stage == ZIO_STAGE_READY);
579 	ASSERT(!BP_IS_GANG(zio->io_bp));
580 
581 	zio->io_pipeline &= ~ZIO_VDEV_IO_STAGES;
582 }
583 
584 zio_t *
585 zio_write(zio_t *pio, spa_t *spa, uint64_t txg, blkptr_t *bp,
586     void *data, uint64_t size, zio_prop_t *zp,
587     zio_done_func_t *ready, zio_done_func_t *done, void *private,
588     int priority, int flags, const zbookmark_t *zb)
589 {
590 	zio_t *zio;
591 
592 	ASSERT(zp->zp_checksum >= ZIO_CHECKSUM_OFF &&
593 	    zp->zp_checksum < ZIO_CHECKSUM_FUNCTIONS &&
594 	    zp->zp_compress >= ZIO_COMPRESS_OFF &&
595 	    zp->zp_compress < ZIO_COMPRESS_FUNCTIONS &&
596 	    zp->zp_type < DMU_OT_NUMTYPES &&
597 	    zp->zp_level < 32 &&
598 	    zp->zp_ndvas > 0 &&
599 	    zp->zp_ndvas <= spa_max_replication(spa));
600 	ASSERT(ready != NULL);
601 
602 	zio = zio_create(pio, spa, txg, bp, data, size, done, private,
603 	    ZIO_TYPE_WRITE, priority, flags, NULL, 0, zb,
604 	    ZIO_STAGE_OPEN, ZIO_WRITE_PIPELINE);
605 
606 	zio->io_ready = ready;
607 	zio->io_prop = *zp;
608 
609 	return (zio);
610 }
611 
612 zio_t *
613 zio_rewrite(zio_t *pio, spa_t *spa, uint64_t txg, blkptr_t *bp, void *data,
614     uint64_t size, zio_done_func_t *done, void *private, int priority,
615     int flags, zbookmark_t *zb)
616 {
617 	zio_t *zio;
618 
619 	zio = zio_create(pio, spa, txg, bp, data, size, done, private,
620 	    ZIO_TYPE_WRITE, priority, flags, NULL, 0, zb,
621 	    ZIO_STAGE_OPEN, ZIO_REWRITE_PIPELINE);
622 
623 	return (zio);
624 }
625 
626 zio_t *
627 zio_free(zio_t *pio, spa_t *spa, uint64_t txg, blkptr_t *bp,
628     zio_done_func_t *done, void *private, int flags)
629 {
630 	zio_t *zio;
631 
632 	ASSERT(!BP_IS_HOLE(bp));
633 
634 	if (bp->blk_fill == BLK_FILL_ALREADY_FREED)
635 		return (zio_null(pio, spa, NULL, NULL, NULL, flags));
636 
637 	if (txg == spa->spa_syncing_txg &&
638 	    spa_sync_pass(spa) > SYNC_PASS_DEFERRED_FREE) {
639 		bplist_enqueue_deferred(&spa->spa_sync_bplist, bp);
640 		return (zio_null(pio, spa, NULL, NULL, NULL, flags));
641 	}
642 
643 	zio = zio_create(pio, spa, txg, bp, NULL, BP_GET_PSIZE(bp),
644 	    done, private, ZIO_TYPE_FREE, ZIO_PRIORITY_FREE, flags,
645 	    NULL, 0, NULL, ZIO_STAGE_OPEN, ZIO_FREE_PIPELINE);
646 
647 	return (zio);
648 }
649 
650 zio_t *
651 zio_claim(zio_t *pio, spa_t *spa, uint64_t txg, blkptr_t *bp,
652     zio_done_func_t *done, void *private, int flags)
653 {
654 	zio_t *zio;
655 
656 	/*
657 	 * A claim is an allocation of a specific block.  Claims are needed
658 	 * to support immediate writes in the intent log.  The issue is that
659 	 * immediate writes contain committed data, but in a txg that was
660 	 * *not* committed.  Upon opening the pool after an unclean shutdown,
661 	 * the intent log claims all blocks that contain immediate write data
662 	 * so that the SPA knows they're in use.
663 	 *
664 	 * All claims *must* be resolved in the first txg -- before the SPA
665 	 * starts allocating blocks -- so that nothing is allocated twice.
666 	 */
667 	ASSERT3U(spa->spa_uberblock.ub_rootbp.blk_birth, <, spa_first_txg(spa));
668 	ASSERT3U(spa_first_txg(spa), <=, txg);
669 
670 	zio = zio_create(pio, spa, txg, bp, NULL, BP_GET_PSIZE(bp),
671 	    done, private, ZIO_TYPE_CLAIM, ZIO_PRIORITY_NOW, flags,
672 	    NULL, 0, NULL, ZIO_STAGE_OPEN, ZIO_CLAIM_PIPELINE);
673 
674 	return (zio);
675 }
676 
677 zio_t *
678 zio_ioctl(zio_t *pio, spa_t *spa, vdev_t *vd, int cmd,
679     zio_done_func_t *done, void *private, int priority, int flags)
680 {
681 	zio_t *zio;
682 	int c;
683 
684 	if (vd->vdev_children == 0) {
685 		zio = zio_create(pio, spa, 0, NULL, NULL, 0, done, private,
686 		    ZIO_TYPE_IOCTL, priority, flags, vd, 0, NULL,
687 		    ZIO_STAGE_OPEN, ZIO_IOCTL_PIPELINE);
688 
689 		zio->io_cmd = cmd;
690 	} else {
691 		zio = zio_null(pio, spa, NULL, NULL, NULL, flags);
692 
693 		for (c = 0; c < vd->vdev_children; c++)
694 			zio_nowait(zio_ioctl(zio, spa, vd->vdev_child[c], cmd,
695 			    done, private, priority, flags));
696 	}
697 
698 	return (zio);
699 }
700 
701 zio_t *
702 zio_read_phys(zio_t *pio, vdev_t *vd, uint64_t offset, uint64_t size,
703     void *data, int checksum, zio_done_func_t *done, void *private,
704     int priority, int flags, boolean_t labels)
705 {
706 	zio_t *zio;
707 
708 	ASSERT(vd->vdev_children == 0);
709 	ASSERT(!labels || offset + size <= VDEV_LABEL_START_SIZE ||
710 	    offset >= vd->vdev_psize - VDEV_LABEL_END_SIZE);
711 	ASSERT3U(offset + size, <=, vd->vdev_psize);
712 
713 	zio = zio_create(pio, vd->vdev_spa, 0, NULL, data, size, done, private,
714 	    ZIO_TYPE_READ, priority, flags, vd, offset, NULL,
715 	    ZIO_STAGE_OPEN, ZIO_READ_PHYS_PIPELINE);
716 
717 	zio->io_prop.zp_checksum = checksum;
718 
719 	return (zio);
720 }
721 
722 zio_t *
723 zio_write_phys(zio_t *pio, vdev_t *vd, uint64_t offset, uint64_t size,
724     void *data, int checksum, zio_done_func_t *done, void *private,
725     int priority, int flags, boolean_t labels)
726 {
727 	zio_t *zio;
728 
729 	ASSERT(vd->vdev_children == 0);
730 	ASSERT(!labels || offset + size <= VDEV_LABEL_START_SIZE ||
731 	    offset >= vd->vdev_psize - VDEV_LABEL_END_SIZE);
732 	ASSERT3U(offset + size, <=, vd->vdev_psize);
733 
734 	zio = zio_create(pio, vd->vdev_spa, 0, NULL, data, size, done, private,
735 	    ZIO_TYPE_WRITE, priority, flags, vd, offset, NULL,
736 	    ZIO_STAGE_OPEN, ZIO_WRITE_PHYS_PIPELINE);
737 
738 	zio->io_prop.zp_checksum = checksum;
739 
740 	if (zio_checksum_table[checksum].ci_zbt) {
741 		/*
742 		 * zbt checksums are necessarily destructive -- they modify
743 		 * the end of the write buffer to hold the verifier/checksum.
744 		 * Therefore, we must make a local copy in case the data is
745 		 * being written to multiple places in parallel.
746 		 */
747 		void *wbuf = zio_buf_alloc(size);
748 		bcopy(data, wbuf, size);
749 		zio_push_transform(zio, wbuf, size, size, NULL);
750 	}
751 
752 	return (zio);
753 }
754 
755 /*
756  * Create a child I/O to do some work for us.
757  */
758 zio_t *
759 zio_vdev_child_io(zio_t *pio, blkptr_t *bp, vdev_t *vd, uint64_t offset,
760 	void *data, uint64_t size, int type, int priority, int flags,
761 	zio_done_func_t *done, void *private)
762 {
763 	uint32_t pipeline = ZIO_VDEV_CHILD_PIPELINE;
764 	zio_t *zio;
765 
766 	ASSERT(vd->vdev_parent ==
767 	    (pio->io_vd ? pio->io_vd : pio->io_spa->spa_root_vdev));
768 
769 	if (type == ZIO_TYPE_READ && bp != NULL) {
770 		/*
771 		 * If we have the bp, then the child should perform the
772 		 * checksum and the parent need not.  This pushes error
773 		 * detection as close to the leaves as possible and
774 		 * eliminates redundant checksums in the interior nodes.
775 		 */
776 		pipeline |= 1U << ZIO_STAGE_CHECKSUM_VERIFY;
777 		pio->io_pipeline &= ~(1U << ZIO_STAGE_CHECKSUM_VERIFY);
778 	}
779 
780 	if (vd->vdev_children == 0)
781 		offset += VDEV_LABEL_START_SIZE;
782 
783 	zio = zio_create(pio, pio->io_spa, pio->io_txg, bp, data, size,
784 	    done, private, type, priority,
785 	    (pio->io_flags & ZIO_FLAG_VDEV_INHERIT) |
786 	    ZIO_FLAG_CANFAIL | ZIO_FLAG_DONT_PROPAGATE | flags,
787 	    vd, offset, &pio->io_bookmark,
788 	    ZIO_STAGE_VDEV_IO_START - 1, pipeline);
789 
790 	return (zio);
791 }
792 
793 zio_t *
794 zio_vdev_delegated_io(vdev_t *vd, uint64_t offset, void *data, uint64_t size,
795 	int type, int priority, int flags, zio_done_func_t *done, void *private)
796 {
797 	zio_t *zio;
798 
799 	ASSERT(vd->vdev_ops->vdev_op_leaf);
800 
801 	zio = zio_create(NULL, vd->vdev_spa, 0, NULL,
802 	    data, size, done, private, type, priority,
803 	    flags | ZIO_FLAG_CANFAIL | ZIO_FLAG_DONT_RETRY,
804 	    vd, offset, NULL,
805 	    ZIO_STAGE_VDEV_IO_START - 1, ZIO_VDEV_CHILD_PIPELINE);
806 
807 	return (zio);
808 }
809 
810 void
811 zio_flush(zio_t *zio, vdev_t *vd)
812 {
813 	zio_nowait(zio_ioctl(zio, zio->io_spa, vd, DKIOCFLUSHWRITECACHE,
814 	    NULL, NULL, ZIO_PRIORITY_NOW,
815 	    ZIO_FLAG_CANFAIL | ZIO_FLAG_DONT_PROPAGATE | ZIO_FLAG_DONT_RETRY));
816 }
817 
818 /*
819  * ==========================================================================
820  * Prepare to read and write logical blocks
821  * ==========================================================================
822  */
823 
824 static int
825 zio_read_bp_init(zio_t *zio)
826 {
827 	blkptr_t *bp = zio->io_bp;
828 
829 	if (BP_GET_COMPRESS(bp) != ZIO_COMPRESS_OFF &&
830 	    zio->io_child_type == ZIO_CHILD_LOGICAL &&
831 	    !(zio->io_flags & ZIO_FLAG_RAW)) {
832 		uint64_t csize = BP_GET_PSIZE(bp);
833 		void *cbuf = zio_buf_alloc(csize);
834 
835 		zio_push_transform(zio, cbuf, csize, csize, zio_decompress);
836 	}
837 
838 	if (!dmu_ot[BP_GET_TYPE(bp)].ot_metadata && BP_GET_LEVEL(bp) == 0)
839 		zio->io_flags |= ZIO_FLAG_DONT_CACHE;
840 
841 	return (ZIO_PIPELINE_CONTINUE);
842 }
843 
844 static int
845 zio_write_bp_init(zio_t *zio)
846 {
847 	zio_prop_t *zp = &zio->io_prop;
848 	int compress = zp->zp_compress;
849 	blkptr_t *bp = zio->io_bp;
850 	void *cbuf;
851 	uint64_t lsize = zio->io_size;
852 	uint64_t csize = lsize;
853 	uint64_t cbufsize = 0;
854 	int pass = 1;
855 
856 	/*
857 	 * If our children haven't all reached the ready stage,
858 	 * wait for them and then repeat this pipeline stage.
859 	 */
860 	if (zio_wait_for_children(zio, ZIO_CHILD_GANG, ZIO_WAIT_READY) ||
861 	    zio_wait_for_children(zio, ZIO_CHILD_LOGICAL, ZIO_WAIT_READY))
862 		return (ZIO_PIPELINE_STOP);
863 
864 	if (!IO_IS_ALLOCATING(zio))
865 		return (ZIO_PIPELINE_CONTINUE);
866 
867 	ASSERT(compress != ZIO_COMPRESS_INHERIT);
868 
869 	if (bp->blk_birth == zio->io_txg) {
870 		/*
871 		 * We're rewriting an existing block, which means we're
872 		 * working on behalf of spa_sync().  For spa_sync() to
873 		 * converge, it must eventually be the case that we don't
874 		 * have to allocate new blocks.  But compression changes
875 		 * the blocksize, which forces a reallocate, and makes
876 		 * convergence take longer.  Therefore, after the first
877 		 * few passes, stop compressing to ensure convergence.
878 		 */
879 		pass = spa_sync_pass(zio->io_spa);
880 
881 		if (pass > SYNC_PASS_DONT_COMPRESS)
882 			compress = ZIO_COMPRESS_OFF;
883 
884 		/* Make sure someone doesn't change their mind on overwrites */
885 		ASSERT(MIN(zp->zp_ndvas + BP_IS_GANG(bp),
886 		    spa_max_replication(zio->io_spa)) == BP_GET_NDVAS(bp));
887 	}
888 
889 	if (compress != ZIO_COMPRESS_OFF) {
890 		if (!zio_compress_data(compress, zio->io_data, zio->io_size,
891 		    &cbuf, &csize, &cbufsize)) {
892 			compress = ZIO_COMPRESS_OFF;
893 		} else if (csize != 0) {
894 			zio_push_transform(zio, cbuf, csize, cbufsize, NULL);
895 		}
896 	}
897 
898 	/*
899 	 * The final pass of spa_sync() must be all rewrites, but the first
900 	 * few passes offer a trade-off: allocating blocks defers convergence,
901 	 * but newly allocated blocks are sequential, so they can be written
902 	 * to disk faster.  Therefore, we allow the first few passes of
903 	 * spa_sync() to allocate new blocks, but force rewrites after that.
904 	 * There should only be a handful of blocks after pass 1 in any case.
905 	 */
906 	if (bp->blk_birth == zio->io_txg && BP_GET_PSIZE(bp) == csize &&
907 	    pass > SYNC_PASS_REWRITE) {
908 		ASSERT(csize != 0);
909 		uint32_t gang_stages = zio->io_pipeline & ZIO_GANG_STAGES;
910 		zio->io_pipeline = ZIO_REWRITE_PIPELINE | gang_stages;
911 		zio->io_flags |= ZIO_FLAG_IO_REWRITE;
912 	} else {
913 		BP_ZERO(bp);
914 		zio->io_pipeline = ZIO_WRITE_PIPELINE;
915 	}
916 
917 	if (csize == 0) {
918 		zio->io_pipeline = ZIO_INTERLOCK_PIPELINE;
919 	} else {
920 		ASSERT(zp->zp_checksum != ZIO_CHECKSUM_GANG_HEADER);
921 		BP_SET_LSIZE(bp, lsize);
922 		BP_SET_PSIZE(bp, csize);
923 		BP_SET_COMPRESS(bp, compress);
924 		BP_SET_CHECKSUM(bp, zp->zp_checksum);
925 		BP_SET_TYPE(bp, zp->zp_type);
926 		BP_SET_LEVEL(bp, zp->zp_level);
927 		BP_SET_BYTEORDER(bp, ZFS_HOST_BYTEORDER);
928 	}
929 
930 	return (ZIO_PIPELINE_CONTINUE);
931 }
932 
933 /*
934  * ==========================================================================
935  * Execute the I/O pipeline
936  * ==========================================================================
937  */
938 
939 static void
940 zio_taskq_dispatch(zio_t *zio, enum zio_taskq_type q)
941 {
942 	zio_type_t t = zio->io_type;
943 
944 	/*
945 	 * If we're a config writer or a probe, the normal issue and
946 	 * interrupt threads may all be blocked waiting for the config lock.
947 	 * In this case, select the otherwise-unused taskq for ZIO_TYPE_NULL.
948 	 */
949 	if (zio->io_flags & (ZIO_FLAG_CONFIG_WRITER | ZIO_FLAG_PROBE))
950 		t = ZIO_TYPE_NULL;
951 
952 	/*
953 	 * A similar issue exists for the L2ARC write thread until L2ARC 2.0.
954 	 */
955 	if (t == ZIO_TYPE_WRITE && zio->io_vd && zio->io_vd->vdev_aux)
956 		t = ZIO_TYPE_NULL;
957 
958 	(void) taskq_dispatch(zio->io_spa->spa_zio_taskq[t][q],
959 	    (task_func_t *)zio_execute, zio, TQ_SLEEP);
960 }
961 
962 static boolean_t
963 zio_taskq_member(zio_t *zio, enum zio_taskq_type q)
964 {
965 	kthread_t *executor = zio->io_executor;
966 	spa_t *spa = zio->io_spa;
967 
968 	for (zio_type_t t = 0; t < ZIO_TYPES; t++)
969 		if (taskq_member(spa->spa_zio_taskq[t][q], executor))
970 			return (B_TRUE);
971 
972 	return (B_FALSE);
973 }
974 
975 static int
976 zio_issue_async(zio_t *zio)
977 {
978 	zio_taskq_dispatch(zio, ZIO_TASKQ_ISSUE);
979 
980 	return (ZIO_PIPELINE_STOP);
981 }
982 
983 void
984 zio_interrupt(zio_t *zio)
985 {
986 	zio_taskq_dispatch(zio, ZIO_TASKQ_INTERRUPT);
987 }
988 
989 /*
990  * Execute the I/O pipeline until one of the following occurs:
991  * (1) the I/O completes; (2) the pipeline stalls waiting for
992  * dependent child I/Os; (3) the I/O issues, so we're waiting
993  * for an I/O completion interrupt; (4) the I/O is delegated by
994  * vdev-level caching or aggregation; (5) the I/O is deferred
995  * due to vdev-level queueing; (6) the I/O is handed off to
996  * another thread.  In all cases, the pipeline stops whenever
997  * there's no CPU work; it never burns a thread in cv_wait().
998  *
999  * There's no locking on io_stage because there's no legitimate way
1000  * for multiple threads to be attempting to process the same I/O.
1001  */
1002 static zio_pipe_stage_t *zio_pipeline[ZIO_STAGES];
1003 
1004 void
1005 zio_execute(zio_t *zio)
1006 {
1007 	zio->io_executor = curthread;
1008 
1009 	while (zio->io_stage < ZIO_STAGE_DONE) {
1010 		uint32_t pipeline = zio->io_pipeline;
1011 		zio_stage_t stage = zio->io_stage;
1012 		int rv;
1013 
1014 		ASSERT(!MUTEX_HELD(&zio->io_lock));
1015 
1016 		while (((1U << ++stage) & pipeline) == 0)
1017 			continue;
1018 
1019 		ASSERT(stage <= ZIO_STAGE_DONE);
1020 		ASSERT(zio->io_stall == NULL);
1021 
1022 		/*
1023 		 * If we are in interrupt context and this pipeline stage
1024 		 * will grab a config lock that is held across I/O,
1025 		 * issue async to avoid deadlock.
1026 		 */
1027 		if (((1U << stage) & ZIO_CONFIG_LOCK_BLOCKING_STAGES) &&
1028 		    zio->io_vd == NULL &&
1029 		    zio_taskq_member(zio, ZIO_TASKQ_INTERRUPT)) {
1030 			zio_taskq_dispatch(zio, ZIO_TASKQ_ISSUE);
1031 			return;
1032 		}
1033 
1034 		zio->io_stage = stage;
1035 		rv = zio_pipeline[stage](zio);
1036 
1037 		if (rv == ZIO_PIPELINE_STOP)
1038 			return;
1039 
1040 		ASSERT(rv == ZIO_PIPELINE_CONTINUE);
1041 	}
1042 }
1043 
1044 /*
1045  * ==========================================================================
1046  * Initiate I/O, either sync or async
1047  * ==========================================================================
1048  */
1049 int
1050 zio_wait(zio_t *zio)
1051 {
1052 	int error;
1053 
1054 	ASSERT(zio->io_stage == ZIO_STAGE_OPEN);
1055 	ASSERT(zio->io_executor == NULL);
1056 
1057 	zio->io_waiter = curthread;
1058 
1059 	zio_execute(zio);
1060 
1061 	mutex_enter(&zio->io_lock);
1062 	while (zio->io_executor != NULL)
1063 		cv_wait(&zio->io_cv, &zio->io_lock);
1064 	mutex_exit(&zio->io_lock);
1065 
1066 	error = zio->io_error;
1067 	zio_destroy(zio);
1068 
1069 	return (error);
1070 }
1071 
1072 void
1073 zio_nowait(zio_t *zio)
1074 {
1075 	ASSERT(zio->io_executor == NULL);
1076 
1077 	if (zio->io_child_type == ZIO_CHILD_LOGICAL &&
1078 	    zio_unique_parent(zio) == NULL) {
1079 		/*
1080 		 * This is a logical async I/O with no parent to wait for it.
1081 		 * We add it to the spa_async_root_zio "Godfather" I/O which
1082 		 * will ensure they complete prior to unloading the pool.
1083 		 */
1084 		spa_t *spa = zio->io_spa;
1085 
1086 		zio_add_child(spa->spa_async_zio_root, zio);
1087 	}
1088 
1089 	zio_execute(zio);
1090 }
1091 
1092 /*
1093  * ==========================================================================
1094  * Reexecute or suspend/resume failed I/O
1095  * ==========================================================================
1096  */
1097 
1098 static void
1099 zio_reexecute(zio_t *pio)
1100 {
1101 	zio_t *cio, *cio_next;
1102 
1103 	ASSERT(pio->io_child_type == ZIO_CHILD_LOGICAL);
1104 	ASSERT(pio->io_orig_stage == ZIO_STAGE_OPEN);
1105 	ASSERT(pio->io_gang_leader == NULL);
1106 	ASSERT(pio->io_gang_tree == NULL);
1107 
1108 	pio->io_flags = pio->io_orig_flags;
1109 	pio->io_stage = pio->io_orig_stage;
1110 	pio->io_pipeline = pio->io_orig_pipeline;
1111 	pio->io_reexecute = 0;
1112 	pio->io_error = 0;
1113 	for (int w = 0; w < ZIO_WAIT_TYPES; w++)
1114 		pio->io_state[w] = 0;
1115 	for (int c = 0; c < ZIO_CHILD_TYPES; c++)
1116 		pio->io_child_error[c] = 0;
1117 
1118 	if (IO_IS_ALLOCATING(pio)) {
1119 		/*
1120 		 * Remember the failed bp so that the io_ready() callback
1121 		 * can update its accounting upon reexecution.  The block
1122 		 * was already freed in zio_done(); we indicate this with
1123 		 * a fill count of -1 so that zio_free() knows to skip it.
1124 		 */
1125 		blkptr_t *bp = pio->io_bp;
1126 		ASSERT(bp->blk_birth == 0 || bp->blk_birth == pio->io_txg);
1127 		bp->blk_fill = BLK_FILL_ALREADY_FREED;
1128 		pio->io_bp_orig = *bp;
1129 		BP_ZERO(bp);
1130 	}
1131 
1132 	/*
1133 	 * As we reexecute pio's children, new children could be created.
1134 	 * New children go to the head of pio's io_child_list, however,
1135 	 * so we will (correctly) not reexecute them.  The key is that
1136 	 * the remainder of pio's io_child_list, from 'cio_next' onward,
1137 	 * cannot be affected by any side effects of reexecuting 'cio'.
1138 	 */
1139 	for (cio = zio_walk_children(pio); cio != NULL; cio = cio_next) {
1140 		cio_next = zio_walk_children(pio);
1141 		mutex_enter(&pio->io_lock);
1142 		for (int w = 0; w < ZIO_WAIT_TYPES; w++)
1143 			pio->io_children[cio->io_child_type][w]++;
1144 		mutex_exit(&pio->io_lock);
1145 		zio_reexecute(cio);
1146 	}
1147 
1148 	/*
1149 	 * Now that all children have been reexecuted, execute the parent.
1150 	 * We don't reexecute "The Godfather" I/O here as it's the
1151 	 * responsibility of the caller to wait on him.
1152 	 */
1153 	if (!(pio->io_flags & ZIO_FLAG_GODFATHER))
1154 		zio_execute(pio);
1155 }
1156 
1157 void
1158 zio_suspend(spa_t *spa, zio_t *zio)
1159 {
1160 	if (spa_get_failmode(spa) == ZIO_FAILURE_MODE_PANIC)
1161 		fm_panic("Pool '%s' has encountered an uncorrectable I/O "
1162 		    "failure and the failure mode property for this pool "
1163 		    "is set to panic.", spa_name(spa));
1164 
1165 	zfs_ereport_post(FM_EREPORT_ZFS_IO_FAILURE, spa, NULL, NULL, 0, 0);
1166 
1167 	mutex_enter(&spa->spa_suspend_lock);
1168 
1169 	if (spa->spa_suspend_zio_root == NULL)
1170 		spa->spa_suspend_zio_root = zio_root(spa, NULL, NULL,
1171 		    ZIO_FLAG_CANFAIL | ZIO_FLAG_SPECULATIVE |
1172 		    ZIO_FLAG_GODFATHER);
1173 
1174 	spa->spa_suspended = B_TRUE;
1175 
1176 	if (zio != NULL) {
1177 		ASSERT(!(zio->io_flags & ZIO_FLAG_GODFATHER));
1178 		ASSERT(zio != spa->spa_suspend_zio_root);
1179 		ASSERT(zio->io_child_type == ZIO_CHILD_LOGICAL);
1180 		ASSERT(zio_unique_parent(zio) == NULL);
1181 		ASSERT(zio->io_stage == ZIO_STAGE_DONE);
1182 		zio_add_child(spa->spa_suspend_zio_root, zio);
1183 	}
1184 
1185 	mutex_exit(&spa->spa_suspend_lock);
1186 }
1187 
1188 int
1189 zio_resume(spa_t *spa)
1190 {
1191 	zio_t *pio;
1192 
1193 	/*
1194 	 * Reexecute all previously suspended i/o.
1195 	 */
1196 	mutex_enter(&spa->spa_suspend_lock);
1197 	spa->spa_suspended = B_FALSE;
1198 	cv_broadcast(&spa->spa_suspend_cv);
1199 	pio = spa->spa_suspend_zio_root;
1200 	spa->spa_suspend_zio_root = NULL;
1201 	mutex_exit(&spa->spa_suspend_lock);
1202 
1203 	if (pio == NULL)
1204 		return (0);
1205 
1206 	zio_reexecute(pio);
1207 	return (zio_wait(pio));
1208 }
1209 
1210 void
1211 zio_resume_wait(spa_t *spa)
1212 {
1213 	mutex_enter(&spa->spa_suspend_lock);
1214 	while (spa_suspended(spa))
1215 		cv_wait(&spa->spa_suspend_cv, &spa->spa_suspend_lock);
1216 	mutex_exit(&spa->spa_suspend_lock);
1217 }
1218 
1219 /*
1220  * ==========================================================================
1221  * Gang blocks.
1222  *
1223  * A gang block is a collection of small blocks that looks to the DMU
1224  * like one large block.  When zio_dva_allocate() cannot find a block
1225  * of the requested size, due to either severe fragmentation or the pool
1226  * being nearly full, it calls zio_write_gang_block() to construct the
1227  * block from smaller fragments.
1228  *
1229  * A gang block consists of a gang header (zio_gbh_phys_t) and up to
1230  * three (SPA_GBH_NBLKPTRS) gang members.  The gang header is just like
1231  * an indirect block: it's an array of block pointers.  It consumes
1232  * only one sector and hence is allocatable regardless of fragmentation.
1233  * The gang header's bps point to its gang members, which hold the data.
1234  *
1235  * Gang blocks are self-checksumming, using the bp's <vdev, offset, txg>
1236  * as the verifier to ensure uniqueness of the SHA256 checksum.
1237  * Critically, the gang block bp's blk_cksum is the checksum of the data,
1238  * not the gang header.  This ensures that data block signatures (needed for
1239  * deduplication) are independent of how the block is physically stored.
1240  *
1241  * Gang blocks can be nested: a gang member may itself be a gang block.
1242  * Thus every gang block is a tree in which root and all interior nodes are
1243  * gang headers, and the leaves are normal blocks that contain user data.
1244  * The root of the gang tree is called the gang leader.
1245  *
1246  * To perform any operation (read, rewrite, free, claim) on a gang block,
1247  * zio_gang_assemble() first assembles the gang tree (minus data leaves)
1248  * in the io_gang_tree field of the original logical i/o by recursively
1249  * reading the gang leader and all gang headers below it.  This yields
1250  * an in-core tree containing the contents of every gang header and the
1251  * bps for every constituent of the gang block.
1252  *
1253  * With the gang tree now assembled, zio_gang_issue() just walks the gang tree
1254  * and invokes a callback on each bp.  To free a gang block, zio_gang_issue()
1255  * calls zio_free_gang() -- a trivial wrapper around zio_free() -- for each bp.
1256  * zio_claim_gang() provides a similarly trivial wrapper for zio_claim().
1257  * zio_read_gang() is a wrapper around zio_read() that omits reading gang
1258  * headers, since we already have those in io_gang_tree.  zio_rewrite_gang()
1259  * performs a zio_rewrite() of the data or, for gang headers, a zio_rewrite()
1260  * of the gang header plus zio_checksum_compute() of the data to update the
1261  * gang header's blk_cksum as described above.
1262  *
1263  * The two-phase assemble/issue model solves the problem of partial failure --
1264  * what if you'd freed part of a gang block but then couldn't read the
1265  * gang header for another part?  Assembling the entire gang tree first
1266  * ensures that all the necessary gang header I/O has succeeded before
1267  * starting the actual work of free, claim, or write.  Once the gang tree
1268  * is assembled, free and claim are in-memory operations that cannot fail.
1269  *
1270  * In the event that a gang write fails, zio_dva_unallocate() walks the
1271  * gang tree to immediately free (i.e. insert back into the space map)
1272  * everything we've allocated.  This ensures that we don't get ENOSPC
1273  * errors during repeated suspend/resume cycles due to a flaky device.
1274  *
1275  * Gang rewrites only happen during sync-to-convergence.  If we can't assemble
1276  * the gang tree, we won't modify the block, so we can safely defer the free
1277  * (knowing that the block is still intact).  If we *can* assemble the gang
1278  * tree, then even if some of the rewrites fail, zio_dva_unallocate() will free
1279  * each constituent bp and we can allocate a new block on the next sync pass.
1280  *
1281  * In all cases, the gang tree allows complete recovery from partial failure.
1282  * ==========================================================================
1283  */
1284 
1285 static zio_t *
1286 zio_read_gang(zio_t *pio, blkptr_t *bp, zio_gang_node_t *gn, void *data)
1287 {
1288 	if (gn != NULL)
1289 		return (pio);
1290 
1291 	return (zio_read(pio, pio->io_spa, bp, data, BP_GET_PSIZE(bp),
1292 	    NULL, NULL, pio->io_priority, ZIO_GANG_CHILD_FLAGS(pio),
1293 	    &pio->io_bookmark));
1294 }
1295 
1296 zio_t *
1297 zio_rewrite_gang(zio_t *pio, blkptr_t *bp, zio_gang_node_t *gn, void *data)
1298 {
1299 	zio_t *zio;
1300 
1301 	if (gn != NULL) {
1302 		zio = zio_rewrite(pio, pio->io_spa, pio->io_txg, bp,
1303 		    gn->gn_gbh, SPA_GANGBLOCKSIZE, NULL, NULL, pio->io_priority,
1304 		    ZIO_GANG_CHILD_FLAGS(pio), &pio->io_bookmark);
1305 		/*
1306 		 * As we rewrite each gang header, the pipeline will compute
1307 		 * a new gang block header checksum for it; but no one will
1308 		 * compute a new data checksum, so we do that here.  The one
1309 		 * exception is the gang leader: the pipeline already computed
1310 		 * its data checksum because that stage precedes gang assembly.
1311 		 * (Presently, nothing actually uses interior data checksums;
1312 		 * this is just good hygiene.)
1313 		 */
1314 		if (gn != pio->io_gang_leader->io_gang_tree) {
1315 			zio_checksum_compute(zio, BP_GET_CHECKSUM(bp),
1316 			    data, BP_GET_PSIZE(bp));
1317 		}
1318 	} else {
1319 		zio = zio_rewrite(pio, pio->io_spa, pio->io_txg, bp,
1320 		    data, BP_GET_PSIZE(bp), NULL, NULL, pio->io_priority,
1321 		    ZIO_GANG_CHILD_FLAGS(pio), &pio->io_bookmark);
1322 	}
1323 
1324 	return (zio);
1325 }
1326 
1327 /* ARGSUSED */
1328 zio_t *
1329 zio_free_gang(zio_t *pio, blkptr_t *bp, zio_gang_node_t *gn, void *data)
1330 {
1331 	return (zio_free(pio, pio->io_spa, pio->io_txg, bp,
1332 	    NULL, NULL, ZIO_GANG_CHILD_FLAGS(pio)));
1333 }
1334 
1335 /* ARGSUSED */
1336 zio_t *
1337 zio_claim_gang(zio_t *pio, blkptr_t *bp, zio_gang_node_t *gn, void *data)
1338 {
1339 	return (zio_claim(pio, pio->io_spa, pio->io_txg, bp,
1340 	    NULL, NULL, ZIO_GANG_CHILD_FLAGS(pio)));
1341 }
1342 
1343 static zio_gang_issue_func_t *zio_gang_issue_func[ZIO_TYPES] = {
1344 	NULL,
1345 	zio_read_gang,
1346 	zio_rewrite_gang,
1347 	zio_free_gang,
1348 	zio_claim_gang,
1349 	NULL
1350 };
1351 
1352 static void zio_gang_tree_assemble_done(zio_t *zio);
1353 
1354 static zio_gang_node_t *
1355 zio_gang_node_alloc(zio_gang_node_t **gnpp)
1356 {
1357 	zio_gang_node_t *gn;
1358 
1359 	ASSERT(*gnpp == NULL);
1360 
1361 	gn = kmem_zalloc(sizeof (*gn), KM_SLEEP);
1362 	gn->gn_gbh = zio_buf_alloc(SPA_GANGBLOCKSIZE);
1363 	*gnpp = gn;
1364 
1365 	return (gn);
1366 }
1367 
1368 static void
1369 zio_gang_node_free(zio_gang_node_t **gnpp)
1370 {
1371 	zio_gang_node_t *gn = *gnpp;
1372 
1373 	for (int g = 0; g < SPA_GBH_NBLKPTRS; g++)
1374 		ASSERT(gn->gn_child[g] == NULL);
1375 
1376 	zio_buf_free(gn->gn_gbh, SPA_GANGBLOCKSIZE);
1377 	kmem_free(gn, sizeof (*gn));
1378 	*gnpp = NULL;
1379 }
1380 
1381 static void
1382 zio_gang_tree_free(zio_gang_node_t **gnpp)
1383 {
1384 	zio_gang_node_t *gn = *gnpp;
1385 
1386 	if (gn == NULL)
1387 		return;
1388 
1389 	for (int g = 0; g < SPA_GBH_NBLKPTRS; g++)
1390 		zio_gang_tree_free(&gn->gn_child[g]);
1391 
1392 	zio_gang_node_free(gnpp);
1393 }
1394 
1395 static void
1396 zio_gang_tree_assemble(zio_t *gio, blkptr_t *bp, zio_gang_node_t **gnpp)
1397 {
1398 	zio_gang_node_t *gn = zio_gang_node_alloc(gnpp);
1399 
1400 	ASSERT(gio->io_gang_leader == gio);
1401 	ASSERT(BP_IS_GANG(bp));
1402 
1403 	zio_nowait(zio_read(gio, gio->io_spa, bp, gn->gn_gbh,
1404 	    SPA_GANGBLOCKSIZE, zio_gang_tree_assemble_done, gn,
1405 	    gio->io_priority, ZIO_GANG_CHILD_FLAGS(gio), &gio->io_bookmark));
1406 }
1407 
1408 static void
1409 zio_gang_tree_assemble_done(zio_t *zio)
1410 {
1411 	zio_t *gio = zio->io_gang_leader;
1412 	zio_gang_node_t *gn = zio->io_private;
1413 	blkptr_t *bp = zio->io_bp;
1414 
1415 	ASSERT(gio == zio_unique_parent(zio));
1416 	ASSERT(zio_walk_children(zio) == NULL);
1417 
1418 	if (zio->io_error)
1419 		return;
1420 
1421 	if (BP_SHOULD_BYTESWAP(bp))
1422 		byteswap_uint64_array(zio->io_data, zio->io_size);
1423 
1424 	ASSERT(zio->io_data == gn->gn_gbh);
1425 	ASSERT(zio->io_size == SPA_GANGBLOCKSIZE);
1426 	ASSERT(gn->gn_gbh->zg_tail.zbt_magic == ZBT_MAGIC);
1427 
1428 	for (int g = 0; g < SPA_GBH_NBLKPTRS; g++) {
1429 		blkptr_t *gbp = &gn->gn_gbh->zg_blkptr[g];
1430 		if (!BP_IS_GANG(gbp))
1431 			continue;
1432 		zio_gang_tree_assemble(gio, gbp, &gn->gn_child[g]);
1433 	}
1434 }
1435 
1436 static void
1437 zio_gang_tree_issue(zio_t *pio, zio_gang_node_t *gn, blkptr_t *bp, void *data)
1438 {
1439 	zio_t *gio = pio->io_gang_leader;
1440 	zio_t *zio;
1441 
1442 	ASSERT(BP_IS_GANG(bp) == !!gn);
1443 	ASSERT(BP_GET_CHECKSUM(bp) == BP_GET_CHECKSUM(gio->io_bp));
1444 	ASSERT(BP_GET_LSIZE(bp) == BP_GET_PSIZE(bp) || gn == gio->io_gang_tree);
1445 
1446 	/*
1447 	 * If you're a gang header, your data is in gn->gn_gbh.
1448 	 * If you're a gang member, your data is in 'data' and gn == NULL.
1449 	 */
1450 	zio = zio_gang_issue_func[gio->io_type](pio, bp, gn, data);
1451 
1452 	if (gn != NULL) {
1453 		ASSERT(gn->gn_gbh->zg_tail.zbt_magic == ZBT_MAGIC);
1454 
1455 		for (int g = 0; g < SPA_GBH_NBLKPTRS; g++) {
1456 			blkptr_t *gbp = &gn->gn_gbh->zg_blkptr[g];
1457 			if (BP_IS_HOLE(gbp))
1458 				continue;
1459 			zio_gang_tree_issue(zio, gn->gn_child[g], gbp, data);
1460 			data = (char *)data + BP_GET_PSIZE(gbp);
1461 		}
1462 	}
1463 
1464 	if (gn == gio->io_gang_tree)
1465 		ASSERT3P((char *)gio->io_data + gio->io_size, ==, data);
1466 
1467 	if (zio != pio)
1468 		zio_nowait(zio);
1469 }
1470 
1471 static int
1472 zio_gang_assemble(zio_t *zio)
1473 {
1474 	blkptr_t *bp = zio->io_bp;
1475 
1476 	ASSERT(BP_IS_GANG(bp) && zio->io_gang_leader == NULL);
1477 	ASSERT(zio->io_child_type > ZIO_CHILD_GANG);
1478 
1479 	zio->io_gang_leader = zio;
1480 
1481 	zio_gang_tree_assemble(zio, bp, &zio->io_gang_tree);
1482 
1483 	return (ZIO_PIPELINE_CONTINUE);
1484 }
1485 
1486 static int
1487 zio_gang_issue(zio_t *zio)
1488 {
1489 	blkptr_t *bp = zio->io_bp;
1490 
1491 	if (zio_wait_for_children(zio, ZIO_CHILD_GANG, ZIO_WAIT_DONE))
1492 		return (ZIO_PIPELINE_STOP);
1493 
1494 	ASSERT(BP_IS_GANG(bp) && zio->io_gang_leader == zio);
1495 	ASSERT(zio->io_child_type > ZIO_CHILD_GANG);
1496 
1497 	if (zio->io_child_error[ZIO_CHILD_GANG] == 0)
1498 		zio_gang_tree_issue(zio, zio->io_gang_tree, bp, zio->io_data);
1499 	else
1500 		zio_gang_tree_free(&zio->io_gang_tree);
1501 
1502 	zio->io_pipeline = ZIO_INTERLOCK_PIPELINE;
1503 
1504 	return (ZIO_PIPELINE_CONTINUE);
1505 }
1506 
1507 static void
1508 zio_write_gang_member_ready(zio_t *zio)
1509 {
1510 	zio_t *pio = zio_unique_parent(zio);
1511 	zio_t *gio = zio->io_gang_leader;
1512 	dva_t *cdva = zio->io_bp->blk_dva;
1513 	dva_t *pdva = pio->io_bp->blk_dva;
1514 	uint64_t asize;
1515 
1516 	if (BP_IS_HOLE(zio->io_bp))
1517 		return;
1518 
1519 	ASSERT(BP_IS_HOLE(&zio->io_bp_orig));
1520 
1521 	ASSERT(zio->io_child_type == ZIO_CHILD_GANG);
1522 	ASSERT3U(zio->io_prop.zp_ndvas, ==, gio->io_prop.zp_ndvas);
1523 	ASSERT3U(zio->io_prop.zp_ndvas, <=, BP_GET_NDVAS(zio->io_bp));
1524 	ASSERT3U(pio->io_prop.zp_ndvas, <=, BP_GET_NDVAS(pio->io_bp));
1525 	ASSERT3U(BP_GET_NDVAS(zio->io_bp), <=, BP_GET_NDVAS(pio->io_bp));
1526 
1527 	mutex_enter(&pio->io_lock);
1528 	for (int d = 0; d < BP_GET_NDVAS(zio->io_bp); d++) {
1529 		ASSERT(DVA_GET_GANG(&pdva[d]));
1530 		asize = DVA_GET_ASIZE(&pdva[d]);
1531 		asize += DVA_GET_ASIZE(&cdva[d]);
1532 		DVA_SET_ASIZE(&pdva[d], asize);
1533 	}
1534 	mutex_exit(&pio->io_lock);
1535 }
1536 
1537 static int
1538 zio_write_gang_block(zio_t *pio)
1539 {
1540 	spa_t *spa = pio->io_spa;
1541 	blkptr_t *bp = pio->io_bp;
1542 	zio_t *gio = pio->io_gang_leader;
1543 	zio_t *zio;
1544 	zio_gang_node_t *gn, **gnpp;
1545 	zio_gbh_phys_t *gbh;
1546 	uint64_t txg = pio->io_txg;
1547 	uint64_t resid = pio->io_size;
1548 	uint64_t lsize;
1549 	int ndvas = gio->io_prop.zp_ndvas;
1550 	int gbh_ndvas = MIN(ndvas + 1, spa_max_replication(spa));
1551 	zio_prop_t zp;
1552 	int error;
1553 
1554 	error = metaslab_alloc(spa, spa->spa_normal_class, SPA_GANGBLOCKSIZE,
1555 	    bp, gbh_ndvas, txg, pio == gio ? NULL : gio->io_bp,
1556 	    METASLAB_HINTBP_FAVOR | METASLAB_GANG_HEADER);
1557 	if (error) {
1558 		pio->io_error = error;
1559 		return (ZIO_PIPELINE_CONTINUE);
1560 	}
1561 
1562 	if (pio == gio) {
1563 		gnpp = &gio->io_gang_tree;
1564 	} else {
1565 		gnpp = pio->io_private;
1566 		ASSERT(pio->io_ready == zio_write_gang_member_ready);
1567 	}
1568 
1569 	gn = zio_gang_node_alloc(gnpp);
1570 	gbh = gn->gn_gbh;
1571 	bzero(gbh, SPA_GANGBLOCKSIZE);
1572 
1573 	/*
1574 	 * Create the gang header.
1575 	 */
1576 	zio = zio_rewrite(pio, spa, txg, bp, gbh, SPA_GANGBLOCKSIZE, NULL, NULL,
1577 	    pio->io_priority, ZIO_GANG_CHILD_FLAGS(pio), &pio->io_bookmark);
1578 
1579 	/*
1580 	 * Create and nowait the gang children.
1581 	 */
1582 	for (int g = 0; resid != 0; resid -= lsize, g++) {
1583 		lsize = P2ROUNDUP(resid / (SPA_GBH_NBLKPTRS - g),
1584 		    SPA_MINBLOCKSIZE);
1585 		ASSERT(lsize >= SPA_MINBLOCKSIZE && lsize <= resid);
1586 
1587 		zp.zp_checksum = gio->io_prop.zp_checksum;
1588 		zp.zp_compress = ZIO_COMPRESS_OFF;
1589 		zp.zp_type = DMU_OT_NONE;
1590 		zp.zp_level = 0;
1591 		zp.zp_ndvas = gio->io_prop.zp_ndvas;
1592 
1593 		zio_nowait(zio_write(zio, spa, txg, &gbh->zg_blkptr[g],
1594 		    (char *)pio->io_data + (pio->io_size - resid), lsize, &zp,
1595 		    zio_write_gang_member_ready, NULL, &gn->gn_child[g],
1596 		    pio->io_priority, ZIO_GANG_CHILD_FLAGS(pio),
1597 		    &pio->io_bookmark));
1598 	}
1599 
1600 	/*
1601 	 * Set pio's pipeline to just wait for zio to finish.
1602 	 */
1603 	pio->io_pipeline = ZIO_INTERLOCK_PIPELINE;
1604 
1605 	zio_nowait(zio);
1606 
1607 	return (ZIO_PIPELINE_CONTINUE);
1608 }
1609 
1610 /*
1611  * ==========================================================================
1612  * Allocate and free blocks
1613  * ==========================================================================
1614  */
1615 
1616 static int
1617 zio_dva_allocate(zio_t *zio)
1618 {
1619 	spa_t *spa = zio->io_spa;
1620 	metaslab_class_t *mc = spa->spa_normal_class;
1621 	blkptr_t *bp = zio->io_bp;
1622 	int error;
1623 
1624 	if (zio->io_gang_leader == NULL) {
1625 		ASSERT(zio->io_child_type > ZIO_CHILD_GANG);
1626 		zio->io_gang_leader = zio;
1627 	}
1628 
1629 	ASSERT(BP_IS_HOLE(bp));
1630 	ASSERT3U(BP_GET_NDVAS(bp), ==, 0);
1631 	ASSERT3U(zio->io_prop.zp_ndvas, >, 0);
1632 	ASSERT3U(zio->io_prop.zp_ndvas, <=, spa_max_replication(spa));
1633 	ASSERT3U(zio->io_size, ==, BP_GET_PSIZE(bp));
1634 
1635 	error = metaslab_alloc(spa, mc, zio->io_size, bp,
1636 	    zio->io_prop.zp_ndvas, zio->io_txg, NULL, 0);
1637 
1638 	if (error) {
1639 		if (error == ENOSPC && zio->io_size > SPA_MINBLOCKSIZE)
1640 			return (zio_write_gang_block(zio));
1641 		zio->io_error = error;
1642 	}
1643 
1644 	return (ZIO_PIPELINE_CONTINUE);
1645 }
1646 
1647 static int
1648 zio_dva_free(zio_t *zio)
1649 {
1650 	metaslab_free(zio->io_spa, zio->io_bp, zio->io_txg, B_FALSE);
1651 
1652 	return (ZIO_PIPELINE_CONTINUE);
1653 }
1654 
1655 static int
1656 zio_dva_claim(zio_t *zio)
1657 {
1658 	int error;
1659 
1660 	error = metaslab_claim(zio->io_spa, zio->io_bp, zio->io_txg);
1661 	if (error)
1662 		zio->io_error = error;
1663 
1664 	return (ZIO_PIPELINE_CONTINUE);
1665 }
1666 
1667 /*
1668  * Undo an allocation.  This is used by zio_done() when an I/O fails
1669  * and we want to give back the block we just allocated.
1670  * This handles both normal blocks and gang blocks.
1671  */
1672 static void
1673 zio_dva_unallocate(zio_t *zio, zio_gang_node_t *gn, blkptr_t *bp)
1674 {
1675 	spa_t *spa = zio->io_spa;
1676 	boolean_t now = !(zio->io_flags & ZIO_FLAG_IO_REWRITE);
1677 
1678 	ASSERT(bp->blk_birth == zio->io_txg || BP_IS_HOLE(bp));
1679 
1680 	if (zio->io_bp == bp && !now) {
1681 		/*
1682 		 * This is a rewrite for sync-to-convergence.
1683 		 * We can't do a metaslab_free(NOW) because bp wasn't allocated
1684 		 * during this sync pass, which means that metaslab_sync()
1685 		 * already committed the allocation.
1686 		 */
1687 		ASSERT(DVA_EQUAL(BP_IDENTITY(bp),
1688 		    BP_IDENTITY(&zio->io_bp_orig)));
1689 		ASSERT(spa_sync_pass(spa) > 1);
1690 
1691 		if (BP_IS_GANG(bp) && gn == NULL) {
1692 			/*
1693 			 * This is a gang leader whose gang header(s) we
1694 			 * couldn't read now, so defer the free until later.
1695 			 * The block should still be intact because without
1696 			 * the headers, we'd never even start the rewrite.
1697 			 */
1698 			bplist_enqueue_deferred(&spa->spa_sync_bplist, bp);
1699 			return;
1700 		}
1701 	}
1702 
1703 	if (!BP_IS_HOLE(bp))
1704 		metaslab_free(spa, bp, bp->blk_birth, now);
1705 
1706 	if (gn != NULL) {
1707 		for (int g = 0; g < SPA_GBH_NBLKPTRS; g++) {
1708 			zio_dva_unallocate(zio, gn->gn_child[g],
1709 			    &gn->gn_gbh->zg_blkptr[g]);
1710 		}
1711 	}
1712 }
1713 
1714 /*
1715  * Try to allocate an intent log block.  Return 0 on success, errno on failure.
1716  */
1717 int
1718 zio_alloc_blk(spa_t *spa, uint64_t size, blkptr_t *new_bp, blkptr_t *old_bp,
1719     uint64_t txg, boolean_t bypass_slog)
1720 {
1721 	int error = 1;
1722 
1723 	if (!bypass_slog)
1724 		error = metaslab_alloc(spa, spa->spa_log_class, size,
1725 		    new_bp, 1, txg, old_bp, METASLAB_HINTBP_AVOID);
1726 
1727 	if (error)
1728 		error = metaslab_alloc(spa, spa->spa_normal_class, size,
1729 		    new_bp, 1, txg, old_bp, METASLAB_HINTBP_AVOID);
1730 
1731 	if (error == 0) {
1732 		BP_SET_LSIZE(new_bp, size);
1733 		BP_SET_PSIZE(new_bp, size);
1734 		BP_SET_COMPRESS(new_bp, ZIO_COMPRESS_OFF);
1735 		BP_SET_CHECKSUM(new_bp, ZIO_CHECKSUM_ZILOG);
1736 		BP_SET_TYPE(new_bp, DMU_OT_INTENT_LOG);
1737 		BP_SET_LEVEL(new_bp, 0);
1738 		BP_SET_BYTEORDER(new_bp, ZFS_HOST_BYTEORDER);
1739 	}
1740 
1741 	return (error);
1742 }
1743 
1744 /*
1745  * Free an intent log block.  We know it can't be a gang block, so there's
1746  * nothing to do except metaslab_free() it.
1747  */
1748 void
1749 zio_free_blk(spa_t *spa, blkptr_t *bp, uint64_t txg)
1750 {
1751 	ASSERT(!BP_IS_GANG(bp));
1752 
1753 	metaslab_free(spa, bp, txg, B_FALSE);
1754 }
1755 
1756 /*
1757  * ==========================================================================
1758  * Read and write to physical devices
1759  * ==========================================================================
1760  */
1761 static int
1762 zio_vdev_io_start(zio_t *zio)
1763 {
1764 	vdev_t *vd = zio->io_vd;
1765 	uint64_t align;
1766 	spa_t *spa = zio->io_spa;
1767 
1768 	ASSERT(zio->io_error == 0);
1769 	ASSERT(zio->io_child_error[ZIO_CHILD_VDEV] == 0);
1770 
1771 	if (vd == NULL) {
1772 		if (!(zio->io_flags & ZIO_FLAG_CONFIG_WRITER))
1773 			spa_config_enter(spa, SCL_ZIO, zio, RW_READER);
1774 
1775 		/*
1776 		 * The mirror_ops handle multiple DVAs in a single BP.
1777 		 */
1778 		return (vdev_mirror_ops.vdev_op_io_start(zio));
1779 	}
1780 
1781 	align = 1ULL << vd->vdev_top->vdev_ashift;
1782 
1783 	if (P2PHASE(zio->io_size, align) != 0) {
1784 		uint64_t asize = P2ROUNDUP(zio->io_size, align);
1785 		char *abuf = zio_buf_alloc(asize);
1786 		ASSERT(vd == vd->vdev_top);
1787 		if (zio->io_type == ZIO_TYPE_WRITE) {
1788 			bcopy(zio->io_data, abuf, zio->io_size);
1789 			bzero(abuf + zio->io_size, asize - zio->io_size);
1790 		}
1791 		zio_push_transform(zio, abuf, asize, asize, zio_subblock);
1792 	}
1793 
1794 	ASSERT(P2PHASE(zio->io_offset, align) == 0);
1795 	ASSERT(P2PHASE(zio->io_size, align) == 0);
1796 	ASSERT(zio->io_type != ZIO_TYPE_WRITE || spa_writeable(spa));
1797 
1798 	/*
1799 	 * If this is a repair I/O, and there's no self-healing involved --
1800 	 * that is, we're just resilvering what we expect to resilver --
1801 	 * then don't do the I/O unless zio's txg is actually in vd's DTL.
1802 	 * This prevents spurious resilvering with nested replication.
1803 	 * For example, given a mirror of mirrors, (A+B)+(C+D), if only
1804 	 * A is out of date, we'll read from C+D, then use the data to
1805 	 * resilver A+B -- but we don't actually want to resilver B, just A.
1806 	 * The top-level mirror has no way to know this, so instead we just
1807 	 * discard unnecessary repairs as we work our way down the vdev tree.
1808 	 * The same logic applies to any form of nested replication:
1809 	 * ditto + mirror, RAID-Z + replacing, etc.  This covers them all.
1810 	 */
1811 	if ((zio->io_flags & ZIO_FLAG_IO_REPAIR) &&
1812 	    !(zio->io_flags & ZIO_FLAG_SELF_HEAL) &&
1813 	    zio->io_txg != 0 &&	/* not a delegated i/o */
1814 	    !vdev_dtl_contains(vd, DTL_PARTIAL, zio->io_txg, 1)) {
1815 		ASSERT(zio->io_type == ZIO_TYPE_WRITE);
1816 		zio_vdev_io_bypass(zio);
1817 		return (ZIO_PIPELINE_CONTINUE);
1818 	}
1819 
1820 	if (vd->vdev_ops->vdev_op_leaf &&
1821 	    (zio->io_type == ZIO_TYPE_READ || zio->io_type == ZIO_TYPE_WRITE)) {
1822 
1823 		if (zio->io_type == ZIO_TYPE_READ && vdev_cache_read(zio) == 0)
1824 			return (ZIO_PIPELINE_CONTINUE);
1825 
1826 		if ((zio = vdev_queue_io(zio)) == NULL)
1827 			return (ZIO_PIPELINE_STOP);
1828 
1829 		if (!vdev_accessible(vd, zio)) {
1830 			zio->io_error = ENXIO;
1831 			zio_interrupt(zio);
1832 			return (ZIO_PIPELINE_STOP);
1833 		}
1834 	}
1835 
1836 	return (vd->vdev_ops->vdev_op_io_start(zio));
1837 }
1838 
1839 static int
1840 zio_vdev_io_done(zio_t *zio)
1841 {
1842 	vdev_t *vd = zio->io_vd;
1843 	vdev_ops_t *ops = vd ? vd->vdev_ops : &vdev_mirror_ops;
1844 	boolean_t unexpected_error = B_FALSE;
1845 
1846 	if (zio_wait_for_children(zio, ZIO_CHILD_VDEV, ZIO_WAIT_DONE))
1847 		return (ZIO_PIPELINE_STOP);
1848 
1849 	ASSERT(zio->io_type == ZIO_TYPE_READ || zio->io_type == ZIO_TYPE_WRITE);
1850 
1851 	if (vd != NULL && vd->vdev_ops->vdev_op_leaf) {
1852 
1853 		vdev_queue_io_done(zio);
1854 
1855 		if (zio->io_type == ZIO_TYPE_WRITE)
1856 			vdev_cache_write(zio);
1857 
1858 		if (zio_injection_enabled && zio->io_error == 0)
1859 			zio->io_error = zio_handle_device_injection(vd,
1860 			    zio, EIO);
1861 
1862 		if (zio_injection_enabled && zio->io_error == 0)
1863 			zio->io_error = zio_handle_label_injection(zio, EIO);
1864 
1865 		if (zio->io_error) {
1866 			if (!vdev_accessible(vd, zio)) {
1867 				zio->io_error = ENXIO;
1868 			} else {
1869 				unexpected_error = B_TRUE;
1870 			}
1871 		}
1872 	}
1873 
1874 	ops->vdev_op_io_done(zio);
1875 
1876 	if (unexpected_error)
1877 		VERIFY(vdev_probe(vd, zio) == NULL);
1878 
1879 	return (ZIO_PIPELINE_CONTINUE);
1880 }
1881 
1882 /*
1883  * For non-raidz ZIOs, we can just copy aside the bad data read from the
1884  * disk, and use that to finish the checksum ereport later.
1885  */
1886 static void
1887 zio_vsd_default_cksum_finish(zio_cksum_report_t *zcr,
1888     const void *good_buf)
1889 {
1890 	/* no processing needed */
1891 	zfs_ereport_finish_checksum(zcr, good_buf, zcr->zcr_cbdata, B_FALSE);
1892 }
1893 
1894 /*ARGSUSED*/
1895 void
1896 zio_vsd_default_cksum_report(zio_t *zio, zio_cksum_report_t *zcr, void *ignored)
1897 {
1898 	void *buf = zio_buf_alloc(zio->io_size);
1899 
1900 	bcopy(zio->io_data, buf, zio->io_size);
1901 
1902 	zcr->zcr_cbinfo = zio->io_size;
1903 	zcr->zcr_cbdata = buf;
1904 	zcr->zcr_finish = zio_vsd_default_cksum_finish;
1905 	zcr->zcr_free = zio_buf_free;
1906 }
1907 
1908 static int
1909 zio_vdev_io_assess(zio_t *zio)
1910 {
1911 	vdev_t *vd = zio->io_vd;
1912 
1913 	if (zio_wait_for_children(zio, ZIO_CHILD_VDEV, ZIO_WAIT_DONE))
1914 		return (ZIO_PIPELINE_STOP);
1915 
1916 	if (vd == NULL && !(zio->io_flags & ZIO_FLAG_CONFIG_WRITER))
1917 		spa_config_exit(zio->io_spa, SCL_ZIO, zio);
1918 
1919 	if (zio->io_vsd != NULL) {
1920 		zio->io_vsd_ops->vsd_free(zio);
1921 		zio->io_vsd = NULL;
1922 	}
1923 
1924 	if (zio_injection_enabled && zio->io_error == 0)
1925 		zio->io_error = zio_handle_fault_injection(zio, EIO);
1926 
1927 	/*
1928 	 * If the I/O failed, determine whether we should attempt to retry it.
1929 	 */
1930 	if (zio->io_error && vd == NULL &&
1931 	    !(zio->io_flags & (ZIO_FLAG_DONT_RETRY | ZIO_FLAG_IO_RETRY))) {
1932 		ASSERT(!(zio->io_flags & ZIO_FLAG_DONT_QUEUE));	/* not a leaf */
1933 		ASSERT(!(zio->io_flags & ZIO_FLAG_IO_BYPASS));	/* not a leaf */
1934 		zio->io_error = 0;
1935 		zio->io_flags |= ZIO_FLAG_IO_RETRY |
1936 		    ZIO_FLAG_DONT_CACHE | ZIO_FLAG_DONT_AGGREGATE;
1937 		zio->io_stage = ZIO_STAGE_VDEV_IO_START - 1;
1938 		zio_taskq_dispatch(zio, ZIO_TASKQ_ISSUE);
1939 		return (ZIO_PIPELINE_STOP);
1940 	}
1941 
1942 	/*
1943 	 * If we got an error on a leaf device, convert it to ENXIO
1944 	 * if the device is not accessible at all.
1945 	 */
1946 	if (zio->io_error && vd != NULL && vd->vdev_ops->vdev_op_leaf &&
1947 	    !vdev_accessible(vd, zio))
1948 		zio->io_error = ENXIO;
1949 
1950 	/*
1951 	 * If we can't write to an interior vdev (mirror or RAID-Z),
1952 	 * set vdev_cant_write so that we stop trying to allocate from it.
1953 	 */
1954 	if (zio->io_error == ENXIO && zio->io_type == ZIO_TYPE_WRITE &&
1955 	    vd != NULL && !vd->vdev_ops->vdev_op_leaf)
1956 		vd->vdev_cant_write = B_TRUE;
1957 
1958 	if (zio->io_error)
1959 		zio->io_pipeline = ZIO_INTERLOCK_PIPELINE;
1960 
1961 	return (ZIO_PIPELINE_CONTINUE);
1962 }
1963 
1964 void
1965 zio_vdev_io_reissue(zio_t *zio)
1966 {
1967 	ASSERT(zio->io_stage == ZIO_STAGE_VDEV_IO_START);
1968 	ASSERT(zio->io_error == 0);
1969 
1970 	zio->io_stage--;
1971 }
1972 
1973 void
1974 zio_vdev_io_redone(zio_t *zio)
1975 {
1976 	ASSERT(zio->io_stage == ZIO_STAGE_VDEV_IO_DONE);
1977 
1978 	zio->io_stage--;
1979 }
1980 
1981 void
1982 zio_vdev_io_bypass(zio_t *zio)
1983 {
1984 	ASSERT(zio->io_stage == ZIO_STAGE_VDEV_IO_START);
1985 	ASSERT(zio->io_error == 0);
1986 
1987 	zio->io_flags |= ZIO_FLAG_IO_BYPASS;
1988 	zio->io_stage = ZIO_STAGE_VDEV_IO_ASSESS - 1;
1989 }
1990 
1991 /*
1992  * ==========================================================================
1993  * Generate and verify checksums
1994  * ==========================================================================
1995  */
1996 static int
1997 zio_checksum_generate(zio_t *zio)
1998 {
1999 	blkptr_t *bp = zio->io_bp;
2000 	enum zio_checksum checksum;
2001 
2002 	if (bp == NULL) {
2003 		/*
2004 		 * This is zio_write_phys().
2005 		 * We're either generating a label checksum, or none at all.
2006 		 */
2007 		checksum = zio->io_prop.zp_checksum;
2008 
2009 		if (checksum == ZIO_CHECKSUM_OFF)
2010 			return (ZIO_PIPELINE_CONTINUE);
2011 
2012 		ASSERT(checksum == ZIO_CHECKSUM_LABEL);
2013 	} else {
2014 		if (BP_IS_GANG(bp) && zio->io_child_type == ZIO_CHILD_GANG) {
2015 			ASSERT(!IO_IS_ALLOCATING(zio));
2016 			checksum = ZIO_CHECKSUM_GANG_HEADER;
2017 		} else {
2018 			checksum = BP_GET_CHECKSUM(bp);
2019 		}
2020 	}
2021 
2022 	zio_checksum_compute(zio, checksum, zio->io_data, zio->io_size);
2023 
2024 	return (ZIO_PIPELINE_CONTINUE);
2025 }
2026 
2027 static int
2028 zio_checksum_verify(zio_t *zio)
2029 {
2030 	zio_bad_cksum_t info;
2031 
2032 	blkptr_t *bp = zio->io_bp;
2033 	int error;
2034 
2035 	if (bp == NULL) {
2036 		/*
2037 		 * This is zio_read_phys().
2038 		 * We're either verifying a label checksum, or nothing at all.
2039 		 */
2040 		if (zio->io_prop.zp_checksum == ZIO_CHECKSUM_OFF)
2041 			return (ZIO_PIPELINE_CONTINUE);
2042 
2043 		ASSERT(zio->io_prop.zp_checksum == ZIO_CHECKSUM_LABEL);
2044 	}
2045 
2046 	if ((error = zio_checksum_error(zio, &info)) != 0) {
2047 		zio->io_error = error;
2048 		if (!(zio->io_flags & ZIO_FLAG_SPECULATIVE)) {
2049 			zfs_ereport_start_checksum(zio->io_spa,
2050 			    zio->io_vd, zio, zio->io_offset,
2051 			    zio->io_size, NULL, &info);
2052 		}
2053 	}
2054 
2055 	return (ZIO_PIPELINE_CONTINUE);
2056 }
2057 
2058 /*
2059  * Called by RAID-Z to ensure we don't compute the checksum twice.
2060  */
2061 void
2062 zio_checksum_verified(zio_t *zio)
2063 {
2064 	zio->io_pipeline &= ~(1U << ZIO_STAGE_CHECKSUM_VERIFY);
2065 }
2066 
2067 /*
2068  * ==========================================================================
2069  * Error rank.  Error are ranked in the order 0, ENXIO, ECKSUM, EIO, other.
2070  * An error of 0 indictes success.  ENXIO indicates whole-device failure,
2071  * which may be transient (e.g. unplugged) or permament.  ECKSUM and EIO
2072  * indicate errors that are specific to one I/O, and most likely permanent.
2073  * Any other error is presumed to be worse because we weren't expecting it.
2074  * ==========================================================================
2075  */
2076 int
2077 zio_worst_error(int e1, int e2)
2078 {
2079 	static int zio_error_rank[] = { 0, ENXIO, ECKSUM, EIO };
2080 	int r1, r2;
2081 
2082 	for (r1 = 0; r1 < sizeof (zio_error_rank) / sizeof (int); r1++)
2083 		if (e1 == zio_error_rank[r1])
2084 			break;
2085 
2086 	for (r2 = 0; r2 < sizeof (zio_error_rank) / sizeof (int); r2++)
2087 		if (e2 == zio_error_rank[r2])
2088 			break;
2089 
2090 	return (r1 > r2 ? e1 : e2);
2091 }
2092 
2093 /*
2094  * ==========================================================================
2095  * I/O completion
2096  * ==========================================================================
2097  */
2098 static int
2099 zio_ready(zio_t *zio)
2100 {
2101 	blkptr_t *bp = zio->io_bp;
2102 	zio_t *pio, *pio_next;
2103 
2104 	if (zio_wait_for_children(zio, ZIO_CHILD_GANG, ZIO_WAIT_READY))
2105 		return (ZIO_PIPELINE_STOP);
2106 
2107 	if (zio->io_ready) {
2108 		ASSERT(IO_IS_ALLOCATING(zio));
2109 		ASSERT(bp->blk_birth == zio->io_txg || BP_IS_HOLE(bp));
2110 		ASSERT(zio->io_children[ZIO_CHILD_GANG][ZIO_WAIT_READY] == 0);
2111 
2112 		zio->io_ready(zio);
2113 	}
2114 
2115 	if (bp != NULL && bp != &zio->io_bp_copy)
2116 		zio->io_bp_copy = *bp;
2117 
2118 	if (zio->io_error)
2119 		zio->io_pipeline = ZIO_INTERLOCK_PIPELINE;
2120 
2121 	mutex_enter(&zio->io_lock);
2122 	zio->io_state[ZIO_WAIT_READY] = 1;
2123 	pio = zio_walk_parents(zio);
2124 	mutex_exit(&zio->io_lock);
2125 
2126 	/*
2127 	 * As we notify zio's parents, new parents could be added.
2128 	 * New parents go to the head of zio's io_parent_list, however,
2129 	 * so we will (correctly) not notify them.  The remainder of zio's
2130 	 * io_parent_list, from 'pio_next' onward, cannot change because
2131 	 * all parents must wait for us to be done before they can be done.
2132 	 */
2133 	for (; pio != NULL; pio = pio_next) {
2134 		pio_next = zio_walk_parents(zio);
2135 		zio_notify_parent(pio, zio, ZIO_WAIT_READY);
2136 	}
2137 
2138 	return (ZIO_PIPELINE_CONTINUE);
2139 }
2140 
2141 static int
2142 zio_done(zio_t *zio)
2143 {
2144 	spa_t *spa = zio->io_spa;
2145 	zio_t *lio = zio->io_logical;
2146 	blkptr_t *bp = zio->io_bp;
2147 	vdev_t *vd = zio->io_vd;
2148 	uint64_t psize = zio->io_size;
2149 	zio_t *pio, *pio_next;
2150 
2151 	/*
2152 	 * If our children haven't all completed,
2153 	 * wait for them and then repeat this pipeline stage.
2154 	 */
2155 	if (zio_wait_for_children(zio, ZIO_CHILD_VDEV, ZIO_WAIT_DONE) ||
2156 	    zio_wait_for_children(zio, ZIO_CHILD_GANG, ZIO_WAIT_DONE) ||
2157 	    zio_wait_for_children(zio, ZIO_CHILD_LOGICAL, ZIO_WAIT_DONE))
2158 		return (ZIO_PIPELINE_STOP);
2159 
2160 	for (int c = 0; c < ZIO_CHILD_TYPES; c++)
2161 		for (int w = 0; w < ZIO_WAIT_TYPES; w++)
2162 			ASSERT(zio->io_children[c][w] == 0);
2163 
2164 	if (bp != NULL) {
2165 		ASSERT(bp->blk_pad[0] == 0);
2166 		ASSERT(bp->blk_pad[1] == 0);
2167 		ASSERT(bp->blk_pad[2] == 0);
2168 		ASSERT(bcmp(bp, &zio->io_bp_copy, sizeof (blkptr_t)) == 0 ||
2169 		    (bp == zio_unique_parent(zio)->io_bp));
2170 		if (zio->io_type == ZIO_TYPE_WRITE && !BP_IS_HOLE(bp) &&
2171 		    !(zio->io_flags & ZIO_FLAG_IO_REPAIR)) {
2172 			ASSERT(!BP_SHOULD_BYTESWAP(bp));
2173 			ASSERT3U(zio->io_prop.zp_ndvas, <=, BP_GET_NDVAS(bp));
2174 			ASSERT(BP_COUNT_GANG(bp) == 0 ||
2175 			    (BP_COUNT_GANG(bp) == BP_GET_NDVAS(bp)));
2176 		}
2177 	}
2178 
2179 	/*
2180 	 * If there were child vdev or gang errors, they apply to us now.
2181 	 */
2182 	zio_inherit_child_errors(zio, ZIO_CHILD_VDEV);
2183 	zio_inherit_child_errors(zio, ZIO_CHILD_GANG);
2184 
2185 	zio_pop_transforms(zio);	/* note: may set zio->io_error */
2186 
2187 	vdev_stat_update(zio, psize);
2188 
2189 	if (zio->io_error) {
2190 		/*
2191 		 * If this I/O is attached to a particular vdev,
2192 		 * generate an error message describing the I/O failure
2193 		 * at the block level.  We ignore these errors if the
2194 		 * device is currently unavailable.
2195 		 */
2196 		if (zio->io_error != ECKSUM && vd != NULL && !vdev_is_dead(vd))
2197 			zfs_ereport_post(FM_EREPORT_ZFS_IO, spa, vd, zio, 0, 0);
2198 
2199 		if ((zio->io_error == EIO ||
2200 		    !(zio->io_flags & ZIO_FLAG_SPECULATIVE)) && zio == lio) {
2201 			/*
2202 			 * For logical I/O requests, tell the SPA to log the
2203 			 * error and generate a logical data ereport.
2204 			 */
2205 			spa_log_error(spa, zio);
2206 			zfs_ereport_post(FM_EREPORT_ZFS_DATA, spa, NULL, zio,
2207 			    0, 0);
2208 		}
2209 	}
2210 
2211 	if (zio->io_error && zio == lio) {
2212 		/*
2213 		 * Determine whether zio should be reexecuted.  This will
2214 		 * propagate all the way to the root via zio_notify_parent().
2215 		 */
2216 		ASSERT(vd == NULL && bp != NULL);
2217 
2218 		if (IO_IS_ALLOCATING(zio))
2219 			if (zio->io_error != ENOSPC)
2220 				zio->io_reexecute |= ZIO_REEXECUTE_NOW;
2221 			else
2222 				zio->io_reexecute |= ZIO_REEXECUTE_SUSPEND;
2223 
2224 		if ((zio->io_type == ZIO_TYPE_READ ||
2225 		    zio->io_type == ZIO_TYPE_FREE) &&
2226 		    zio->io_error == ENXIO &&
2227 		    spa->spa_load_state == SPA_LOAD_NONE &&
2228 		    spa_get_failmode(spa) != ZIO_FAILURE_MODE_CONTINUE)
2229 			zio->io_reexecute |= ZIO_REEXECUTE_SUSPEND;
2230 
2231 		if (!(zio->io_flags & ZIO_FLAG_CANFAIL) && !zio->io_reexecute)
2232 			zio->io_reexecute |= ZIO_REEXECUTE_SUSPEND;
2233 
2234 		/*
2235 		 * Here is a possibly good place to attempt to do
2236 		 * either combinatorial reconstruction or error correction
2237 		 * based on checksums.  It also might be a good place
2238 		 * to send out preliminary ereports before we suspend
2239 		 * processing.
2240 		 */
2241 	}
2242 
2243 	/*
2244 	 * If there were logical child errors, they apply to us now.
2245 	 * We defer this until now to avoid conflating logical child
2246 	 * errors with errors that happened to the zio itself when
2247 	 * updating vdev stats and reporting FMA events above.
2248 	 */
2249 	zio_inherit_child_errors(zio, ZIO_CHILD_LOGICAL);
2250 
2251 	if ((zio->io_error || zio->io_reexecute) && IO_IS_ALLOCATING(zio) &&
2252 	    zio->io_child_type == ZIO_CHILD_LOGICAL) {
2253 		ASSERT(zio->io_child_type != ZIO_CHILD_GANG);
2254 		zio_dva_unallocate(zio, zio->io_gang_tree, bp);
2255 	}
2256 
2257 	zio_gang_tree_free(&zio->io_gang_tree);
2258 
2259 	/*
2260 	 * Godfather I/Os should never suspend.
2261 	 */
2262 	if ((zio->io_flags & ZIO_FLAG_GODFATHER) &&
2263 	    (zio->io_reexecute & ZIO_REEXECUTE_SUSPEND))
2264 		zio->io_reexecute = 0;
2265 
2266 	if (zio->io_reexecute) {
2267 		/*
2268 		 * This is a logical I/O that wants to reexecute.
2269 		 *
2270 		 * Reexecute is top-down.  When an i/o fails, if it's not
2271 		 * the root, it simply notifies its parent and sticks around.
2272 		 * The parent, seeing that it still has children in zio_done(),
2273 		 * does the same.  This percolates all the way up to the root.
2274 		 * The root i/o will reexecute or suspend the entire tree.
2275 		 *
2276 		 * This approach ensures that zio_reexecute() honors
2277 		 * all the original i/o dependency relationships, e.g.
2278 		 * parents not executing until children are ready.
2279 		 */
2280 		ASSERT(zio->io_child_type == ZIO_CHILD_LOGICAL);
2281 
2282 		zio->io_gang_leader = NULL;
2283 
2284 		mutex_enter(&zio->io_lock);
2285 		zio->io_state[ZIO_WAIT_DONE] = 1;
2286 		mutex_exit(&zio->io_lock);
2287 
2288 		/*
2289 		 * "The Godfather" I/O monitors its children but is
2290 		 * not a true parent to them. It will track them through
2291 		 * the pipeline but severs its ties whenever they get into
2292 		 * trouble (e.g. suspended). This allows "The Godfather"
2293 		 * I/O to return status without blocking.
2294 		 */
2295 		for (pio = zio_walk_parents(zio); pio != NULL; pio = pio_next) {
2296 			zio_link_t *zl = zio->io_walk_link;
2297 			pio_next = zio_walk_parents(zio);
2298 
2299 			if ((pio->io_flags & ZIO_FLAG_GODFATHER) &&
2300 			    (zio->io_reexecute & ZIO_REEXECUTE_SUSPEND)) {
2301 				zio_remove_child(pio, zio, zl);
2302 				zio_notify_parent(pio, zio, ZIO_WAIT_DONE);
2303 			}
2304 		}
2305 
2306 		if ((pio = zio_unique_parent(zio)) != NULL) {
2307 			/*
2308 			 * We're not a root i/o, so there's nothing to do
2309 			 * but notify our parent.  Don't propagate errors
2310 			 * upward since we haven't permanently failed yet.
2311 			 */
2312 			ASSERT(!(zio->io_flags & ZIO_FLAG_GODFATHER));
2313 			zio->io_flags |= ZIO_FLAG_DONT_PROPAGATE;
2314 			zio_notify_parent(pio, zio, ZIO_WAIT_DONE);
2315 		} else if (zio->io_reexecute & ZIO_REEXECUTE_SUSPEND) {
2316 			/*
2317 			 * We'd fail again if we reexecuted now, so suspend
2318 			 * until conditions improve (e.g. device comes online).
2319 			 */
2320 			zio_suspend(spa, zio);
2321 		} else {
2322 			/*
2323 			 * Reexecution is potentially a huge amount of work.
2324 			 * Hand it off to the otherwise-unused claim taskq.
2325 			 */
2326 			(void) taskq_dispatch(
2327 			    spa->spa_zio_taskq[ZIO_TYPE_CLAIM][ZIO_TASKQ_ISSUE],
2328 			    (task_func_t *)zio_reexecute, zio, TQ_SLEEP);
2329 		}
2330 		return (ZIO_PIPELINE_STOP);
2331 	}
2332 
2333 	ASSERT(zio_walk_children(zio) == NULL);
2334 	ASSERT(zio->io_reexecute == 0);
2335 	ASSERT(zio->io_error == 0 || (zio->io_flags & ZIO_FLAG_CANFAIL));
2336 
2337 	/* Report any checksum errors, since the IO is complete */
2338 	while (zio->io_cksum_report != NULL) {
2339 		zio_cksum_report_t *rpt = zio->io_cksum_report;
2340 
2341 		zio->io_cksum_report = rpt->zcr_next;
2342 		rpt->zcr_next = NULL;
2343 
2344 		/* only pass in our data buffer if we've succeeded. */
2345 		rpt->zcr_finish(rpt,
2346 		    (zio->io_error == 0) ? zio->io_data : NULL);
2347 
2348 		zfs_ereport_free_checksum(rpt);
2349 	}
2350 
2351 	/*
2352 	 * It is the responsibility of the done callback to ensure that this
2353 	 * particular zio is no longer discoverable for adoption, and as
2354 	 * such, cannot acquire any new parents.
2355 	 */
2356 	if (zio->io_done)
2357 		zio->io_done(zio);
2358 
2359 	mutex_enter(&zio->io_lock);
2360 	zio->io_state[ZIO_WAIT_DONE] = 1;
2361 	mutex_exit(&zio->io_lock);
2362 
2363 	for (pio = zio_walk_parents(zio); pio != NULL; pio = pio_next) {
2364 		zio_link_t *zl = zio->io_walk_link;
2365 		pio_next = zio_walk_parents(zio);
2366 		zio_remove_child(pio, zio, zl);
2367 		zio_notify_parent(pio, zio, ZIO_WAIT_DONE);
2368 	}
2369 
2370 	if (zio->io_waiter != NULL) {
2371 		mutex_enter(&zio->io_lock);
2372 		zio->io_executor = NULL;
2373 		cv_broadcast(&zio->io_cv);
2374 		mutex_exit(&zio->io_lock);
2375 	} else {
2376 		zio_destroy(zio);
2377 	}
2378 
2379 	return (ZIO_PIPELINE_STOP);
2380 }
2381 
2382 /*
2383  * ==========================================================================
2384  * I/O pipeline definition
2385  * ==========================================================================
2386  */
2387 static zio_pipe_stage_t *zio_pipeline[ZIO_STAGES] = {
2388 	NULL,
2389 	zio_issue_async,
2390 	zio_read_bp_init,
2391 	zio_write_bp_init,
2392 	zio_checksum_generate,
2393 	zio_gang_assemble,
2394 	zio_gang_issue,
2395 	zio_dva_allocate,
2396 	zio_dva_free,
2397 	zio_dva_claim,
2398 	zio_ready,
2399 	zio_vdev_io_start,
2400 	zio_vdev_io_done,
2401 	zio_vdev_io_assess,
2402 	zio_checksum_verify,
2403 	zio_done
2404 };
2405