xref: /illumos-gate/usr/src/uts/common/fs/zfs/zil.c (revision cab3a55e)
1 /*
2  * CDDL HEADER START
3  *
4  * The contents of this file are subject to the terms of the
5  * Common Development and Distribution License (the "License").
6  * You may not use this file except in compliance with the License.
7  *
8  * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
9  * or http://www.opensolaris.org/os/licensing.
10  * See the License for the specific language governing permissions
11  * and limitations under the License.
12  *
13  * When distributing Covered Code, include this CDDL HEADER in each
14  * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
15  * If applicable, add the following below this CDDL HEADER, with the
16  * fields enclosed by brackets "[]" replaced with your own identifying
17  * information: Portions Copyright [yyyy] [name of copyright owner]
18  *
19  * CDDL HEADER END
20  */
21 /*
22  * Copyright (c) 2005, 2010, Oracle and/or its affiliates. All rights reserved.
23  * Copyright (c) 2011, 2018 by Delphix. All rights reserved.
24  * Copyright (c) 2014 Integros [integros.com]
25  */
26 
27 /* Portions Copyright 2010 Robert Milkowski */
28 
29 #include <sys/zfs_context.h>
30 #include <sys/spa.h>
31 #include <sys/spa_impl.h>
32 #include <sys/dmu.h>
33 #include <sys/zap.h>
34 #include <sys/arc.h>
35 #include <sys/stat.h>
36 #include <sys/resource.h>
37 #include <sys/zil.h>
38 #include <sys/zil_impl.h>
39 #include <sys/dsl_dataset.h>
40 #include <sys/vdev_impl.h>
41 #include <sys/dmu_tx.h>
42 #include <sys/dsl_pool.h>
43 #include <sys/abd.h>
44 
45 /*
46  * The ZFS Intent Log (ZIL) saves "transaction records" (itxs) of system
47  * calls that change the file system. Each itx has enough information to
48  * be able to replay them after a system crash, power loss, or
49  * equivalent failure mode. These are stored in memory until either:
50  *
51  *   1. they are committed to the pool by the DMU transaction group
52  *      (txg), at which point they can be discarded; or
53  *   2. they are committed to the on-disk ZIL for the dataset being
54  *      modified (e.g. due to an fsync, O_DSYNC, or other synchronous
55  *      requirement).
56  *
57  * In the event of a crash or power loss, the itxs contained by each
58  * dataset's on-disk ZIL will be replayed when that dataset is first
59  * instantianted (e.g. if the dataset is a normal fileystem, when it is
60  * first mounted).
61  *
62  * As hinted at above, there is one ZIL per dataset (both the in-memory
63  * representation, and the on-disk representation). The on-disk format
64  * consists of 3 parts:
65  *
66  * 	- a single, per-dataset, ZIL header; which points to a chain of
67  * 	- zero or more ZIL blocks; each of which contains
68  * 	- zero or more ZIL records
69  *
70  * A ZIL record holds the information necessary to replay a single
71  * system call transaction. A ZIL block can hold many ZIL records, and
72  * the blocks are chained together, similarly to a singly linked list.
73  *
74  * Each ZIL block contains a block pointer (blkptr_t) to the next ZIL
75  * block in the chain, and the ZIL header points to the first block in
76  * the chain.
77  *
78  * Note, there is not a fixed place in the pool to hold these ZIL
79  * blocks; they are dynamically allocated and freed as needed from the
80  * blocks available on the pool, though they can be preferentially
81  * allocated from a dedicated "log" vdev.
82  */
83 
84 /*
85  * This controls the amount of time that a ZIL block (lwb) will remain
86  * "open" when it isn't "full", and it has a thread waiting for it to be
87  * committed to stable storage. Please refer to the zil_commit_waiter()
88  * function (and the comments within it) for more details.
89  */
90 int zfs_commit_timeout_pct = 5;
91 
92 /*
93  * Disable intent logging replay.  This global ZIL switch affects all pools.
94  */
95 int zil_replay_disable = 0;
96 
97 /*
98  * Disable the DKIOCFLUSHWRITECACHE commands that are normally sent to
99  * the disk(s) by the ZIL after an LWB write has completed. Setting this
100  * will cause ZIL corruption on power loss if a volatile out-of-order
101  * write cache is enabled.
102  */
103 boolean_t zil_nocacheflush = B_FALSE;
104 
105 /*
106  * Limit SLOG write size per commit executed with synchronous priority.
107  * Any writes above that will be executed with lower (asynchronous) priority
108  * to limit potential SLOG device abuse by single active ZIL writer.
109  */
110 uint64_t zil_slog_bulk = 768 * 1024;
111 
112 static kmem_cache_t *zil_lwb_cache;
113 static kmem_cache_t *zil_zcw_cache;
114 
115 static void zil_async_to_sync(zilog_t *zilog, uint64_t foid);
116 
117 #define	LWB_EMPTY(lwb) ((BP_GET_LSIZE(&lwb->lwb_blk) - \
118     sizeof (zil_chain_t)) == (lwb->lwb_sz - lwb->lwb_nused))
119 
120 static int
121 zil_bp_compare(const void *x1, const void *x2)
122 {
123 	const dva_t *dva1 = &((zil_bp_node_t *)x1)->zn_dva;
124 	const dva_t *dva2 = &((zil_bp_node_t *)x2)->zn_dva;
125 
126 	if (DVA_GET_VDEV(dva1) < DVA_GET_VDEV(dva2))
127 		return (-1);
128 	if (DVA_GET_VDEV(dva1) > DVA_GET_VDEV(dva2))
129 		return (1);
130 
131 	if (DVA_GET_OFFSET(dva1) < DVA_GET_OFFSET(dva2))
132 		return (-1);
133 	if (DVA_GET_OFFSET(dva1) > DVA_GET_OFFSET(dva2))
134 		return (1);
135 
136 	return (0);
137 }
138 
139 static void
140 zil_bp_tree_init(zilog_t *zilog)
141 {
142 	avl_create(&zilog->zl_bp_tree, zil_bp_compare,
143 	    sizeof (zil_bp_node_t), offsetof(zil_bp_node_t, zn_node));
144 }
145 
146 static void
147 zil_bp_tree_fini(zilog_t *zilog)
148 {
149 	avl_tree_t *t = &zilog->zl_bp_tree;
150 	zil_bp_node_t *zn;
151 	void *cookie = NULL;
152 
153 	while ((zn = avl_destroy_nodes(t, &cookie)) != NULL)
154 		kmem_free(zn, sizeof (zil_bp_node_t));
155 
156 	avl_destroy(t);
157 }
158 
159 int
160 zil_bp_tree_add(zilog_t *zilog, const blkptr_t *bp)
161 {
162 	avl_tree_t *t = &zilog->zl_bp_tree;
163 	const dva_t *dva;
164 	zil_bp_node_t *zn;
165 	avl_index_t where;
166 
167 	if (BP_IS_EMBEDDED(bp))
168 		return (0);
169 
170 	dva = BP_IDENTITY(bp);
171 
172 	if (avl_find(t, dva, &where) != NULL)
173 		return (SET_ERROR(EEXIST));
174 
175 	zn = kmem_alloc(sizeof (zil_bp_node_t), KM_SLEEP);
176 	zn->zn_dva = *dva;
177 	avl_insert(t, zn, where);
178 
179 	return (0);
180 }
181 
182 static zil_header_t *
183 zil_header_in_syncing_context(zilog_t *zilog)
184 {
185 	return ((zil_header_t *)zilog->zl_header);
186 }
187 
188 static void
189 zil_init_log_chain(zilog_t *zilog, blkptr_t *bp)
190 {
191 	zio_cksum_t *zc = &bp->blk_cksum;
192 
193 	zc->zc_word[ZIL_ZC_GUID_0] = spa_get_random(-1ULL);
194 	zc->zc_word[ZIL_ZC_GUID_1] = spa_get_random(-1ULL);
195 	zc->zc_word[ZIL_ZC_OBJSET] = dmu_objset_id(zilog->zl_os);
196 	zc->zc_word[ZIL_ZC_SEQ] = 1ULL;
197 }
198 
199 /*
200  * Read a log block and make sure it's valid.
201  */
202 static int
203 zil_read_log_block(zilog_t *zilog, const blkptr_t *bp, blkptr_t *nbp, void *dst,
204     char **end)
205 {
206 	enum zio_flag zio_flags = ZIO_FLAG_CANFAIL;
207 	arc_flags_t aflags = ARC_FLAG_WAIT;
208 	arc_buf_t *abuf = NULL;
209 	zbookmark_phys_t zb;
210 	int error;
211 
212 	if (zilog->zl_header->zh_claim_txg == 0)
213 		zio_flags |= ZIO_FLAG_SPECULATIVE | ZIO_FLAG_SCRUB;
214 
215 	if (!(zilog->zl_header->zh_flags & ZIL_CLAIM_LR_SEQ_VALID))
216 		zio_flags |= ZIO_FLAG_SPECULATIVE;
217 
218 	SET_BOOKMARK(&zb, bp->blk_cksum.zc_word[ZIL_ZC_OBJSET],
219 	    ZB_ZIL_OBJECT, ZB_ZIL_LEVEL, bp->blk_cksum.zc_word[ZIL_ZC_SEQ]);
220 
221 	error = arc_read(NULL, zilog->zl_spa, bp, arc_getbuf_func, &abuf,
222 	    ZIO_PRIORITY_SYNC_READ, zio_flags, &aflags, &zb);
223 
224 	if (error == 0) {
225 		zio_cksum_t cksum = bp->blk_cksum;
226 
227 		/*
228 		 * Validate the checksummed log block.
229 		 *
230 		 * Sequence numbers should be... sequential.  The checksum
231 		 * verifier for the next block should be bp's checksum plus 1.
232 		 *
233 		 * Also check the log chain linkage and size used.
234 		 */
235 		cksum.zc_word[ZIL_ZC_SEQ]++;
236 
237 		if (BP_GET_CHECKSUM(bp) == ZIO_CHECKSUM_ZILOG2) {
238 			zil_chain_t *zilc = abuf->b_data;
239 			char *lr = (char *)(zilc + 1);
240 			uint64_t len = zilc->zc_nused - sizeof (zil_chain_t);
241 
242 			if (bcmp(&cksum, &zilc->zc_next_blk.blk_cksum,
243 			    sizeof (cksum)) || BP_IS_HOLE(&zilc->zc_next_blk)) {
244 				error = SET_ERROR(ECKSUM);
245 			} else {
246 				ASSERT3U(len, <=, SPA_OLD_MAXBLOCKSIZE);
247 				bcopy(lr, dst, len);
248 				*end = (char *)dst + len;
249 				*nbp = zilc->zc_next_blk;
250 			}
251 		} else {
252 			char *lr = abuf->b_data;
253 			uint64_t size = BP_GET_LSIZE(bp);
254 			zil_chain_t *zilc = (zil_chain_t *)(lr + size) - 1;
255 
256 			if (bcmp(&cksum, &zilc->zc_next_blk.blk_cksum,
257 			    sizeof (cksum)) || BP_IS_HOLE(&zilc->zc_next_blk) ||
258 			    (zilc->zc_nused > (size - sizeof (*zilc)))) {
259 				error = SET_ERROR(ECKSUM);
260 			} else {
261 				ASSERT3U(zilc->zc_nused, <=,
262 				    SPA_OLD_MAXBLOCKSIZE);
263 				bcopy(lr, dst, zilc->zc_nused);
264 				*end = (char *)dst + zilc->zc_nused;
265 				*nbp = zilc->zc_next_blk;
266 			}
267 		}
268 
269 		arc_buf_destroy(abuf, &abuf);
270 	}
271 
272 	return (error);
273 }
274 
275 /*
276  * Read a TX_WRITE log data block.
277  */
278 static int
279 zil_read_log_data(zilog_t *zilog, const lr_write_t *lr, void *wbuf)
280 {
281 	enum zio_flag zio_flags = ZIO_FLAG_CANFAIL;
282 	const blkptr_t *bp = &lr->lr_blkptr;
283 	arc_flags_t aflags = ARC_FLAG_WAIT;
284 	arc_buf_t *abuf = NULL;
285 	zbookmark_phys_t zb;
286 	int error;
287 
288 	if (BP_IS_HOLE(bp)) {
289 		if (wbuf != NULL)
290 			bzero(wbuf, MAX(BP_GET_LSIZE(bp), lr->lr_length));
291 		return (0);
292 	}
293 
294 	if (zilog->zl_header->zh_claim_txg == 0)
295 		zio_flags |= ZIO_FLAG_SPECULATIVE | ZIO_FLAG_SCRUB;
296 
297 	SET_BOOKMARK(&zb, dmu_objset_id(zilog->zl_os), lr->lr_foid,
298 	    ZB_ZIL_LEVEL, lr->lr_offset / BP_GET_LSIZE(bp));
299 
300 	error = arc_read(NULL, zilog->zl_spa, bp, arc_getbuf_func, &abuf,
301 	    ZIO_PRIORITY_SYNC_READ, zio_flags, &aflags, &zb);
302 
303 	if (error == 0) {
304 		if (wbuf != NULL)
305 			bcopy(abuf->b_data, wbuf, arc_buf_size(abuf));
306 		arc_buf_destroy(abuf, &abuf);
307 	}
308 
309 	return (error);
310 }
311 
312 /*
313  * Parse the intent log, and call parse_func for each valid record within.
314  */
315 int
316 zil_parse(zilog_t *zilog, zil_parse_blk_func_t *parse_blk_func,
317     zil_parse_lr_func_t *parse_lr_func, void *arg, uint64_t txg)
318 {
319 	const zil_header_t *zh = zilog->zl_header;
320 	boolean_t claimed = !!zh->zh_claim_txg;
321 	uint64_t claim_blk_seq = claimed ? zh->zh_claim_blk_seq : UINT64_MAX;
322 	uint64_t claim_lr_seq = claimed ? zh->zh_claim_lr_seq : UINT64_MAX;
323 	uint64_t max_blk_seq = 0;
324 	uint64_t max_lr_seq = 0;
325 	uint64_t blk_count = 0;
326 	uint64_t lr_count = 0;
327 	blkptr_t blk, next_blk;
328 	char *lrbuf, *lrp;
329 	int error = 0;
330 
331 	/*
332 	 * Old logs didn't record the maximum zh_claim_lr_seq.
333 	 */
334 	if (!(zh->zh_flags & ZIL_CLAIM_LR_SEQ_VALID))
335 		claim_lr_seq = UINT64_MAX;
336 
337 	/*
338 	 * Starting at the block pointed to by zh_log we read the log chain.
339 	 * For each block in the chain we strongly check that block to
340 	 * ensure its validity.  We stop when an invalid block is found.
341 	 * For each block pointer in the chain we call parse_blk_func().
342 	 * For each record in each valid block we call parse_lr_func().
343 	 * If the log has been claimed, stop if we encounter a sequence
344 	 * number greater than the highest claimed sequence number.
345 	 */
346 	lrbuf = zio_buf_alloc(SPA_OLD_MAXBLOCKSIZE);
347 	zil_bp_tree_init(zilog);
348 
349 	for (blk = zh->zh_log; !BP_IS_HOLE(&blk); blk = next_blk) {
350 		uint64_t blk_seq = blk.blk_cksum.zc_word[ZIL_ZC_SEQ];
351 		int reclen;
352 		char *end;
353 
354 		if (blk_seq > claim_blk_seq)
355 			break;
356 		if ((error = parse_blk_func(zilog, &blk, arg, txg)) != 0)
357 			break;
358 		ASSERT3U(max_blk_seq, <, blk_seq);
359 		max_blk_seq = blk_seq;
360 		blk_count++;
361 
362 		if (max_lr_seq == claim_lr_seq && max_blk_seq == claim_blk_seq)
363 			break;
364 
365 		error = zil_read_log_block(zilog, &blk, &next_blk, lrbuf, &end);
366 		if (error != 0)
367 			break;
368 
369 		for (lrp = lrbuf; lrp < end; lrp += reclen) {
370 			lr_t *lr = (lr_t *)lrp;
371 			reclen = lr->lrc_reclen;
372 			ASSERT3U(reclen, >=, sizeof (lr_t));
373 			if (lr->lrc_seq > claim_lr_seq)
374 				goto done;
375 			if ((error = parse_lr_func(zilog, lr, arg, txg)) != 0)
376 				goto done;
377 			ASSERT3U(max_lr_seq, <, lr->lrc_seq);
378 			max_lr_seq = lr->lrc_seq;
379 			lr_count++;
380 		}
381 	}
382 done:
383 	zilog->zl_parse_error = error;
384 	zilog->zl_parse_blk_seq = max_blk_seq;
385 	zilog->zl_parse_lr_seq = max_lr_seq;
386 	zilog->zl_parse_blk_count = blk_count;
387 	zilog->zl_parse_lr_count = lr_count;
388 
389 	ASSERT(!claimed || !(zh->zh_flags & ZIL_CLAIM_LR_SEQ_VALID) ||
390 	    (max_blk_seq == claim_blk_seq && max_lr_seq == claim_lr_seq));
391 
392 	zil_bp_tree_fini(zilog);
393 	zio_buf_free(lrbuf, SPA_OLD_MAXBLOCKSIZE);
394 
395 	return (error);
396 }
397 
398 /* ARGSUSED */
399 static int
400 zil_clear_log_block(zilog_t *zilog, blkptr_t *bp, void *tx, uint64_t first_txg)
401 {
402 	ASSERT(!BP_IS_HOLE(bp));
403 
404 	/*
405 	 * As we call this function from the context of a rewind to a
406 	 * checkpoint, each ZIL block whose txg is later than the txg
407 	 * that we rewind to is invalid. Thus, we return -1 so
408 	 * zil_parse() doesn't attempt to read it.
409 	 */
410 	if (bp->blk_birth >= first_txg)
411 		return (-1);
412 
413 	if (zil_bp_tree_add(zilog, bp) != 0)
414 		return (0);
415 
416 	zio_free(zilog->zl_spa, first_txg, bp);
417 	return (0);
418 }
419 
420 /* ARGSUSED */
421 static int
422 zil_noop_log_record(zilog_t *zilog, lr_t *lrc, void *tx, uint64_t first_txg)
423 {
424 	return (0);
425 }
426 
427 static int
428 zil_claim_log_block(zilog_t *zilog, blkptr_t *bp, void *tx, uint64_t first_txg)
429 {
430 	/*
431 	 * Claim log block if not already committed and not already claimed.
432 	 * If tx == NULL, just verify that the block is claimable.
433 	 */
434 	if (BP_IS_HOLE(bp) || bp->blk_birth < first_txg ||
435 	    zil_bp_tree_add(zilog, bp) != 0)
436 		return (0);
437 
438 	return (zio_wait(zio_claim(NULL, zilog->zl_spa,
439 	    tx == NULL ? 0 : first_txg, bp, spa_claim_notify, NULL,
440 	    ZIO_FLAG_CANFAIL | ZIO_FLAG_SPECULATIVE | ZIO_FLAG_SCRUB)));
441 }
442 
443 static int
444 zil_claim_log_record(zilog_t *zilog, lr_t *lrc, void *tx, uint64_t first_txg)
445 {
446 	lr_write_t *lr = (lr_write_t *)lrc;
447 	int error;
448 
449 	if (lrc->lrc_txtype != TX_WRITE)
450 		return (0);
451 
452 	/*
453 	 * If the block is not readable, don't claim it.  This can happen
454 	 * in normal operation when a log block is written to disk before
455 	 * some of the dmu_sync() blocks it points to.  In this case, the
456 	 * transaction cannot have been committed to anyone (we would have
457 	 * waited for all writes to be stable first), so it is semantically
458 	 * correct to declare this the end of the log.
459 	 */
460 	if (lr->lr_blkptr.blk_birth >= first_txg &&
461 	    (error = zil_read_log_data(zilog, lr, NULL)) != 0)
462 		return (error);
463 	return (zil_claim_log_block(zilog, &lr->lr_blkptr, tx, first_txg));
464 }
465 
466 /* ARGSUSED */
467 static int
468 zil_free_log_block(zilog_t *zilog, blkptr_t *bp, void *tx, uint64_t claim_txg)
469 {
470 	zio_free(zilog->zl_spa, dmu_tx_get_txg(tx), bp);
471 
472 	return (0);
473 }
474 
475 static int
476 zil_free_log_record(zilog_t *zilog, lr_t *lrc, void *tx, uint64_t claim_txg)
477 {
478 	lr_write_t *lr = (lr_write_t *)lrc;
479 	blkptr_t *bp = &lr->lr_blkptr;
480 
481 	/*
482 	 * If we previously claimed it, we need to free it.
483 	 */
484 	if (claim_txg != 0 && lrc->lrc_txtype == TX_WRITE &&
485 	    bp->blk_birth >= claim_txg && zil_bp_tree_add(zilog, bp) == 0 &&
486 	    !BP_IS_HOLE(bp))
487 		zio_free(zilog->zl_spa, dmu_tx_get_txg(tx), bp);
488 
489 	return (0);
490 }
491 
492 static int
493 zil_lwb_vdev_compare(const void *x1, const void *x2)
494 {
495 	const uint64_t v1 = ((zil_vdev_node_t *)x1)->zv_vdev;
496 	const uint64_t v2 = ((zil_vdev_node_t *)x2)->zv_vdev;
497 
498 	if (v1 < v2)
499 		return (-1);
500 	if (v1 > v2)
501 		return (1);
502 
503 	return (0);
504 }
505 
506 static lwb_t *
507 zil_alloc_lwb(zilog_t *zilog, blkptr_t *bp, boolean_t slog, uint64_t txg)
508 {
509 	lwb_t *lwb;
510 
511 	lwb = kmem_cache_alloc(zil_lwb_cache, KM_SLEEP);
512 	lwb->lwb_zilog = zilog;
513 	lwb->lwb_blk = *bp;
514 	lwb->lwb_slog = slog;
515 	lwb->lwb_state = LWB_STATE_CLOSED;
516 	lwb->lwb_buf = zio_buf_alloc(BP_GET_LSIZE(bp));
517 	lwb->lwb_max_txg = txg;
518 	lwb->lwb_write_zio = NULL;
519 	lwb->lwb_root_zio = NULL;
520 	lwb->lwb_tx = NULL;
521 	lwb->lwb_issued_timestamp = 0;
522 	if (BP_GET_CHECKSUM(bp) == ZIO_CHECKSUM_ZILOG2) {
523 		lwb->lwb_nused = sizeof (zil_chain_t);
524 		lwb->lwb_sz = BP_GET_LSIZE(bp);
525 	} else {
526 		lwb->lwb_nused = 0;
527 		lwb->lwb_sz = BP_GET_LSIZE(bp) - sizeof (zil_chain_t);
528 	}
529 
530 	mutex_enter(&zilog->zl_lock);
531 	list_insert_tail(&zilog->zl_lwb_list, lwb);
532 	mutex_exit(&zilog->zl_lock);
533 
534 	ASSERT(!MUTEX_HELD(&lwb->lwb_vdev_lock));
535 	ASSERT(avl_is_empty(&lwb->lwb_vdev_tree));
536 	VERIFY(list_is_empty(&lwb->lwb_waiters));
537 
538 	return (lwb);
539 }
540 
541 static void
542 zil_free_lwb(zilog_t *zilog, lwb_t *lwb)
543 {
544 	ASSERT(MUTEX_HELD(&zilog->zl_lock));
545 	ASSERT(!MUTEX_HELD(&lwb->lwb_vdev_lock));
546 	VERIFY(list_is_empty(&lwb->lwb_waiters));
547 	ASSERT(avl_is_empty(&lwb->lwb_vdev_tree));
548 	ASSERT3P(lwb->lwb_write_zio, ==, NULL);
549 	ASSERT3P(lwb->lwb_root_zio, ==, NULL);
550 	ASSERT3U(lwb->lwb_max_txg, <=, spa_syncing_txg(zilog->zl_spa));
551 	ASSERT(lwb->lwb_state == LWB_STATE_CLOSED ||
552 	    lwb->lwb_state == LWB_STATE_FLUSH_DONE);
553 
554 	/*
555 	 * Clear the zilog's field to indicate this lwb is no longer
556 	 * valid, and prevent use-after-free errors.
557 	 */
558 	if (zilog->zl_last_lwb_opened == lwb)
559 		zilog->zl_last_lwb_opened = NULL;
560 
561 	kmem_cache_free(zil_lwb_cache, lwb);
562 }
563 
564 /*
565  * Called when we create in-memory log transactions so that we know
566  * to cleanup the itxs at the end of spa_sync().
567  */
568 void
569 zilog_dirty(zilog_t *zilog, uint64_t txg)
570 {
571 	dsl_pool_t *dp = zilog->zl_dmu_pool;
572 	dsl_dataset_t *ds = dmu_objset_ds(zilog->zl_os);
573 
574 	ASSERT(spa_writeable(zilog->zl_spa));
575 
576 	if (ds->ds_is_snapshot)
577 		panic("dirtying snapshot!");
578 
579 	if (txg_list_add(&dp->dp_dirty_zilogs, zilog, txg)) {
580 		/* up the hold count until we can be written out */
581 		dmu_buf_add_ref(ds->ds_dbuf, zilog);
582 
583 		zilog->zl_dirty_max_txg = MAX(txg, zilog->zl_dirty_max_txg);
584 	}
585 }
586 
587 /*
588  * Determine if the zil is dirty in the specified txg. Callers wanting to
589  * ensure that the dirty state does not change must hold the itxg_lock for
590  * the specified txg. Holding the lock will ensure that the zil cannot be
591  * dirtied (zil_itx_assign) or cleaned (zil_clean) while we check its current
592  * state.
593  */
594 boolean_t
595 zilog_is_dirty_in_txg(zilog_t *zilog, uint64_t txg)
596 {
597 	dsl_pool_t *dp = zilog->zl_dmu_pool;
598 
599 	if (txg_list_member(&dp->dp_dirty_zilogs, zilog, txg & TXG_MASK))
600 		return (B_TRUE);
601 	return (B_FALSE);
602 }
603 
604 /*
605  * Determine if the zil is dirty. The zil is considered dirty if it has
606  * any pending itx records that have not been cleaned by zil_clean().
607  */
608 boolean_t
609 zilog_is_dirty(zilog_t *zilog)
610 {
611 	dsl_pool_t *dp = zilog->zl_dmu_pool;
612 
613 	for (int t = 0; t < TXG_SIZE; t++) {
614 		if (txg_list_member(&dp->dp_dirty_zilogs, zilog, t))
615 			return (B_TRUE);
616 	}
617 	return (B_FALSE);
618 }
619 
620 /*
621  * Create an on-disk intent log.
622  */
623 static lwb_t *
624 zil_create(zilog_t *zilog)
625 {
626 	const zil_header_t *zh = zilog->zl_header;
627 	lwb_t *lwb = NULL;
628 	uint64_t txg = 0;
629 	dmu_tx_t *tx = NULL;
630 	blkptr_t blk;
631 	int error = 0;
632 	boolean_t slog = FALSE;
633 
634 	/*
635 	 * Wait for any previous destroy to complete.
636 	 */
637 	txg_wait_synced(zilog->zl_dmu_pool, zilog->zl_destroy_txg);
638 
639 	ASSERT(zh->zh_claim_txg == 0);
640 	ASSERT(zh->zh_replay_seq == 0);
641 
642 	blk = zh->zh_log;
643 
644 	/*
645 	 * Allocate an initial log block if:
646 	 *    - there isn't one already
647 	 *    - the existing block is the wrong endianess
648 	 */
649 	if (BP_IS_HOLE(&blk) || BP_SHOULD_BYTESWAP(&blk)) {
650 		tx = dmu_tx_create(zilog->zl_os);
651 		VERIFY0(dmu_tx_assign(tx, TXG_WAIT));
652 		dsl_dataset_dirty(dmu_objset_ds(zilog->zl_os), tx);
653 		txg = dmu_tx_get_txg(tx);
654 
655 		if (!BP_IS_HOLE(&blk)) {
656 			zio_free(zilog->zl_spa, txg, &blk);
657 			BP_ZERO(&blk);
658 		}
659 
660 		error = zio_alloc_zil(zilog->zl_spa,
661 		    zilog->zl_os->os_dsl_dataset->ds_object, txg, &blk, NULL,
662 		    ZIL_MIN_BLKSZ, &slog);
663 
664 		if (error == 0)
665 			zil_init_log_chain(zilog, &blk);
666 	}
667 
668 	/*
669 	 * Allocate a log write block (lwb) for the first log block.
670 	 */
671 	if (error == 0)
672 		lwb = zil_alloc_lwb(zilog, &blk, slog, txg);
673 
674 	/*
675 	 * If we just allocated the first log block, commit our transaction
676 	 * and wait for zil_sync() to stuff the block poiner into zh_log.
677 	 * (zh is part of the MOS, so we cannot modify it in open context.)
678 	 */
679 	if (tx != NULL) {
680 		dmu_tx_commit(tx);
681 		txg_wait_synced(zilog->zl_dmu_pool, txg);
682 	}
683 
684 	ASSERT(bcmp(&blk, &zh->zh_log, sizeof (blk)) == 0);
685 
686 	return (lwb);
687 }
688 
689 /*
690  * In one tx, free all log blocks and clear the log header. If keep_first
691  * is set, then we're replaying a log with no content. We want to keep the
692  * first block, however, so that the first synchronous transaction doesn't
693  * require a txg_wait_synced() in zil_create(). We don't need to
694  * txg_wait_synced() here either when keep_first is set, because both
695  * zil_create() and zil_destroy() will wait for any in-progress destroys
696  * to complete.
697  */
698 void
699 zil_destroy(zilog_t *zilog, boolean_t keep_first)
700 {
701 	const zil_header_t *zh = zilog->zl_header;
702 	lwb_t *lwb;
703 	dmu_tx_t *tx;
704 	uint64_t txg;
705 
706 	/*
707 	 * Wait for any previous destroy to complete.
708 	 */
709 	txg_wait_synced(zilog->zl_dmu_pool, zilog->zl_destroy_txg);
710 
711 	zilog->zl_old_header = *zh;		/* debugging aid */
712 
713 	if (BP_IS_HOLE(&zh->zh_log))
714 		return;
715 
716 	tx = dmu_tx_create(zilog->zl_os);
717 	VERIFY0(dmu_tx_assign(tx, TXG_WAIT));
718 	dsl_dataset_dirty(dmu_objset_ds(zilog->zl_os), tx);
719 	txg = dmu_tx_get_txg(tx);
720 
721 	mutex_enter(&zilog->zl_lock);
722 
723 	ASSERT3U(zilog->zl_destroy_txg, <, txg);
724 	zilog->zl_destroy_txg = txg;
725 	zilog->zl_keep_first = keep_first;
726 
727 	if (!list_is_empty(&zilog->zl_lwb_list)) {
728 		ASSERT(zh->zh_claim_txg == 0);
729 		VERIFY(!keep_first);
730 		while ((lwb = list_head(&zilog->zl_lwb_list)) != NULL) {
731 			list_remove(&zilog->zl_lwb_list, lwb);
732 			if (lwb->lwb_buf != NULL)
733 				zio_buf_free(lwb->lwb_buf, lwb->lwb_sz);
734 			zio_free(zilog->zl_spa, txg, &lwb->lwb_blk);
735 			zil_free_lwb(zilog, lwb);
736 		}
737 	} else if (!keep_first) {
738 		zil_destroy_sync(zilog, tx);
739 	}
740 	mutex_exit(&zilog->zl_lock);
741 
742 	dmu_tx_commit(tx);
743 }
744 
745 void
746 zil_destroy_sync(zilog_t *zilog, dmu_tx_t *tx)
747 {
748 	ASSERT(list_is_empty(&zilog->zl_lwb_list));
749 	(void) zil_parse(zilog, zil_free_log_block,
750 	    zil_free_log_record, tx, zilog->zl_header->zh_claim_txg);
751 }
752 
753 int
754 zil_claim(dsl_pool_t *dp, dsl_dataset_t *ds, void *txarg)
755 {
756 	dmu_tx_t *tx = txarg;
757 	zilog_t *zilog;
758 	uint64_t first_txg;
759 	zil_header_t *zh;
760 	objset_t *os;
761 	int error;
762 
763 	error = dmu_objset_own_obj(dp, ds->ds_object,
764 	    DMU_OST_ANY, B_FALSE, FTAG, &os);
765 	if (error != 0) {
766 		/*
767 		 * EBUSY indicates that the objset is inconsistent, in which
768 		 * case it can not have a ZIL.
769 		 */
770 		if (error != EBUSY) {
771 			cmn_err(CE_WARN, "can't open objset for %llu, error %u",
772 			    (unsigned long long)ds->ds_object, error);
773 		}
774 		return (0);
775 	}
776 
777 	zilog = dmu_objset_zil(os);
778 	zh = zil_header_in_syncing_context(zilog);
779 	ASSERT3U(tx->tx_txg, ==, spa_first_txg(zilog->zl_spa));
780 	first_txg = spa_min_claim_txg(zilog->zl_spa);
781 
782 	/*
783 	 * If the spa_log_state is not set to be cleared, check whether
784 	 * the current uberblock is a checkpoint one and if the current
785 	 * header has been claimed before moving on.
786 	 *
787 	 * If the current uberblock is a checkpointed uberblock then
788 	 * one of the following scenarios took place:
789 	 *
790 	 * 1] We are currently rewinding to the checkpoint of the pool.
791 	 * 2] We crashed in the middle of a checkpoint rewind but we
792 	 *    did manage to write the checkpointed uberblock to the
793 	 *    vdev labels, so when we tried to import the pool again
794 	 *    the checkpointed uberblock was selected from the import
795 	 *    procedure.
796 	 *
797 	 * In both cases we want to zero out all the ZIL blocks, except
798 	 * the ones that have been claimed at the time of the checkpoint
799 	 * (their zh_claim_txg != 0). The reason is that these blocks
800 	 * may be corrupted since we may have reused their locations on
801 	 * disk after we took the checkpoint.
802 	 *
803 	 * We could try to set spa_log_state to SPA_LOG_CLEAR earlier
804 	 * when we first figure out whether the current uberblock is
805 	 * checkpointed or not. Unfortunately, that would discard all
806 	 * the logs, including the ones that are claimed, and we would
807 	 * leak space.
808 	 */
809 	if (spa_get_log_state(zilog->zl_spa) == SPA_LOG_CLEAR ||
810 	    (zilog->zl_spa->spa_uberblock.ub_checkpoint_txg != 0 &&
811 	    zh->zh_claim_txg == 0)) {
812 		if (!BP_IS_HOLE(&zh->zh_log)) {
813 			(void) zil_parse(zilog, zil_clear_log_block,
814 			    zil_noop_log_record, tx, first_txg);
815 		}
816 		BP_ZERO(&zh->zh_log);
817 		dsl_dataset_dirty(dmu_objset_ds(os), tx);
818 		dmu_objset_disown(os, FTAG);
819 		return (0);
820 	}
821 
822 	/*
823 	 * If we are not rewinding and opening the pool normally, then
824 	 * the min_claim_txg should be equal to the first txg of the pool.
825 	 */
826 	ASSERT3U(first_txg, ==, spa_first_txg(zilog->zl_spa));
827 
828 	/*
829 	 * Claim all log blocks if we haven't already done so, and remember
830 	 * the highest claimed sequence number.  This ensures that if we can
831 	 * read only part of the log now (e.g. due to a missing device),
832 	 * but we can read the entire log later, we will not try to replay
833 	 * or destroy beyond the last block we successfully claimed.
834 	 */
835 	ASSERT3U(zh->zh_claim_txg, <=, first_txg);
836 	if (zh->zh_claim_txg == 0 && !BP_IS_HOLE(&zh->zh_log)) {
837 		(void) zil_parse(zilog, zil_claim_log_block,
838 		    zil_claim_log_record, tx, first_txg);
839 		zh->zh_claim_txg = first_txg;
840 		zh->zh_claim_blk_seq = zilog->zl_parse_blk_seq;
841 		zh->zh_claim_lr_seq = zilog->zl_parse_lr_seq;
842 		if (zilog->zl_parse_lr_count || zilog->zl_parse_blk_count > 1)
843 			zh->zh_flags |= ZIL_REPLAY_NEEDED;
844 		zh->zh_flags |= ZIL_CLAIM_LR_SEQ_VALID;
845 		dsl_dataset_dirty(dmu_objset_ds(os), tx);
846 	}
847 
848 	ASSERT3U(first_txg, ==, (spa_last_synced_txg(zilog->zl_spa) + 1));
849 	dmu_objset_disown(os, FTAG);
850 	return (0);
851 }
852 
853 /*
854  * Check the log by walking the log chain.
855  * Checksum errors are ok as they indicate the end of the chain.
856  * Any other error (no device or read failure) returns an error.
857  */
858 /* ARGSUSED */
859 int
860 zil_check_log_chain(dsl_pool_t *dp, dsl_dataset_t *ds, void *tx)
861 {
862 	zilog_t *zilog;
863 	objset_t *os;
864 	blkptr_t *bp;
865 	int error;
866 
867 	ASSERT(tx == NULL);
868 
869 	error = dmu_objset_from_ds(ds, &os);
870 	if (error != 0) {
871 		cmn_err(CE_WARN, "can't open objset %llu, error %d",
872 		    (unsigned long long)ds->ds_object, error);
873 		return (0);
874 	}
875 
876 	zilog = dmu_objset_zil(os);
877 	bp = (blkptr_t *)&zilog->zl_header->zh_log;
878 
879 	if (!BP_IS_HOLE(bp)) {
880 		vdev_t *vd;
881 		boolean_t valid = B_TRUE;
882 
883 		/*
884 		 * Check the first block and determine if it's on a log device
885 		 * which may have been removed or faulted prior to loading this
886 		 * pool.  If so, there's no point in checking the rest of the
887 		 * log as its content should have already been synced to the
888 		 * pool.
889 		 */
890 		spa_config_enter(os->os_spa, SCL_STATE, FTAG, RW_READER);
891 		vd = vdev_lookup_top(os->os_spa, DVA_GET_VDEV(&bp->blk_dva[0]));
892 		if (vd->vdev_islog && vdev_is_dead(vd))
893 			valid = vdev_log_state_valid(vd);
894 		spa_config_exit(os->os_spa, SCL_STATE, FTAG);
895 
896 		if (!valid)
897 			return (0);
898 
899 		/*
900 		 * Check whether the current uberblock is checkpointed (e.g.
901 		 * we are rewinding) and whether the current header has been
902 		 * claimed or not. If it hasn't then skip verifying it. We
903 		 * do this because its ZIL blocks may be part of the pool's
904 		 * state before the rewind, which is no longer valid.
905 		 */
906 		zil_header_t *zh = zil_header_in_syncing_context(zilog);
907 		if (zilog->zl_spa->spa_uberblock.ub_checkpoint_txg != 0 &&
908 		    zh->zh_claim_txg == 0)
909 			return (0);
910 	}
911 
912 	/*
913 	 * Because tx == NULL, zil_claim_log_block() will not actually claim
914 	 * any blocks, but just determine whether it is possible to do so.
915 	 * In addition to checking the log chain, zil_claim_log_block()
916 	 * will invoke zio_claim() with a done func of spa_claim_notify(),
917 	 * which will update spa_max_claim_txg.  See spa_load() for details.
918 	 */
919 	error = zil_parse(zilog, zil_claim_log_block, zil_claim_log_record, tx,
920 	    zilog->zl_header->zh_claim_txg ? -1ULL :
921 	    spa_min_claim_txg(os->os_spa));
922 
923 	return ((error == ECKSUM || error == ENOENT) ? 0 : error);
924 }
925 
926 /*
927  * When an itx is "skipped", this function is used to properly mark the
928  * waiter as "done, and signal any thread(s) waiting on it. An itx can
929  * be skipped (and not committed to an lwb) for a variety of reasons,
930  * one of them being that the itx was committed via spa_sync(), prior to
931  * it being committed to an lwb; this can happen if a thread calling
932  * zil_commit() is racing with spa_sync().
933  */
934 static void
935 zil_commit_waiter_skip(zil_commit_waiter_t *zcw)
936 {
937 	mutex_enter(&zcw->zcw_lock);
938 	ASSERT3B(zcw->zcw_done, ==, B_FALSE);
939 	zcw->zcw_done = B_TRUE;
940 	cv_broadcast(&zcw->zcw_cv);
941 	mutex_exit(&zcw->zcw_lock);
942 }
943 
944 /*
945  * This function is used when the given waiter is to be linked into an
946  * lwb's "lwb_waiter" list; i.e. when the itx is committed to the lwb.
947  * At this point, the waiter will no longer be referenced by the itx,
948  * and instead, will be referenced by the lwb.
949  */
950 static void
951 zil_commit_waiter_link_lwb(zil_commit_waiter_t *zcw, lwb_t *lwb)
952 {
953 	/*
954 	 * The lwb_waiters field of the lwb is protected by the zilog's
955 	 * zl_lock, thus it must be held when calling this function.
956 	 */
957 	ASSERT(MUTEX_HELD(&lwb->lwb_zilog->zl_lock));
958 
959 	mutex_enter(&zcw->zcw_lock);
960 	ASSERT(!list_link_active(&zcw->zcw_node));
961 	ASSERT3P(zcw->zcw_lwb, ==, NULL);
962 	ASSERT3P(lwb, !=, NULL);
963 	ASSERT(lwb->lwb_state == LWB_STATE_OPENED ||
964 	    lwb->lwb_state == LWB_STATE_ISSUED ||
965 	    lwb->lwb_state == LWB_STATE_WRITE_DONE);
966 
967 	list_insert_tail(&lwb->lwb_waiters, zcw);
968 	zcw->zcw_lwb = lwb;
969 	mutex_exit(&zcw->zcw_lock);
970 }
971 
972 /*
973  * This function is used when zio_alloc_zil() fails to allocate a ZIL
974  * block, and the given waiter must be linked to the "nolwb waiters"
975  * list inside of zil_process_commit_list().
976  */
977 static void
978 zil_commit_waiter_link_nolwb(zil_commit_waiter_t *zcw, list_t *nolwb)
979 {
980 	mutex_enter(&zcw->zcw_lock);
981 	ASSERT(!list_link_active(&zcw->zcw_node));
982 	ASSERT3P(zcw->zcw_lwb, ==, NULL);
983 	list_insert_tail(nolwb, zcw);
984 	mutex_exit(&zcw->zcw_lock);
985 }
986 
987 void
988 zil_lwb_add_block(lwb_t *lwb, const blkptr_t *bp)
989 {
990 	avl_tree_t *t = &lwb->lwb_vdev_tree;
991 	avl_index_t where;
992 	zil_vdev_node_t *zv, zvsearch;
993 	int ndvas = BP_GET_NDVAS(bp);
994 	int i;
995 
996 	if (zil_nocacheflush)
997 		return;
998 
999 	mutex_enter(&lwb->lwb_vdev_lock);
1000 	for (i = 0; i < ndvas; i++) {
1001 		zvsearch.zv_vdev = DVA_GET_VDEV(&bp->blk_dva[i]);
1002 		if (avl_find(t, &zvsearch, &where) == NULL) {
1003 			zv = kmem_alloc(sizeof (*zv), KM_SLEEP);
1004 			zv->zv_vdev = zvsearch.zv_vdev;
1005 			avl_insert(t, zv, where);
1006 		}
1007 	}
1008 	mutex_exit(&lwb->lwb_vdev_lock);
1009 }
1010 
1011 static void
1012 zil_lwb_flush_defer(lwb_t *lwb, lwb_t *nlwb)
1013 {
1014 	avl_tree_t *src = &lwb->lwb_vdev_tree;
1015 	avl_tree_t *dst = &nlwb->lwb_vdev_tree;
1016 	void *cookie = NULL;
1017 	zil_vdev_node_t *zv;
1018 
1019 	ASSERT3S(lwb->lwb_state, ==, LWB_STATE_WRITE_DONE);
1020 	ASSERT3S(nlwb->lwb_state, !=, LWB_STATE_WRITE_DONE);
1021 	ASSERT3S(nlwb->lwb_state, !=, LWB_STATE_FLUSH_DONE);
1022 
1023 	/*
1024 	 * While 'lwb' is at a point in its lifetime where lwb_vdev_tree does
1025 	 * not need the protection of lwb_vdev_lock (it will only be modified
1026 	 * while holding zilog->zl_lock) as its writes and those of its
1027 	 * children have all completed.  The younger 'nlwb' may be waiting on
1028 	 * future writes to additional vdevs.
1029 	 */
1030 	mutex_enter(&nlwb->lwb_vdev_lock);
1031 	/*
1032 	 * Tear down the 'lwb' vdev tree, ensuring that entries which do not
1033 	 * exist in 'nlwb' are moved to it, freeing any would-be duplicates.
1034 	 */
1035 	while ((zv = avl_destroy_nodes(src, &cookie)) != NULL) {
1036 		avl_index_t where;
1037 
1038 		if (avl_find(dst, zv, &where) == NULL) {
1039 			avl_insert(dst, zv, where);
1040 		} else {
1041 			kmem_free(zv, sizeof (*zv));
1042 		}
1043 	}
1044 	mutex_exit(&nlwb->lwb_vdev_lock);
1045 }
1046 
1047 void
1048 zil_lwb_add_txg(lwb_t *lwb, uint64_t txg)
1049 {
1050 	lwb->lwb_max_txg = MAX(lwb->lwb_max_txg, txg);
1051 }
1052 
1053 /*
1054  * This function is a called after all vdevs associated with a given lwb
1055  * write have completed their DKIOCFLUSHWRITECACHE command; or as soon
1056  * as the lwb write completes, if "zil_nocacheflush" is set. Further,
1057  * all "previous" lwb's will have completed before this function is
1058  * called; i.e. this function is called for all previous lwbs before
1059  * it's called for "this" lwb (enforced via zio the dependencies
1060  * configured in zil_lwb_set_zio_dependency()).
1061  *
1062  * The intention is for this function to be called as soon as the
1063  * contents of an lwb are considered "stable" on disk, and will survive
1064  * any sudden loss of power. At this point, any threads waiting for the
1065  * lwb to reach this state are signalled, and the "waiter" structures
1066  * are marked "done".
1067  */
1068 static void
1069 zil_lwb_flush_vdevs_done(zio_t *zio)
1070 {
1071 	lwb_t *lwb = zio->io_private;
1072 	zilog_t *zilog = lwb->lwb_zilog;
1073 	dmu_tx_t *tx = lwb->lwb_tx;
1074 	zil_commit_waiter_t *zcw;
1075 
1076 	spa_config_exit(zilog->zl_spa, SCL_STATE, lwb);
1077 
1078 	zio_buf_free(lwb->lwb_buf, lwb->lwb_sz);
1079 
1080 	mutex_enter(&zilog->zl_lock);
1081 
1082 	/*
1083 	 * Ensure the lwb buffer pointer is cleared before releasing the
1084 	 * txg. If we have had an allocation failure and the txg is
1085 	 * waiting to sync then we want zil_sync() to remove the lwb so
1086 	 * that it's not picked up as the next new one in
1087 	 * zil_process_commit_list(). zil_sync() will only remove the
1088 	 * lwb if lwb_buf is null.
1089 	 */
1090 	lwb->lwb_buf = NULL;
1091 	lwb->lwb_tx = NULL;
1092 
1093 	ASSERT3U(lwb->lwb_issued_timestamp, >, 0);
1094 	zilog->zl_last_lwb_latency = gethrtime() - lwb->lwb_issued_timestamp;
1095 
1096 	lwb->lwb_root_zio = NULL;
1097 
1098 	ASSERT3S(lwb->lwb_state, ==, LWB_STATE_WRITE_DONE);
1099 	lwb->lwb_state = LWB_STATE_FLUSH_DONE;
1100 
1101 	if (zilog->zl_last_lwb_opened == lwb) {
1102 		/*
1103 		 * Remember the highest committed log sequence number
1104 		 * for ztest. We only update this value when all the log
1105 		 * writes succeeded, because ztest wants to ASSERT that
1106 		 * it got the whole log chain.
1107 		 */
1108 		zilog->zl_commit_lr_seq = zilog->zl_lr_seq;
1109 	}
1110 
1111 	while ((zcw = list_head(&lwb->lwb_waiters)) != NULL) {
1112 		mutex_enter(&zcw->zcw_lock);
1113 
1114 		ASSERT(list_link_active(&zcw->zcw_node));
1115 		list_remove(&lwb->lwb_waiters, zcw);
1116 
1117 		ASSERT3P(zcw->zcw_lwb, ==, lwb);
1118 		zcw->zcw_lwb = NULL;
1119 
1120 		zcw->zcw_zio_error = zio->io_error;
1121 
1122 		ASSERT3B(zcw->zcw_done, ==, B_FALSE);
1123 		zcw->zcw_done = B_TRUE;
1124 		cv_broadcast(&zcw->zcw_cv);
1125 
1126 		mutex_exit(&zcw->zcw_lock);
1127 	}
1128 
1129 	mutex_exit(&zilog->zl_lock);
1130 
1131 	/*
1132 	 * Now that we've written this log block, we have a stable pointer
1133 	 * to the next block in the chain, so it's OK to let the txg in
1134 	 * which we allocated the next block sync.
1135 	 */
1136 	dmu_tx_commit(tx);
1137 }
1138 
1139 /*
1140  * This is called when an lwb's write zio completes. The callback's
1141  * purpose is to issue the DKIOCFLUSHWRITECACHE commands for the vdevs
1142  * in the lwb's lwb_vdev_tree. The tree will contain the vdevs involved
1143  * in writing out this specific lwb's data, and in the case that cache
1144  * flushes have been deferred, vdevs involved in writing the data for
1145  * previous lwbs. The writes corresponding to all the vdevs in the
1146  * lwb_vdev_tree will have completed by the time this is called, due to
1147  * the zio dependencies configured in zil_lwb_set_zio_dependency(),
1148  * which takes deferred flushes into account. The lwb will be "done"
1149  * once zil_lwb_flush_vdevs_done() is called, which occurs in the zio
1150  * completion callback for the lwb's root zio.
1151  */
1152 static void
1153 zil_lwb_write_done(zio_t *zio)
1154 {
1155 	lwb_t *lwb = zio->io_private;
1156 	spa_t *spa = zio->io_spa;
1157 	zilog_t *zilog = lwb->lwb_zilog;
1158 	avl_tree_t *t = &lwb->lwb_vdev_tree;
1159 	void *cookie = NULL;
1160 	zil_vdev_node_t *zv;
1161 	lwb_t *nlwb;
1162 
1163 	ASSERT3S(spa_config_held(spa, SCL_STATE, RW_READER), !=, 0);
1164 
1165 	ASSERT(BP_GET_COMPRESS(zio->io_bp) == ZIO_COMPRESS_OFF);
1166 	ASSERT(BP_GET_TYPE(zio->io_bp) == DMU_OT_INTENT_LOG);
1167 	ASSERT(BP_GET_LEVEL(zio->io_bp) == 0);
1168 	ASSERT(BP_GET_BYTEORDER(zio->io_bp) == ZFS_HOST_BYTEORDER);
1169 	ASSERT(!BP_IS_GANG(zio->io_bp));
1170 	ASSERT(!BP_IS_HOLE(zio->io_bp));
1171 	ASSERT(BP_GET_FILL(zio->io_bp) == 0);
1172 
1173 	abd_put(zio->io_abd);
1174 
1175 	mutex_enter(&zilog->zl_lock);
1176 	ASSERT3S(lwb->lwb_state, ==, LWB_STATE_ISSUED);
1177 	lwb->lwb_state = LWB_STATE_WRITE_DONE;
1178 	lwb->lwb_write_zio = NULL;
1179 	nlwb = list_next(&zilog->zl_lwb_list, lwb);
1180 	mutex_exit(&zilog->zl_lock);
1181 
1182 	if (avl_numnodes(t) == 0)
1183 		return;
1184 
1185 	/*
1186 	 * If there was an IO error, we're not going to call zio_flush()
1187 	 * on these vdevs, so we simply empty the tree and free the
1188 	 * nodes. We avoid calling zio_flush() since there isn't any
1189 	 * good reason for doing so, after the lwb block failed to be
1190 	 * written out.
1191 	 */
1192 	if (zio->io_error != 0) {
1193 		while ((zv = avl_destroy_nodes(t, &cookie)) != NULL)
1194 			kmem_free(zv, sizeof (*zv));
1195 		return;
1196 	}
1197 
1198 	/*
1199 	 * If this lwb does not have any threads waiting for it to
1200 	 * complete, we want to defer issuing the DKIOCFLUSHWRITECACHE
1201 	 * command to the vdevs written to by "this" lwb, and instead
1202 	 * rely on the "next" lwb to handle the DKIOCFLUSHWRITECACHE
1203 	 * command for those vdevs. Thus, we merge the vdev tree of
1204 	 * "this" lwb with the vdev tree of the "next" lwb in the list,
1205 	 * and assume the "next" lwb will handle flushing the vdevs (or
1206 	 * deferring the flush(s) again).
1207 	 *
1208 	 * This is a useful performance optimization, especially for
1209 	 * workloads with lots of async write activity and few sync
1210 	 * write and/or fsync activity, as it has the potential to
1211 	 * coalesce multiple flush commands to a vdev into one.
1212 	 */
1213 	if (list_head(&lwb->lwb_waiters) == NULL && nlwb != NULL) {
1214 		zil_lwb_flush_defer(lwb, nlwb);
1215 		ASSERT(avl_is_empty(&lwb->lwb_vdev_tree));
1216 		return;
1217 	}
1218 
1219 	while ((zv = avl_destroy_nodes(t, &cookie)) != NULL) {
1220 		vdev_t *vd = vdev_lookup_top(spa, zv->zv_vdev);
1221 		if (vd != NULL)
1222 			zio_flush(lwb->lwb_root_zio, vd);
1223 		kmem_free(zv, sizeof (*zv));
1224 	}
1225 }
1226 
1227 static void
1228 zil_lwb_set_zio_dependency(zilog_t *zilog, lwb_t *lwb)
1229 {
1230 	lwb_t *last_lwb_opened = zilog->zl_last_lwb_opened;
1231 
1232 	ASSERT(MUTEX_HELD(&zilog->zl_issuer_lock));
1233 	ASSERT(MUTEX_HELD(&zilog->zl_lock));
1234 
1235 	/*
1236 	 * The zilog's "zl_last_lwb_opened" field is used to build the
1237 	 * lwb/zio dependency chain, which is used to preserve the
1238 	 * ordering of lwb completions that is required by the semantics
1239 	 * of the ZIL. Each new lwb zio becomes a parent of the
1240 	 * "previous" lwb zio, such that the new lwb's zio cannot
1241 	 * complete until the "previous" lwb's zio completes.
1242 	 *
1243 	 * This is required by the semantics of zil_commit(); the commit
1244 	 * waiters attached to the lwbs will be woken in the lwb zio's
1245 	 * completion callback, so this zio dependency graph ensures the
1246 	 * waiters are woken in the correct order (the same order the
1247 	 * lwbs were created).
1248 	 */
1249 	if (last_lwb_opened != NULL &&
1250 	    last_lwb_opened->lwb_state != LWB_STATE_FLUSH_DONE) {
1251 		ASSERT(last_lwb_opened->lwb_state == LWB_STATE_OPENED ||
1252 		    last_lwb_opened->lwb_state == LWB_STATE_ISSUED ||
1253 		    last_lwb_opened->lwb_state == LWB_STATE_WRITE_DONE);
1254 
1255 		ASSERT3P(last_lwb_opened->lwb_root_zio, !=, NULL);
1256 		zio_add_child(lwb->lwb_root_zio,
1257 		    last_lwb_opened->lwb_root_zio);
1258 
1259 		/*
1260 		 * If the previous lwb's write hasn't already completed,
1261 		 * we also want to order the completion of the lwb write
1262 		 * zios (above, we only order the completion of the lwb
1263 		 * root zios). This is required because of how we can
1264 		 * defer the DKIOCFLUSHWRITECACHE commands for each lwb.
1265 		 *
1266 		 * When the DKIOCFLUSHWRITECACHE commands are defered,
1267 		 * the previous lwb will rely on this lwb to flush the
1268 		 * vdevs written to by that previous lwb. Thus, we need
1269 		 * to ensure this lwb doesn't issue the flush until
1270 		 * after the previous lwb's write completes. We ensure
1271 		 * this ordering by setting the zio parent/child
1272 		 * relationship here.
1273 		 *
1274 		 * Without this relationship on the lwb's write zio,
1275 		 * it's possible for this lwb's write to complete prior
1276 		 * to the previous lwb's write completing; and thus, the
1277 		 * vdevs for the previous lwb would be flushed prior to
1278 		 * that lwb's data being written to those vdevs (the
1279 		 * vdevs are flushed in the lwb write zio's completion
1280 		 * handler, zil_lwb_write_done()).
1281 		 */
1282 		if (last_lwb_opened->lwb_state != LWB_STATE_WRITE_DONE) {
1283 			ASSERT(last_lwb_opened->lwb_state == LWB_STATE_OPENED ||
1284 			    last_lwb_opened->lwb_state == LWB_STATE_ISSUED);
1285 
1286 			ASSERT3P(last_lwb_opened->lwb_write_zio, !=, NULL);
1287 			zio_add_child(lwb->lwb_write_zio,
1288 			    last_lwb_opened->lwb_write_zio);
1289 		}
1290 	}
1291 }
1292 
1293 
1294 /*
1295  * This function's purpose is to "open" an lwb such that it is ready to
1296  * accept new itxs being committed to it. To do this, the lwb's zio
1297  * structures are created, and linked to the lwb. This function is
1298  * idempotent; if the passed in lwb has already been opened, this
1299  * function is essentially a no-op.
1300  */
1301 static void
1302 zil_lwb_write_open(zilog_t *zilog, lwb_t *lwb)
1303 {
1304 	zbookmark_phys_t zb;
1305 	zio_priority_t prio;
1306 
1307 	ASSERT(MUTEX_HELD(&zilog->zl_issuer_lock));
1308 	ASSERT3P(lwb, !=, NULL);
1309 	EQUIV(lwb->lwb_root_zio == NULL, lwb->lwb_state == LWB_STATE_CLOSED);
1310 	EQUIV(lwb->lwb_root_zio != NULL, lwb->lwb_state == LWB_STATE_OPENED);
1311 
1312 	SET_BOOKMARK(&zb, lwb->lwb_blk.blk_cksum.zc_word[ZIL_ZC_OBJSET],
1313 	    ZB_ZIL_OBJECT, ZB_ZIL_LEVEL,
1314 	    lwb->lwb_blk.blk_cksum.zc_word[ZIL_ZC_SEQ]);
1315 
1316 	if (lwb->lwb_root_zio == NULL) {
1317 		abd_t *lwb_abd = abd_get_from_buf(lwb->lwb_buf,
1318 		    BP_GET_LSIZE(&lwb->lwb_blk));
1319 
1320 		if (!lwb->lwb_slog || zilog->zl_cur_used <= zil_slog_bulk)
1321 			prio = ZIO_PRIORITY_SYNC_WRITE;
1322 		else
1323 			prio = ZIO_PRIORITY_ASYNC_WRITE;
1324 
1325 		lwb->lwb_root_zio = zio_root(zilog->zl_spa,
1326 		    zil_lwb_flush_vdevs_done, lwb, ZIO_FLAG_CANFAIL);
1327 		ASSERT3P(lwb->lwb_root_zio, !=, NULL);
1328 
1329 		lwb->lwb_write_zio = zio_rewrite(lwb->lwb_root_zio,
1330 		    zilog->zl_spa, 0, &lwb->lwb_blk, lwb_abd,
1331 		    BP_GET_LSIZE(&lwb->lwb_blk), zil_lwb_write_done, lwb,
1332 		    prio, ZIO_FLAG_CANFAIL | ZIO_FLAG_DONT_PROPAGATE, &zb);
1333 		ASSERT3P(lwb->lwb_write_zio, !=, NULL);
1334 
1335 		lwb->lwb_state = LWB_STATE_OPENED;
1336 
1337 		mutex_enter(&zilog->zl_lock);
1338 		zil_lwb_set_zio_dependency(zilog, lwb);
1339 		zilog->zl_last_lwb_opened = lwb;
1340 		mutex_exit(&zilog->zl_lock);
1341 	}
1342 
1343 	ASSERT3P(lwb->lwb_root_zio, !=, NULL);
1344 	ASSERT3P(lwb->lwb_write_zio, !=, NULL);
1345 	ASSERT3S(lwb->lwb_state, ==, LWB_STATE_OPENED);
1346 }
1347 
1348 /*
1349  * Define a limited set of intent log block sizes.
1350  *
1351  * These must be a multiple of 4KB. Note only the amount used (again
1352  * aligned to 4KB) actually gets written. However, we can't always just
1353  * allocate SPA_OLD_MAXBLOCKSIZE as the slog space could be exhausted.
1354  */
1355 uint64_t zil_block_buckets[] = {
1356     4096,		/* non TX_WRITE */
1357     8192+4096,		/* data base */
1358     32*1024 + 4096, 	/* NFS writes */
1359     UINT64_MAX
1360 };
1361 
1362 /*
1363  * Start a log block write and advance to the next log block.
1364  * Calls are serialized.
1365  */
1366 static lwb_t *
1367 zil_lwb_write_issue(zilog_t *zilog, lwb_t *lwb)
1368 {
1369 	lwb_t *nlwb = NULL;
1370 	zil_chain_t *zilc;
1371 	spa_t *spa = zilog->zl_spa;
1372 	blkptr_t *bp;
1373 	dmu_tx_t *tx;
1374 	uint64_t txg;
1375 	uint64_t zil_blksz, wsz;
1376 	int i, error;
1377 	boolean_t slog;
1378 
1379 	ASSERT(MUTEX_HELD(&zilog->zl_issuer_lock));
1380 	ASSERT3P(lwb->lwb_root_zio, !=, NULL);
1381 	ASSERT3P(lwb->lwb_write_zio, !=, NULL);
1382 	ASSERT3S(lwb->lwb_state, ==, LWB_STATE_OPENED);
1383 
1384 	if (BP_GET_CHECKSUM(&lwb->lwb_blk) == ZIO_CHECKSUM_ZILOG2) {
1385 		zilc = (zil_chain_t *)lwb->lwb_buf;
1386 		bp = &zilc->zc_next_blk;
1387 	} else {
1388 		zilc = (zil_chain_t *)(lwb->lwb_buf + lwb->lwb_sz);
1389 		bp = &zilc->zc_next_blk;
1390 	}
1391 
1392 	ASSERT(lwb->lwb_nused <= lwb->lwb_sz);
1393 
1394 	/*
1395 	 * Allocate the next block and save its address in this block
1396 	 * before writing it in order to establish the log chain.
1397 	 * Note that if the allocation of nlwb synced before we wrote
1398 	 * the block that points at it (lwb), we'd leak it if we crashed.
1399 	 * Therefore, we don't do dmu_tx_commit() until zil_lwb_write_done().
1400 	 * We dirty the dataset to ensure that zil_sync() will be called
1401 	 * to clean up in the event of allocation failure or I/O failure.
1402 	 */
1403 
1404 	tx = dmu_tx_create(zilog->zl_os);
1405 
1406 	/*
1407 	 * Since we are not going to create any new dirty data, and we
1408 	 * can even help with clearing the existing dirty data, we
1409 	 * should not be subject to the dirty data based delays. We
1410 	 * use TXG_NOTHROTTLE to bypass the delay mechanism.
1411 	 */
1412 	VERIFY0(dmu_tx_assign(tx, TXG_WAIT | TXG_NOTHROTTLE));
1413 
1414 	dsl_dataset_dirty(dmu_objset_ds(zilog->zl_os), tx);
1415 	txg = dmu_tx_get_txg(tx);
1416 
1417 	lwb->lwb_tx = tx;
1418 
1419 	/*
1420 	 * Log blocks are pre-allocated. Here we select the size of the next
1421 	 * block, based on size used in the last block.
1422 	 * - first find the smallest bucket that will fit the block from a
1423 	 *   limited set of block sizes. This is because it's faster to write
1424 	 *   blocks allocated from the same metaslab as they are adjacent or
1425 	 *   close.
1426 	 * - next find the maximum from the new suggested size and an array of
1427 	 *   previous sizes. This lessens a picket fence effect of wrongly
1428 	 *   guesssing the size if we have a stream of say 2k, 64k, 2k, 64k
1429 	 *   requests.
1430 	 *
1431 	 * Note we only write what is used, but we can't just allocate
1432 	 * the maximum block size because we can exhaust the available
1433 	 * pool log space.
1434 	 */
1435 	zil_blksz = zilog->zl_cur_used + sizeof (zil_chain_t);
1436 	for (i = 0; zil_blksz > zil_block_buckets[i]; i++)
1437 		continue;
1438 	zil_blksz = zil_block_buckets[i];
1439 	if (zil_blksz == UINT64_MAX)
1440 		zil_blksz = SPA_OLD_MAXBLOCKSIZE;
1441 	zilog->zl_prev_blks[zilog->zl_prev_rotor] = zil_blksz;
1442 	for (i = 0; i < ZIL_PREV_BLKS; i++)
1443 		zil_blksz = MAX(zil_blksz, zilog->zl_prev_blks[i]);
1444 	zilog->zl_prev_rotor = (zilog->zl_prev_rotor + 1) & (ZIL_PREV_BLKS - 1);
1445 
1446 	BP_ZERO(bp);
1447 
1448 	/* pass the old blkptr in order to spread log blocks across devs */
1449 	error = zio_alloc_zil(spa, zilog->zl_os->os_dsl_dataset->ds_object,
1450 	    txg, bp, &lwb->lwb_blk, zil_blksz, &slog);
1451 	if (error == 0) {
1452 		ASSERT3U(bp->blk_birth, ==, txg);
1453 		bp->blk_cksum = lwb->lwb_blk.blk_cksum;
1454 		bp->blk_cksum.zc_word[ZIL_ZC_SEQ]++;
1455 
1456 		/*
1457 		 * Allocate a new log write block (lwb).
1458 		 */
1459 		nlwb = zil_alloc_lwb(zilog, bp, slog, txg);
1460 	}
1461 
1462 	if (BP_GET_CHECKSUM(&lwb->lwb_blk) == ZIO_CHECKSUM_ZILOG2) {
1463 		/* For Slim ZIL only write what is used. */
1464 		wsz = P2ROUNDUP_TYPED(lwb->lwb_nused, ZIL_MIN_BLKSZ, uint64_t);
1465 		ASSERT3U(wsz, <=, lwb->lwb_sz);
1466 		zio_shrink(lwb->lwb_write_zio, wsz);
1467 
1468 	} else {
1469 		wsz = lwb->lwb_sz;
1470 	}
1471 
1472 	zilc->zc_pad = 0;
1473 	zilc->zc_nused = lwb->lwb_nused;
1474 	zilc->zc_eck.zec_cksum = lwb->lwb_blk.blk_cksum;
1475 
1476 	/*
1477 	 * clear unused data for security
1478 	 */
1479 	bzero(lwb->lwb_buf + lwb->lwb_nused, wsz - lwb->lwb_nused);
1480 
1481 	spa_config_enter(zilog->zl_spa, SCL_STATE, lwb, RW_READER);
1482 
1483 	zil_lwb_add_block(lwb, &lwb->lwb_blk);
1484 	lwb->lwb_issued_timestamp = gethrtime();
1485 	lwb->lwb_state = LWB_STATE_ISSUED;
1486 
1487 	zio_nowait(lwb->lwb_root_zio);
1488 	zio_nowait(lwb->lwb_write_zio);
1489 
1490 	/*
1491 	 * If there was an allocation failure then nlwb will be null which
1492 	 * forces a txg_wait_synced().
1493 	 */
1494 	return (nlwb);
1495 }
1496 
1497 static lwb_t *
1498 zil_lwb_commit(zilog_t *zilog, itx_t *itx, lwb_t *lwb)
1499 {
1500 	lr_t *lrcb, *lrc;
1501 	lr_write_t *lrwb, *lrw;
1502 	char *lr_buf;
1503 	uint64_t dlen, dnow, lwb_sp, reclen, txg;
1504 
1505 	ASSERT(MUTEX_HELD(&zilog->zl_issuer_lock));
1506 	ASSERT3P(lwb, !=, NULL);
1507 	ASSERT3P(lwb->lwb_buf, !=, NULL);
1508 
1509 	zil_lwb_write_open(zilog, lwb);
1510 
1511 	lrc = &itx->itx_lr;
1512 	lrw = (lr_write_t *)lrc;
1513 
1514 	/*
1515 	 * A commit itx doesn't represent any on-disk state; instead
1516 	 * it's simply used as a place holder on the commit list, and
1517 	 * provides a mechanism for attaching a "commit waiter" onto the
1518 	 * correct lwb (such that the waiter can be signalled upon
1519 	 * completion of that lwb). Thus, we don't process this itx's
1520 	 * log record if it's a commit itx (these itx's don't have log
1521 	 * records), and instead link the itx's waiter onto the lwb's
1522 	 * list of waiters.
1523 	 *
1524 	 * For more details, see the comment above zil_commit().
1525 	 */
1526 	if (lrc->lrc_txtype == TX_COMMIT) {
1527 		mutex_enter(&zilog->zl_lock);
1528 		zil_commit_waiter_link_lwb(itx->itx_private, lwb);
1529 		itx->itx_private = NULL;
1530 		mutex_exit(&zilog->zl_lock);
1531 		return (lwb);
1532 	}
1533 
1534 	if (lrc->lrc_txtype == TX_WRITE && itx->itx_wr_state == WR_NEED_COPY) {
1535 		dlen = P2ROUNDUP_TYPED(
1536 		    lrw->lr_length, sizeof (uint64_t), uint64_t);
1537 	} else {
1538 		dlen = 0;
1539 	}
1540 	reclen = lrc->lrc_reclen;
1541 	zilog->zl_cur_used += (reclen + dlen);
1542 	txg = lrc->lrc_txg;
1543 
1544 	ASSERT3U(zilog->zl_cur_used, <, UINT64_MAX - (reclen + dlen));
1545 
1546 cont:
1547 	/*
1548 	 * If this record won't fit in the current log block, start a new one.
1549 	 * For WR_NEED_COPY optimize layout for minimal number of chunks.
1550 	 */
1551 	lwb_sp = lwb->lwb_sz - lwb->lwb_nused;
1552 	if (reclen > lwb_sp || (reclen + dlen > lwb_sp &&
1553 	    lwb_sp < ZIL_MAX_WASTE_SPACE && (dlen % ZIL_MAX_LOG_DATA == 0 ||
1554 	    lwb_sp < reclen + dlen % ZIL_MAX_LOG_DATA))) {
1555 		lwb = zil_lwb_write_issue(zilog, lwb);
1556 		if (lwb == NULL)
1557 			return (NULL);
1558 		zil_lwb_write_open(zilog, lwb);
1559 		ASSERT(LWB_EMPTY(lwb));
1560 		lwb_sp = lwb->lwb_sz - lwb->lwb_nused;
1561 		ASSERT3U(reclen + MIN(dlen, sizeof (uint64_t)), <=, lwb_sp);
1562 	}
1563 
1564 	dnow = MIN(dlen, lwb_sp - reclen);
1565 	lr_buf = lwb->lwb_buf + lwb->lwb_nused;
1566 	bcopy(lrc, lr_buf, reclen);
1567 	lrcb = (lr_t *)lr_buf;		/* Like lrc, but inside lwb. */
1568 	lrwb = (lr_write_t *)lrcb;	/* Like lrw, but inside lwb. */
1569 
1570 	/*
1571 	 * If it's a write, fetch the data or get its blkptr as appropriate.
1572 	 */
1573 	if (lrc->lrc_txtype == TX_WRITE) {
1574 		if (txg > spa_freeze_txg(zilog->zl_spa))
1575 			txg_wait_synced(zilog->zl_dmu_pool, txg);
1576 		if (itx->itx_wr_state != WR_COPIED) {
1577 			char *dbuf;
1578 			int error;
1579 
1580 			if (itx->itx_wr_state == WR_NEED_COPY) {
1581 				dbuf = lr_buf + reclen;
1582 				lrcb->lrc_reclen += dnow;
1583 				if (lrwb->lr_length > dnow)
1584 					lrwb->lr_length = dnow;
1585 				lrw->lr_offset += dnow;
1586 				lrw->lr_length -= dnow;
1587 			} else {
1588 				ASSERT(itx->itx_wr_state == WR_INDIRECT);
1589 				dbuf = NULL;
1590 			}
1591 
1592 			/*
1593 			 * We pass in the "lwb_write_zio" rather than
1594 			 * "lwb_root_zio" so that the "lwb_write_zio"
1595 			 * becomes the parent of any zio's created by
1596 			 * the "zl_get_data" callback. The vdevs are
1597 			 * flushed after the "lwb_write_zio" completes,
1598 			 * so we want to make sure that completion
1599 			 * callback waits for these additional zio's,
1600 			 * such that the vdevs used by those zio's will
1601 			 * be included in the lwb's vdev tree, and those
1602 			 * vdevs will be properly flushed. If we passed
1603 			 * in "lwb_root_zio" here, then these additional
1604 			 * vdevs may not be flushed; e.g. if these zio's
1605 			 * completed after "lwb_write_zio" completed.
1606 			 */
1607 			error = zilog->zl_get_data(itx->itx_private,
1608 			    lrwb, dbuf, lwb, lwb->lwb_write_zio);
1609 
1610 			if (error == EIO) {
1611 				txg_wait_synced(zilog->zl_dmu_pool, txg);
1612 				return (lwb);
1613 			}
1614 			if (error != 0) {
1615 				ASSERT(error == ENOENT || error == EEXIST ||
1616 				    error == EALREADY);
1617 				return (lwb);
1618 			}
1619 		}
1620 	}
1621 
1622 	/*
1623 	 * We're actually making an entry, so update lrc_seq to be the
1624 	 * log record sequence number.  Note that this is generally not
1625 	 * equal to the itx sequence number because not all transactions
1626 	 * are synchronous, and sometimes spa_sync() gets there first.
1627 	 */
1628 	lrcb->lrc_seq = ++zilog->zl_lr_seq;
1629 	lwb->lwb_nused += reclen + dnow;
1630 
1631 	zil_lwb_add_txg(lwb, txg);
1632 
1633 	ASSERT3U(lwb->lwb_nused, <=, lwb->lwb_sz);
1634 	ASSERT0(P2PHASE(lwb->lwb_nused, sizeof (uint64_t)));
1635 
1636 	dlen -= dnow;
1637 	if (dlen > 0) {
1638 		zilog->zl_cur_used += reclen;
1639 		goto cont;
1640 	}
1641 
1642 	return (lwb);
1643 }
1644 
1645 itx_t *
1646 zil_itx_create(uint64_t txtype, size_t lrsize)
1647 {
1648 	itx_t *itx;
1649 
1650 	lrsize = P2ROUNDUP_TYPED(lrsize, sizeof (uint64_t), size_t);
1651 
1652 	itx = kmem_alloc(offsetof(itx_t, itx_lr) + lrsize, KM_SLEEP);
1653 	itx->itx_lr.lrc_txtype = txtype;
1654 	itx->itx_lr.lrc_reclen = lrsize;
1655 	itx->itx_lr.lrc_seq = 0;	/* defensive */
1656 	itx->itx_sync = B_TRUE;		/* default is synchronous */
1657 
1658 	return (itx);
1659 }
1660 
1661 void
1662 zil_itx_destroy(itx_t *itx)
1663 {
1664 	kmem_free(itx, offsetof(itx_t, itx_lr) + itx->itx_lr.lrc_reclen);
1665 }
1666 
1667 /*
1668  * Free up the sync and async itxs. The itxs_t has already been detached
1669  * so no locks are needed.
1670  */
1671 static void
1672 zil_itxg_clean(itxs_t *itxs)
1673 {
1674 	itx_t *itx;
1675 	list_t *list;
1676 	avl_tree_t *t;
1677 	void *cookie;
1678 	itx_async_node_t *ian;
1679 
1680 	list = &itxs->i_sync_list;
1681 	while ((itx = list_head(list)) != NULL) {
1682 		/*
1683 		 * In the general case, commit itxs will not be found
1684 		 * here, as they'll be committed to an lwb via
1685 		 * zil_lwb_commit(), and free'd in that function. Having
1686 		 * said that, it is still possible for commit itxs to be
1687 		 * found here, due to the following race:
1688 		 *
1689 		 *	- a thread calls zil_commit() which assigns the
1690 		 *	  commit itx to a per-txg i_sync_list
1691 		 *	- zil_itxg_clean() is called (e.g. via spa_sync())
1692 		 *	  while the waiter is still on the i_sync_list
1693 		 *
1694 		 * There's nothing to prevent syncing the txg while the
1695 		 * waiter is on the i_sync_list. This normally doesn't
1696 		 * happen because spa_sync() is slower than zil_commit(),
1697 		 * but if zil_commit() calls txg_wait_synced() (e.g.
1698 		 * because zil_create() or zil_commit_writer_stall() is
1699 		 * called) we will hit this case.
1700 		 */
1701 		if (itx->itx_lr.lrc_txtype == TX_COMMIT)
1702 			zil_commit_waiter_skip(itx->itx_private);
1703 
1704 		list_remove(list, itx);
1705 		zil_itx_destroy(itx);
1706 	}
1707 
1708 	cookie = NULL;
1709 	t = &itxs->i_async_tree;
1710 	while ((ian = avl_destroy_nodes(t, &cookie)) != NULL) {
1711 		list = &ian->ia_list;
1712 		while ((itx = list_head(list)) != NULL) {
1713 			list_remove(list, itx);
1714 			/* commit itxs should never be on the async lists. */
1715 			ASSERT3U(itx->itx_lr.lrc_txtype, !=, TX_COMMIT);
1716 			zil_itx_destroy(itx);
1717 		}
1718 		list_destroy(list);
1719 		kmem_free(ian, sizeof (itx_async_node_t));
1720 	}
1721 	avl_destroy(t);
1722 
1723 	kmem_free(itxs, sizeof (itxs_t));
1724 }
1725 
1726 static int
1727 zil_aitx_compare(const void *x1, const void *x2)
1728 {
1729 	const uint64_t o1 = ((itx_async_node_t *)x1)->ia_foid;
1730 	const uint64_t o2 = ((itx_async_node_t *)x2)->ia_foid;
1731 
1732 	if (o1 < o2)
1733 		return (-1);
1734 	if (o1 > o2)
1735 		return (1);
1736 
1737 	return (0);
1738 }
1739 
1740 /*
1741  * Remove all async itx with the given oid.
1742  */
1743 static void
1744 zil_remove_async(zilog_t *zilog, uint64_t oid)
1745 {
1746 	uint64_t otxg, txg;
1747 	itx_async_node_t *ian;
1748 	avl_tree_t *t;
1749 	avl_index_t where;
1750 	list_t clean_list;
1751 	itx_t *itx;
1752 
1753 	ASSERT(oid != 0);
1754 	list_create(&clean_list, sizeof (itx_t), offsetof(itx_t, itx_node));
1755 
1756 	if (spa_freeze_txg(zilog->zl_spa) != UINT64_MAX) /* ziltest support */
1757 		otxg = ZILTEST_TXG;
1758 	else
1759 		otxg = spa_last_synced_txg(zilog->zl_spa) + 1;
1760 
1761 	for (txg = otxg; txg < (otxg + TXG_CONCURRENT_STATES); txg++) {
1762 		itxg_t *itxg = &zilog->zl_itxg[txg & TXG_MASK];
1763 
1764 		mutex_enter(&itxg->itxg_lock);
1765 		if (itxg->itxg_txg != txg) {
1766 			mutex_exit(&itxg->itxg_lock);
1767 			continue;
1768 		}
1769 
1770 		/*
1771 		 * Locate the object node and append its list.
1772 		 */
1773 		t = &itxg->itxg_itxs->i_async_tree;
1774 		ian = avl_find(t, &oid, &where);
1775 		if (ian != NULL)
1776 			list_move_tail(&clean_list, &ian->ia_list);
1777 		mutex_exit(&itxg->itxg_lock);
1778 	}
1779 	while ((itx = list_head(&clean_list)) != NULL) {
1780 		list_remove(&clean_list, itx);
1781 		/* commit itxs should never be on the async lists. */
1782 		ASSERT3U(itx->itx_lr.lrc_txtype, !=, TX_COMMIT);
1783 		zil_itx_destroy(itx);
1784 	}
1785 	list_destroy(&clean_list);
1786 }
1787 
1788 void
1789 zil_itx_assign(zilog_t *zilog, itx_t *itx, dmu_tx_t *tx)
1790 {
1791 	uint64_t txg;
1792 	itxg_t *itxg;
1793 	itxs_t *itxs, *clean = NULL;
1794 
1795 	/*
1796 	 * Object ids can be re-instantiated in the next txg so
1797 	 * remove any async transactions to avoid future leaks.
1798 	 * This can happen if a fsync occurs on the re-instantiated
1799 	 * object for a WR_INDIRECT or WR_NEED_COPY write, which gets
1800 	 * the new file data and flushes a write record for the old object.
1801 	 */
1802 	if ((itx->itx_lr.lrc_txtype & ~TX_CI) == TX_REMOVE)
1803 		zil_remove_async(zilog, itx->itx_oid);
1804 
1805 	/*
1806 	 * Ensure the data of a renamed file is committed before the rename.
1807 	 */
1808 	if ((itx->itx_lr.lrc_txtype & ~TX_CI) == TX_RENAME)
1809 		zil_async_to_sync(zilog, itx->itx_oid);
1810 
1811 	if (spa_freeze_txg(zilog->zl_spa) != UINT64_MAX)
1812 		txg = ZILTEST_TXG;
1813 	else
1814 		txg = dmu_tx_get_txg(tx);
1815 
1816 	itxg = &zilog->zl_itxg[txg & TXG_MASK];
1817 	mutex_enter(&itxg->itxg_lock);
1818 	itxs = itxg->itxg_itxs;
1819 	if (itxg->itxg_txg != txg) {
1820 		if (itxs != NULL) {
1821 			/*
1822 			 * The zil_clean callback hasn't got around to cleaning
1823 			 * this itxg. Save the itxs for release below.
1824 			 * This should be rare.
1825 			 */
1826 			zfs_dbgmsg("zil_itx_assign: missed itx cleanup for "
1827 			    "txg %llu", itxg->itxg_txg);
1828 			clean = itxg->itxg_itxs;
1829 		}
1830 		itxg->itxg_txg = txg;
1831 		itxs = itxg->itxg_itxs = kmem_zalloc(sizeof (itxs_t), KM_SLEEP);
1832 
1833 		list_create(&itxs->i_sync_list, sizeof (itx_t),
1834 		    offsetof(itx_t, itx_node));
1835 		avl_create(&itxs->i_async_tree, zil_aitx_compare,
1836 		    sizeof (itx_async_node_t),
1837 		    offsetof(itx_async_node_t, ia_node));
1838 	}
1839 	if (itx->itx_sync) {
1840 		list_insert_tail(&itxs->i_sync_list, itx);
1841 	} else {
1842 		avl_tree_t *t = &itxs->i_async_tree;
1843 		uint64_t foid = ((lr_ooo_t *)&itx->itx_lr)->lr_foid;
1844 		itx_async_node_t *ian;
1845 		avl_index_t where;
1846 
1847 		ian = avl_find(t, &foid, &where);
1848 		if (ian == NULL) {
1849 			ian = kmem_alloc(sizeof (itx_async_node_t), KM_SLEEP);
1850 			list_create(&ian->ia_list, sizeof (itx_t),
1851 			    offsetof(itx_t, itx_node));
1852 			ian->ia_foid = foid;
1853 			avl_insert(t, ian, where);
1854 		}
1855 		list_insert_tail(&ian->ia_list, itx);
1856 	}
1857 
1858 	itx->itx_lr.lrc_txg = dmu_tx_get_txg(tx);
1859 
1860 	/*
1861 	 * We don't want to dirty the ZIL using ZILTEST_TXG, because
1862 	 * zil_clean() will never be called using ZILTEST_TXG. Thus, we
1863 	 * need to be careful to always dirty the ZIL using the "real"
1864 	 * TXG (not itxg_txg) even when the SPA is frozen.
1865 	 */
1866 	zilog_dirty(zilog, dmu_tx_get_txg(tx));
1867 	mutex_exit(&itxg->itxg_lock);
1868 
1869 	/* Release the old itxs now we've dropped the lock */
1870 	if (clean != NULL)
1871 		zil_itxg_clean(clean);
1872 }
1873 
1874 /*
1875  * If there are any in-memory intent log transactions which have now been
1876  * synced then start up a taskq to free them. We should only do this after we
1877  * have written out the uberblocks (i.e. txg has been comitted) so that
1878  * don't inadvertently clean out in-memory log records that would be required
1879  * by zil_commit().
1880  */
1881 void
1882 zil_clean(zilog_t *zilog, uint64_t synced_txg)
1883 {
1884 	itxg_t *itxg = &zilog->zl_itxg[synced_txg & TXG_MASK];
1885 	itxs_t *clean_me;
1886 
1887 	ASSERT3U(synced_txg, <, ZILTEST_TXG);
1888 
1889 	mutex_enter(&itxg->itxg_lock);
1890 	if (itxg->itxg_itxs == NULL || itxg->itxg_txg == ZILTEST_TXG) {
1891 		mutex_exit(&itxg->itxg_lock);
1892 		return;
1893 	}
1894 	ASSERT3U(itxg->itxg_txg, <=, synced_txg);
1895 	ASSERT3U(itxg->itxg_txg, !=, 0);
1896 	clean_me = itxg->itxg_itxs;
1897 	itxg->itxg_itxs = NULL;
1898 	itxg->itxg_txg = 0;
1899 	mutex_exit(&itxg->itxg_lock);
1900 	/*
1901 	 * Preferably start a task queue to free up the old itxs but
1902 	 * if taskq_dispatch can't allocate resources to do that then
1903 	 * free it in-line. This should be rare. Note, using TQ_SLEEP
1904 	 * created a bad performance problem.
1905 	 */
1906 	ASSERT3P(zilog->zl_dmu_pool, !=, NULL);
1907 	ASSERT3P(zilog->zl_dmu_pool->dp_zil_clean_taskq, !=, NULL);
1908 	if (taskq_dispatch(zilog->zl_dmu_pool->dp_zil_clean_taskq,
1909 	    (void (*)(void *))zil_itxg_clean, clean_me, TQ_NOSLEEP) == NULL)
1910 		zil_itxg_clean(clean_me);
1911 }
1912 
1913 /*
1914  * This function will traverse the queue of itxs that need to be
1915  * committed, and move them onto the ZIL's zl_itx_commit_list.
1916  */
1917 static void
1918 zil_get_commit_list(zilog_t *zilog)
1919 {
1920 	uint64_t otxg, txg;
1921 	list_t *commit_list = &zilog->zl_itx_commit_list;
1922 
1923 	ASSERT(MUTEX_HELD(&zilog->zl_issuer_lock));
1924 
1925 	if (spa_freeze_txg(zilog->zl_spa) != UINT64_MAX) /* ziltest support */
1926 		otxg = ZILTEST_TXG;
1927 	else
1928 		otxg = spa_last_synced_txg(zilog->zl_spa) + 1;
1929 
1930 	/*
1931 	 * This is inherently racy, since there is nothing to prevent
1932 	 * the last synced txg from changing. That's okay since we'll
1933 	 * only commit things in the future.
1934 	 */
1935 	for (txg = otxg; txg < (otxg + TXG_CONCURRENT_STATES); txg++) {
1936 		itxg_t *itxg = &zilog->zl_itxg[txg & TXG_MASK];
1937 
1938 		mutex_enter(&itxg->itxg_lock);
1939 		if (itxg->itxg_txg != txg) {
1940 			mutex_exit(&itxg->itxg_lock);
1941 			continue;
1942 		}
1943 
1944 		/*
1945 		 * If we're adding itx records to the zl_itx_commit_list,
1946 		 * then the zil better be dirty in this "txg". We can assert
1947 		 * that here since we're holding the itxg_lock which will
1948 		 * prevent spa_sync from cleaning it. Once we add the itxs
1949 		 * to the zl_itx_commit_list we must commit it to disk even
1950 		 * if it's unnecessary (i.e. the txg was synced).
1951 		 */
1952 		ASSERT(zilog_is_dirty_in_txg(zilog, txg) ||
1953 		    spa_freeze_txg(zilog->zl_spa) != UINT64_MAX);
1954 		list_move_tail(commit_list, &itxg->itxg_itxs->i_sync_list);
1955 
1956 		mutex_exit(&itxg->itxg_lock);
1957 	}
1958 }
1959 
1960 /*
1961  * Move the async itxs for a specified object to commit into sync lists.
1962  */
1963 static void
1964 zil_async_to_sync(zilog_t *zilog, uint64_t foid)
1965 {
1966 	uint64_t otxg, txg;
1967 	itx_async_node_t *ian;
1968 	avl_tree_t *t;
1969 	avl_index_t where;
1970 
1971 	if (spa_freeze_txg(zilog->zl_spa) != UINT64_MAX) /* ziltest support */
1972 		otxg = ZILTEST_TXG;
1973 	else
1974 		otxg = spa_last_synced_txg(zilog->zl_spa) + 1;
1975 
1976 	/*
1977 	 * This is inherently racy, since there is nothing to prevent
1978 	 * the last synced txg from changing.
1979 	 */
1980 	for (txg = otxg; txg < (otxg + TXG_CONCURRENT_STATES); txg++) {
1981 		itxg_t *itxg = &zilog->zl_itxg[txg & TXG_MASK];
1982 
1983 		mutex_enter(&itxg->itxg_lock);
1984 		if (itxg->itxg_txg != txg) {
1985 			mutex_exit(&itxg->itxg_lock);
1986 			continue;
1987 		}
1988 
1989 		/*
1990 		 * If a foid is specified then find that node and append its
1991 		 * list. Otherwise walk the tree appending all the lists
1992 		 * to the sync list. We add to the end rather than the
1993 		 * beginning to ensure the create has happened.
1994 		 */
1995 		t = &itxg->itxg_itxs->i_async_tree;
1996 		if (foid != 0) {
1997 			ian = avl_find(t, &foid, &where);
1998 			if (ian != NULL) {
1999 				list_move_tail(&itxg->itxg_itxs->i_sync_list,
2000 				    &ian->ia_list);
2001 			}
2002 		} else {
2003 			void *cookie = NULL;
2004 
2005 			while ((ian = avl_destroy_nodes(t, &cookie)) != NULL) {
2006 				list_move_tail(&itxg->itxg_itxs->i_sync_list,
2007 				    &ian->ia_list);
2008 				list_destroy(&ian->ia_list);
2009 				kmem_free(ian, sizeof (itx_async_node_t));
2010 			}
2011 		}
2012 		mutex_exit(&itxg->itxg_lock);
2013 	}
2014 }
2015 
2016 /*
2017  * This function will prune commit itxs that are at the head of the
2018  * commit list (it won't prune past the first non-commit itx), and
2019  * either: a) attach them to the last lwb that's still pending
2020  * completion, or b) skip them altogether.
2021  *
2022  * This is used as a performance optimization to prevent commit itxs
2023  * from generating new lwbs when it's unnecessary to do so.
2024  */
2025 static void
2026 zil_prune_commit_list(zilog_t *zilog)
2027 {
2028 	itx_t *itx;
2029 
2030 	ASSERT(MUTEX_HELD(&zilog->zl_issuer_lock));
2031 
2032 	while (itx = list_head(&zilog->zl_itx_commit_list)) {
2033 		lr_t *lrc = &itx->itx_lr;
2034 		if (lrc->lrc_txtype != TX_COMMIT)
2035 			break;
2036 
2037 		mutex_enter(&zilog->zl_lock);
2038 
2039 		lwb_t *last_lwb = zilog->zl_last_lwb_opened;
2040 		if (last_lwb == NULL ||
2041 		    last_lwb->lwb_state == LWB_STATE_FLUSH_DONE) {
2042 			/*
2043 			 * All of the itxs this waiter was waiting on
2044 			 * must have already completed (or there were
2045 			 * never any itx's for it to wait on), so it's
2046 			 * safe to skip this waiter and mark it done.
2047 			 */
2048 			zil_commit_waiter_skip(itx->itx_private);
2049 		} else {
2050 			zil_commit_waiter_link_lwb(itx->itx_private, last_lwb);
2051 			itx->itx_private = NULL;
2052 		}
2053 
2054 		mutex_exit(&zilog->zl_lock);
2055 
2056 		list_remove(&zilog->zl_itx_commit_list, itx);
2057 		zil_itx_destroy(itx);
2058 	}
2059 
2060 	IMPLY(itx != NULL, itx->itx_lr.lrc_txtype != TX_COMMIT);
2061 }
2062 
2063 static void
2064 zil_commit_writer_stall(zilog_t *zilog)
2065 {
2066 	/*
2067 	 * When zio_alloc_zil() fails to allocate the next lwb block on
2068 	 * disk, we must call txg_wait_synced() to ensure all of the
2069 	 * lwbs in the zilog's zl_lwb_list are synced and then freed (in
2070 	 * zil_sync()), such that any subsequent ZIL writer (i.e. a call
2071 	 * to zil_process_commit_list()) will have to call zil_create(),
2072 	 * and start a new ZIL chain.
2073 	 *
2074 	 * Since zil_alloc_zil() failed, the lwb that was previously
2075 	 * issued does not have a pointer to the "next" lwb on disk.
2076 	 * Thus, if another ZIL writer thread was to allocate the "next"
2077 	 * on-disk lwb, that block could be leaked in the event of a
2078 	 * crash (because the previous lwb on-disk would not point to
2079 	 * it).
2080 	 *
2081 	 * We must hold the zilog's zl_issuer_lock while we do this, to
2082 	 * ensure no new threads enter zil_process_commit_list() until
2083 	 * all lwb's in the zl_lwb_list have been synced and freed
2084 	 * (which is achieved via the txg_wait_synced() call).
2085 	 */
2086 	ASSERT(MUTEX_HELD(&zilog->zl_issuer_lock));
2087 	txg_wait_synced(zilog->zl_dmu_pool, 0);
2088 	ASSERT3P(list_tail(&zilog->zl_lwb_list), ==, NULL);
2089 }
2090 
2091 /*
2092  * This function will traverse the commit list, creating new lwbs as
2093  * needed, and committing the itxs from the commit list to these newly
2094  * created lwbs. Additionally, as a new lwb is created, the previous
2095  * lwb will be issued to the zio layer to be written to disk.
2096  */
2097 static void
2098 zil_process_commit_list(zilog_t *zilog)
2099 {
2100 	spa_t *spa = zilog->zl_spa;
2101 	list_t nolwb_waiters;
2102 	lwb_t *lwb;
2103 	itx_t *itx;
2104 
2105 	ASSERT(MUTEX_HELD(&zilog->zl_issuer_lock));
2106 
2107 	/*
2108 	 * Return if there's nothing to commit before we dirty the fs by
2109 	 * calling zil_create().
2110 	 */
2111 	if (list_head(&zilog->zl_itx_commit_list) == NULL)
2112 		return;
2113 
2114 	list_create(&nolwb_waiters, sizeof (zil_commit_waiter_t),
2115 	    offsetof(zil_commit_waiter_t, zcw_node));
2116 
2117 	lwb = list_tail(&zilog->zl_lwb_list);
2118 	if (lwb == NULL) {
2119 		lwb = zil_create(zilog);
2120 	} else {
2121 		ASSERT3S(lwb->lwb_state, !=, LWB_STATE_ISSUED);
2122 		ASSERT3S(lwb->lwb_state, !=, LWB_STATE_WRITE_DONE);
2123 		ASSERT3S(lwb->lwb_state, !=, LWB_STATE_FLUSH_DONE);
2124 	}
2125 
2126 	while (itx = list_head(&zilog->zl_itx_commit_list)) {
2127 		lr_t *lrc = &itx->itx_lr;
2128 		uint64_t txg = lrc->lrc_txg;
2129 
2130 		ASSERT3U(txg, !=, 0);
2131 
2132 		if (lrc->lrc_txtype == TX_COMMIT) {
2133 			DTRACE_PROBE2(zil__process__commit__itx,
2134 			    zilog_t *, zilog, itx_t *, itx);
2135 		} else {
2136 			DTRACE_PROBE2(zil__process__normal__itx,
2137 			    zilog_t *, zilog, itx_t *, itx);
2138 		}
2139 
2140 		boolean_t synced = txg <= spa_last_synced_txg(spa);
2141 		boolean_t frozen = txg > spa_freeze_txg(spa);
2142 
2143 		/*
2144 		 * If the txg of this itx has already been synced out, then
2145 		 * we don't need to commit this itx to an lwb. This is
2146 		 * because the data of this itx will have already been
2147 		 * written to the main pool. This is inherently racy, and
2148 		 * it's still ok to commit an itx whose txg has already
2149 		 * been synced; this will result in a write that's
2150 		 * unnecessary, but will do no harm.
2151 		 *
2152 		 * With that said, we always want to commit TX_COMMIT itxs
2153 		 * to an lwb, regardless of whether or not that itx's txg
2154 		 * has been synced out. We do this to ensure any OPENED lwb
2155 		 * will always have at least one zil_commit_waiter_t linked
2156 		 * to the lwb.
2157 		 *
2158 		 * As a counter-example, if we skipped TX_COMMIT itx's
2159 		 * whose txg had already been synced, the following
2160 		 * situation could occur if we happened to be racing with
2161 		 * spa_sync:
2162 		 *
2163 		 * 1. we commit a non-TX_COMMIT itx to an lwb, where the
2164 		 *    itx's txg is 10 and the last synced txg is 9.
2165 		 * 2. spa_sync finishes syncing out txg 10.
2166 		 * 3. we move to the next itx in the list, it's a TX_COMMIT
2167 		 *    whose txg is 10, so we skip it rather than committing
2168 		 *    it to the lwb used in (1).
2169 		 *
2170 		 * If the itx that is skipped in (3) is the last TX_COMMIT
2171 		 * itx in the commit list, than it's possible for the lwb
2172 		 * used in (1) to remain in the OPENED state indefinitely.
2173 		 *
2174 		 * To prevent the above scenario from occuring, ensuring
2175 		 * that once an lwb is OPENED it will transition to ISSUED
2176 		 * and eventually DONE, we always commit TX_COMMIT itx's to
2177 		 * an lwb here, even if that itx's txg has already been
2178 		 * synced.
2179 		 *
2180 		 * Finally, if the pool is frozen, we _always_ commit the
2181 		 * itx.  The point of freezing the pool is to prevent data
2182 		 * from being written to the main pool via spa_sync, and
2183 		 * instead rely solely on the ZIL to persistently store the
2184 		 * data; i.e.  when the pool is frozen, the last synced txg
2185 		 * value can't be trusted.
2186 		 */
2187 		if (frozen || !synced || lrc->lrc_txtype == TX_COMMIT) {
2188 			if (lwb != NULL) {
2189 				lwb = zil_lwb_commit(zilog, itx, lwb);
2190 			} else if (lrc->lrc_txtype == TX_COMMIT) {
2191 				ASSERT3P(lwb, ==, NULL);
2192 				zil_commit_waiter_link_nolwb(
2193 				    itx->itx_private, &nolwb_waiters);
2194 			}
2195 		}
2196 
2197 		list_remove(&zilog->zl_itx_commit_list, itx);
2198 		zil_itx_destroy(itx);
2199 	}
2200 
2201 	if (lwb == NULL) {
2202 		/*
2203 		 * This indicates zio_alloc_zil() failed to allocate the
2204 		 * "next" lwb on-disk. When this happens, we must stall
2205 		 * the ZIL write pipeline; see the comment within
2206 		 * zil_commit_writer_stall() for more details.
2207 		 */
2208 		zil_commit_writer_stall(zilog);
2209 
2210 		/*
2211 		 * Additionally, we have to signal and mark the "nolwb"
2212 		 * waiters as "done" here, since without an lwb, we
2213 		 * can't do this via zil_lwb_flush_vdevs_done() like
2214 		 * normal.
2215 		 */
2216 		zil_commit_waiter_t *zcw;
2217 		while (zcw = list_head(&nolwb_waiters)) {
2218 			zil_commit_waiter_skip(zcw);
2219 			list_remove(&nolwb_waiters, zcw);
2220 		}
2221 	} else {
2222 		ASSERT(list_is_empty(&nolwb_waiters));
2223 		ASSERT3P(lwb, !=, NULL);
2224 		ASSERT3S(lwb->lwb_state, !=, LWB_STATE_ISSUED);
2225 		ASSERT3S(lwb->lwb_state, !=, LWB_STATE_WRITE_DONE);
2226 		ASSERT3S(lwb->lwb_state, !=, LWB_STATE_FLUSH_DONE);
2227 
2228 		/*
2229 		 * At this point, the ZIL block pointed at by the "lwb"
2230 		 * variable is in one of the following states: "closed"
2231 		 * or "open".
2232 		 *
2233 		 * If its "closed", then no itxs have been committed to
2234 		 * it, so there's no point in issuing its zio (i.e.
2235 		 * it's "empty").
2236 		 *
2237 		 * If its "open" state, then it contains one or more
2238 		 * itxs that eventually need to be committed to stable
2239 		 * storage. In this case we intentionally do not issue
2240 		 * the lwb's zio to disk yet, and instead rely on one of
2241 		 * the following two mechanisms for issuing the zio:
2242 		 *
2243 		 * 1. Ideally, there will be more ZIL activity occuring
2244 		 * on the system, such that this function will be
2245 		 * immediately called again (not necessarily by the same
2246 		 * thread) and this lwb's zio will be issued via
2247 		 * zil_lwb_commit(). This way, the lwb is guaranteed to
2248 		 * be "full" when it is issued to disk, and we'll make
2249 		 * use of the lwb's size the best we can.
2250 		 *
2251 		 * 2. If there isn't sufficient ZIL activity occuring on
2252 		 * the system, such that this lwb's zio isn't issued via
2253 		 * zil_lwb_commit(), zil_commit_waiter() will issue the
2254 		 * lwb's zio. If this occurs, the lwb is not guaranteed
2255 		 * to be "full" by the time its zio is issued, and means
2256 		 * the size of the lwb was "too large" given the amount
2257 		 * of ZIL activity occuring on the system at that time.
2258 		 *
2259 		 * We do this for a couple of reasons:
2260 		 *
2261 		 * 1. To try and reduce the number of IOPs needed to
2262 		 * write the same number of itxs. If an lwb has space
2263 		 * available in it's buffer for more itxs, and more itxs
2264 		 * will be committed relatively soon (relative to the
2265 		 * latency of performing a write), then it's beneficial
2266 		 * to wait for these "next" itxs. This way, more itxs
2267 		 * can be committed to stable storage with fewer writes.
2268 		 *
2269 		 * 2. To try and use the largest lwb block size that the
2270 		 * incoming rate of itxs can support. Again, this is to
2271 		 * try and pack as many itxs into as few lwbs as
2272 		 * possible, without significantly impacting the latency
2273 		 * of each individual itx.
2274 		 */
2275 	}
2276 }
2277 
2278 /*
2279  * This function is responsible for ensuring the passed in commit waiter
2280  * (and associated commit itx) is committed to an lwb. If the waiter is
2281  * not already committed to an lwb, all itxs in the zilog's queue of
2282  * itxs will be processed. The assumption is the passed in waiter's
2283  * commit itx will found in the queue just like the other non-commit
2284  * itxs, such that when the entire queue is processed, the waiter will
2285  * have been commited to an lwb.
2286  *
2287  * The lwb associated with the passed in waiter is not guaranteed to
2288  * have been issued by the time this function completes. If the lwb is
2289  * not issued, we rely on future calls to zil_commit_writer() to issue
2290  * the lwb, or the timeout mechanism found in zil_commit_waiter().
2291  */
2292 static void
2293 zil_commit_writer(zilog_t *zilog, zil_commit_waiter_t *zcw)
2294 {
2295 	ASSERT(!MUTEX_HELD(&zilog->zl_lock));
2296 	ASSERT(spa_writeable(zilog->zl_spa));
2297 
2298 	mutex_enter(&zilog->zl_issuer_lock);
2299 
2300 	if (zcw->zcw_lwb != NULL || zcw->zcw_done) {
2301 		/*
2302 		 * It's possible that, while we were waiting to acquire
2303 		 * the "zl_issuer_lock", another thread committed this
2304 		 * waiter to an lwb. If that occurs, we bail out early,
2305 		 * without processing any of the zilog's queue of itxs.
2306 		 *
2307 		 * On certain workloads and system configurations, the
2308 		 * "zl_issuer_lock" can become highly contended. In an
2309 		 * attempt to reduce this contention, we immediately drop
2310 		 * the lock if the waiter has already been processed.
2311 		 *
2312 		 * We've measured this optimization to reduce CPU spent
2313 		 * contending on this lock by up to 5%, using a system
2314 		 * with 32 CPUs, low latency storage (~50 usec writes),
2315 		 * and 1024 threads performing sync writes.
2316 		 */
2317 		goto out;
2318 	}
2319 
2320 	zil_get_commit_list(zilog);
2321 	zil_prune_commit_list(zilog);
2322 	zil_process_commit_list(zilog);
2323 
2324 out:
2325 	mutex_exit(&zilog->zl_issuer_lock);
2326 }
2327 
2328 static void
2329 zil_commit_waiter_timeout(zilog_t *zilog, zil_commit_waiter_t *zcw)
2330 {
2331 	ASSERT(!MUTEX_HELD(&zilog->zl_issuer_lock));
2332 	ASSERT(MUTEX_HELD(&zcw->zcw_lock));
2333 	ASSERT3B(zcw->zcw_done, ==, B_FALSE);
2334 
2335 	lwb_t *lwb = zcw->zcw_lwb;
2336 	ASSERT3P(lwb, !=, NULL);
2337 	ASSERT3S(lwb->lwb_state, !=, LWB_STATE_CLOSED);
2338 
2339 	/*
2340 	 * If the lwb has already been issued by another thread, we can
2341 	 * immediately return since there's no work to be done (the
2342 	 * point of this function is to issue the lwb). Additionally, we
2343 	 * do this prior to acquiring the zl_issuer_lock, to avoid
2344 	 * acquiring it when it's not necessary to do so.
2345 	 */
2346 	if (lwb->lwb_state == LWB_STATE_ISSUED ||
2347 	    lwb->lwb_state == LWB_STATE_WRITE_DONE ||
2348 	    lwb->lwb_state == LWB_STATE_FLUSH_DONE)
2349 		return;
2350 
2351 	/*
2352 	 * In order to call zil_lwb_write_issue() we must hold the
2353 	 * zilog's "zl_issuer_lock". We can't simply acquire that lock,
2354 	 * since we're already holding the commit waiter's "zcw_lock",
2355 	 * and those two locks are aquired in the opposite order
2356 	 * elsewhere.
2357 	 */
2358 	mutex_exit(&zcw->zcw_lock);
2359 	mutex_enter(&zilog->zl_issuer_lock);
2360 	mutex_enter(&zcw->zcw_lock);
2361 
2362 	/*
2363 	 * Since we just dropped and re-acquired the commit waiter's
2364 	 * lock, we have to re-check to see if the waiter was marked
2365 	 * "done" during that process. If the waiter was marked "done",
2366 	 * the "lwb" pointer is no longer valid (it can be free'd after
2367 	 * the waiter is marked "done"), so without this check we could
2368 	 * wind up with a use-after-free error below.
2369 	 */
2370 	if (zcw->zcw_done)
2371 		goto out;
2372 
2373 	ASSERT3P(lwb, ==, zcw->zcw_lwb);
2374 
2375 	/*
2376 	 * We've already checked this above, but since we hadn't acquired
2377 	 * the zilog's zl_issuer_lock, we have to perform this check a
2378 	 * second time while holding the lock.
2379 	 *
2380 	 * We don't need to hold the zl_lock since the lwb cannot transition
2381 	 * from OPENED to ISSUED while we hold the zl_issuer_lock. The lwb
2382 	 * _can_ transition from ISSUED to DONE, but it's OK to race with
2383 	 * that transition since we treat the lwb the same, whether it's in
2384 	 * the ISSUED or DONE states.
2385 	 *
2386 	 * The important thing, is we treat the lwb differently depending on
2387 	 * if it's ISSUED or OPENED, and block any other threads that might
2388 	 * attempt to issue this lwb. For that reason we hold the
2389 	 * zl_issuer_lock when checking the lwb_state; we must not call
2390 	 * zil_lwb_write_issue() if the lwb had already been issued.
2391 	 *
2392 	 * See the comment above the lwb_state_t structure definition for
2393 	 * more details on the lwb states, and locking requirements.
2394 	 */
2395 	if (lwb->lwb_state == LWB_STATE_ISSUED ||
2396 	    lwb->lwb_state == LWB_STATE_WRITE_DONE ||
2397 	    lwb->lwb_state == LWB_STATE_FLUSH_DONE)
2398 		goto out;
2399 
2400 	ASSERT3S(lwb->lwb_state, ==, LWB_STATE_OPENED);
2401 
2402 	/*
2403 	 * As described in the comments above zil_commit_waiter() and
2404 	 * zil_process_commit_list(), we need to issue this lwb's zio
2405 	 * since we've reached the commit waiter's timeout and it still
2406 	 * hasn't been issued.
2407 	 */
2408 	lwb_t *nlwb = zil_lwb_write_issue(zilog, lwb);
2409 
2410 	IMPLY(nlwb != NULL, lwb->lwb_state != LWB_STATE_OPENED);
2411 
2412 	/*
2413 	 * Since the lwb's zio hadn't been issued by the time this thread
2414 	 * reached its timeout, we reset the zilog's "zl_cur_used" field
2415 	 * to influence the zil block size selection algorithm.
2416 	 *
2417 	 * By having to issue the lwb's zio here, it means the size of the
2418 	 * lwb was too large, given the incoming throughput of itxs.  By
2419 	 * setting "zl_cur_used" to zero, we communicate this fact to the
2420 	 * block size selection algorithm, so it can take this informaiton
2421 	 * into account, and potentially select a smaller size for the
2422 	 * next lwb block that is allocated.
2423 	 */
2424 	zilog->zl_cur_used = 0;
2425 
2426 	if (nlwb == NULL) {
2427 		/*
2428 		 * When zil_lwb_write_issue() returns NULL, this
2429 		 * indicates zio_alloc_zil() failed to allocate the
2430 		 * "next" lwb on-disk. When this occurs, the ZIL write
2431 		 * pipeline must be stalled; see the comment within the
2432 		 * zil_commit_writer_stall() function for more details.
2433 		 *
2434 		 * We must drop the commit waiter's lock prior to
2435 		 * calling zil_commit_writer_stall() or else we can wind
2436 		 * up with the following deadlock:
2437 		 *
2438 		 * - This thread is waiting for the txg to sync while
2439 		 *   holding the waiter's lock; txg_wait_synced() is
2440 		 *   used within txg_commit_writer_stall().
2441 		 *
2442 		 * - The txg can't sync because it is waiting for this
2443 		 *   lwb's zio callback to call dmu_tx_commit().
2444 		 *
2445 		 * - The lwb's zio callback can't call dmu_tx_commit()
2446 		 *   because it's blocked trying to acquire the waiter's
2447 		 *   lock, which occurs prior to calling dmu_tx_commit()
2448 		 */
2449 		mutex_exit(&zcw->zcw_lock);
2450 		zil_commit_writer_stall(zilog);
2451 		mutex_enter(&zcw->zcw_lock);
2452 	}
2453 
2454 out:
2455 	mutex_exit(&zilog->zl_issuer_lock);
2456 	ASSERT(MUTEX_HELD(&zcw->zcw_lock));
2457 }
2458 
2459 /*
2460  * This function is responsible for performing the following two tasks:
2461  *
2462  * 1. its primary responsibility is to block until the given "commit
2463  *    waiter" is considered "done".
2464  *
2465  * 2. its secondary responsibility is to issue the zio for the lwb that
2466  *    the given "commit waiter" is waiting on, if this function has
2467  *    waited "long enough" and the lwb is still in the "open" state.
2468  *
2469  * Given a sufficient amount of itxs being generated and written using
2470  * the ZIL, the lwb's zio will be issued via the zil_lwb_commit()
2471  * function. If this does not occur, this secondary responsibility will
2472  * ensure the lwb is issued even if there is not other synchronous
2473  * activity on the system.
2474  *
2475  * For more details, see zil_process_commit_list(); more specifically,
2476  * the comment at the bottom of that function.
2477  */
2478 static void
2479 zil_commit_waiter(zilog_t *zilog, zil_commit_waiter_t *zcw)
2480 {
2481 	ASSERT(!MUTEX_HELD(&zilog->zl_lock));
2482 	ASSERT(!MUTEX_HELD(&zilog->zl_issuer_lock));
2483 	ASSERT(spa_writeable(zilog->zl_spa));
2484 
2485 	mutex_enter(&zcw->zcw_lock);
2486 
2487 	/*
2488 	 * The timeout is scaled based on the lwb latency to avoid
2489 	 * significantly impacting the latency of each individual itx.
2490 	 * For more details, see the comment at the bottom of the
2491 	 * zil_process_commit_list() function.
2492 	 */
2493 	int pct = MAX(zfs_commit_timeout_pct, 1);
2494 	hrtime_t sleep = (zilog->zl_last_lwb_latency * pct) / 100;
2495 	hrtime_t wakeup = gethrtime() + sleep;
2496 	boolean_t timedout = B_FALSE;
2497 
2498 	while (!zcw->zcw_done) {
2499 		ASSERT(MUTEX_HELD(&zcw->zcw_lock));
2500 
2501 		lwb_t *lwb = zcw->zcw_lwb;
2502 
2503 		/*
2504 		 * Usually, the waiter will have a non-NULL lwb field here,
2505 		 * but it's possible for it to be NULL as a result of
2506 		 * zil_commit() racing with spa_sync().
2507 		 *
2508 		 * When zil_clean() is called, it's possible for the itxg
2509 		 * list (which may be cleaned via a taskq) to contain
2510 		 * commit itxs. When this occurs, the commit waiters linked
2511 		 * off of these commit itxs will not be committed to an
2512 		 * lwb.  Additionally, these commit waiters will not be
2513 		 * marked done until zil_commit_waiter_skip() is called via
2514 		 * zil_itxg_clean().
2515 		 *
2516 		 * Thus, it's possible for this commit waiter (i.e. the
2517 		 * "zcw" variable) to be found in this "in between" state;
2518 		 * where it's "zcw_lwb" field is NULL, and it hasn't yet
2519 		 * been skipped, so it's "zcw_done" field is still B_FALSE.
2520 		 */
2521 		IMPLY(lwb != NULL, lwb->lwb_state != LWB_STATE_CLOSED);
2522 
2523 		if (lwb != NULL && lwb->lwb_state == LWB_STATE_OPENED) {
2524 			ASSERT3B(timedout, ==, B_FALSE);
2525 
2526 			/*
2527 			 * If the lwb hasn't been issued yet, then we
2528 			 * need to wait with a timeout, in case this
2529 			 * function needs to issue the lwb after the
2530 			 * timeout is reached; responsibility (2) from
2531 			 * the comment above this function.
2532 			 */
2533 			clock_t timeleft = cv_timedwait_hires(&zcw->zcw_cv,
2534 			    &zcw->zcw_lock, wakeup, USEC2NSEC(1),
2535 			    CALLOUT_FLAG_ABSOLUTE);
2536 
2537 			if (timeleft >= 0 || zcw->zcw_done)
2538 				continue;
2539 
2540 			timedout = B_TRUE;
2541 			zil_commit_waiter_timeout(zilog, zcw);
2542 
2543 			if (!zcw->zcw_done) {
2544 				/*
2545 				 * If the commit waiter has already been
2546 				 * marked "done", it's possible for the
2547 				 * waiter's lwb structure to have already
2548 				 * been freed.  Thus, we can only reliably
2549 				 * make these assertions if the waiter
2550 				 * isn't done.
2551 				 */
2552 				ASSERT3P(lwb, ==, zcw->zcw_lwb);
2553 				ASSERT3S(lwb->lwb_state, !=, LWB_STATE_OPENED);
2554 			}
2555 		} else {
2556 			/*
2557 			 * If the lwb isn't open, then it must have already
2558 			 * been issued. In that case, there's no need to
2559 			 * use a timeout when waiting for the lwb to
2560 			 * complete.
2561 			 *
2562 			 * Additionally, if the lwb is NULL, the waiter
2563 			 * will soon be signalled and marked done via
2564 			 * zil_clean() and zil_itxg_clean(), so no timeout
2565 			 * is required.
2566 			 */
2567 
2568 			IMPLY(lwb != NULL,
2569 			    lwb->lwb_state == LWB_STATE_ISSUED ||
2570 			    lwb->lwb_state == LWB_STATE_WRITE_DONE ||
2571 			    lwb->lwb_state == LWB_STATE_FLUSH_DONE);
2572 			cv_wait(&zcw->zcw_cv, &zcw->zcw_lock);
2573 		}
2574 	}
2575 
2576 	mutex_exit(&zcw->zcw_lock);
2577 }
2578 
2579 static zil_commit_waiter_t *
2580 zil_alloc_commit_waiter()
2581 {
2582 	zil_commit_waiter_t *zcw = kmem_cache_alloc(zil_zcw_cache, KM_SLEEP);
2583 
2584 	cv_init(&zcw->zcw_cv, NULL, CV_DEFAULT, NULL);
2585 	mutex_init(&zcw->zcw_lock, NULL, MUTEX_DEFAULT, NULL);
2586 	list_link_init(&zcw->zcw_node);
2587 	zcw->zcw_lwb = NULL;
2588 	zcw->zcw_done = B_FALSE;
2589 	zcw->zcw_zio_error = 0;
2590 
2591 	return (zcw);
2592 }
2593 
2594 static void
2595 zil_free_commit_waiter(zil_commit_waiter_t *zcw)
2596 {
2597 	ASSERT(!list_link_active(&zcw->zcw_node));
2598 	ASSERT3P(zcw->zcw_lwb, ==, NULL);
2599 	ASSERT3B(zcw->zcw_done, ==, B_TRUE);
2600 	mutex_destroy(&zcw->zcw_lock);
2601 	cv_destroy(&zcw->zcw_cv);
2602 	kmem_cache_free(zil_zcw_cache, zcw);
2603 }
2604 
2605 /*
2606  * This function is used to create a TX_COMMIT itx and assign it. This
2607  * way, it will be linked into the ZIL's list of synchronous itxs, and
2608  * then later committed to an lwb (or skipped) when
2609  * zil_process_commit_list() is called.
2610  */
2611 static void
2612 zil_commit_itx_assign(zilog_t *zilog, zil_commit_waiter_t *zcw)
2613 {
2614 	dmu_tx_t *tx = dmu_tx_create(zilog->zl_os);
2615 	VERIFY0(dmu_tx_assign(tx, TXG_WAIT));
2616 
2617 	itx_t *itx = zil_itx_create(TX_COMMIT, sizeof (lr_t));
2618 	itx->itx_sync = B_TRUE;
2619 	itx->itx_private = zcw;
2620 
2621 	zil_itx_assign(zilog, itx, tx);
2622 
2623 	dmu_tx_commit(tx);
2624 }
2625 
2626 /*
2627  * Commit ZFS Intent Log transactions (itxs) to stable storage.
2628  *
2629  * When writing ZIL transactions to the on-disk representation of the
2630  * ZIL, the itxs are committed to a Log Write Block (lwb). Multiple
2631  * itxs can be committed to a single lwb. Once a lwb is written and
2632  * committed to stable storage (i.e. the lwb is written, and vdevs have
2633  * been flushed), each itx that was committed to that lwb is also
2634  * considered to be committed to stable storage.
2635  *
2636  * When an itx is committed to an lwb, the log record (lr_t) contained
2637  * by the itx is copied into the lwb's zio buffer, and once this buffer
2638  * is written to disk, it becomes an on-disk ZIL block.
2639  *
2640  * As itxs are generated, they're inserted into the ZIL's queue of
2641  * uncommitted itxs. The semantics of zil_commit() are such that it will
2642  * block until all itxs that were in the queue when it was called, are
2643  * committed to stable storage.
2644  *
2645  * If "foid" is zero, this means all "synchronous" and "asynchronous"
2646  * itxs, for all objects in the dataset, will be committed to stable
2647  * storage prior to zil_commit() returning. If "foid" is non-zero, all
2648  * "synchronous" itxs for all objects, but only "asynchronous" itxs
2649  * that correspond to the foid passed in, will be committed to stable
2650  * storage prior to zil_commit() returning.
2651  *
2652  * Generally speaking, when zil_commit() is called, the consumer doesn't
2653  * actually care about _all_ of the uncommitted itxs. Instead, they're
2654  * simply trying to waiting for a specific itx to be committed to disk,
2655  * but the interface(s) for interacting with the ZIL don't allow such
2656  * fine-grained communication. A better interface would allow a consumer
2657  * to create and assign an itx, and then pass a reference to this itx to
2658  * zil_commit(); such that zil_commit() would return as soon as that
2659  * specific itx was committed to disk (instead of waiting for _all_
2660  * itxs to be committed).
2661  *
2662  * When a thread calls zil_commit() a special "commit itx" will be
2663  * generated, along with a corresponding "waiter" for this commit itx.
2664  * zil_commit() will wait on this waiter's CV, such that when the waiter
2665  * is marked done, and signalled, zil_commit() will return.
2666  *
2667  * This commit itx is inserted into the queue of uncommitted itxs. This
2668  * provides an easy mechanism for determining which itxs were in the
2669  * queue prior to zil_commit() having been called, and which itxs were
2670  * added after zil_commit() was called.
2671  *
2672  * The commit it is special; it doesn't have any on-disk representation.
2673  * When a commit itx is "committed" to an lwb, the waiter associated
2674  * with it is linked onto the lwb's list of waiters. Then, when that lwb
2675  * completes, each waiter on the lwb's list is marked done and signalled
2676  * -- allowing the thread waiting on the waiter to return from zil_commit().
2677  *
2678  * It's important to point out a few critical factors that allow us
2679  * to make use of the commit itxs, commit waiters, per-lwb lists of
2680  * commit waiters, and zio completion callbacks like we're doing:
2681  *
2682  *   1. The list of waiters for each lwb is traversed, and each commit
2683  *      waiter is marked "done" and signalled, in the zio completion
2684  *      callback of the lwb's zio[*].
2685  *
2686  *      * Actually, the waiters are signalled in the zio completion
2687  *        callback of the root zio for the DKIOCFLUSHWRITECACHE commands
2688  *        that are sent to the vdevs upon completion of the lwb zio.
2689  *
2690  *   2. When the itxs are inserted into the ZIL's queue of uncommitted
2691  *      itxs, the order in which they are inserted is preserved[*]; as
2692  *      itxs are added to the queue, they are added to the tail of
2693  *      in-memory linked lists.
2694  *
2695  *      When committing the itxs to lwbs (to be written to disk), they
2696  *      are committed in the same order in which the itxs were added to
2697  *      the uncommitted queue's linked list(s); i.e. the linked list of
2698  *      itxs to commit is traversed from head to tail, and each itx is
2699  *      committed to an lwb in that order.
2700  *
2701  *      * To clarify:
2702  *
2703  *        - the order of "sync" itxs is preserved w.r.t. other
2704  *          "sync" itxs, regardless of the corresponding objects.
2705  *        - the order of "async" itxs is preserved w.r.t. other
2706  *          "async" itxs corresponding to the same object.
2707  *        - the order of "async" itxs is *not* preserved w.r.t. other
2708  *          "async" itxs corresponding to different objects.
2709  *        - the order of "sync" itxs w.r.t. "async" itxs (or vice
2710  *          versa) is *not* preserved, even for itxs that correspond
2711  *          to the same object.
2712  *
2713  *      For more details, see: zil_itx_assign(), zil_async_to_sync(),
2714  *      zil_get_commit_list(), and zil_process_commit_list().
2715  *
2716  *   3. The lwbs represent a linked list of blocks on disk. Thus, any
2717  *      lwb cannot be considered committed to stable storage, until its
2718  *      "previous" lwb is also committed to stable storage. This fact,
2719  *      coupled with the fact described above, means that itxs are
2720  *      committed in (roughly) the order in which they were generated.
2721  *      This is essential because itxs are dependent on prior itxs.
2722  *      Thus, we *must not* deem an itx as being committed to stable
2723  *      storage, until *all* prior itxs have also been committed to
2724  *      stable storage.
2725  *
2726  *      To enforce this ordering of lwb zio's, while still leveraging as
2727  *      much of the underlying storage performance as possible, we rely
2728  *      on two fundamental concepts:
2729  *
2730  *          1. The creation and issuance of lwb zio's is protected by
2731  *             the zilog's "zl_issuer_lock", which ensures only a single
2732  *             thread is creating and/or issuing lwb's at a time
2733  *          2. The "previous" lwb is a child of the "current" lwb
2734  *             (leveraging the zio parent-child depenency graph)
2735  *
2736  *      By relying on this parent-child zio relationship, we can have
2737  *      many lwb zio's concurrently issued to the underlying storage,
2738  *      but the order in which they complete will be the same order in
2739  *      which they were created.
2740  */
2741 void
2742 zil_commit(zilog_t *zilog, uint64_t foid)
2743 {
2744 	/*
2745 	 * We should never attempt to call zil_commit on a snapshot for
2746 	 * a couple of reasons:
2747 	 *
2748 	 * 1. A snapshot may never be modified, thus it cannot have any
2749 	 *    in-flight itxs that would have modified the dataset.
2750 	 *
2751 	 * 2. By design, when zil_commit() is called, a commit itx will
2752 	 *    be assigned to this zilog; as a result, the zilog will be
2753 	 *    dirtied. We must not dirty the zilog of a snapshot; there's
2754 	 *    checks in the code that enforce this invariant, and will
2755 	 *    cause a panic if it's not upheld.
2756 	 */
2757 	ASSERT3B(dmu_objset_is_snapshot(zilog->zl_os), ==, B_FALSE);
2758 
2759 	if (zilog->zl_sync == ZFS_SYNC_DISABLED)
2760 		return;
2761 
2762 	if (!spa_writeable(zilog->zl_spa)) {
2763 		/*
2764 		 * If the SPA is not writable, there should never be any
2765 		 * pending itxs waiting to be committed to disk. If that
2766 		 * weren't true, we'd skip writing those itxs out, and
2767 		 * would break the sematics of zil_commit(); thus, we're
2768 		 * verifying that truth before we return to the caller.
2769 		 */
2770 		ASSERT(list_is_empty(&zilog->zl_lwb_list));
2771 		ASSERT3P(zilog->zl_last_lwb_opened, ==, NULL);
2772 		for (int i = 0; i < TXG_SIZE; i++)
2773 			ASSERT3P(zilog->zl_itxg[i].itxg_itxs, ==, NULL);
2774 		return;
2775 	}
2776 
2777 	/*
2778 	 * If the ZIL is suspended, we don't want to dirty it by calling
2779 	 * zil_commit_itx_assign() below, nor can we write out
2780 	 * lwbs like would be done in zil_commit_write(). Thus, we
2781 	 * simply rely on txg_wait_synced() to maintain the necessary
2782 	 * semantics, and avoid calling those functions altogether.
2783 	 */
2784 	if (zilog->zl_suspend > 0) {
2785 		txg_wait_synced(zilog->zl_dmu_pool, 0);
2786 		return;
2787 	}
2788 
2789 	zil_commit_impl(zilog, foid);
2790 }
2791 
2792 void
2793 zil_commit_impl(zilog_t *zilog, uint64_t foid)
2794 {
2795 	/*
2796 	 * Move the "async" itxs for the specified foid to the "sync"
2797 	 * queues, such that they will be later committed (or skipped)
2798 	 * to an lwb when zil_process_commit_list() is called.
2799 	 *
2800 	 * Since these "async" itxs must be committed prior to this
2801 	 * call to zil_commit returning, we must perform this operation
2802 	 * before we call zil_commit_itx_assign().
2803 	 */
2804 	zil_async_to_sync(zilog, foid);
2805 
2806 	/*
2807 	 * We allocate a new "waiter" structure which will initially be
2808 	 * linked to the commit itx using the itx's "itx_private" field.
2809 	 * Since the commit itx doesn't represent any on-disk state,
2810 	 * when it's committed to an lwb, rather than copying the its
2811 	 * lr_t into the lwb's buffer, the commit itx's "waiter" will be
2812 	 * added to the lwb's list of waiters. Then, when the lwb is
2813 	 * committed to stable storage, each waiter in the lwb's list of
2814 	 * waiters will be marked "done", and signalled.
2815 	 *
2816 	 * We must create the waiter and assign the commit itx prior to
2817 	 * calling zil_commit_writer(), or else our specific commit itx
2818 	 * is not guaranteed to be committed to an lwb prior to calling
2819 	 * zil_commit_waiter().
2820 	 */
2821 	zil_commit_waiter_t *zcw = zil_alloc_commit_waiter();
2822 	zil_commit_itx_assign(zilog, zcw);
2823 
2824 	zil_commit_writer(zilog, zcw);
2825 	zil_commit_waiter(zilog, zcw);
2826 
2827 	if (zcw->zcw_zio_error != 0) {
2828 		/*
2829 		 * If there was an error writing out the ZIL blocks that
2830 		 * this thread is waiting on, then we fallback to
2831 		 * relying on spa_sync() to write out the data this
2832 		 * thread is waiting on. Obviously this has performance
2833 		 * implications, but the expectation is for this to be
2834 		 * an exceptional case, and shouldn't occur often.
2835 		 */
2836 		DTRACE_PROBE2(zil__commit__io__error,
2837 		    zilog_t *, zilog, zil_commit_waiter_t *, zcw);
2838 		txg_wait_synced(zilog->zl_dmu_pool, 0);
2839 	}
2840 
2841 	zil_free_commit_waiter(zcw);
2842 }
2843 
2844 /*
2845  * Called in syncing context to free committed log blocks and update log header.
2846  */
2847 void
2848 zil_sync(zilog_t *zilog, dmu_tx_t *tx)
2849 {
2850 	zil_header_t *zh = zil_header_in_syncing_context(zilog);
2851 	uint64_t txg = dmu_tx_get_txg(tx);
2852 	spa_t *spa = zilog->zl_spa;
2853 	uint64_t *replayed_seq = &zilog->zl_replayed_seq[txg & TXG_MASK];
2854 	lwb_t *lwb;
2855 
2856 	/*
2857 	 * We don't zero out zl_destroy_txg, so make sure we don't try
2858 	 * to destroy it twice.
2859 	 */
2860 	if (spa_sync_pass(spa) != 1)
2861 		return;
2862 
2863 	mutex_enter(&zilog->zl_lock);
2864 
2865 	ASSERT(zilog->zl_stop_sync == 0);
2866 
2867 	if (*replayed_seq != 0) {
2868 		ASSERT(zh->zh_replay_seq < *replayed_seq);
2869 		zh->zh_replay_seq = *replayed_seq;
2870 		*replayed_seq = 0;
2871 	}
2872 
2873 	if (zilog->zl_destroy_txg == txg) {
2874 		blkptr_t blk = zh->zh_log;
2875 
2876 		ASSERT(list_head(&zilog->zl_lwb_list) == NULL);
2877 
2878 		bzero(zh, sizeof (zil_header_t));
2879 		bzero(zilog->zl_replayed_seq, sizeof (zilog->zl_replayed_seq));
2880 
2881 		if (zilog->zl_keep_first) {
2882 			/*
2883 			 * If this block was part of log chain that couldn't
2884 			 * be claimed because a device was missing during
2885 			 * zil_claim(), but that device later returns,
2886 			 * then this block could erroneously appear valid.
2887 			 * To guard against this, assign a new GUID to the new
2888 			 * log chain so it doesn't matter what blk points to.
2889 			 */
2890 			zil_init_log_chain(zilog, &blk);
2891 			zh->zh_log = blk;
2892 		}
2893 	}
2894 
2895 	while ((lwb = list_head(&zilog->zl_lwb_list)) != NULL) {
2896 		zh->zh_log = lwb->lwb_blk;
2897 		if (lwb->lwb_buf != NULL || lwb->lwb_max_txg > txg)
2898 			break;
2899 		list_remove(&zilog->zl_lwb_list, lwb);
2900 		zio_free(spa, txg, &lwb->lwb_blk);
2901 		zil_free_lwb(zilog, lwb);
2902 
2903 		/*
2904 		 * If we don't have anything left in the lwb list then
2905 		 * we've had an allocation failure and we need to zero
2906 		 * out the zil_header blkptr so that we don't end
2907 		 * up freeing the same block twice.
2908 		 */
2909 		if (list_head(&zilog->zl_lwb_list) == NULL)
2910 			BP_ZERO(&zh->zh_log);
2911 	}
2912 	mutex_exit(&zilog->zl_lock);
2913 }
2914 
2915 /* ARGSUSED */
2916 static int
2917 zil_lwb_cons(void *vbuf, void *unused, int kmflag)
2918 {
2919 	lwb_t *lwb = vbuf;
2920 	list_create(&lwb->lwb_waiters, sizeof (zil_commit_waiter_t),
2921 	    offsetof(zil_commit_waiter_t, zcw_node));
2922 	avl_create(&lwb->lwb_vdev_tree, zil_lwb_vdev_compare,
2923 	    sizeof (zil_vdev_node_t), offsetof(zil_vdev_node_t, zv_node));
2924 	mutex_init(&lwb->lwb_vdev_lock, NULL, MUTEX_DEFAULT, NULL);
2925 	return (0);
2926 }
2927 
2928 /* ARGSUSED */
2929 static void
2930 zil_lwb_dest(void *vbuf, void *unused)
2931 {
2932 	lwb_t *lwb = vbuf;
2933 	mutex_destroy(&lwb->lwb_vdev_lock);
2934 	avl_destroy(&lwb->lwb_vdev_tree);
2935 	list_destroy(&lwb->lwb_waiters);
2936 }
2937 
2938 void
2939 zil_init(void)
2940 {
2941 	zil_lwb_cache = kmem_cache_create("zil_lwb_cache",
2942 	    sizeof (lwb_t), 0, zil_lwb_cons, zil_lwb_dest, NULL, NULL, NULL, 0);
2943 
2944 	zil_zcw_cache = kmem_cache_create("zil_zcw_cache",
2945 	    sizeof (zil_commit_waiter_t), 0, NULL, NULL, NULL, NULL, NULL, 0);
2946 }
2947 
2948 void
2949 zil_fini(void)
2950 {
2951 	kmem_cache_destroy(zil_zcw_cache);
2952 	kmem_cache_destroy(zil_lwb_cache);
2953 }
2954 
2955 void
2956 zil_set_sync(zilog_t *zilog, uint64_t sync)
2957 {
2958 	zilog->zl_sync = sync;
2959 }
2960 
2961 void
2962 zil_set_logbias(zilog_t *zilog, uint64_t logbias)
2963 {
2964 	zilog->zl_logbias = logbias;
2965 }
2966 
2967 zilog_t *
2968 zil_alloc(objset_t *os, zil_header_t *zh_phys)
2969 {
2970 	zilog_t *zilog;
2971 
2972 	zilog = kmem_zalloc(sizeof (zilog_t), KM_SLEEP);
2973 
2974 	zilog->zl_header = zh_phys;
2975 	zilog->zl_os = os;
2976 	zilog->zl_spa = dmu_objset_spa(os);
2977 	zilog->zl_dmu_pool = dmu_objset_pool(os);
2978 	zilog->zl_destroy_txg = TXG_INITIAL - 1;
2979 	zilog->zl_logbias = dmu_objset_logbias(os);
2980 	zilog->zl_sync = dmu_objset_syncprop(os);
2981 	zilog->zl_dirty_max_txg = 0;
2982 	zilog->zl_last_lwb_opened = NULL;
2983 	zilog->zl_last_lwb_latency = 0;
2984 
2985 	mutex_init(&zilog->zl_lock, NULL, MUTEX_DEFAULT, NULL);
2986 	mutex_init(&zilog->zl_issuer_lock, NULL, MUTEX_DEFAULT, NULL);
2987 
2988 	for (int i = 0; i < TXG_SIZE; i++) {
2989 		mutex_init(&zilog->zl_itxg[i].itxg_lock, NULL,
2990 		    MUTEX_DEFAULT, NULL);
2991 	}
2992 
2993 	list_create(&zilog->zl_lwb_list, sizeof (lwb_t),
2994 	    offsetof(lwb_t, lwb_node));
2995 
2996 	list_create(&zilog->zl_itx_commit_list, sizeof (itx_t),
2997 	    offsetof(itx_t, itx_node));
2998 
2999 	cv_init(&zilog->zl_cv_suspend, NULL, CV_DEFAULT, NULL);
3000 
3001 	return (zilog);
3002 }
3003 
3004 void
3005 zil_free(zilog_t *zilog)
3006 {
3007 	zilog->zl_stop_sync = 1;
3008 
3009 	ASSERT0(zilog->zl_suspend);
3010 	ASSERT0(zilog->zl_suspending);
3011 
3012 	ASSERT(list_is_empty(&zilog->zl_lwb_list));
3013 	list_destroy(&zilog->zl_lwb_list);
3014 
3015 	ASSERT(list_is_empty(&zilog->zl_itx_commit_list));
3016 	list_destroy(&zilog->zl_itx_commit_list);
3017 
3018 	for (int i = 0; i < TXG_SIZE; i++) {
3019 		/*
3020 		 * It's possible for an itx to be generated that doesn't dirty
3021 		 * a txg (e.g. ztest TX_TRUNCATE). So there's no zil_clean()
3022 		 * callback to remove the entry. We remove those here.
3023 		 *
3024 		 * Also free up the ziltest itxs.
3025 		 */
3026 		if (zilog->zl_itxg[i].itxg_itxs)
3027 			zil_itxg_clean(zilog->zl_itxg[i].itxg_itxs);
3028 		mutex_destroy(&zilog->zl_itxg[i].itxg_lock);
3029 	}
3030 
3031 	mutex_destroy(&zilog->zl_issuer_lock);
3032 	mutex_destroy(&zilog->zl_lock);
3033 
3034 	cv_destroy(&zilog->zl_cv_suspend);
3035 
3036 	kmem_free(zilog, sizeof (zilog_t));
3037 }
3038 
3039 /*
3040  * Open an intent log.
3041  */
3042 zilog_t *
3043 zil_open(objset_t *os, zil_get_data_t *get_data)
3044 {
3045 	zilog_t *zilog = dmu_objset_zil(os);
3046 
3047 	ASSERT3P(zilog->zl_get_data, ==, NULL);
3048 	ASSERT3P(zilog->zl_last_lwb_opened, ==, NULL);
3049 	ASSERT(list_is_empty(&zilog->zl_lwb_list));
3050 
3051 	zilog->zl_get_data = get_data;
3052 
3053 	return (zilog);
3054 }
3055 
3056 /*
3057  * Close an intent log.
3058  */
3059 void
3060 zil_close(zilog_t *zilog)
3061 {
3062 	lwb_t *lwb;
3063 	uint64_t txg;
3064 
3065 	if (!dmu_objset_is_snapshot(zilog->zl_os)) {
3066 		zil_commit(zilog, 0);
3067 	} else {
3068 		ASSERT3P(list_tail(&zilog->zl_lwb_list), ==, NULL);
3069 		ASSERT0(zilog->zl_dirty_max_txg);
3070 		ASSERT3B(zilog_is_dirty(zilog), ==, B_FALSE);
3071 	}
3072 
3073 	mutex_enter(&zilog->zl_lock);
3074 	lwb = list_tail(&zilog->zl_lwb_list);
3075 	if (lwb == NULL)
3076 		txg = zilog->zl_dirty_max_txg;
3077 	else
3078 		txg = MAX(zilog->zl_dirty_max_txg, lwb->lwb_max_txg);
3079 	mutex_exit(&zilog->zl_lock);
3080 
3081 	/*
3082 	 * We need to use txg_wait_synced() to wait long enough for the
3083 	 * ZIL to be clean, and to wait for all pending lwbs to be
3084 	 * written out.
3085 	 */
3086 	if (txg != 0)
3087 		txg_wait_synced(zilog->zl_dmu_pool, txg);
3088 
3089 	if (zilog_is_dirty(zilog))
3090 		zfs_dbgmsg("zil (%p) is dirty, txg %llu", zilog, txg);
3091 	VERIFY(!zilog_is_dirty(zilog));
3092 
3093 	zilog->zl_get_data = NULL;
3094 
3095 	/*
3096 	 * We should have only one lwb left on the list; remove it now.
3097 	 */
3098 	mutex_enter(&zilog->zl_lock);
3099 	lwb = list_head(&zilog->zl_lwb_list);
3100 	if (lwb != NULL) {
3101 		ASSERT3P(lwb, ==, list_tail(&zilog->zl_lwb_list));
3102 		ASSERT3S(lwb->lwb_state, !=, LWB_STATE_ISSUED);
3103 		list_remove(&zilog->zl_lwb_list, lwb);
3104 		zio_buf_free(lwb->lwb_buf, lwb->lwb_sz);
3105 		zil_free_lwb(zilog, lwb);
3106 	}
3107 	mutex_exit(&zilog->zl_lock);
3108 }
3109 
3110 static char *suspend_tag = "zil suspending";
3111 
3112 /*
3113  * Suspend an intent log.  While in suspended mode, we still honor
3114  * synchronous semantics, but we rely on txg_wait_synced() to do it.
3115  * On old version pools, we suspend the log briefly when taking a
3116  * snapshot so that it will have an empty intent log.
3117  *
3118  * Long holds are not really intended to be used the way we do here --
3119  * held for such a short time.  A concurrent caller of dsl_dataset_long_held()
3120  * could fail.  Therefore we take pains to only put a long hold if it is
3121  * actually necessary.  Fortunately, it will only be necessary if the
3122  * objset is currently mounted (or the ZVOL equivalent).  In that case it
3123  * will already have a long hold, so we are not really making things any worse.
3124  *
3125  * Ideally, we would locate the existing long-holder (i.e. the zfsvfs_t or
3126  * zvol_state_t), and use their mechanism to prevent their hold from being
3127  * dropped (e.g. VFS_HOLD()).  However, that would be even more pain for
3128  * very little gain.
3129  *
3130  * if cookiep == NULL, this does both the suspend & resume.
3131  * Otherwise, it returns with the dataset "long held", and the cookie
3132  * should be passed into zil_resume().
3133  */
3134 int
3135 zil_suspend(const char *osname, void **cookiep)
3136 {
3137 	objset_t *os;
3138 	zilog_t *zilog;
3139 	const zil_header_t *zh;
3140 	int error;
3141 
3142 	error = dmu_objset_hold(osname, suspend_tag, &os);
3143 	if (error != 0)
3144 		return (error);
3145 	zilog = dmu_objset_zil(os);
3146 
3147 	mutex_enter(&zilog->zl_lock);
3148 	zh = zilog->zl_header;
3149 
3150 	if (zh->zh_flags & ZIL_REPLAY_NEEDED) {		/* unplayed log */
3151 		mutex_exit(&zilog->zl_lock);
3152 		dmu_objset_rele(os, suspend_tag);
3153 		return (SET_ERROR(EBUSY));
3154 	}
3155 
3156 	/*
3157 	 * Don't put a long hold in the cases where we can avoid it.  This
3158 	 * is when there is no cookie so we are doing a suspend & resume
3159 	 * (i.e. called from zil_vdev_offline()), and there's nothing to do
3160 	 * for the suspend because it's already suspended, or there's no ZIL.
3161 	 */
3162 	if (cookiep == NULL && !zilog->zl_suspending &&
3163 	    (zilog->zl_suspend > 0 || BP_IS_HOLE(&zh->zh_log))) {
3164 		mutex_exit(&zilog->zl_lock);
3165 		dmu_objset_rele(os, suspend_tag);
3166 		return (0);
3167 	}
3168 
3169 	dsl_dataset_long_hold(dmu_objset_ds(os), suspend_tag);
3170 	dsl_pool_rele(dmu_objset_pool(os), suspend_tag);
3171 
3172 	zilog->zl_suspend++;
3173 
3174 	if (zilog->zl_suspend > 1) {
3175 		/*
3176 		 * Someone else is already suspending it.
3177 		 * Just wait for them to finish.
3178 		 */
3179 
3180 		while (zilog->zl_suspending)
3181 			cv_wait(&zilog->zl_cv_suspend, &zilog->zl_lock);
3182 		mutex_exit(&zilog->zl_lock);
3183 
3184 		if (cookiep == NULL)
3185 			zil_resume(os);
3186 		else
3187 			*cookiep = os;
3188 		return (0);
3189 	}
3190 
3191 	/*
3192 	 * If there is no pointer to an on-disk block, this ZIL must not
3193 	 * be active (e.g. filesystem not mounted), so there's nothing
3194 	 * to clean up.
3195 	 */
3196 	if (BP_IS_HOLE(&zh->zh_log)) {
3197 		ASSERT(cookiep != NULL); /* fast path already handled */
3198 
3199 		*cookiep = os;
3200 		mutex_exit(&zilog->zl_lock);
3201 		return (0);
3202 	}
3203 
3204 	zilog->zl_suspending = B_TRUE;
3205 	mutex_exit(&zilog->zl_lock);
3206 
3207 	/*
3208 	 * We need to use zil_commit_impl to ensure we wait for all
3209 	 * LWB_STATE_OPENED and LWB_STATE_ISSUED lwb's to be committed
3210 	 * to disk before proceeding. If we used zil_commit instead, it
3211 	 * would just call txg_wait_synced(), because zl_suspend is set.
3212 	 * txg_wait_synced() doesn't wait for these lwb's to be
3213 	 * LWB_STATE_FLUSH_DONE before returning.
3214 	 */
3215 	zil_commit_impl(zilog, 0);
3216 
3217 	/*
3218 	 * Now that we've ensured all lwb's are LWB_STATE_FLUSH_DONE, we
3219 	 * use txg_wait_synced() to ensure the data from the zilog has
3220 	 * migrated to the main pool before calling zil_destroy().
3221 	 */
3222 	txg_wait_synced(zilog->zl_dmu_pool, 0);
3223 
3224 	zil_destroy(zilog, B_FALSE);
3225 
3226 	mutex_enter(&zilog->zl_lock);
3227 	zilog->zl_suspending = B_FALSE;
3228 	cv_broadcast(&zilog->zl_cv_suspend);
3229 	mutex_exit(&zilog->zl_lock);
3230 
3231 	if (cookiep == NULL)
3232 		zil_resume(os);
3233 	else
3234 		*cookiep = os;
3235 	return (0);
3236 }
3237 
3238 void
3239 zil_resume(void *cookie)
3240 {
3241 	objset_t *os = cookie;
3242 	zilog_t *zilog = dmu_objset_zil(os);
3243 
3244 	mutex_enter(&zilog->zl_lock);
3245 	ASSERT(zilog->zl_suspend != 0);
3246 	zilog->zl_suspend--;
3247 	mutex_exit(&zilog->zl_lock);
3248 	dsl_dataset_long_rele(dmu_objset_ds(os), suspend_tag);
3249 	dsl_dataset_rele(dmu_objset_ds(os), suspend_tag);
3250 }
3251 
3252 typedef struct zil_replay_arg {
3253 	zil_replay_func_t **zr_replay;
3254 	void		*zr_arg;
3255 	boolean_t	zr_byteswap;
3256 	char		*zr_lr;
3257 } zil_replay_arg_t;
3258 
3259 static int
3260 zil_replay_error(zilog_t *zilog, lr_t *lr, int error)
3261 {
3262 	char name[ZFS_MAX_DATASET_NAME_LEN];
3263 
3264 	zilog->zl_replaying_seq--;	/* didn't actually replay this one */
3265 
3266 	dmu_objset_name(zilog->zl_os, name);
3267 
3268 	cmn_err(CE_WARN, "ZFS replay transaction error %d, "
3269 	    "dataset %s, seq 0x%llx, txtype %llu %s\n", error, name,
3270 	    (u_longlong_t)lr->lrc_seq,
3271 	    (u_longlong_t)(lr->lrc_txtype & ~TX_CI),
3272 	    (lr->lrc_txtype & TX_CI) ? "CI" : "");
3273 
3274 	return (error);
3275 }
3276 
3277 static int
3278 zil_replay_log_record(zilog_t *zilog, lr_t *lr, void *zra, uint64_t claim_txg)
3279 {
3280 	zil_replay_arg_t *zr = zra;
3281 	const zil_header_t *zh = zilog->zl_header;
3282 	uint64_t reclen = lr->lrc_reclen;
3283 	uint64_t txtype = lr->lrc_txtype;
3284 	int error = 0;
3285 
3286 	zilog->zl_replaying_seq = lr->lrc_seq;
3287 
3288 	if (lr->lrc_seq <= zh->zh_replay_seq)	/* already replayed */
3289 		return (0);
3290 
3291 	if (lr->lrc_txg < claim_txg)		/* already committed */
3292 		return (0);
3293 
3294 	/* Strip case-insensitive bit, still present in log record */
3295 	txtype &= ~TX_CI;
3296 
3297 	if (txtype == 0 || txtype >= TX_MAX_TYPE)
3298 		return (zil_replay_error(zilog, lr, EINVAL));
3299 
3300 	/*
3301 	 * If this record type can be logged out of order, the object
3302 	 * (lr_foid) may no longer exist.  That's legitimate, not an error.
3303 	 */
3304 	if (TX_OOO(txtype)) {
3305 		error = dmu_object_info(zilog->zl_os,
3306 		    ((lr_ooo_t *)lr)->lr_foid, NULL);
3307 		if (error == ENOENT || error == EEXIST)
3308 			return (0);
3309 	}
3310 
3311 	/*
3312 	 * Make a copy of the data so we can revise and extend it.
3313 	 */
3314 	bcopy(lr, zr->zr_lr, reclen);
3315 
3316 	/*
3317 	 * If this is a TX_WRITE with a blkptr, suck in the data.
3318 	 */
3319 	if (txtype == TX_WRITE && reclen == sizeof (lr_write_t)) {
3320 		error = zil_read_log_data(zilog, (lr_write_t *)lr,
3321 		    zr->zr_lr + reclen);
3322 		if (error != 0)
3323 			return (zil_replay_error(zilog, lr, error));
3324 	}
3325 
3326 	/*
3327 	 * The log block containing this lr may have been byteswapped
3328 	 * so that we can easily examine common fields like lrc_txtype.
3329 	 * However, the log is a mix of different record types, and only the
3330 	 * replay vectors know how to byteswap their records.  Therefore, if
3331 	 * the lr was byteswapped, undo it before invoking the replay vector.
3332 	 */
3333 	if (zr->zr_byteswap)
3334 		byteswap_uint64_array(zr->zr_lr, reclen);
3335 
3336 	/*
3337 	 * We must now do two things atomically: replay this log record,
3338 	 * and update the log header sequence number to reflect the fact that
3339 	 * we did so. At the end of each replay function the sequence number
3340 	 * is updated if we are in replay mode.
3341 	 */
3342 	error = zr->zr_replay[txtype](zr->zr_arg, zr->zr_lr, zr->zr_byteswap);
3343 	if (error != 0) {
3344 		/*
3345 		 * The DMU's dnode layer doesn't see removes until the txg
3346 		 * commits, so a subsequent claim can spuriously fail with
3347 		 * EEXIST. So if we receive any error we try syncing out
3348 		 * any removes then retry the transaction.  Note that we
3349 		 * specify B_FALSE for byteswap now, so we don't do it twice.
3350 		 */
3351 		txg_wait_synced(spa_get_dsl(zilog->zl_spa), 0);
3352 		error = zr->zr_replay[txtype](zr->zr_arg, zr->zr_lr, B_FALSE);
3353 		if (error != 0)
3354 			return (zil_replay_error(zilog, lr, error));
3355 	}
3356 	return (0);
3357 }
3358 
3359 /* ARGSUSED */
3360 static int
3361 zil_incr_blks(zilog_t *zilog, blkptr_t *bp, void *arg, uint64_t claim_txg)
3362 {
3363 	zilog->zl_replay_blks++;
3364 
3365 	return (0);
3366 }
3367 
3368 /*
3369  * If this dataset has a non-empty intent log, replay it and destroy it.
3370  */
3371 void
3372 zil_replay(objset_t *os, void *arg, zil_replay_func_t *replay_func[TX_MAX_TYPE])
3373 {
3374 	zilog_t *zilog = dmu_objset_zil(os);
3375 	const zil_header_t *zh = zilog->zl_header;
3376 	zil_replay_arg_t zr;
3377 
3378 	if ((zh->zh_flags & ZIL_REPLAY_NEEDED) == 0) {
3379 		zil_destroy(zilog, B_TRUE);
3380 		return;
3381 	}
3382 
3383 	zr.zr_replay = replay_func;
3384 	zr.zr_arg = arg;
3385 	zr.zr_byteswap = BP_SHOULD_BYTESWAP(&zh->zh_log);
3386 	zr.zr_lr = kmem_alloc(2 * SPA_MAXBLOCKSIZE, KM_SLEEP);
3387 
3388 	/*
3389 	 * Wait for in-progress removes to sync before starting replay.
3390 	 */
3391 	txg_wait_synced(zilog->zl_dmu_pool, 0);
3392 
3393 	zilog->zl_replay = B_TRUE;
3394 	zilog->zl_replay_time = ddi_get_lbolt();
3395 	ASSERT(zilog->zl_replay_blks == 0);
3396 	(void) zil_parse(zilog, zil_incr_blks, zil_replay_log_record, &zr,
3397 	    zh->zh_claim_txg);
3398 	kmem_free(zr.zr_lr, 2 * SPA_MAXBLOCKSIZE);
3399 
3400 	zil_destroy(zilog, B_FALSE);
3401 	txg_wait_synced(zilog->zl_dmu_pool, zilog->zl_destroy_txg);
3402 	zilog->zl_replay = B_FALSE;
3403 }
3404 
3405 boolean_t
3406 zil_replaying(zilog_t *zilog, dmu_tx_t *tx)
3407 {
3408 	if (zilog->zl_sync == ZFS_SYNC_DISABLED)
3409 		return (B_TRUE);
3410 
3411 	if (zilog->zl_replay) {
3412 		dsl_dataset_dirty(dmu_objset_ds(zilog->zl_os), tx);
3413 		zilog->zl_replayed_seq[dmu_tx_get_txg(tx) & TXG_MASK] =
3414 		    zilog->zl_replaying_seq;
3415 		return (B_TRUE);
3416 	}
3417 
3418 	return (B_FALSE);
3419 }
3420 
3421 /* ARGSUSED */
3422 int
3423 zil_reset(const char *osname, void *arg)
3424 {
3425 	int error;
3426 
3427 	error = zil_suspend(osname, NULL);
3428 	if (error != 0)
3429 		return (SET_ERROR(EEXIST));
3430 	return (0);
3431 }
3432