xref: /illumos-gate/usr/src/uts/common/fs/zfs/zil.c (revision 6e1f5caa9321646aa4212d48e32a0d241866d85d)
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 2010 Sun Microsystems, Inc.  All rights reserved.
23  * Use is subject to license terms.
24  */
25 
26 #include <sys/zfs_context.h>
27 #include <sys/spa.h>
28 #include <sys/dmu.h>
29 #include <sys/zap.h>
30 #include <sys/arc.h>
31 #include <sys/stat.h>
32 #include <sys/resource.h>
33 #include <sys/zil.h>
34 #include <sys/zil_impl.h>
35 #include <sys/dsl_dataset.h>
36 #include <sys/vdev.h>
37 #include <sys/dmu_tx.h>
38 
39 /*
40  * The zfs intent log (ZIL) saves transaction records of system calls
41  * that change the file system in memory with enough information
42  * to be able to replay them. These are stored in memory until
43  * either the DMU transaction group (txg) commits them to the stable pool
44  * and they can be discarded, or they are flushed to the stable log
45  * (also in the pool) due to a fsync, O_DSYNC or other synchronous
46  * requirement. In the event of a panic or power fail then those log
47  * records (transactions) are replayed.
48  *
49  * There is one ZIL per file system. Its on-disk (pool) format consists
50  * of 3 parts:
51  *
52  * 	- ZIL header
53  * 	- ZIL blocks
54  * 	- ZIL records
55  *
56  * A log record holds a system call transaction. Log blocks can
57  * hold many log records and the blocks are chained together.
58  * Each ZIL block contains a block pointer (blkptr_t) to the next
59  * ZIL block in the chain. The ZIL header points to the first
60  * block in the chain. Note there is not a fixed place in the pool
61  * to hold blocks. They are dynamically allocated and freed as
62  * needed from the blocks available. Figure X shows the ZIL structure:
63  */
64 
65 /*
66  * This global ZIL switch affects all pools
67  */
68 int zil_disable = 0;	/* disable intent logging */
69 
70 /*
71  * Tunable parameter for debugging or performance analysis.  Setting
72  * zfs_nocacheflush will cause corruption on power loss if a volatile
73  * out-of-order write cache is enabled.
74  */
75 boolean_t zfs_nocacheflush = B_FALSE;
76 
77 static kmem_cache_t *zil_lwb_cache;
78 
79 static boolean_t zil_empty(zilog_t *zilog);
80 
81 #define	LWB_EMPTY(lwb) ((BP_GET_LSIZE(&lwb->lwb_blk) - \
82     sizeof (zil_chain_t)) == (lwb->lwb_sz - lwb->lwb_nused))
83 
84 
85 static int
86 zil_bp_compare(const void *x1, const void *x2)
87 {
88 	const dva_t *dva1 = &((zil_bp_node_t *)x1)->zn_dva;
89 	const dva_t *dva2 = &((zil_bp_node_t *)x2)->zn_dva;
90 
91 	if (DVA_GET_VDEV(dva1) < DVA_GET_VDEV(dva2))
92 		return (-1);
93 	if (DVA_GET_VDEV(dva1) > DVA_GET_VDEV(dva2))
94 		return (1);
95 
96 	if (DVA_GET_OFFSET(dva1) < DVA_GET_OFFSET(dva2))
97 		return (-1);
98 	if (DVA_GET_OFFSET(dva1) > DVA_GET_OFFSET(dva2))
99 		return (1);
100 
101 	return (0);
102 }
103 
104 static void
105 zil_bp_tree_init(zilog_t *zilog)
106 {
107 	avl_create(&zilog->zl_bp_tree, zil_bp_compare,
108 	    sizeof (zil_bp_node_t), offsetof(zil_bp_node_t, zn_node));
109 }
110 
111 static void
112 zil_bp_tree_fini(zilog_t *zilog)
113 {
114 	avl_tree_t *t = &zilog->zl_bp_tree;
115 	zil_bp_node_t *zn;
116 	void *cookie = NULL;
117 
118 	while ((zn = avl_destroy_nodes(t, &cookie)) != NULL)
119 		kmem_free(zn, sizeof (zil_bp_node_t));
120 
121 	avl_destroy(t);
122 }
123 
124 int
125 zil_bp_tree_add(zilog_t *zilog, const blkptr_t *bp)
126 {
127 	avl_tree_t *t = &zilog->zl_bp_tree;
128 	const dva_t *dva = BP_IDENTITY(bp);
129 	zil_bp_node_t *zn;
130 	avl_index_t where;
131 
132 	if (avl_find(t, dva, &where) != NULL)
133 		return (EEXIST);
134 
135 	zn = kmem_alloc(sizeof (zil_bp_node_t), KM_SLEEP);
136 	zn->zn_dva = *dva;
137 	avl_insert(t, zn, where);
138 
139 	return (0);
140 }
141 
142 static zil_header_t *
143 zil_header_in_syncing_context(zilog_t *zilog)
144 {
145 	return ((zil_header_t *)zilog->zl_header);
146 }
147 
148 static void
149 zil_init_log_chain(zilog_t *zilog, blkptr_t *bp)
150 {
151 	zio_cksum_t *zc = &bp->blk_cksum;
152 
153 	zc->zc_word[ZIL_ZC_GUID_0] = spa_get_random(-1ULL);
154 	zc->zc_word[ZIL_ZC_GUID_1] = spa_get_random(-1ULL);
155 	zc->zc_word[ZIL_ZC_OBJSET] = dmu_objset_id(zilog->zl_os);
156 	zc->zc_word[ZIL_ZC_SEQ] = 1ULL;
157 }
158 
159 /*
160  * Read a log block and make sure it's valid.
161  */
162 static int
163 zil_read_log_block(zilog_t *zilog, const blkptr_t *bp, blkptr_t *nbp, void *dst,
164     char **end)
165 {
166 	enum zio_flag zio_flags = ZIO_FLAG_CANFAIL;
167 	uint32_t aflags = ARC_WAIT;
168 	arc_buf_t *abuf = NULL;
169 	zbookmark_t zb;
170 	int error;
171 
172 	if (zilog->zl_header->zh_claim_txg == 0)
173 		zio_flags |= ZIO_FLAG_SPECULATIVE | ZIO_FLAG_SCRUB;
174 
175 	if (!(zilog->zl_header->zh_flags & ZIL_CLAIM_LR_SEQ_VALID))
176 		zio_flags |= ZIO_FLAG_SPECULATIVE;
177 
178 	SET_BOOKMARK(&zb, bp->blk_cksum.zc_word[ZIL_ZC_OBJSET],
179 	    ZB_ZIL_OBJECT, ZB_ZIL_LEVEL, bp->blk_cksum.zc_word[ZIL_ZC_SEQ]);
180 
181 	error = arc_read_nolock(NULL, zilog->zl_spa, bp, arc_getbuf_func, &abuf,
182 	    ZIO_PRIORITY_SYNC_READ, zio_flags, &aflags, &zb);
183 
184 	if (error == 0) {
185 		zio_cksum_t cksum = bp->blk_cksum;
186 
187 		/*
188 		 * Validate the checksummed log block.
189 		 *
190 		 * Sequence numbers should be... sequential.  The checksum
191 		 * verifier for the next block should be bp's checksum plus 1.
192 		 *
193 		 * Also check the log chain linkage and size used.
194 		 */
195 		cksum.zc_word[ZIL_ZC_SEQ]++;
196 
197 		if (BP_GET_CHECKSUM(bp) == ZIO_CHECKSUM_ZILOG2) {
198 			zil_chain_t *zilc = abuf->b_data;
199 			char *lr = (char *)(zilc + 1);
200 			uint64_t len = zilc->zc_nused - sizeof (zil_chain_t);
201 
202 			if (bcmp(&cksum, &zilc->zc_next_blk.blk_cksum,
203 			    sizeof (cksum)) || BP_IS_HOLE(&zilc->zc_next_blk)) {
204 				error = ECKSUM;
205 			} else {
206 				bcopy(lr, dst, len);
207 				*end = (char *)dst + len;
208 				*nbp = zilc->zc_next_blk;
209 			}
210 		} else {
211 			char *lr = abuf->b_data;
212 			uint64_t size = BP_GET_LSIZE(bp);
213 			zil_chain_t *zilc = (zil_chain_t *)(lr + size) - 1;
214 
215 			if (bcmp(&cksum, &zilc->zc_next_blk.blk_cksum,
216 			    sizeof (cksum)) || BP_IS_HOLE(&zilc->zc_next_blk) ||
217 			    (zilc->zc_nused > (size - sizeof (*zilc)))) {
218 				error = ECKSUM;
219 			} else {
220 				bcopy(lr, dst, zilc->zc_nused);
221 				*end = (char *)dst + zilc->zc_nused;
222 				*nbp = zilc->zc_next_blk;
223 			}
224 		}
225 
226 		VERIFY(arc_buf_remove_ref(abuf, &abuf) == 1);
227 	}
228 
229 	return (error);
230 }
231 
232 /*
233  * Read a TX_WRITE log data block.
234  */
235 static int
236 zil_read_log_data(zilog_t *zilog, const lr_write_t *lr, void *wbuf)
237 {
238 	enum zio_flag zio_flags = ZIO_FLAG_CANFAIL;
239 	const blkptr_t *bp = &lr->lr_blkptr;
240 	uint32_t aflags = ARC_WAIT;
241 	arc_buf_t *abuf = NULL;
242 	zbookmark_t zb;
243 	int error;
244 
245 	if (BP_IS_HOLE(bp)) {
246 		if (wbuf != NULL)
247 			bzero(wbuf, MAX(BP_GET_LSIZE(bp), lr->lr_length));
248 		return (0);
249 	}
250 
251 	if (zilog->zl_header->zh_claim_txg == 0)
252 		zio_flags |= ZIO_FLAG_SPECULATIVE | ZIO_FLAG_SCRUB;
253 
254 	SET_BOOKMARK(&zb, dmu_objset_id(zilog->zl_os), lr->lr_foid,
255 	    ZB_ZIL_LEVEL, lr->lr_offset / BP_GET_LSIZE(bp));
256 
257 	error = arc_read_nolock(NULL, zilog->zl_spa, bp, arc_getbuf_func, &abuf,
258 	    ZIO_PRIORITY_SYNC_READ, zio_flags, &aflags, &zb);
259 
260 	if (error == 0) {
261 		if (wbuf != NULL)
262 			bcopy(abuf->b_data, wbuf, arc_buf_size(abuf));
263 		(void) arc_buf_remove_ref(abuf, &abuf);
264 	}
265 
266 	return (error);
267 }
268 
269 /*
270  * Parse the intent log, and call parse_func for each valid record within.
271  */
272 int
273 zil_parse(zilog_t *zilog, zil_parse_blk_func_t *parse_blk_func,
274     zil_parse_lr_func_t *parse_lr_func, void *arg, uint64_t txg)
275 {
276 	const zil_header_t *zh = zilog->zl_header;
277 	boolean_t claimed = !!zh->zh_claim_txg;
278 	uint64_t claim_blk_seq = claimed ? zh->zh_claim_blk_seq : UINT64_MAX;
279 	uint64_t claim_lr_seq = claimed ? zh->zh_claim_lr_seq : UINT64_MAX;
280 	uint64_t max_blk_seq = 0;
281 	uint64_t max_lr_seq = 0;
282 	uint64_t blk_count = 0;
283 	uint64_t lr_count = 0;
284 	blkptr_t blk, next_blk;
285 	char *lrbuf, *lrp;
286 	int error = 0;
287 
288 	/*
289 	 * Old logs didn't record the maximum zh_claim_lr_seq.
290 	 */
291 	if (!(zh->zh_flags & ZIL_CLAIM_LR_SEQ_VALID))
292 		claim_lr_seq = UINT64_MAX;
293 
294 	/*
295 	 * Starting at the block pointed to by zh_log we read the log chain.
296 	 * For each block in the chain we strongly check that block to
297 	 * ensure its validity.  We stop when an invalid block is found.
298 	 * For each block pointer in the chain we call parse_blk_func().
299 	 * For each record in each valid block we call parse_lr_func().
300 	 * If the log has been claimed, stop if we encounter a sequence
301 	 * number greater than the highest claimed sequence number.
302 	 */
303 	lrbuf = zio_buf_alloc(SPA_MAXBLOCKSIZE);
304 	zil_bp_tree_init(zilog);
305 
306 	for (blk = zh->zh_log; !BP_IS_HOLE(&blk); blk = next_blk) {
307 		uint64_t blk_seq = blk.blk_cksum.zc_word[ZIL_ZC_SEQ];
308 		int reclen;
309 		char *end;
310 
311 		if (blk_seq > claim_blk_seq)
312 			break;
313 		if ((error = parse_blk_func(zilog, &blk, arg, txg)) != 0)
314 			break;
315 		ASSERT3U(max_blk_seq, <, blk_seq);
316 		max_blk_seq = blk_seq;
317 		blk_count++;
318 
319 		if (max_lr_seq == claim_lr_seq && max_blk_seq == claim_blk_seq)
320 			break;
321 
322 		error = zil_read_log_block(zilog, &blk, &next_blk, lrbuf, &end);
323 		if (error)
324 			break;
325 
326 		for (lrp = lrbuf; lrp < end; lrp += reclen) {
327 			lr_t *lr = (lr_t *)lrp;
328 			reclen = lr->lrc_reclen;
329 			ASSERT3U(reclen, >=, sizeof (lr_t));
330 			if (lr->lrc_seq > claim_lr_seq)
331 				goto done;
332 			if ((error = parse_lr_func(zilog, lr, arg, txg)) != 0)
333 				goto done;
334 			ASSERT3U(max_lr_seq, <, lr->lrc_seq);
335 			max_lr_seq = lr->lrc_seq;
336 			lr_count++;
337 		}
338 	}
339 done:
340 	zilog->zl_parse_error = error;
341 	zilog->zl_parse_blk_seq = max_blk_seq;
342 	zilog->zl_parse_lr_seq = max_lr_seq;
343 	zilog->zl_parse_blk_count = blk_count;
344 	zilog->zl_parse_lr_count = lr_count;
345 
346 	ASSERT(!claimed || !(zh->zh_flags & ZIL_CLAIM_LR_SEQ_VALID) ||
347 	    (max_blk_seq == claim_blk_seq && max_lr_seq == claim_lr_seq));
348 
349 	zil_bp_tree_fini(zilog);
350 	zio_buf_free(lrbuf, SPA_MAXBLOCKSIZE);
351 
352 	return (error);
353 }
354 
355 static int
356 zil_claim_log_block(zilog_t *zilog, blkptr_t *bp, void *tx, uint64_t first_txg)
357 {
358 	/*
359 	 * Claim log block if not already committed and not already claimed.
360 	 * If tx == NULL, just verify that the block is claimable.
361 	 */
362 	if (bp->blk_birth < first_txg || zil_bp_tree_add(zilog, bp) != 0)
363 		return (0);
364 
365 	return (zio_wait(zio_claim(NULL, zilog->zl_spa,
366 	    tx == NULL ? 0 : first_txg, bp, spa_claim_notify, NULL,
367 	    ZIO_FLAG_CANFAIL | ZIO_FLAG_SPECULATIVE | ZIO_FLAG_SCRUB)));
368 }
369 
370 static int
371 zil_claim_log_record(zilog_t *zilog, lr_t *lrc, void *tx, uint64_t first_txg)
372 {
373 	lr_write_t *lr = (lr_write_t *)lrc;
374 	int error;
375 
376 	if (lrc->lrc_txtype != TX_WRITE)
377 		return (0);
378 
379 	/*
380 	 * If the block is not readable, don't claim it.  This can happen
381 	 * in normal operation when a log block is written to disk before
382 	 * some of the dmu_sync() blocks it points to.  In this case, the
383 	 * transaction cannot have been committed to anyone (we would have
384 	 * waited for all writes to be stable first), so it is semantically
385 	 * correct to declare this the end of the log.
386 	 */
387 	if (lr->lr_blkptr.blk_birth >= first_txg &&
388 	    (error = zil_read_log_data(zilog, lr, NULL)) != 0)
389 		return (error);
390 	return (zil_claim_log_block(zilog, &lr->lr_blkptr, tx, first_txg));
391 }
392 
393 /* ARGSUSED */
394 static int
395 zil_free_log_block(zilog_t *zilog, blkptr_t *bp, void *tx, uint64_t claim_txg)
396 {
397 	zio_free_zil(zilog->zl_spa, dmu_tx_get_txg(tx), bp);
398 
399 	return (0);
400 }
401 
402 static int
403 zil_free_log_record(zilog_t *zilog, lr_t *lrc, void *tx, uint64_t claim_txg)
404 {
405 	lr_write_t *lr = (lr_write_t *)lrc;
406 	blkptr_t *bp = &lr->lr_blkptr;
407 
408 	/*
409 	 * If we previously claimed it, we need to free it.
410 	 */
411 	if (claim_txg != 0 && lrc->lrc_txtype == TX_WRITE &&
412 	    bp->blk_birth >= claim_txg && zil_bp_tree_add(zilog, bp) == 0)
413 		zio_free(zilog->zl_spa, dmu_tx_get_txg(tx), bp);
414 
415 	return (0);
416 }
417 
418 static lwb_t *
419 zil_alloc_lwb(zilog_t *zilog, blkptr_t *bp, uint64_t txg)
420 {
421 	lwb_t *lwb;
422 
423 	lwb = kmem_cache_alloc(zil_lwb_cache, KM_SLEEP);
424 	lwb->lwb_zilog = zilog;
425 	lwb->lwb_blk = *bp;
426 	lwb->lwb_buf = zio_buf_alloc(BP_GET_LSIZE(bp));
427 	lwb->lwb_max_txg = txg;
428 	lwb->lwb_zio = NULL;
429 	lwb->lwb_tx = NULL;
430 	if (BP_GET_CHECKSUM(bp) == ZIO_CHECKSUM_ZILOG2) {
431 		lwb->lwb_nused = sizeof (zil_chain_t);
432 		lwb->lwb_sz = BP_GET_LSIZE(bp);
433 	} else {
434 		lwb->lwb_nused = 0;
435 		lwb->lwb_sz = BP_GET_LSIZE(bp) - sizeof (zil_chain_t);
436 	}
437 
438 	mutex_enter(&zilog->zl_lock);
439 	list_insert_tail(&zilog->zl_lwb_list, lwb);
440 	mutex_exit(&zilog->zl_lock);
441 
442 	return (lwb);
443 }
444 
445 /*
446  * Create an on-disk intent log.
447  */
448 static lwb_t *
449 zil_create(zilog_t *zilog)
450 {
451 	const zil_header_t *zh = zilog->zl_header;
452 	lwb_t *lwb = NULL;
453 	uint64_t txg = 0;
454 	dmu_tx_t *tx = NULL;
455 	blkptr_t blk;
456 	int error = 0;
457 
458 	/*
459 	 * Wait for any previous destroy to complete.
460 	 */
461 	txg_wait_synced(zilog->zl_dmu_pool, zilog->zl_destroy_txg);
462 
463 	ASSERT(zh->zh_claim_txg == 0);
464 	ASSERT(zh->zh_replay_seq == 0);
465 
466 	blk = zh->zh_log;
467 
468 	/*
469 	 * Allocate an initial log block if:
470 	 *    - there isn't one already
471 	 *    - the existing block is the wrong endianess
472 	 */
473 	if (BP_IS_HOLE(&blk) || BP_SHOULD_BYTESWAP(&blk)) {
474 		tx = dmu_tx_create(zilog->zl_os);
475 		VERIFY(dmu_tx_assign(tx, TXG_WAIT) == 0);
476 		dsl_dataset_dirty(dmu_objset_ds(zilog->zl_os), tx);
477 		txg = dmu_tx_get_txg(tx);
478 
479 		if (!BP_IS_HOLE(&blk)) {
480 			zio_free_zil(zilog->zl_spa, txg, &blk);
481 			BP_ZERO(&blk);
482 		}
483 
484 		error = zio_alloc_zil(zilog->zl_spa, txg, &blk, NULL,
485 		    ZIL_MIN_BLKSZ, zilog->zl_logbias == ZFS_LOGBIAS_LATENCY);
486 
487 		if (error == 0)
488 			zil_init_log_chain(zilog, &blk);
489 	}
490 
491 	/*
492 	 * Allocate a log write buffer (lwb) for the first log block.
493 	 */
494 	if (error == 0)
495 		lwb = zil_alloc_lwb(zilog, &blk, txg);
496 
497 	/*
498 	 * If we just allocated the first log block, commit our transaction
499 	 * and wait for zil_sync() to stuff the block poiner into zh_log.
500 	 * (zh is part of the MOS, so we cannot modify it in open context.)
501 	 */
502 	if (tx != NULL) {
503 		dmu_tx_commit(tx);
504 		txg_wait_synced(zilog->zl_dmu_pool, txg);
505 	}
506 
507 	ASSERT(bcmp(&blk, &zh->zh_log, sizeof (blk)) == 0);
508 
509 	return (lwb);
510 }
511 
512 /*
513  * In one tx, free all log blocks and clear the log header.
514  * If keep_first is set, then we're replaying a log with no content.
515  * We want to keep the first block, however, so that the first
516  * synchronous transaction doesn't require a txg_wait_synced()
517  * in zil_create().  We don't need to txg_wait_synced() here either
518  * when keep_first is set, because both zil_create() and zil_destroy()
519  * will wait for any in-progress destroys to complete.
520  */
521 void
522 zil_destroy(zilog_t *zilog, boolean_t keep_first)
523 {
524 	const zil_header_t *zh = zilog->zl_header;
525 	lwb_t *lwb;
526 	dmu_tx_t *tx;
527 	uint64_t txg;
528 
529 	/*
530 	 * Wait for any previous destroy to complete.
531 	 */
532 	txg_wait_synced(zilog->zl_dmu_pool, zilog->zl_destroy_txg);
533 
534 	zilog->zl_old_header = *zh;		/* debugging aid */
535 
536 	if (BP_IS_HOLE(&zh->zh_log))
537 		return;
538 
539 	tx = dmu_tx_create(zilog->zl_os);
540 	VERIFY(dmu_tx_assign(tx, TXG_WAIT) == 0);
541 	dsl_dataset_dirty(dmu_objset_ds(zilog->zl_os), tx);
542 	txg = dmu_tx_get_txg(tx);
543 
544 	mutex_enter(&zilog->zl_lock);
545 
546 	ASSERT3U(zilog->zl_destroy_txg, <, txg);
547 	zilog->zl_destroy_txg = txg;
548 	zilog->zl_keep_first = keep_first;
549 
550 	if (!list_is_empty(&zilog->zl_lwb_list)) {
551 		ASSERT(zh->zh_claim_txg == 0);
552 		ASSERT(!keep_first);
553 		while ((lwb = list_head(&zilog->zl_lwb_list)) != NULL) {
554 			list_remove(&zilog->zl_lwb_list, lwb);
555 			if (lwb->lwb_buf != NULL)
556 				zio_buf_free(lwb->lwb_buf, lwb->lwb_sz);
557 			zio_free_zil(zilog->zl_spa, txg, &lwb->lwb_blk);
558 			kmem_cache_free(zil_lwb_cache, lwb);
559 		}
560 	} else if (!keep_first) {
561 		(void) zil_parse(zilog, zil_free_log_block,
562 		    zil_free_log_record, tx, zh->zh_claim_txg);
563 	}
564 	mutex_exit(&zilog->zl_lock);
565 
566 	dmu_tx_commit(tx);
567 }
568 
569 int
570 zil_claim(const char *osname, void *txarg)
571 {
572 	dmu_tx_t *tx = txarg;
573 	uint64_t first_txg = dmu_tx_get_txg(tx);
574 	zilog_t *zilog;
575 	zil_header_t *zh;
576 	objset_t *os;
577 	int error;
578 
579 	error = dmu_objset_hold(osname, FTAG, &os);
580 	if (error) {
581 		cmn_err(CE_WARN, "can't open objset for %s", osname);
582 		return (0);
583 	}
584 
585 	zilog = dmu_objset_zil(os);
586 	zh = zil_header_in_syncing_context(zilog);
587 
588 	if (spa_get_log_state(zilog->zl_spa) == SPA_LOG_CLEAR) {
589 		if (!BP_IS_HOLE(&zh->zh_log))
590 			zio_free_zil(zilog->zl_spa, first_txg, &zh->zh_log);
591 		BP_ZERO(&zh->zh_log);
592 		dsl_dataset_dirty(dmu_objset_ds(os), tx);
593 		dmu_objset_rele(os, FTAG);
594 		return (0);
595 	}
596 
597 	/*
598 	 * Claim all log blocks if we haven't already done so, and remember
599 	 * the highest claimed sequence number.  This ensures that if we can
600 	 * read only part of the log now (e.g. due to a missing device),
601 	 * but we can read the entire log later, we will not try to replay
602 	 * or destroy beyond the last block we successfully claimed.
603 	 */
604 	ASSERT3U(zh->zh_claim_txg, <=, first_txg);
605 	if (zh->zh_claim_txg == 0 && !BP_IS_HOLE(&zh->zh_log)) {
606 		(void) zil_parse(zilog, zil_claim_log_block,
607 		    zil_claim_log_record, tx, first_txg);
608 		zh->zh_claim_txg = first_txg;
609 		zh->zh_claim_blk_seq = zilog->zl_parse_blk_seq;
610 		zh->zh_claim_lr_seq = zilog->zl_parse_lr_seq;
611 		if (zilog->zl_parse_lr_count || zilog->zl_parse_blk_count > 1)
612 			zh->zh_flags |= ZIL_REPLAY_NEEDED;
613 		zh->zh_flags |= ZIL_CLAIM_LR_SEQ_VALID;
614 		dsl_dataset_dirty(dmu_objset_ds(os), tx);
615 	}
616 
617 	ASSERT3U(first_txg, ==, (spa_last_synced_txg(zilog->zl_spa) + 1));
618 	dmu_objset_rele(os, FTAG);
619 	return (0);
620 }
621 
622 /*
623  * Check the log by walking the log chain.
624  * Checksum errors are ok as they indicate the end of the chain.
625  * Any other error (no device or read failure) returns an error.
626  */
627 int
628 zil_check_log_chain(const char *osname, void *tx)
629 {
630 	zilog_t *zilog;
631 	objset_t *os;
632 	int error;
633 
634 	ASSERT(tx == NULL);
635 
636 	error = dmu_objset_hold(osname, FTAG, &os);
637 	if (error) {
638 		cmn_err(CE_WARN, "can't open objset for %s", osname);
639 		return (0);
640 	}
641 
642 	zilog = dmu_objset_zil(os);
643 
644 	/*
645 	 * Because tx == NULL, zil_claim_log_block() will not actually claim
646 	 * any blocks, but just determine whether it is possible to do so.
647 	 * In addition to checking the log chain, zil_claim_log_block()
648 	 * will invoke zio_claim() with a done func of spa_claim_notify(),
649 	 * which will update spa_max_claim_txg.  See spa_load() for details.
650 	 */
651 	error = zil_parse(zilog, zil_claim_log_block, zil_claim_log_record, tx,
652 	    zilog->zl_header->zh_claim_txg ? -1ULL : spa_first_txg(os->os_spa));
653 
654 	dmu_objset_rele(os, FTAG);
655 
656 	return ((error == ECKSUM || error == ENOENT) ? 0 : error);
657 }
658 
659 static int
660 zil_vdev_compare(const void *x1, const void *x2)
661 {
662 	uint64_t v1 = ((zil_vdev_node_t *)x1)->zv_vdev;
663 	uint64_t v2 = ((zil_vdev_node_t *)x2)->zv_vdev;
664 
665 	if (v1 < v2)
666 		return (-1);
667 	if (v1 > v2)
668 		return (1);
669 
670 	return (0);
671 }
672 
673 void
674 zil_add_block(zilog_t *zilog, const blkptr_t *bp)
675 {
676 	avl_tree_t *t = &zilog->zl_vdev_tree;
677 	avl_index_t where;
678 	zil_vdev_node_t *zv, zvsearch;
679 	int ndvas = BP_GET_NDVAS(bp);
680 	int i;
681 
682 	if (zfs_nocacheflush)
683 		return;
684 
685 	ASSERT(zilog->zl_writer);
686 
687 	/*
688 	 * Even though we're zl_writer, we still need a lock because the
689 	 * zl_get_data() callbacks may have dmu_sync() done callbacks
690 	 * that will run concurrently.
691 	 */
692 	mutex_enter(&zilog->zl_vdev_lock);
693 	for (i = 0; i < ndvas; i++) {
694 		zvsearch.zv_vdev = DVA_GET_VDEV(&bp->blk_dva[i]);
695 		if (avl_find(t, &zvsearch, &where) == NULL) {
696 			zv = kmem_alloc(sizeof (*zv), KM_SLEEP);
697 			zv->zv_vdev = zvsearch.zv_vdev;
698 			avl_insert(t, zv, where);
699 		}
700 	}
701 	mutex_exit(&zilog->zl_vdev_lock);
702 }
703 
704 void
705 zil_flush_vdevs(zilog_t *zilog)
706 {
707 	spa_t *spa = zilog->zl_spa;
708 	avl_tree_t *t = &zilog->zl_vdev_tree;
709 	void *cookie = NULL;
710 	zil_vdev_node_t *zv;
711 	zio_t *zio;
712 
713 	ASSERT(zilog->zl_writer);
714 
715 	/*
716 	 * We don't need zl_vdev_lock here because we're the zl_writer,
717 	 * and all zl_get_data() callbacks are done.
718 	 */
719 	if (avl_numnodes(t) == 0)
720 		return;
721 
722 	spa_config_enter(spa, SCL_STATE, FTAG, RW_READER);
723 
724 	zio = zio_root(spa, NULL, NULL, ZIO_FLAG_CANFAIL);
725 
726 	while ((zv = avl_destroy_nodes(t, &cookie)) != NULL) {
727 		vdev_t *vd = vdev_lookup_top(spa, zv->zv_vdev);
728 		if (vd != NULL)
729 			zio_flush(zio, vd);
730 		kmem_free(zv, sizeof (*zv));
731 	}
732 
733 	/*
734 	 * Wait for all the flushes to complete.  Not all devices actually
735 	 * support the DKIOCFLUSHWRITECACHE ioctl, so it's OK if it fails.
736 	 */
737 	(void) zio_wait(zio);
738 
739 	spa_config_exit(spa, SCL_STATE, FTAG);
740 }
741 
742 /*
743  * Function called when a log block write completes
744  */
745 static void
746 zil_lwb_write_done(zio_t *zio)
747 {
748 	lwb_t *lwb = zio->io_private;
749 	zilog_t *zilog = lwb->lwb_zilog;
750 	dmu_tx_t *tx = lwb->lwb_tx;
751 
752 	ASSERT(BP_GET_COMPRESS(zio->io_bp) == ZIO_COMPRESS_OFF);
753 	ASSERT(BP_GET_TYPE(zio->io_bp) == DMU_OT_INTENT_LOG);
754 	ASSERT(BP_GET_LEVEL(zio->io_bp) == 0);
755 	ASSERT(BP_GET_BYTEORDER(zio->io_bp) == ZFS_HOST_BYTEORDER);
756 	ASSERT(!BP_IS_GANG(zio->io_bp));
757 	ASSERT(!BP_IS_HOLE(zio->io_bp));
758 	ASSERT(zio->io_bp->blk_fill == 0);
759 
760 	/*
761 	 * Ensure the lwb buffer pointer is cleared before releasing
762 	 * the txg. If we have had an allocation failure and
763 	 * the txg is waiting to sync then we want want zil_sync()
764 	 * to remove the lwb so that it's not picked up as the next new
765 	 * one in zil_commit_writer(). zil_sync() will only remove
766 	 * the lwb if lwb_buf is null.
767 	 */
768 	zio_buf_free(lwb->lwb_buf, lwb->lwb_sz);
769 	mutex_enter(&zilog->zl_lock);
770 	lwb->lwb_buf = NULL;
771 	lwb->lwb_tx = NULL;
772 	mutex_exit(&zilog->zl_lock);
773 
774 	/*
775 	 * Now that we've written this log block, we have a stable pointer
776 	 * to the next block in the chain, so it's OK to let the txg in
777 	 * which we allocated the next block sync.
778 	 */
779 	dmu_tx_commit(tx);
780 }
781 
782 /*
783  * Initialize the io for a log block.
784  */
785 static void
786 zil_lwb_write_init(zilog_t *zilog, lwb_t *lwb)
787 {
788 	zbookmark_t zb;
789 
790 	SET_BOOKMARK(&zb, lwb->lwb_blk.blk_cksum.zc_word[ZIL_ZC_OBJSET],
791 	    ZB_ZIL_OBJECT, ZB_ZIL_LEVEL,
792 	    lwb->lwb_blk.blk_cksum.zc_word[ZIL_ZC_SEQ]);
793 
794 	if (zilog->zl_root_zio == NULL) {
795 		zilog->zl_root_zio = zio_root(zilog->zl_spa, NULL, NULL,
796 		    ZIO_FLAG_CANFAIL);
797 	}
798 	if (lwb->lwb_zio == NULL) {
799 		lwb->lwb_zio = zio_rewrite(zilog->zl_root_zio, zilog->zl_spa,
800 		    0, &lwb->lwb_blk, lwb->lwb_buf, BP_GET_LSIZE(&lwb->lwb_blk),
801 		    zil_lwb_write_done, lwb, ZIO_PRIORITY_LOG_WRITE,
802 		    ZIO_FLAG_CANFAIL | ZIO_FLAG_DONT_PROPAGATE, &zb);
803 	}
804 }
805 
806 /*
807  * Define a limited set of intent log block sizes.
808  * These must be a multiple of 4KB. Note only the amount used (again
809  * aligned to 4KB) actually gets written. However, we can't always just
810  * allocate SPA_MAXBLOCKSIZE as the slog space could be exhausted.
811  */
812 uint64_t zil_block_buckets[] = {
813     4096,		/* non TX_WRITE */
814     8192+4096,		/* data base */
815     32*1024 + 4096, 	/* NFS writes */
816     UINT64_MAX
817 };
818 
819 /*
820  * Use the slog as long as the logbias is 'latency' and the current commit size
821  * is less than the limit or the total list size is less than 2X the limit.
822  * Limit checking is disabled by setting zil_slog_limit to UINT64_MAX.
823  */
824 uint64_t zil_slog_limit = 1024 * 1024;
825 #define	USE_SLOG(zilog) (((zilog)->zl_logbias == ZFS_LOGBIAS_LATENCY) && \
826 	(((zilog)->zl_cur_used < zil_slog_limit) || \
827 	((zilog)->zl_itx_list_sz < (zil_slog_limit << 1))))
828 
829 /*
830  * Start a log block write and advance to the next log block.
831  * Calls are serialized.
832  */
833 static lwb_t *
834 zil_lwb_write_start(zilog_t *zilog, lwb_t *lwb)
835 {
836 	lwb_t *nlwb = NULL;
837 	zil_chain_t *zilc;
838 	spa_t *spa = zilog->zl_spa;
839 	blkptr_t *bp;
840 	dmu_tx_t *tx;
841 	uint64_t txg;
842 	uint64_t zil_blksz;
843 	int i, error;
844 
845 	if (BP_GET_CHECKSUM(&lwb->lwb_blk) == ZIO_CHECKSUM_ZILOG2) {
846 		zilc = (zil_chain_t *)lwb->lwb_buf;
847 		bp = &zilc->zc_next_blk;
848 	} else {
849 		zilc = (zil_chain_t *)(lwb->lwb_buf + lwb->lwb_sz);
850 		bp = &zilc->zc_next_blk;
851 	}
852 
853 	ASSERT(lwb->lwb_nused <= lwb->lwb_sz);
854 
855 	/*
856 	 * Allocate the next block and save its address in this block
857 	 * before writing it in order to establish the log chain.
858 	 * Note that if the allocation of nlwb synced before we wrote
859 	 * the block that points at it (lwb), we'd leak it if we crashed.
860 	 * Therefore, we don't do dmu_tx_commit() until zil_lwb_write_done().
861 	 * We dirty the dataset to ensure that zil_sync() will be called
862 	 * to clean up in the event of allocation failure or I/O failure.
863 	 */
864 	tx = dmu_tx_create(zilog->zl_os);
865 	VERIFY(dmu_tx_assign(tx, TXG_WAIT) == 0);
866 	dsl_dataset_dirty(dmu_objset_ds(zilog->zl_os), tx);
867 	txg = dmu_tx_get_txg(tx);
868 
869 	lwb->lwb_tx = tx;
870 
871 	/*
872 	 * Log blocks are pre-allocated. Here we select the size of the next
873 	 * block, based on size used in the last block.
874 	 * - first find the smallest bucket that will fit the block from a
875 	 *   limited set of block sizes. This is because it's faster to write
876 	 *   blocks allocated from the same metaslab as they are adjacent or
877 	 *   close.
878 	 * - next find the maximum from the new suggested size and an array of
879 	 *   previous sizes. This lessens a picket fence effect of wrongly
880 	 *   guesssing the size if we have a stream of say 2k, 64k, 2k, 64k
881 	 *   requests.
882 	 *
883 	 * Note we only write what is used, but we can't just allocate
884 	 * the maximum block size because we can exhaust the available
885 	 * pool log space.
886 	 */
887 	zil_blksz = zilog->zl_cur_used + sizeof (zil_chain_t);
888 	for (i = 0; zil_blksz > zil_block_buckets[i]; i++)
889 		continue;
890 	zil_blksz = zil_block_buckets[i];
891 	if (zil_blksz == UINT64_MAX)
892 		zil_blksz = SPA_MAXBLOCKSIZE;
893 	zilog->zl_prev_blks[zilog->zl_prev_rotor] = zil_blksz;
894 	for (i = 0; i < ZIL_PREV_BLKS; i++)
895 		zil_blksz = MAX(zil_blksz, zilog->zl_prev_blks[i]);
896 	zilog->zl_prev_rotor = (zilog->zl_prev_rotor + 1) & (ZIL_PREV_BLKS - 1);
897 
898 	BP_ZERO(bp);
899 	/* pass the old blkptr in order to spread log blocks across devs */
900 	error = zio_alloc_zil(spa, txg, bp, &lwb->lwb_blk, zil_blksz,
901 	    USE_SLOG(zilog));
902 	if (!error) {
903 		ASSERT3U(bp->blk_birth, ==, txg);
904 		bp->blk_cksum = lwb->lwb_blk.blk_cksum;
905 		bp->blk_cksum.zc_word[ZIL_ZC_SEQ]++;
906 
907 		/*
908 		 * Allocate a new log write buffer (lwb).
909 		 */
910 		nlwb = zil_alloc_lwb(zilog, bp, txg);
911 
912 		/* Record the block for later vdev flushing */
913 		zil_add_block(zilog, &lwb->lwb_blk);
914 	}
915 
916 	if (BP_GET_CHECKSUM(&lwb->lwb_blk) == ZIO_CHECKSUM_ZILOG2) {
917 		uint64_t len;
918 
919 		/* For Slim ZIL only write what is used. */
920 		len = P2ROUNDUP_TYPED(lwb->lwb_nused, ZIL_MIN_BLKSZ, uint64_t);
921 		ASSERT3U(len, <=, lwb->lwb_sz);
922 		zio_shrink(lwb->lwb_zio, len);
923 
924 	}
925 	zilc->zc_pad = 0;
926 	zilc->zc_nused = lwb->lwb_nused;
927 	zilc->zc_eck.zec_cksum = lwb->lwb_blk.blk_cksum;
928 
929 	zio_nowait(lwb->lwb_zio); /* Kick off the write for the old log block */
930 
931 	/*
932 	 * If there was an allocation failure then nlwb will be null which
933 	 * forces a txg_wait_synced().
934 	 */
935 	return (nlwb);
936 }
937 
938 static lwb_t *
939 zil_lwb_commit(zilog_t *zilog, itx_t *itx, lwb_t *lwb)
940 {
941 	lr_t *lrc = &itx->itx_lr; /* common log record */
942 	lr_write_t *lrw = (lr_write_t *)lrc;
943 	char *lr_buf;
944 	uint64_t txg = lrc->lrc_txg;
945 	uint64_t reclen = lrc->lrc_reclen;
946 	uint64_t dlen = 0;
947 
948 	if (lwb == NULL)
949 		return (NULL);
950 
951 	ASSERT(lwb->lwb_buf != NULL);
952 
953 	if (lrc->lrc_txtype == TX_WRITE && itx->itx_wr_state == WR_NEED_COPY)
954 		dlen = P2ROUNDUP_TYPED(
955 		    lrw->lr_length, sizeof (uint64_t), uint64_t);
956 
957 	zilog->zl_cur_used += (reclen + dlen);
958 
959 	zil_lwb_write_init(zilog, lwb);
960 
961 	/*
962 	 * If this record won't fit in the current log block, start a new one.
963 	 */
964 	if (lwb->lwb_nused + reclen + dlen > lwb->lwb_sz) {
965 		lwb = zil_lwb_write_start(zilog, lwb);
966 		if (lwb == NULL)
967 			return (NULL);
968 		zil_lwb_write_init(zilog, lwb);
969 		ASSERT(LWB_EMPTY(lwb));
970 		if (lwb->lwb_nused + reclen + dlen > lwb->lwb_sz) {
971 			txg_wait_synced(zilog->zl_dmu_pool, txg);
972 			return (lwb);
973 		}
974 	}
975 
976 	lr_buf = lwb->lwb_buf + lwb->lwb_nused;
977 	bcopy(lrc, lr_buf, reclen);
978 	lrc = (lr_t *)lr_buf;
979 	lrw = (lr_write_t *)lrc;
980 
981 	/*
982 	 * If it's a write, fetch the data or get its blkptr as appropriate.
983 	 */
984 	if (lrc->lrc_txtype == TX_WRITE) {
985 		if (txg > spa_freeze_txg(zilog->zl_spa))
986 			txg_wait_synced(zilog->zl_dmu_pool, txg);
987 		if (itx->itx_wr_state != WR_COPIED) {
988 			char *dbuf;
989 			int error;
990 
991 			if (dlen) {
992 				ASSERT(itx->itx_wr_state == WR_NEED_COPY);
993 				dbuf = lr_buf + reclen;
994 				lrw->lr_common.lrc_reclen += dlen;
995 			} else {
996 				ASSERT(itx->itx_wr_state == WR_INDIRECT);
997 				dbuf = NULL;
998 			}
999 			error = zilog->zl_get_data(
1000 			    itx->itx_private, lrw, dbuf, lwb->lwb_zio);
1001 			if (error == EIO) {
1002 				txg_wait_synced(zilog->zl_dmu_pool, txg);
1003 				return (lwb);
1004 			}
1005 			if (error) {
1006 				ASSERT(error == ENOENT || error == EEXIST ||
1007 				    error == EALREADY);
1008 				return (lwb);
1009 			}
1010 		}
1011 	}
1012 
1013 	/*
1014 	 * We're actually making an entry, so update lrc_seq to be the
1015 	 * log record sequence number.  Note that this is generally not
1016 	 * equal to the itx sequence number because not all transactions
1017 	 * are synchronous, and sometimes spa_sync() gets there first.
1018 	 */
1019 	lrc->lrc_seq = ++zilog->zl_lr_seq; /* we are single threaded */
1020 	lwb->lwb_nused += reclen + dlen;
1021 	lwb->lwb_max_txg = MAX(lwb->lwb_max_txg, txg);
1022 	ASSERT3U(lwb->lwb_nused, <=, lwb->lwb_sz);
1023 	ASSERT3U(P2PHASE(lwb->lwb_nused, sizeof (uint64_t)), ==, 0);
1024 
1025 	return (lwb);
1026 }
1027 
1028 itx_t *
1029 zil_itx_create(uint64_t txtype, size_t lrsize)
1030 {
1031 	itx_t *itx;
1032 
1033 	lrsize = P2ROUNDUP_TYPED(lrsize, sizeof (uint64_t), size_t);
1034 
1035 	itx = kmem_alloc(offsetof(itx_t, itx_lr) + lrsize, KM_SLEEP);
1036 	itx->itx_lr.lrc_txtype = txtype;
1037 	itx->itx_lr.lrc_reclen = lrsize;
1038 	itx->itx_sod = lrsize; /* if write & WR_NEED_COPY will be increased */
1039 	itx->itx_lr.lrc_seq = 0;	/* defensive */
1040 
1041 	return (itx);
1042 }
1043 
1044 void
1045 zil_itx_destroy(itx_t *itx)
1046 {
1047 	kmem_free(itx, offsetof(itx_t, itx_lr) + itx->itx_lr.lrc_reclen);
1048 }
1049 
1050 uint64_t
1051 zil_itx_assign(zilog_t *zilog, itx_t *itx, dmu_tx_t *tx)
1052 {
1053 	uint64_t seq;
1054 
1055 	ASSERT(itx->itx_lr.lrc_seq == 0);
1056 	ASSERT(!zilog->zl_replay);
1057 
1058 	mutex_enter(&zilog->zl_lock);
1059 	list_insert_tail(&zilog->zl_itx_list, itx);
1060 	zilog->zl_itx_list_sz += itx->itx_sod;
1061 	itx->itx_lr.lrc_txg = dmu_tx_get_txg(tx);
1062 	itx->itx_lr.lrc_seq = seq = ++zilog->zl_itx_seq;
1063 	mutex_exit(&zilog->zl_lock);
1064 
1065 	return (seq);
1066 }
1067 
1068 /*
1069  * Free up all in-memory intent log transactions that have now been synced.
1070  */
1071 static void
1072 zil_itx_clean(zilog_t *zilog)
1073 {
1074 	uint64_t synced_txg = spa_last_synced_txg(zilog->zl_spa);
1075 	uint64_t freeze_txg = spa_freeze_txg(zilog->zl_spa);
1076 	list_t clean_list;
1077 	itx_t *itx;
1078 
1079 	list_create(&clean_list, sizeof (itx_t), offsetof(itx_t, itx_node));
1080 
1081 	mutex_enter(&zilog->zl_lock);
1082 	/* wait for a log writer to finish walking list */
1083 	while (zilog->zl_writer) {
1084 		cv_wait(&zilog->zl_cv_writer, &zilog->zl_lock);
1085 	}
1086 
1087 	/*
1088 	 * Move the sync'd log transactions to a separate list so we can call
1089 	 * kmem_free without holding the zl_lock.
1090 	 *
1091 	 * There is no need to set zl_writer as we don't drop zl_lock here
1092 	 */
1093 	while ((itx = list_head(&zilog->zl_itx_list)) != NULL &&
1094 	    itx->itx_lr.lrc_txg <= MIN(synced_txg, freeze_txg)) {
1095 		list_remove(&zilog->zl_itx_list, itx);
1096 		zilog->zl_itx_list_sz -= itx->itx_sod;
1097 		list_insert_tail(&clean_list, itx);
1098 	}
1099 	cv_broadcast(&zilog->zl_cv_writer);
1100 	mutex_exit(&zilog->zl_lock);
1101 
1102 	/* destroy sync'd log transactions */
1103 	while ((itx = list_head(&clean_list)) != NULL) {
1104 		list_remove(&clean_list, itx);
1105 		zil_itx_destroy(itx);
1106 	}
1107 	list_destroy(&clean_list);
1108 }
1109 
1110 /*
1111  * If there are any in-memory intent log transactions which have now been
1112  * synced then start up a taskq to free them.
1113  */
1114 void
1115 zil_clean(zilog_t *zilog)
1116 {
1117 	itx_t *itx;
1118 
1119 	mutex_enter(&zilog->zl_lock);
1120 	itx = list_head(&zilog->zl_itx_list);
1121 	if ((itx != NULL) &&
1122 	    (itx->itx_lr.lrc_txg <= spa_last_synced_txg(zilog->zl_spa))) {
1123 		(void) taskq_dispatch(zilog->zl_clean_taskq,
1124 		    (task_func_t *)zil_itx_clean, zilog, TQ_NOSLEEP);
1125 	}
1126 	mutex_exit(&zilog->zl_lock);
1127 }
1128 
1129 static void
1130 zil_commit_writer(zilog_t *zilog, uint64_t seq, uint64_t foid)
1131 {
1132 	uint64_t txg;
1133 	uint64_t commit_seq = 0;
1134 	itx_t *itx, *itx_next;
1135 	lwb_t *lwb;
1136 	spa_t *spa;
1137 	int error = 0;
1138 
1139 	zilog->zl_writer = B_TRUE;
1140 	ASSERT(zilog->zl_root_zio == NULL);
1141 	spa = zilog->zl_spa;
1142 
1143 	if (zilog->zl_suspend) {
1144 		lwb = NULL;
1145 	} else {
1146 		lwb = list_tail(&zilog->zl_lwb_list);
1147 		if (lwb == NULL) {
1148 			/*
1149 			 * Return if there's nothing to flush before we
1150 			 * dirty the fs by calling zil_create()
1151 			 */
1152 			if (list_is_empty(&zilog->zl_itx_list)) {
1153 				zilog->zl_writer = B_FALSE;
1154 				return;
1155 			}
1156 			mutex_exit(&zilog->zl_lock);
1157 			lwb = zil_create(zilog);
1158 			mutex_enter(&zilog->zl_lock);
1159 		}
1160 	}
1161 	ASSERT(lwb == NULL || lwb->lwb_zio == NULL);
1162 
1163 	/* Loop through in-memory log transactions filling log blocks. */
1164 	DTRACE_PROBE1(zil__cw1, zilog_t *, zilog);
1165 
1166 	for (itx = list_head(&zilog->zl_itx_list); itx; itx = itx_next) {
1167 		/*
1168 		 * Save the next pointer.  Even though we drop zl_lock below,
1169 		 * all threads that can remove itx list entries (other writers
1170 		 * and zil_itx_clean()) can't do so until they have zl_writer.
1171 		 */
1172 		itx_next = list_next(&zilog->zl_itx_list, itx);
1173 
1174 		/*
1175 		 * Determine whether to push this itx.
1176 		 * Push all transactions related to specified foid and
1177 		 * all other transactions except those that can be logged
1178 		 * out of order (TX_WRITE, TX_TRUNCATE, TX_SETATTR, TX_ACL)
1179 		 * for all other files.
1180 		 *
1181 		 * If foid == 0 (meaning "push all foids") or
1182 		 * itx->itx_sync is set (meaning O_[D]SYNC), push regardless.
1183 		 */
1184 		if (foid != 0 && !itx->itx_sync &&
1185 		    TX_OOO(itx->itx_lr.lrc_txtype) &&
1186 		    ((lr_ooo_t *)&itx->itx_lr)->lr_foid != foid)
1187 			continue; /* skip this record */
1188 
1189 		if ((itx->itx_lr.lrc_seq > seq) &&
1190 		    ((lwb == NULL) || (LWB_EMPTY(lwb)) ||
1191 		    (lwb->lwb_nused + itx->itx_sod > lwb->lwb_sz)))
1192 			break;
1193 
1194 		list_remove(&zilog->zl_itx_list, itx);
1195 		zilog->zl_itx_list_sz -= itx->itx_sod;
1196 
1197 		mutex_exit(&zilog->zl_lock);
1198 
1199 		txg = itx->itx_lr.lrc_txg;
1200 		ASSERT(txg);
1201 
1202 		if (txg > spa_last_synced_txg(spa) ||
1203 		    txg > spa_freeze_txg(spa))
1204 			lwb = zil_lwb_commit(zilog, itx, lwb);
1205 
1206 		zil_itx_destroy(itx);
1207 
1208 		mutex_enter(&zilog->zl_lock);
1209 	}
1210 	DTRACE_PROBE1(zil__cw2, zilog_t *, zilog);
1211 	/* determine commit sequence number */
1212 	itx = list_head(&zilog->zl_itx_list);
1213 	if (itx)
1214 		commit_seq = itx->itx_lr.lrc_seq - 1;
1215 	else
1216 		commit_seq = zilog->zl_itx_seq;
1217 	mutex_exit(&zilog->zl_lock);
1218 
1219 	/* write the last block out */
1220 	if (lwb != NULL && lwb->lwb_zio != NULL)
1221 		lwb = zil_lwb_write_start(zilog, lwb);
1222 
1223 	zilog->zl_prev_used = zilog->zl_cur_used;
1224 	zilog->zl_cur_used = 0;
1225 
1226 	/*
1227 	 * Wait if necessary for the log blocks to be on stable storage.
1228 	 */
1229 	if (zilog->zl_root_zio) {
1230 		DTRACE_PROBE1(zil__cw3, zilog_t *, zilog);
1231 		error = zio_wait(zilog->zl_root_zio);
1232 		zilog->zl_root_zio = NULL;
1233 		DTRACE_PROBE1(zil__cw4, zilog_t *, zilog);
1234 		zil_flush_vdevs(zilog);
1235 	}
1236 
1237 	if (error || lwb == NULL)
1238 		txg_wait_synced(zilog->zl_dmu_pool, 0);
1239 
1240 	mutex_enter(&zilog->zl_lock);
1241 	zilog->zl_writer = B_FALSE;
1242 
1243 	ASSERT3U(commit_seq, >=, zilog->zl_commit_seq);
1244 	zilog->zl_commit_seq = commit_seq;
1245 
1246 	/*
1247 	 * Remember the highest committed log sequence number for ztest.
1248 	 * We only update this value when all the log writes succeeded,
1249 	 * because ztest wants to ASSERT that it got the whole log chain.
1250 	 */
1251 	if (error == 0 && lwb != NULL)
1252 		zilog->zl_commit_lr_seq = zilog->zl_lr_seq;
1253 }
1254 
1255 /*
1256  * Push zfs transactions to stable storage up to the supplied sequence number.
1257  * If foid is 0 push out all transactions, otherwise push only those
1258  * for that file or might have been used to create that file.
1259  */
1260 void
1261 zil_commit(zilog_t *zilog, uint64_t seq, uint64_t foid)
1262 {
1263 	if (zilog == NULL || seq == 0)
1264 		return;
1265 
1266 	mutex_enter(&zilog->zl_lock);
1267 
1268 	seq = MIN(seq, zilog->zl_itx_seq);	/* cap seq at largest itx seq */
1269 
1270 	while (zilog->zl_writer) {
1271 		cv_wait(&zilog->zl_cv_writer, &zilog->zl_lock);
1272 		if (seq <= zilog->zl_commit_seq) {
1273 			mutex_exit(&zilog->zl_lock);
1274 			return;
1275 		}
1276 	}
1277 	zil_commit_writer(zilog, seq, foid); /* drops zl_lock */
1278 	/* wake up others waiting on the commit */
1279 	cv_broadcast(&zilog->zl_cv_writer);
1280 	mutex_exit(&zilog->zl_lock);
1281 }
1282 
1283 /*
1284  * Report whether all transactions are committed.
1285  */
1286 static boolean_t
1287 zil_is_committed(zilog_t *zilog)
1288 {
1289 	lwb_t *lwb;
1290 	boolean_t committed;
1291 
1292 	mutex_enter(&zilog->zl_lock);
1293 
1294 	while (zilog->zl_writer)
1295 		cv_wait(&zilog->zl_cv_writer, &zilog->zl_lock);
1296 
1297 	if (!list_is_empty(&zilog->zl_itx_list))
1298 		committed = B_FALSE;		/* unpushed transactions */
1299 	else if ((lwb = list_head(&zilog->zl_lwb_list)) == NULL)
1300 		committed = B_TRUE;		/* intent log never used */
1301 	else if (list_next(&zilog->zl_lwb_list, lwb) != NULL)
1302 		committed = B_FALSE;		/* zil_sync() not done yet */
1303 	else
1304 		committed = B_TRUE;		/* everything synced */
1305 
1306 	mutex_exit(&zilog->zl_lock);
1307 	return (committed);
1308 }
1309 
1310 /*
1311  * Called in syncing context to free committed log blocks and update log header.
1312  */
1313 void
1314 zil_sync(zilog_t *zilog, dmu_tx_t *tx)
1315 {
1316 	zil_header_t *zh = zil_header_in_syncing_context(zilog);
1317 	uint64_t txg = dmu_tx_get_txg(tx);
1318 	spa_t *spa = zilog->zl_spa;
1319 	uint64_t *replayed_seq = &zilog->zl_replayed_seq[txg & TXG_MASK];
1320 	lwb_t *lwb;
1321 
1322 	/*
1323 	 * We don't zero out zl_destroy_txg, so make sure we don't try
1324 	 * to destroy it twice.
1325 	 */
1326 	if (spa_sync_pass(spa) != 1)
1327 		return;
1328 
1329 	mutex_enter(&zilog->zl_lock);
1330 
1331 	ASSERT(zilog->zl_stop_sync == 0);
1332 
1333 	if (*replayed_seq != 0) {
1334 		ASSERT(zh->zh_replay_seq < *replayed_seq);
1335 		zh->zh_replay_seq = *replayed_seq;
1336 		*replayed_seq = 0;
1337 	}
1338 
1339 	if (zilog->zl_destroy_txg == txg) {
1340 		blkptr_t blk = zh->zh_log;
1341 
1342 		ASSERT(list_head(&zilog->zl_lwb_list) == NULL);
1343 
1344 		bzero(zh, sizeof (zil_header_t));
1345 		bzero(zilog->zl_replayed_seq, sizeof (zilog->zl_replayed_seq));
1346 
1347 		if (zilog->zl_keep_first) {
1348 			/*
1349 			 * If this block was part of log chain that couldn't
1350 			 * be claimed because a device was missing during
1351 			 * zil_claim(), but that device later returns,
1352 			 * then this block could erroneously appear valid.
1353 			 * To guard against this, assign a new GUID to the new
1354 			 * log chain so it doesn't matter what blk points to.
1355 			 */
1356 			zil_init_log_chain(zilog, &blk);
1357 			zh->zh_log = blk;
1358 		}
1359 	}
1360 
1361 	while ((lwb = list_head(&zilog->zl_lwb_list)) != NULL) {
1362 		zh->zh_log = lwb->lwb_blk;
1363 		if (lwb->lwb_buf != NULL || lwb->lwb_max_txg > txg)
1364 			break;
1365 		list_remove(&zilog->zl_lwb_list, lwb);
1366 		zio_free_zil(spa, txg, &lwb->lwb_blk);
1367 		kmem_cache_free(zil_lwb_cache, lwb);
1368 
1369 		/*
1370 		 * If we don't have anything left in the lwb list then
1371 		 * we've had an allocation failure and we need to zero
1372 		 * out the zil_header blkptr so that we don't end
1373 		 * up freeing the same block twice.
1374 		 */
1375 		if (list_head(&zilog->zl_lwb_list) == NULL)
1376 			BP_ZERO(&zh->zh_log);
1377 	}
1378 	mutex_exit(&zilog->zl_lock);
1379 }
1380 
1381 void
1382 zil_init(void)
1383 {
1384 	zil_lwb_cache = kmem_cache_create("zil_lwb_cache",
1385 	    sizeof (struct lwb), 0, NULL, NULL, NULL, NULL, NULL, 0);
1386 }
1387 
1388 void
1389 zil_fini(void)
1390 {
1391 	kmem_cache_destroy(zil_lwb_cache);
1392 }
1393 
1394 void
1395 zil_set_logbias(zilog_t *zilog, uint64_t logbias)
1396 {
1397 	zilog->zl_logbias = logbias;
1398 }
1399 
1400 zilog_t *
1401 zil_alloc(objset_t *os, zil_header_t *zh_phys)
1402 {
1403 	zilog_t *zilog;
1404 
1405 	zilog = kmem_zalloc(sizeof (zilog_t), KM_SLEEP);
1406 
1407 	zilog->zl_header = zh_phys;
1408 	zilog->zl_os = os;
1409 	zilog->zl_spa = dmu_objset_spa(os);
1410 	zilog->zl_dmu_pool = dmu_objset_pool(os);
1411 	zilog->zl_destroy_txg = TXG_INITIAL - 1;
1412 	zilog->zl_logbias = dmu_objset_logbias(os);
1413 
1414 	mutex_init(&zilog->zl_lock, NULL, MUTEX_DEFAULT, NULL);
1415 
1416 	list_create(&zilog->zl_itx_list, sizeof (itx_t),
1417 	    offsetof(itx_t, itx_node));
1418 
1419 	list_create(&zilog->zl_lwb_list, sizeof (lwb_t),
1420 	    offsetof(lwb_t, lwb_node));
1421 
1422 	mutex_init(&zilog->zl_vdev_lock, NULL, MUTEX_DEFAULT, NULL);
1423 
1424 	avl_create(&zilog->zl_vdev_tree, zil_vdev_compare,
1425 	    sizeof (zil_vdev_node_t), offsetof(zil_vdev_node_t, zv_node));
1426 
1427 	cv_init(&zilog->zl_cv_writer, NULL, CV_DEFAULT, NULL);
1428 	cv_init(&zilog->zl_cv_suspend, NULL, CV_DEFAULT, NULL);
1429 
1430 	return (zilog);
1431 }
1432 
1433 void
1434 zil_free(zilog_t *zilog)
1435 {
1436 	lwb_t *lwb;
1437 
1438 	zilog->zl_stop_sync = 1;
1439 
1440 	while ((lwb = list_head(&zilog->zl_lwb_list)) != NULL) {
1441 		list_remove(&zilog->zl_lwb_list, lwb);
1442 		if (lwb->lwb_buf != NULL)
1443 			zio_buf_free(lwb->lwb_buf, lwb->lwb_sz);
1444 		kmem_cache_free(zil_lwb_cache, lwb);
1445 	}
1446 	list_destroy(&zilog->zl_lwb_list);
1447 
1448 	avl_destroy(&zilog->zl_vdev_tree);
1449 	mutex_destroy(&zilog->zl_vdev_lock);
1450 
1451 	ASSERT(list_head(&zilog->zl_itx_list) == NULL);
1452 	list_destroy(&zilog->zl_itx_list);
1453 	mutex_destroy(&zilog->zl_lock);
1454 
1455 	cv_destroy(&zilog->zl_cv_writer);
1456 	cv_destroy(&zilog->zl_cv_suspend);
1457 
1458 	kmem_free(zilog, sizeof (zilog_t));
1459 }
1460 
1461 /*
1462  * Open an intent log.
1463  */
1464 zilog_t *
1465 zil_open(objset_t *os, zil_get_data_t *get_data)
1466 {
1467 	zilog_t *zilog = dmu_objset_zil(os);
1468 
1469 	zilog->zl_get_data = get_data;
1470 	zilog->zl_clean_taskq = taskq_create("zil_clean", 1, minclsyspri,
1471 	    2, 2, TASKQ_PREPOPULATE);
1472 
1473 	return (zilog);
1474 }
1475 
1476 /*
1477  * Close an intent log.
1478  */
1479 void
1480 zil_close(zilog_t *zilog)
1481 {
1482 	/*
1483 	 * If the log isn't already committed, mark the objset dirty
1484 	 * (so zil_sync() will be called) and wait for that txg to sync.
1485 	 */
1486 	if (!zil_is_committed(zilog)) {
1487 		uint64_t txg;
1488 		dmu_tx_t *tx = dmu_tx_create(zilog->zl_os);
1489 		VERIFY(dmu_tx_assign(tx, TXG_WAIT) == 0);
1490 		dsl_dataset_dirty(dmu_objset_ds(zilog->zl_os), tx);
1491 		txg = dmu_tx_get_txg(tx);
1492 		dmu_tx_commit(tx);
1493 		txg_wait_synced(zilog->zl_dmu_pool, txg);
1494 	}
1495 
1496 	taskq_destroy(zilog->zl_clean_taskq);
1497 	zilog->zl_clean_taskq = NULL;
1498 	zilog->zl_get_data = NULL;
1499 
1500 	zil_itx_clean(zilog);
1501 	ASSERT(list_head(&zilog->zl_itx_list) == NULL);
1502 }
1503 
1504 /*
1505  * Suspend an intent log.  While in suspended mode, we still honor
1506  * synchronous semantics, but we rely on txg_wait_synced() to do it.
1507  * We suspend the log briefly when taking a snapshot so that the snapshot
1508  * contains all the data it's supposed to, and has an empty intent log.
1509  */
1510 int
1511 zil_suspend(zilog_t *zilog)
1512 {
1513 	const zil_header_t *zh = zilog->zl_header;
1514 
1515 	mutex_enter(&zilog->zl_lock);
1516 	if (zh->zh_flags & ZIL_REPLAY_NEEDED) {		/* unplayed log */
1517 		mutex_exit(&zilog->zl_lock);
1518 		return (EBUSY);
1519 	}
1520 	if (zilog->zl_suspend++ != 0) {
1521 		/*
1522 		 * Someone else already began a suspend.
1523 		 * Just wait for them to finish.
1524 		 */
1525 		while (zilog->zl_suspending)
1526 			cv_wait(&zilog->zl_cv_suspend, &zilog->zl_lock);
1527 		mutex_exit(&zilog->zl_lock);
1528 		return (0);
1529 	}
1530 	zilog->zl_suspending = B_TRUE;
1531 	mutex_exit(&zilog->zl_lock);
1532 
1533 	zil_commit(zilog, UINT64_MAX, 0);
1534 
1535 	/*
1536 	 * Wait for any in-flight log writes to complete.
1537 	 */
1538 	mutex_enter(&zilog->zl_lock);
1539 	while (zilog->zl_writer)
1540 		cv_wait(&zilog->zl_cv_writer, &zilog->zl_lock);
1541 	mutex_exit(&zilog->zl_lock);
1542 
1543 	zil_destroy(zilog, B_FALSE);
1544 
1545 	mutex_enter(&zilog->zl_lock);
1546 	zilog->zl_suspending = B_FALSE;
1547 	cv_broadcast(&zilog->zl_cv_suspend);
1548 	mutex_exit(&zilog->zl_lock);
1549 
1550 	return (0);
1551 }
1552 
1553 void
1554 zil_resume(zilog_t *zilog)
1555 {
1556 	mutex_enter(&zilog->zl_lock);
1557 	ASSERT(zilog->zl_suspend != 0);
1558 	zilog->zl_suspend--;
1559 	mutex_exit(&zilog->zl_lock);
1560 }
1561 
1562 typedef struct zil_replay_arg {
1563 	zil_replay_func_t **zr_replay;
1564 	void		*zr_arg;
1565 	boolean_t	zr_byteswap;
1566 	char		*zr_lr;
1567 } zil_replay_arg_t;
1568 
1569 static int
1570 zil_replay_error(zilog_t *zilog, lr_t *lr, int error)
1571 {
1572 	char name[MAXNAMELEN];
1573 
1574 	zilog->zl_replaying_seq--;	/* didn't actually replay this one */
1575 
1576 	dmu_objset_name(zilog->zl_os, name);
1577 
1578 	cmn_err(CE_WARN, "ZFS replay transaction error %d, "
1579 	    "dataset %s, seq 0x%llx, txtype %llu %s\n", error, name,
1580 	    (u_longlong_t)lr->lrc_seq,
1581 	    (u_longlong_t)(lr->lrc_txtype & ~TX_CI),
1582 	    (lr->lrc_txtype & TX_CI) ? "CI" : "");
1583 
1584 	return (error);
1585 }
1586 
1587 static int
1588 zil_replay_log_record(zilog_t *zilog, lr_t *lr, void *zra, uint64_t claim_txg)
1589 {
1590 	zil_replay_arg_t *zr = zra;
1591 	const zil_header_t *zh = zilog->zl_header;
1592 	uint64_t reclen = lr->lrc_reclen;
1593 	uint64_t txtype = lr->lrc_txtype;
1594 	int error = 0;
1595 
1596 	zilog->zl_replaying_seq = lr->lrc_seq;
1597 
1598 	if (lr->lrc_seq <= zh->zh_replay_seq)	/* already replayed */
1599 		return (0);
1600 
1601 	if (lr->lrc_txg < claim_txg)		/* already committed */
1602 		return (0);
1603 
1604 	/* Strip case-insensitive bit, still present in log record */
1605 	txtype &= ~TX_CI;
1606 
1607 	if (txtype == 0 || txtype >= TX_MAX_TYPE)
1608 		return (zil_replay_error(zilog, lr, EINVAL));
1609 
1610 	/*
1611 	 * If this record type can be logged out of order, the object
1612 	 * (lr_foid) may no longer exist.  That's legitimate, not an error.
1613 	 */
1614 	if (TX_OOO(txtype)) {
1615 		error = dmu_object_info(zilog->zl_os,
1616 		    ((lr_ooo_t *)lr)->lr_foid, NULL);
1617 		if (error == ENOENT || error == EEXIST)
1618 			return (0);
1619 	}
1620 
1621 	/*
1622 	 * Make a copy of the data so we can revise and extend it.
1623 	 */
1624 	bcopy(lr, zr->zr_lr, reclen);
1625 
1626 	/*
1627 	 * If this is a TX_WRITE with a blkptr, suck in the data.
1628 	 */
1629 	if (txtype == TX_WRITE && reclen == sizeof (lr_write_t)) {
1630 		error = zil_read_log_data(zilog, (lr_write_t *)lr,
1631 		    zr->zr_lr + reclen);
1632 		if (error)
1633 			return (zil_replay_error(zilog, lr, error));
1634 	}
1635 
1636 	/*
1637 	 * The log block containing this lr may have been byteswapped
1638 	 * so that we can easily examine common fields like lrc_txtype.
1639 	 * However, the log is a mix of different record types, and only the
1640 	 * replay vectors know how to byteswap their records.  Therefore, if
1641 	 * the lr was byteswapped, undo it before invoking the replay vector.
1642 	 */
1643 	if (zr->zr_byteswap)
1644 		byteswap_uint64_array(zr->zr_lr, reclen);
1645 
1646 	/*
1647 	 * We must now do two things atomically: replay this log record,
1648 	 * and update the log header sequence number to reflect the fact that
1649 	 * we did so. At the end of each replay function the sequence number
1650 	 * is updated if we are in replay mode.
1651 	 */
1652 	error = zr->zr_replay[txtype](zr->zr_arg, zr->zr_lr, zr->zr_byteswap);
1653 	if (error) {
1654 		/*
1655 		 * The DMU's dnode layer doesn't see removes until the txg
1656 		 * commits, so a subsequent claim can spuriously fail with
1657 		 * EEXIST. So if we receive any error we try syncing out
1658 		 * any removes then retry the transaction.  Note that we
1659 		 * specify B_FALSE for byteswap now, so we don't do it twice.
1660 		 */
1661 		txg_wait_synced(spa_get_dsl(zilog->zl_spa), 0);
1662 		error = zr->zr_replay[txtype](zr->zr_arg, zr->zr_lr, B_FALSE);
1663 		if (error)
1664 			return (zil_replay_error(zilog, lr, error));
1665 	}
1666 	return (0);
1667 }
1668 
1669 /* ARGSUSED */
1670 static int
1671 zil_incr_blks(zilog_t *zilog, blkptr_t *bp, void *arg, uint64_t claim_txg)
1672 {
1673 	zilog->zl_replay_blks++;
1674 
1675 	return (0);
1676 }
1677 
1678 /*
1679  * If this dataset has a non-empty intent log, replay it and destroy it.
1680  */
1681 void
1682 zil_replay(objset_t *os, void *arg, zil_replay_func_t *replay_func[TX_MAX_TYPE])
1683 {
1684 	zilog_t *zilog = dmu_objset_zil(os);
1685 	const zil_header_t *zh = zilog->zl_header;
1686 	zil_replay_arg_t zr;
1687 
1688 	if ((zh->zh_flags & ZIL_REPLAY_NEEDED) == 0) {
1689 		zil_destroy(zilog, B_TRUE);
1690 		return;
1691 	}
1692 
1693 	zr.zr_replay = replay_func;
1694 	zr.zr_arg = arg;
1695 	zr.zr_byteswap = BP_SHOULD_BYTESWAP(&zh->zh_log);
1696 	zr.zr_lr = kmem_alloc(2 * SPA_MAXBLOCKSIZE, KM_SLEEP);
1697 
1698 	/*
1699 	 * Wait for in-progress removes to sync before starting replay.
1700 	 */
1701 	txg_wait_synced(zilog->zl_dmu_pool, 0);
1702 
1703 	zilog->zl_replay = B_TRUE;
1704 	zilog->zl_replay_time = ddi_get_lbolt();
1705 	ASSERT(zilog->zl_replay_blks == 0);
1706 	(void) zil_parse(zilog, zil_incr_blks, zil_replay_log_record, &zr,
1707 	    zh->zh_claim_txg);
1708 	kmem_free(zr.zr_lr, 2 * SPA_MAXBLOCKSIZE);
1709 
1710 	zil_destroy(zilog, B_FALSE);
1711 	txg_wait_synced(zilog->zl_dmu_pool, zilog->zl_destroy_txg);
1712 	zilog->zl_replay = B_FALSE;
1713 }
1714 
1715 boolean_t
1716 zil_replaying(zilog_t *zilog, dmu_tx_t *tx)
1717 {
1718 	if (zilog == NULL)
1719 		return (B_TRUE);
1720 
1721 	if (zilog->zl_replay) {
1722 		dsl_dataset_dirty(dmu_objset_ds(zilog->zl_os), tx);
1723 		zilog->zl_replayed_seq[dmu_tx_get_txg(tx) & TXG_MASK] =
1724 		    zilog->zl_replaying_seq;
1725 		return (B_TRUE);
1726 	}
1727 
1728 	return (B_FALSE);
1729 }
1730 
1731 /* ARGSUSED */
1732 int
1733 zil_vdev_offline(const char *osname, void *arg)
1734 {
1735 	objset_t *os;
1736 	zilog_t *zilog;
1737 	int error;
1738 
1739 	error = dmu_objset_hold(osname, FTAG, &os);
1740 	if (error)
1741 		return (error);
1742 
1743 	zilog = dmu_objset_zil(os);
1744 	if (zil_suspend(zilog) != 0)
1745 		error = EEXIST;
1746 	else
1747 		zil_resume(zilog);
1748 	dmu_objset_rele(os, FTAG);
1749 	return (error);
1750 }
1751