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 /*
23 * Copyright (c) 2005, 2010, Oracle and/or its affiliates. All rights reserved.
24 * Copyright (c) 2013 by Delphix. All rights reserved.
25 */
26
27 /*
28 * Virtual Device Labels
29 * ---------------------
30 *
31 * The vdev label serves several distinct purposes:
32 *
33 * 1. Uniquely identify this device as part of a ZFS pool and confirm its
34 * identity within the pool.
35 *
36 * 2. Verify that all the devices given in a configuration are present
37 * within the pool.
38 *
39 * 3. Determine the uberblock for the pool.
40 *
41 * 4. In case of an import operation, determine the configuration of the
42 * toplevel vdev of which it is a part.
43 *
44 * 5. If an import operation cannot find all the devices in the pool,
45 * provide enough information to the administrator to determine which
46 * devices are missing.
47 *
48 * It is important to note that while the kernel is responsible for writing the
49 * label, it only consumes the information in the first three cases. The
50 * latter information is only consumed in userland when determining the
51 * configuration to import a pool.
52 *
53 *
54 * Label Organization
55 * ------------------
56 *
57 * Before describing the contents of the label, it's important to understand how
58 * the labels are written and updated with respect to the uberblock.
59 *
60 * When the pool configuration is altered, either because it was newly created
61 * or a device was added, we want to update all the labels such that we can deal
62 * with fatal failure at any point. To this end, each disk has two labels which
63 * are updated before and after the uberblock is synced. Assuming we have
64 * labels and an uberblock with the following transaction groups:
65 *
66 * L1 UB L2
67 * +------+ +------+ +------+
68 * | | | | | |
69 * | t10 | | t10 | | t10 |
70 * | | | | | |
71 * +------+ +------+ +------+
72 *
73 * In this stable state, the labels and the uberblock were all updated within
74 * the same transaction group (10). Each label is mirrored and checksummed, so
75 * that we can detect when we fail partway through writing the label.
76 *
77 * In order to identify which labels are valid, the labels are written in the
78 * following manner:
79 *
80 * 1. For each vdev, update 'L1' to the new label
81 * 2. Update the uberblock
82 * 3. For each vdev, update 'L2' to the new label
83 *
84 * Given arbitrary failure, we can determine the correct label to use based on
85 * the transaction group. If we fail after updating L1 but before updating the
86 * UB, we will notice that L1's transaction group is greater than the uberblock,
87 * so L2 must be valid. If we fail after writing the uberblock but before
88 * writing L2, we will notice that L2's transaction group is less than L1, and
89 * therefore L1 is valid.
90 *
91 * Another added complexity is that not every label is updated when the config
92 * is synced. If we add a single device, we do not want to have to re-write
93 * every label for every device in the pool. This means that both L1 and L2 may
94 * be older than the pool uberblock, because the necessary information is stored
95 * on another vdev.
96 *
97 *
98 * On-disk Format
99 * --------------
100 *
101 * The vdev label consists of two distinct parts, and is wrapped within the
102 * vdev_label_t structure. The label includes 8k of padding to permit legacy
103 * VTOC disk labels, but is otherwise ignored.
104 *
105 * The first half of the label is a packed nvlist which contains pool wide
106 * properties, per-vdev properties, and configuration information. It is
107 * described in more detail below.
108 *
109 * The latter half of the label consists of a redundant array of uberblocks.
110 * These uberblocks are updated whenever a transaction group is committed,
111 * or when the configuration is updated. When a pool is loaded, we scan each
112 * vdev for the 'best' uberblock.
113 *
114 *
115 * Configuration Information
116 * -------------------------
117 *
118 * The nvlist describing the pool and vdev contains the following elements:
119 *
120 * version ZFS on-disk version
121 * name Pool name
122 * state Pool state
123 * txg Transaction group in which this label was written
124 * pool_guid Unique identifier for this pool
125 * vdev_tree An nvlist describing vdev tree.
126 * features_for_read
127 * An nvlist of the features necessary for reading the MOS.
128 *
129 * Each leaf device label also contains the following:
130 *
131 * top_guid Unique ID for top-level vdev in which this is contained
132 * guid Unique ID for the leaf vdev
133 *
134 * The 'vs' configuration follows the format described in 'spa_config.c'.
135 */
136
137 #include <sys/zfs_context.h>
138 #include <sys/spa.h>
139 #include <sys/spa_impl.h>
140 #include <sys/dmu.h>
141 #include <sys/zap.h>
142 #include <sys/vdev.h>
143 #include <sys/vdev_impl.h>
144 #include <sys/uberblock_impl.h>
145 #include <sys/metaslab.h>
146 #include <sys/zio.h>
147 #include <sys/dsl_scan.h>
148 #include <sys/fs/zfs.h>
149
150 /*
151 * Basic routines to read and write from a vdev label.
152 * Used throughout the rest of this file.
153 */
154 uint64_t
155 vdev_label_offset(uint64_t psize, int l, uint64_t offset)
156 {
157 ASSERT(offset < sizeof (vdev_label_t));
158 ASSERT(P2PHASE_TYPED(psize, sizeof (vdev_label_t), uint64_t) == 0);
159
160 return (offset + l * sizeof (vdev_label_t) + (l < VDEV_LABELS / 2 ?
161 0 : psize - VDEV_LABELS * sizeof (vdev_label_t)));
162 }
163
164 /*
165 * Returns back the vdev label associated with the passed in offset.
166 */
167 int
168 vdev_label_number(uint64_t psize, uint64_t offset)
169 {
170 int l;
171
172 if (offset >= psize - VDEV_LABEL_END_SIZE) {
173 offset -= psize - VDEV_LABEL_END_SIZE;
174 offset += (VDEV_LABELS / 2) * sizeof (vdev_label_t);
175 }
176 l = offset / sizeof (vdev_label_t);
177 return (l < VDEV_LABELS ? l : -1);
178 }
179
180 static void
181 vdev_label_read(zio_t *zio, vdev_t *vd, int l, void *buf, uint64_t offset,
182 uint64_t size, zio_done_func_t *done, void *private, int flags)
183 {
184 ASSERT(spa_config_held(zio->io_spa, SCL_STATE_ALL, RW_WRITER) ==
185 SCL_STATE_ALL);
186 ASSERT(flags & ZIO_FLAG_CONFIG_WRITER);
187
188 zio_nowait(zio_read_phys(zio, vd,
189 vdev_label_offset(vd->vdev_psize, l, offset),
190 size, buf, ZIO_CHECKSUM_LABEL, done, private,
191 ZIO_PRIORITY_SYNC_READ, flags, B_TRUE));
192 }
193
194 static void
195 vdev_label_write(zio_t *zio, vdev_t *vd, int l, void *buf, uint64_t offset,
196 uint64_t size, zio_done_func_t *done, void *private, int flags)
197 {
198 ASSERT(spa_config_held(zio->io_spa, SCL_ALL, RW_WRITER) == SCL_ALL ||
199 (spa_config_held(zio->io_spa, SCL_CONFIG | SCL_STATE, RW_READER) ==
200 (SCL_CONFIG | SCL_STATE) &&
201 dsl_pool_sync_context(spa_get_dsl(zio->io_spa))));
202 ASSERT(flags & ZIO_FLAG_CONFIG_WRITER);
203
204 zio_nowait(zio_write_phys(zio, vd,
205 vdev_label_offset(vd->vdev_psize, l, offset),
206 size, buf, ZIO_CHECKSUM_LABEL, done, private,
207 ZIO_PRIORITY_SYNC_WRITE, flags, B_TRUE));
208 }
209
210 /*
211 * Generate the nvlist representing this vdev's config.
212 */
213 nvlist_t *
214 vdev_config_generate(spa_t *spa, vdev_t *vd, boolean_t getstats,
215 vdev_config_flag_t flags)
216 {
217 nvlist_t *nv = NULL;
218
219 nv = fnvlist_alloc();
220
221 fnvlist_add_string(nv, ZPOOL_CONFIG_TYPE, vd->vdev_ops->vdev_op_type);
222 if (!(flags & (VDEV_CONFIG_SPARE | VDEV_CONFIG_L2CACHE)))
223 fnvlist_add_uint64(nv, ZPOOL_CONFIG_ID, vd->vdev_id);
224 fnvlist_add_uint64(nv, ZPOOL_CONFIG_GUID, vd->vdev_guid);
225
226 if (vd->vdev_path != NULL)
227 fnvlist_add_string(nv, ZPOOL_CONFIG_PATH, vd->vdev_path);
228
229 if (vd->vdev_devid != NULL)
230 fnvlist_add_string(nv, ZPOOL_CONFIG_DEVID, vd->vdev_devid);
231
232 if (vd->vdev_physpath != NULL)
233 fnvlist_add_string(nv, ZPOOL_CONFIG_PHYS_PATH,
234 vd->vdev_physpath);
235
236 if (vd->vdev_fru != NULL)
237 fnvlist_add_string(nv, ZPOOL_CONFIG_FRU, vd->vdev_fru);
238
239 if (vd->vdev_nparity != 0) {
240 ASSERT(strcmp(vd->vdev_ops->vdev_op_type,
241 VDEV_TYPE_RAIDZ) == 0);
242
243 /*
244 * Make sure someone hasn't managed to sneak a fancy new vdev
245 * into a crufty old storage pool.
246 */
247 ASSERT(vd->vdev_nparity == 1 ||
248 (vd->vdev_nparity <= 2 &&
249 spa_version(spa) >= SPA_VERSION_RAIDZ2) ||
250 (vd->vdev_nparity <= 3 &&
251 spa_version(spa) >= SPA_VERSION_RAIDZ3));
252
253 /*
254 * Note that we'll add the nparity tag even on storage pools
255 * that only support a single parity device -- older software
256 * will just ignore it.
257 */
258 fnvlist_add_uint64(nv, ZPOOL_CONFIG_NPARITY, vd->vdev_nparity);
259 }
260
261 if (vd->vdev_wholedisk != -1ULL)
262 fnvlist_add_uint64(nv, ZPOOL_CONFIG_WHOLE_DISK,
263 vd->vdev_wholedisk);
264
265 if (vd->vdev_not_present)
266 fnvlist_add_uint64(nv, ZPOOL_CONFIG_NOT_PRESENT, 1);
267
268 if (vd->vdev_isspare)
269 fnvlist_add_uint64(nv, ZPOOL_CONFIG_IS_SPARE, 1);
270
271 if (!(flags & (VDEV_CONFIG_SPARE | VDEV_CONFIG_L2CACHE)) &&
272 vd == vd->vdev_top) {
273 fnvlist_add_uint64(nv, ZPOOL_CONFIG_METASLAB_ARRAY,
274 vd->vdev_ms_array);
275 fnvlist_add_uint64(nv, ZPOOL_CONFIG_METASLAB_SHIFT,
276 vd->vdev_ms_shift);
277 fnvlist_add_uint64(nv, ZPOOL_CONFIG_ASHIFT, vd->vdev_ashift);
278 fnvlist_add_uint64(nv, ZPOOL_CONFIG_ASIZE,
279 vd->vdev_asize);
280 fnvlist_add_uint64(nv, ZPOOL_CONFIG_IS_LOG, vd->vdev_islog);
281 if (vd->vdev_removing)
282 fnvlist_add_uint64(nv, ZPOOL_CONFIG_REMOVING,
283 vd->vdev_removing);
284 }
285
286 if (flags & VDEV_CONFIG_L2CACHE)
287 /* indicate that we support L2ARC persistency */
288 VERIFY(nvlist_add_boolean_value(nv,
289 ZPOOL_CONFIG_L2CACHE_PERSISTENT, B_TRUE) == 0);
290
291 if (vd->vdev_dtl_sm != NULL) {
292 fnvlist_add_uint64(nv, ZPOOL_CONFIG_DTL,
293 space_map_object(vd->vdev_dtl_sm));
294 }
295
296 if (vd->vdev_crtxg)
297 fnvlist_add_uint64(nv, ZPOOL_CONFIG_CREATE_TXG, vd->vdev_crtxg);
298
299 if (getstats) {
300 vdev_stat_t vs;
301 pool_scan_stat_t ps;
302
303 vdev_get_stats(vd, &vs);
304 fnvlist_add_uint64_array(nv, ZPOOL_CONFIG_VDEV_STATS,
305 (uint64_t *)&vs, sizeof (vs) / sizeof (uint64_t));
306
307 /* provide either current or previous scan information */
308 if (spa_scan_get_stats(spa, &ps) == 0) {
309 fnvlist_add_uint64_array(nv,
310 ZPOOL_CONFIG_SCAN_STATS, (uint64_t *)&ps,
311 sizeof (pool_scan_stat_t) / sizeof (uint64_t));
312 }
313 }
314
315 if (!vd->vdev_ops->vdev_op_leaf) {
316 nvlist_t **child;
317 int c, idx;
318
319 ASSERT(!vd->vdev_ishole);
320
321 child = kmem_alloc(vd->vdev_children * sizeof (nvlist_t *),
322 KM_SLEEP);
323
324 for (c = 0, idx = 0; c < vd->vdev_children; c++) {
325 vdev_t *cvd = vd->vdev_child[c];
326
327 /*
328 * If we're generating an nvlist of removing
329 * vdevs then skip over any device which is
330 * not being removed.
331 */
332 if ((flags & VDEV_CONFIG_REMOVING) &&
333 !cvd->vdev_removing)
334 continue;
335
336 child[idx++] = vdev_config_generate(spa, cvd,
337 getstats, flags);
338 }
339
340 if (idx) {
341 fnvlist_add_nvlist_array(nv, ZPOOL_CONFIG_CHILDREN,
342 child, idx);
343 }
344
345 for (c = 0; c < idx; c++)
346 nvlist_free(child[c]);
347
348 kmem_free(child, vd->vdev_children * sizeof (nvlist_t *));
349
350 } else {
351 const char *aux = NULL;
352
353 if (vd->vdev_offline && !vd->vdev_tmpoffline)
354 fnvlist_add_uint64(nv, ZPOOL_CONFIG_OFFLINE, B_TRUE);
355 if (vd->vdev_resilver_txg != 0)
356 fnvlist_add_uint64(nv, ZPOOL_CONFIG_RESILVER_TXG,
357 vd->vdev_resilver_txg);
358 if (vd->vdev_faulted)
359 fnvlist_add_uint64(nv, ZPOOL_CONFIG_FAULTED, B_TRUE);
360 if (vd->vdev_degraded)
361 fnvlist_add_uint64(nv, ZPOOL_CONFIG_DEGRADED, B_TRUE);
362 if (vd->vdev_removed)
363 fnvlist_add_uint64(nv, ZPOOL_CONFIG_REMOVED, B_TRUE);
364 if (vd->vdev_unspare)
365 fnvlist_add_uint64(nv, ZPOOL_CONFIG_UNSPARE, B_TRUE);
366 if (vd->vdev_ishole)
367 fnvlist_add_uint64(nv, ZPOOL_CONFIG_IS_HOLE, B_TRUE);
368
369 switch (vd->vdev_stat.vs_aux) {
370 case VDEV_AUX_ERR_EXCEEDED:
371 aux = "err_exceeded";
372 break;
373
374 case VDEV_AUX_EXTERNAL:
375 aux = "external";
376 break;
377 }
378
379 if (aux != NULL)
380 fnvlist_add_string(nv, ZPOOL_CONFIG_AUX_STATE, aux);
381
382 if (vd->vdev_splitting && vd->vdev_orig_guid != 0LL) {
383 fnvlist_add_uint64(nv, ZPOOL_CONFIG_ORIG_GUID,
384 vd->vdev_orig_guid);
385 }
386 }
387
388 return (nv);
389 }
390
391 /*
392 * Generate a view of the top-level vdevs. If we currently have holes
393 * in the namespace, then generate an array which contains a list of holey
394 * vdevs. Additionally, add the number of top-level children that currently
395 * exist.
396 */
397 void
398 vdev_top_config_generate(spa_t *spa, nvlist_t *config)
399 {
400 vdev_t *rvd = spa->spa_root_vdev;
401 uint64_t *array;
402 uint_t c, idx;
403
404 array = kmem_alloc(rvd->vdev_children * sizeof (uint64_t), KM_SLEEP);
405
406 for (c = 0, idx = 0; c < rvd->vdev_children; c++) {
407 vdev_t *tvd = rvd->vdev_child[c];
408
409 if (tvd->vdev_ishole)
410 array[idx++] = c;
411 }
412
413 if (idx) {
414 VERIFY(nvlist_add_uint64_array(config, ZPOOL_CONFIG_HOLE_ARRAY,
415 array, idx) == 0);
416 }
417
418 VERIFY(nvlist_add_uint64(config, ZPOOL_CONFIG_VDEV_CHILDREN,
419 rvd->vdev_children) == 0);
420
421 kmem_free(array, rvd->vdev_children * sizeof (uint64_t));
422 }
423
424 /*
425 * Returns the configuration from the label of the given vdev. For vdevs
426 * which don't have a txg value stored on their label (i.e. spares/cache)
427 * or have not been completely initialized (txg = 0) just return
428 * the configuration from the first valid label we find. Otherwise,
429 * find the most up-to-date label that does not exceed the specified
430 * 'txg' value.
431 */
432 nvlist_t *
433 vdev_label_read_config(vdev_t *vd, uint64_t txg)
434 {
435 spa_t *spa = vd->vdev_spa;
436 nvlist_t *config = NULL;
437 vdev_phys_t *vp;
438 zio_t *zio;
439 uint64_t best_txg = 0;
440 int error = 0;
441 int flags = ZIO_FLAG_CONFIG_WRITER | ZIO_FLAG_CANFAIL |
442 ZIO_FLAG_SPECULATIVE;
443
444 ASSERT(spa_config_held(spa, SCL_STATE_ALL, RW_WRITER) == SCL_STATE_ALL);
445
446 if (!vdev_readable(vd))
447 return (NULL);
448
449 vp = zio_buf_alloc(sizeof (vdev_phys_t));
450
451 retry:
452 for (int l = 0; l < VDEV_LABELS; l++) {
453 nvlist_t *label = NULL;
454
455 zio = zio_root(spa, NULL, NULL, flags);
456
457 vdev_label_read(zio, vd, l, vp,
458 offsetof(vdev_label_t, vl_vdev_phys),
459 sizeof (vdev_phys_t), NULL, NULL, flags);
460
461 if (zio_wait(zio) == 0 &&
462 nvlist_unpack(vp->vp_nvlist, sizeof (vp->vp_nvlist),
463 &label, 0) == 0) {
464 uint64_t label_txg = 0;
465
466 /*
467 * Auxiliary vdevs won't have txg values in their
468 * labels and newly added vdevs may not have been
469 * completely initialized so just return the
470 * configuration from the first valid label we
471 * encounter.
472 */
473 error = nvlist_lookup_uint64(label,
474 ZPOOL_CONFIG_POOL_TXG, &label_txg);
475 if ((error || label_txg == 0) && !config) {
476 config = label;
477 break;
478 } else if (label_txg <= txg && label_txg > best_txg) {
479 best_txg = label_txg;
480 nvlist_free(config);
481 config = fnvlist_dup(label);
482 }
483 }
484
485 if (label != NULL) {
486 nvlist_free(label);
487 label = NULL;
488 }
489 }
490
491 if (config == NULL && !(flags & ZIO_FLAG_TRYHARD)) {
492 flags |= ZIO_FLAG_TRYHARD;
493 goto retry;
494 }
495
496 zio_buf_free(vp, sizeof (vdev_phys_t));
497
498 return (config);
499 }
500
501 /*
502 * Determine if a device is in use. The 'spare_guid' parameter will be filled
503 * in with the device guid if this spare is active elsewhere on the system.
504 */
505 static boolean_t
506 vdev_inuse(vdev_t *vd, uint64_t crtxg, vdev_labeltype_t reason,
507 uint64_t *spare_guid, uint64_t *l2cache_guid)
508 {
509 spa_t *spa = vd->vdev_spa;
510 uint64_t state, pool_guid, device_guid, txg, spare_pool;
511 uint64_t vdtxg = 0;
512 nvlist_t *label;
513
514 if (spare_guid)
515 *spare_guid = 0ULL;
516 if (l2cache_guid)
517 *l2cache_guid = 0ULL;
518
519 /*
520 * Read the label, if any, and perform some basic sanity checks.
521 */
522 if ((label = vdev_label_read_config(vd, -1ULL)) == NULL)
523 return (B_FALSE);
524
525 (void) nvlist_lookup_uint64(label, ZPOOL_CONFIG_CREATE_TXG,
526 &vdtxg);
527
528 if (nvlist_lookup_uint64(label, ZPOOL_CONFIG_POOL_STATE,
529 &state) != 0 ||
530 nvlist_lookup_uint64(label, ZPOOL_CONFIG_GUID,
531 &device_guid) != 0) {
532 nvlist_free(label);
533 return (B_FALSE);
534 }
535
536 if (state != POOL_STATE_SPARE && state != POOL_STATE_L2CACHE &&
537 (nvlist_lookup_uint64(label, ZPOOL_CONFIG_POOL_GUID,
538 &pool_guid) != 0 ||
539 nvlist_lookup_uint64(label, ZPOOL_CONFIG_POOL_TXG,
540 &txg) != 0)) {
541 nvlist_free(label);
542 return (B_FALSE);
543 }
544
545 nvlist_free(label);
546
547 /*
548 * Check to see if this device indeed belongs to the pool it claims to
549 * be a part of. The only way this is allowed is if the device is a hot
550 * spare (which we check for later on).
551 */
552 if (state != POOL_STATE_SPARE && state != POOL_STATE_L2CACHE &&
553 !spa_guid_exists(pool_guid, device_guid) &&
554 !spa_spare_exists(device_guid, NULL, NULL) &&
555 !spa_l2cache_exists(device_guid, NULL))
556 return (B_FALSE);
557
558 /*
559 * If the transaction group is zero, then this an initialized (but
560 * unused) label. This is only an error if the create transaction
561 * on-disk is the same as the one we're using now, in which case the
562 * user has attempted to add the same vdev multiple times in the same
563 * transaction.
564 */
565 if (state != POOL_STATE_SPARE && state != POOL_STATE_L2CACHE &&
566 txg == 0 && vdtxg == crtxg)
567 return (B_TRUE);
568
569 /*
570 * Check to see if this is a spare device. We do an explicit check for
571 * spa_has_spare() here because it may be on our pending list of spares
572 * to add. We also check if it is an l2cache device.
573 */
574 if (spa_spare_exists(device_guid, &spare_pool, NULL) ||
575 spa_has_spare(spa, device_guid)) {
576 if (spare_guid)
577 *spare_guid = device_guid;
578
579 switch (reason) {
580 case VDEV_LABEL_CREATE:
581 case VDEV_LABEL_L2CACHE:
582 return (B_TRUE);
583
584 case VDEV_LABEL_REPLACE:
585 return (!spa_has_spare(spa, device_guid) ||
586 spare_pool != 0ULL);
587
588 case VDEV_LABEL_SPARE:
589 return (spa_has_spare(spa, device_guid));
590 }
591 }
592
593 /*
594 * Check to see if this is an l2cache device.
595 */
596 if (spa_l2cache_exists(device_guid, NULL))
597 return (B_TRUE);
598
599 /*
600 * We can't rely on a pool's state if it's been imported
601 * read-only. Instead we look to see if the pools is marked
602 * read-only in the namespace and set the state to active.
603 */
604 if ((spa = spa_by_guid(pool_guid, device_guid)) != NULL &&
605 spa_mode(spa) == FREAD)
606 state = POOL_STATE_ACTIVE;
607
608 /*
609 * If the device is marked ACTIVE, then this device is in use by another
610 * pool on the system.
611 */
612 return (state == POOL_STATE_ACTIVE);
613 }
614
615 /*
616 * Initialize a vdev label. We check to make sure each leaf device is not in
617 * use, and writable. We put down an initial label which we will later
618 * overwrite with a complete label. Note that it's important to do this
619 * sequentially, not in parallel, so that we catch cases of multiple use of the
620 * same leaf vdev in the vdev we're creating -- e.g. mirroring a disk with
621 * itself.
622 */
623 int
624 vdev_label_init(vdev_t *vd, uint64_t crtxg, vdev_labeltype_t reason)
625 {
626 spa_t *spa = vd->vdev_spa;
627 nvlist_t *label;
628 vdev_phys_t *vp;
629 char *pad2;
630 uberblock_t *ub;
631 zio_t *zio;
632 char *buf;
633 size_t buflen;
634 int error;
635 uint64_t spare_guid, l2cache_guid;
636 int flags = ZIO_FLAG_CONFIG_WRITER | ZIO_FLAG_CANFAIL;
637
638 ASSERT(spa_config_held(spa, SCL_ALL, RW_WRITER) == SCL_ALL);
639
640 for (int c = 0; c < vd->vdev_children; c++)
641 if ((error = vdev_label_init(vd->vdev_child[c],
642 crtxg, reason)) != 0)
643 return (error);
644
645 /* Track the creation time for this vdev */
646 vd->vdev_crtxg = crtxg;
647
648 if (!vd->vdev_ops->vdev_op_leaf)
649 return (0);
650
651 /*
652 * Dead vdevs cannot be initialized.
653 */
654 if (vdev_is_dead(vd))
655 return (SET_ERROR(EIO));
656
657 /*
658 * Determine if the vdev is in use.
659 */
660 if (reason != VDEV_LABEL_REMOVE && reason != VDEV_LABEL_SPLIT &&
661 vdev_inuse(vd, crtxg, reason, &spare_guid, &l2cache_guid))
662 return (SET_ERROR(EBUSY));
663
664 /*
665 * If this is a request to add or replace a spare or l2cache device
666 * that is in use elsewhere on the system, then we must update the
667 * guid (which was initialized to a random value) to reflect the
668 * actual GUID (which is shared between multiple pools).
669 */
670 if (reason != VDEV_LABEL_REMOVE && reason != VDEV_LABEL_L2CACHE &&
671 spare_guid != 0ULL) {
672 uint64_t guid_delta = spare_guid - vd->vdev_guid;
673
674 vd->vdev_guid += guid_delta;
675
676 for (vdev_t *pvd = vd; pvd != NULL; pvd = pvd->vdev_parent)
677 pvd->vdev_guid_sum += guid_delta;
678
679 /*
680 * If this is a replacement, then we want to fallthrough to the
681 * rest of the code. If we're adding a spare, then it's already
682 * labeled appropriately and we can just return.
683 */
684 if (reason == VDEV_LABEL_SPARE)
685 return (0);
686 ASSERT(reason == VDEV_LABEL_REPLACE ||
687 reason == VDEV_LABEL_SPLIT);
688 }
689
690 if (reason != VDEV_LABEL_REMOVE && reason != VDEV_LABEL_SPARE &&
691 l2cache_guid != 0ULL) {
692 uint64_t guid_delta = l2cache_guid - vd->vdev_guid;
693
694 vd->vdev_guid += guid_delta;
695
696 for (vdev_t *pvd = vd; pvd != NULL; pvd = pvd->vdev_parent)
697 pvd->vdev_guid_sum += guid_delta;
698
699 /*
700 * If this is a replacement, then we want to fallthrough to the
701 * rest of the code. If we're adding an l2cache, then it's
702 * already labeled appropriately and we can just return.
703 */
704 if (reason == VDEV_LABEL_L2CACHE)
705 return (0);
706 ASSERT(reason == VDEV_LABEL_REPLACE);
707 }
708
709 /*
710 * Initialize its label.
711 */
712 vp = zio_buf_alloc(sizeof (vdev_phys_t));
713 bzero(vp, sizeof (vdev_phys_t));
714
715 /*
716 * Generate a label describing the pool and our top-level vdev.
717 * We mark it as being from txg 0 to indicate that it's not
718 * really part of an active pool just yet. The labels will
719 * be written again with a meaningful txg by spa_sync().
720 */
721 if (reason == VDEV_LABEL_SPARE ||
722 (reason == VDEV_LABEL_REMOVE && vd->vdev_isspare)) {
723 /*
724 * For inactive hot spares, we generate a special label that
725 * identifies as a mutually shared hot spare. We write the
726 * label if we are adding a hot spare, or if we are removing an
727 * active hot spare (in which case we want to revert the
728 * labels).
729 */
730 VERIFY(nvlist_alloc(&label, NV_UNIQUE_NAME, KM_SLEEP) == 0);
731
732 VERIFY(nvlist_add_uint64(label, ZPOOL_CONFIG_VERSION,
733 spa_version(spa)) == 0);
734 VERIFY(nvlist_add_uint64(label, ZPOOL_CONFIG_POOL_STATE,
735 POOL_STATE_SPARE) == 0);
736 VERIFY(nvlist_add_uint64(label, ZPOOL_CONFIG_GUID,
737 vd->vdev_guid) == 0);
738 } else if (reason == VDEV_LABEL_L2CACHE ||
739 (reason == VDEV_LABEL_REMOVE && vd->vdev_isl2cache)) {
740 /*
741 * For level 2 ARC devices, add a special label.
742 */
743 VERIFY(nvlist_alloc(&label, NV_UNIQUE_NAME, KM_SLEEP) == 0);
744
745 VERIFY(nvlist_add_uint64(label, ZPOOL_CONFIG_VERSION,
746 spa_version(spa)) == 0);
747 VERIFY(nvlist_add_uint64(label, ZPOOL_CONFIG_POOL_STATE,
748 POOL_STATE_L2CACHE) == 0);
749 VERIFY(nvlist_add_uint64(label, ZPOOL_CONFIG_GUID,
750 vd->vdev_guid) == 0);
751 } else {
752 uint64_t txg = 0ULL;
753
754 if (reason == VDEV_LABEL_SPLIT)
755 txg = spa->spa_uberblock.ub_txg;
756 label = spa_config_generate(spa, vd, txg, B_FALSE);
757
758 /*
759 * Add our creation time. This allows us to detect multiple
760 * vdev uses as described above, and automatically expires if we
761 * fail.
762 */
763 VERIFY(nvlist_add_uint64(label, ZPOOL_CONFIG_CREATE_TXG,
764 crtxg) == 0);
765 }
766
767 buf = vp->vp_nvlist;
768 buflen = sizeof (vp->vp_nvlist);
769
770 error = nvlist_pack(label, &buf, &buflen, NV_ENCODE_XDR, KM_SLEEP);
771 if (error != 0) {
772 nvlist_free(label);
773 zio_buf_free(vp, sizeof (vdev_phys_t));
774 /* EFAULT means nvlist_pack ran out of room */
775 return (error == EFAULT ? ENAMETOOLONG : EINVAL);
776 }
777
778 /*
779 * Initialize uberblock template.
780 */
781 ub = zio_buf_alloc(VDEV_UBERBLOCK_RING);
782 bzero(ub, VDEV_UBERBLOCK_RING);
783 *ub = spa->spa_uberblock;
784 ub->ub_txg = 0;
785
786 /* Initialize the 2nd padding area. */
787 pad2 = zio_buf_alloc(VDEV_PAD_SIZE);
788 bzero(pad2, VDEV_PAD_SIZE);
789
790 /*
791 * Write everything in parallel.
792 */
793 retry:
794 zio = zio_root(spa, NULL, NULL, flags);
795
796 for (int l = 0; l < VDEV_LABELS; l++) {
797
798 vdev_label_write(zio, vd, l, vp,
799 offsetof(vdev_label_t, vl_vdev_phys),
800 sizeof (vdev_phys_t), NULL, NULL, flags);
801
802 /*
803 * Skip the 1st padding area.
804 * Zero out the 2nd padding area where it might have
805 * left over data from previous filesystem format.
806 */
807 vdev_label_write(zio, vd, l, pad2,
808 offsetof(vdev_label_t, vl_pad2),
809 VDEV_PAD_SIZE, NULL, NULL, flags);
810
811 vdev_label_write(zio, vd, l, ub,
812 offsetof(vdev_label_t, vl_uberblock),
813 VDEV_UBERBLOCK_RING, NULL, NULL, flags);
814 }
815
816 error = zio_wait(zio);
817
818 if (error != 0 && !(flags & ZIO_FLAG_TRYHARD)) {
819 flags |= ZIO_FLAG_TRYHARD;
820 goto retry;
821 }
822
823 nvlist_free(label);
824 zio_buf_free(pad2, VDEV_PAD_SIZE);
825 zio_buf_free(ub, VDEV_UBERBLOCK_RING);
826 zio_buf_free(vp, sizeof (vdev_phys_t));
827
828 /*
829 * If this vdev hasn't been previously identified as a spare, then we
830 * mark it as such only if a) we are labeling it as a spare, or b) it
831 * exists as a spare elsewhere in the system. Do the same for
832 * level 2 ARC devices.
833 */
834 if (error == 0 && !vd->vdev_isspare &&
835 (reason == VDEV_LABEL_SPARE ||
836 spa_spare_exists(vd->vdev_guid, NULL, NULL)))
837 spa_spare_add(vd);
838
839 if (error == 0 && !vd->vdev_isl2cache &&
840 (reason == VDEV_LABEL_L2CACHE ||
841 spa_l2cache_exists(vd->vdev_guid, NULL)))
842 spa_l2cache_add(vd);
843
844 return (error);
845 }
846
847 /*
848 * ==========================================================================
849 * uberblock load/sync
850 * ==========================================================================
851 */
852
853 /*
854 * Consider the following situation: txg is safely synced to disk. We've
855 * written the first uberblock for txg + 1, and then we lose power. When we
856 * come back up, we fail to see the uberblock for txg + 1 because, say,
857 * it was on a mirrored device and the replica to which we wrote txg + 1
858 * is now offline. If we then make some changes and sync txg + 1, and then
859 * the missing replica comes back, then for a few seconds we'll have two
860 * conflicting uberblocks on disk with the same txg. The solution is simple:
861 * among uberblocks with equal txg, choose the one with the latest timestamp.
862 */
863 static int
864 vdev_uberblock_compare(uberblock_t *ub1, uberblock_t *ub2)
865 {
866 if (ub1->ub_txg < ub2->ub_txg)
867 return (-1);
868 if (ub1->ub_txg > ub2->ub_txg)
869 return (1);
870
871 if (ub1->ub_timestamp < ub2->ub_timestamp)
872 return (-1);
873 if (ub1->ub_timestamp > ub2->ub_timestamp)
874 return (1);
875
876 return (0);
877 }
878
879 struct ubl_cbdata {
880 uberblock_t *ubl_ubbest; /* Best uberblock */
881 vdev_t *ubl_vd; /* vdev associated with the above */
882 };
883
884 static void
885 vdev_uberblock_load_done(zio_t *zio)
886 {
887 vdev_t *vd = zio->io_vd;
888 spa_t *spa = zio->io_spa;
889 zio_t *rio = zio->io_private;
890 uberblock_t *ub = zio->io_data;
891 struct ubl_cbdata *cbp = rio->io_private;
892
893 ASSERT3U(zio->io_size, ==, VDEV_UBERBLOCK_SIZE(vd));
894
895 if (zio->io_error == 0 && uberblock_verify(ub) == 0) {
896 mutex_enter(&rio->io_lock);
897 if (ub->ub_txg <= spa->spa_load_max_txg &&
898 vdev_uberblock_compare(ub, cbp->ubl_ubbest) > 0) {
899 /*
900 * Keep track of the vdev in which this uberblock
901 * was found. We will use this information later
902 * to obtain the config nvlist associated with
903 * this uberblock.
904 */
905 *cbp->ubl_ubbest = *ub;
906 cbp->ubl_vd = vd;
907 }
908 mutex_exit(&rio->io_lock);
909 }
910
911 zio_buf_free(zio->io_data, zio->io_size);
912 }
913
914 static void
915 vdev_uberblock_load_impl(zio_t *zio, vdev_t *vd, int flags,
916 struct ubl_cbdata *cbp)
917 {
918 for (int c = 0; c < vd->vdev_children; c++)
919 vdev_uberblock_load_impl(zio, vd->vdev_child[c], flags, cbp);
920
921 if (vd->vdev_ops->vdev_op_leaf && vdev_readable(vd)) {
922 for (int l = 0; l < VDEV_LABELS; l++) {
923 for (int n = 0; n < VDEV_UBERBLOCK_COUNT(vd); n++) {
924 vdev_label_read(zio, vd, l,
925 zio_buf_alloc(VDEV_UBERBLOCK_SIZE(vd)),
926 VDEV_UBERBLOCK_OFFSET(vd, n),
927 VDEV_UBERBLOCK_SIZE(vd),
928 vdev_uberblock_load_done, zio, flags);
929 }
930 }
931 }
932 }
933
934 /*
935 * Reads the 'best' uberblock from disk along with its associated
936 * configuration. First, we read the uberblock array of each label of each
937 * vdev, keeping track of the uberblock with the highest txg in each array.
938 * Then, we read the configuration from the same vdev as the best uberblock.
939 */
940 void
941 vdev_uberblock_load(vdev_t *rvd, uberblock_t *ub, nvlist_t **config)
942 {
943 zio_t *zio;
944 spa_t *spa = rvd->vdev_spa;
945 struct ubl_cbdata cb;
946 int flags = ZIO_FLAG_CONFIG_WRITER | ZIO_FLAG_CANFAIL |
947 ZIO_FLAG_SPECULATIVE | ZIO_FLAG_TRYHARD;
948
949 ASSERT(ub);
950 ASSERT(config);
951
952 bzero(ub, sizeof (uberblock_t));
953 *config = NULL;
954
955 cb.ubl_ubbest = ub;
956 cb.ubl_vd = NULL;
957
958 spa_config_enter(spa, SCL_ALL, FTAG, RW_WRITER);
959 zio = zio_root(spa, NULL, &cb, flags);
960 vdev_uberblock_load_impl(zio, rvd, flags, &cb);
961 (void) zio_wait(zio);
962
963 /*
964 * It's possible that the best uberblock was discovered on a label
965 * that has a configuration which was written in a future txg.
966 * Search all labels on this vdev to find the configuration that
967 * matches the txg for our uberblock.
968 */
969 if (cb.ubl_vd != NULL)
970 *config = vdev_label_read_config(cb.ubl_vd, ub->ub_txg);
971 spa_config_exit(spa, SCL_ALL, FTAG);
972 }
973
974 /*
975 * On success, increment root zio's count of good writes.
976 * We only get credit for writes to known-visible vdevs; see spa_vdev_add().
977 */
978 static void
979 vdev_uberblock_sync_done(zio_t *zio)
980 {
981 uint64_t *good_writes = zio->io_private;
982
983 if (zio->io_error == 0 && zio->io_vd->vdev_top->vdev_ms_array != 0)
984 atomic_add_64(good_writes, 1);
985 }
986
987 /*
988 * Write the uberblock to all labels of all leaves of the specified vdev.
989 */
990 static void
991 vdev_uberblock_sync(zio_t *zio, uberblock_t *ub, vdev_t *vd, int flags)
992 {
993 uberblock_t *ubbuf;
994 int n;
995
996 for (int c = 0; c < vd->vdev_children; c++)
997 vdev_uberblock_sync(zio, ub, vd->vdev_child[c], flags);
998
999 if (!vd->vdev_ops->vdev_op_leaf)
1000 return;
1001
1002 if (!vdev_writeable(vd))
1003 return;
1004
1005 n = ub->ub_txg & (VDEV_UBERBLOCK_COUNT(vd) - 1);
1006
1007 ubbuf = zio_buf_alloc(VDEV_UBERBLOCK_SIZE(vd));
1008 bzero(ubbuf, VDEV_UBERBLOCK_SIZE(vd));
1009 *ubbuf = *ub;
1010
1011 for (int l = 0; l < VDEV_LABELS; l++)
1012 vdev_label_write(zio, vd, l, ubbuf,
1013 VDEV_UBERBLOCK_OFFSET(vd, n), VDEV_UBERBLOCK_SIZE(vd),
1014 vdev_uberblock_sync_done, zio->io_private,
1015 flags | ZIO_FLAG_DONT_PROPAGATE);
1016
1017 zio_buf_free(ubbuf, VDEV_UBERBLOCK_SIZE(vd));
1018 }
1019
1020 /* Sync the uberblocks to all vdevs in svd[] */
1021 int
1022 vdev_uberblock_sync_list(vdev_t **svd, int svdcount, uberblock_t *ub, int flags)
1023 {
1024 spa_t *spa = svd[0]->vdev_spa;
1025 zio_t *zio;
1026 uint64_t good_writes = 0;
1027
1028 zio = zio_root(spa, NULL, &good_writes, flags);
1029
1030 for (int v = 0; v < svdcount; v++)
1031 vdev_uberblock_sync(zio, ub, svd[v], flags);
1032
1033 (void) zio_wait(zio);
1034
1035 /*
1036 * Flush the uberblocks to disk. This ensures that the odd labels
1037 * are no longer needed (because the new uberblocks and the even
1038 * labels are safely on disk), so it is safe to overwrite them.
1039 */
1040 zio = zio_root(spa, NULL, NULL, flags);
1041
1042 for (int v = 0; v < svdcount; v++)
1043 zio_flush(zio, svd[v]);
1044
1045 (void) zio_wait(zio);
1046
1047 return (good_writes >= 1 ? 0 : EIO);
1048 }
1049
1050 /*
1051 * On success, increment the count of good writes for our top-level vdev.
1052 */
1053 static void
1054 vdev_label_sync_done(zio_t *zio)
1055 {
1056 uint64_t *good_writes = zio->io_private;
1057
1058 if (zio->io_error == 0)
1059 atomic_add_64(good_writes, 1);
1060 }
1061
1062 /*
1063 * If there weren't enough good writes, indicate failure to the parent.
1064 */
1065 static void
1066 vdev_label_sync_top_done(zio_t *zio)
1067 {
1068 uint64_t *good_writes = zio->io_private;
1069
1070 if (*good_writes == 0)
1071 zio->io_error = SET_ERROR(EIO);
1072
1073 kmem_free(good_writes, sizeof (uint64_t));
1074 }
1075
1076 /*
1077 * We ignore errors for log and cache devices, simply free the private data.
1078 */
1079 static void
1080 vdev_label_sync_ignore_done(zio_t *zio)
1081 {
1082 kmem_free(zio->io_private, sizeof (uint64_t));
1083 }
1084
1085 /*
1086 * Write all even or odd labels to all leaves of the specified vdev.
1087 */
1088 static void
1089 vdev_label_sync(zio_t *zio, vdev_t *vd, int l, uint64_t txg, int flags)
1090 {
1091 nvlist_t *label;
1092 vdev_phys_t *vp;
1093 char *buf;
1094 size_t buflen;
1095
1096 for (int c = 0; c < vd->vdev_children; c++)
1097 vdev_label_sync(zio, vd->vdev_child[c], l, txg, flags);
1098
1099 if (!vd->vdev_ops->vdev_op_leaf)
1100 return;
1101
1102 if (!vdev_writeable(vd))
1103 return;
1104
1105 /*
1106 * Generate a label describing the top-level config to which we belong.
1107 */
1108 label = spa_config_generate(vd->vdev_spa, vd, txg, B_FALSE);
1109
1110 vp = zio_buf_alloc(sizeof (vdev_phys_t));
1111 bzero(vp, sizeof (vdev_phys_t));
1112
1113 buf = vp->vp_nvlist;
1114 buflen = sizeof (vp->vp_nvlist);
1115
1116 if (nvlist_pack(label, &buf, &buflen, NV_ENCODE_XDR, KM_SLEEP) == 0) {
1117 for (; l < VDEV_LABELS; l += 2) {
1118 vdev_label_write(zio, vd, l, vp,
1119 offsetof(vdev_label_t, vl_vdev_phys),
1120 sizeof (vdev_phys_t),
1121 vdev_label_sync_done, zio->io_private,
1122 flags | ZIO_FLAG_DONT_PROPAGATE);
1123 }
1124 }
1125
1126 zio_buf_free(vp, sizeof (vdev_phys_t));
1127 nvlist_free(label);
1128 }
1129
1130 int
1131 vdev_label_sync_list(spa_t *spa, int l, uint64_t txg, int flags)
1132 {
1133 list_t *dl = &spa->spa_config_dirty_list;
1134 vdev_t *vd;
1135 zio_t *zio;
1136 int error;
1137
1138 /*
1139 * Write the new labels to disk.
1140 */
1141 zio = zio_root(spa, NULL, NULL, flags);
1142
1143 for (vd = list_head(dl); vd != NULL; vd = list_next(dl, vd)) {
1144 uint64_t *good_writes = kmem_zalloc(sizeof (uint64_t),
1145 KM_SLEEP);
1146
1147 ASSERT(!vd->vdev_ishole);
1148
1149 zio_t *vio = zio_null(zio, spa, NULL,
1150 (vd->vdev_islog || vd->vdev_aux != NULL) ?
1151 vdev_label_sync_ignore_done : vdev_label_sync_top_done,
1152 good_writes, flags);
1153 vdev_label_sync(vio, vd, l, txg, flags);
1154 zio_nowait(vio);
1155 }
1156
1157 error = zio_wait(zio);
1158
1159 /*
1160 * Flush the new labels to disk.
1161 */
1162 zio = zio_root(spa, NULL, NULL, flags);
1163
1164 for (vd = list_head(dl); vd != NULL; vd = list_next(dl, vd))
1165 zio_flush(zio, vd);
1166
1167 (void) zio_wait(zio);
1168
1169 return (error);
1170 }
1171
1172 /*
1173 * Sync the uberblock and any changes to the vdev configuration.
1174 *
1175 * The order of operations is carefully crafted to ensure that
1176 * if the system panics or loses power at any time, the state on disk
1177 * is still transactionally consistent. The in-line comments below
1178 * describe the failure semantics at each stage.
1179 *
1180 * Moreover, vdev_config_sync() is designed to be idempotent: if it fails
1181 * at any time, you can just call it again, and it will resume its work.
1182 */
1183 int
1184 vdev_config_sync(vdev_t **svd, int svdcount, uint64_t txg, boolean_t tryhard)
1185 {
1186 spa_t *spa = svd[0]->vdev_spa;
1187 uberblock_t *ub = &spa->spa_uberblock;
1188 vdev_t *vd;
1189 zio_t *zio;
1190 int error;
1191 int flags = ZIO_FLAG_CONFIG_WRITER | ZIO_FLAG_CANFAIL;
1192
1193 /*
1194 * Normally, we don't want to try too hard to write every label and
1195 * uberblock. If there is a flaky disk, we don't want the rest of the
1196 * sync process to block while we retry. But if we can't write a
1197 * single label out, we should retry with ZIO_FLAG_TRYHARD before
1198 * bailing out and declaring the pool faulted.
1199 */
1200 if (tryhard)
1201 flags |= ZIO_FLAG_TRYHARD;
1202
1203 ASSERT(ub->ub_txg <= txg);
1204
1205 /*
1206 * If this isn't a resync due to I/O errors,
1207 * and nothing changed in this transaction group,
1208 * and the vdev configuration hasn't changed,
1209 * then there's nothing to do.
1210 */
1211 if (ub->ub_txg < txg &&
1212 uberblock_update(ub, spa->spa_root_vdev, txg) == B_FALSE &&
1213 list_is_empty(&spa->spa_config_dirty_list))
1214 return (0);
1215
1216 if (txg > spa_freeze_txg(spa))
1217 return (0);
1218
1219 ASSERT(txg <= spa->spa_final_txg);
1220
1221 /*
1222 * Flush the write cache of every disk that's been written to
1223 * in this transaction group. This ensures that all blocks
1224 * written in this txg will be committed to stable storage
1225 * before any uberblock that references them.
1226 */
1227 zio = zio_root(spa, NULL, NULL, flags);
1228
1229 for (vd = txg_list_head(&spa->spa_vdev_txg_list, TXG_CLEAN(txg)); vd;
1230 vd = txg_list_next(&spa->spa_vdev_txg_list, vd, TXG_CLEAN(txg)))
1231 zio_flush(zio, vd);
1232
1233 (void) zio_wait(zio);
1234
1235 /*
1236 * Sync out the even labels (L0, L2) for every dirty vdev. If the
1237 * system dies in the middle of this process, that's OK: all of the
1238 * even labels that made it to disk will be newer than any uberblock,
1239 * and will therefore be considered invalid. The odd labels (L1, L3),
1240 * which have not yet been touched, will still be valid. We flush
1241 * the new labels to disk to ensure that all even-label updates
1242 * are committed to stable storage before the uberblock update.
1243 */
1244 if ((error = vdev_label_sync_list(spa, 0, txg, flags)) != 0)
1245 return (error);
1246
1247 /*
1248 * Sync the uberblocks to all vdevs in svd[].
1249 * If the system dies in the middle of this step, there are two cases
1250 * to consider, and the on-disk state is consistent either way:
1251 *
1252 * (1) If none of the new uberblocks made it to disk, then the
1253 * previous uberblock will be the newest, and the odd labels
1254 * (which had not yet been touched) will be valid with respect
1255 * to that uberblock.
1256 *
1257 * (2) If one or more new uberblocks made it to disk, then they
1258 * will be the newest, and the even labels (which had all
1259 * been successfully committed) will be valid with respect
1260 * to the new uberblocks.
1261 */
1262 if ((error = vdev_uberblock_sync_list(svd, svdcount, ub, flags)) != 0)
1263 return (error);
1264
1265 /*
1266 * Sync out odd labels for every dirty vdev. If the system dies
1267 * in the middle of this process, the even labels and the new
1268 * uberblocks will suffice to open the pool. The next time
1269 * the pool is opened, the first thing we'll do -- before any
1270 * user data is modified -- is mark every vdev dirty so that
1271 * all labels will be brought up to date. We flush the new labels
1272 * to disk to ensure that all odd-label updates are committed to
1273 * stable storage before the next transaction group begins.
1274 */
1275 return (vdev_label_sync_list(spa, 1, txg, flags));
1276 }