1 /* 2 * CDDL HEADER START 3 * 4 * The contents of this file are subject to the terms of the 5 * Common Development and Distribution License (the "License"). 6 * You may not use this file except in compliance with the License. 7 * 8 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE 9 * or http://www.opensolaris.org/os/licensing. 10 * See the License for the specific language governing permissions 11 * and limitations under the License. 12 * 13 * When distributing Covered Code, include this CDDL HEADER in each 14 * file and include the License file at usr/src/OPENSOLARIS.LICENSE. 15 * If applicable, add the following below this CDDL HEADER, with the 16 * fields enclosed by brackets "[]" replaced with your own identifying 17 * information: Portions Copyright [yyyy] [name of copyright owner] 18 * 19 * CDDL HEADER END 20 */ 21 /* 22 * Copyright (c) 2005, 2010, Oracle and/or its affiliates. All rights reserved. 23 * Copyright (c) 2012 by Delphix. All rights reserved. 24 */ 25 26 #include <sys/zfs_context.h> 27 #include <sys/dmu_objset.h> 28 #include <sys/dmu_traverse.h> 29 #include <sys/dsl_dataset.h> 30 #include <sys/dsl_dir.h> 31 #include <sys/dsl_pool.h> 32 #include <sys/dnode.h> 33 #include <sys/spa.h> 34 #include <sys/zio.h> 35 #include <sys/dmu_impl.h> 36 #include <sys/sa.h> 37 #include <sys/sa_impl.h> 38 #include <sys/callb.h> 39 40 int zfs_pd_blks_max = 100; 41 42 typedef struct prefetch_data { 43 kmutex_t pd_mtx; 44 kcondvar_t pd_cv; 45 int pd_blks_max; 46 int pd_blks_fetched; 47 int pd_flags; 48 boolean_t pd_cancel; 49 boolean_t pd_exited; 50 } prefetch_data_t; 51 52 typedef struct traverse_data { 53 spa_t *td_spa; 54 uint64_t td_objset; 55 blkptr_t *td_rootbp; 56 uint64_t td_min_txg; 57 zbookmark_t *td_resume; 58 int td_flags; 59 prefetch_data_t *td_pfd; 60 blkptr_cb_t *td_func; 61 void *td_arg; 62 } traverse_data_t; 63 64 static int traverse_dnode(traverse_data_t *td, const dnode_phys_t *dnp, 65 arc_buf_t *buf, uint64_t objset, uint64_t object); 66 static void prefetch_dnode_metadata(traverse_data_t *td, const dnode_phys_t *, 67 arc_buf_t *buf, uint64_t objset, uint64_t object); 68 69 static int 70 traverse_zil_block(zilog_t *zilog, blkptr_t *bp, void *arg, uint64_t claim_txg) 71 { 72 traverse_data_t *td = arg; 73 zbookmark_t zb; 74 75 if (bp->blk_birth == 0) 76 return (0); 77 78 if (claim_txg == 0 && bp->blk_birth >= spa_first_txg(td->td_spa)) 79 return (0); 80 81 SET_BOOKMARK(&zb, td->td_objset, ZB_ZIL_OBJECT, ZB_ZIL_LEVEL, 82 bp->blk_cksum.zc_word[ZIL_ZC_SEQ]); 83 84 (void) td->td_func(td->td_spa, zilog, bp, NULL, &zb, NULL, td->td_arg); 85 86 return (0); 87 } 88 89 static int 90 traverse_zil_record(zilog_t *zilog, lr_t *lrc, void *arg, uint64_t claim_txg) 91 { 92 traverse_data_t *td = arg; 93 94 if (lrc->lrc_txtype == TX_WRITE) { 95 lr_write_t *lr = (lr_write_t *)lrc; 96 blkptr_t *bp = &lr->lr_blkptr; 97 zbookmark_t zb; 98 99 if (bp->blk_birth == 0) 100 return (0); 101 102 if (claim_txg == 0 || bp->blk_birth < claim_txg) 103 return (0); 104 105 SET_BOOKMARK(&zb, td->td_objset, lr->lr_foid, 106 ZB_ZIL_LEVEL, lr->lr_offset / BP_GET_LSIZE(bp)); 107 108 (void) td->td_func(td->td_spa, zilog, bp, NULL, &zb, NULL, 109 td->td_arg); 110 } 111 return (0); 112 } 113 114 static void 115 traverse_zil(traverse_data_t *td, zil_header_t *zh) 116 { 117 uint64_t claim_txg = zh->zh_claim_txg; 118 zilog_t *zilog; 119 120 /* 121 * We only want to visit blocks that have been claimed but not yet 122 * replayed; plus, in read-only mode, blocks that are already stable. 123 */ 124 if (claim_txg == 0 && spa_writeable(td->td_spa)) 125 return; 126 127 zilog = zil_alloc(spa_get_dsl(td->td_spa)->dp_meta_objset, zh); 128 129 (void) zil_parse(zilog, traverse_zil_block, traverse_zil_record, td, 130 claim_txg); 131 132 zil_free(zilog); 133 } 134 135 typedef enum resume_skip { 136 RESUME_SKIP_ALL, 137 RESUME_SKIP_NONE, 138 RESUME_SKIP_CHILDREN 139 } resume_skip_t; 140 141 /* 142 * Returns RESUME_SKIP_ALL if td indicates that we are resuming a traversal and 143 * the block indicated by zb does not need to be visited at all. Returns 144 * RESUME_SKIP_CHILDREN if we are resuming a post traversal and we reach the 145 * resume point. This indicates that this block should be visited but not its 146 * children (since they must have been visited in a previous traversal). 147 * Otherwise returns RESUME_SKIP_NONE. 148 */ 149 static resume_skip_t 150 resume_skip_check(traverse_data_t *td, const dnode_phys_t *dnp, 151 const zbookmark_t *zb) 152 { 153 if (td->td_resume != NULL && !ZB_IS_ZERO(td->td_resume)) { 154 /* 155 * If we already visited this bp & everything below, 156 * don't bother doing it again. 157 */ 158 if (zbookmark_is_before(dnp, zb, td->td_resume)) 159 return (RESUME_SKIP_ALL); 160 161 /* 162 * If we found the block we're trying to resume from, zero 163 * the bookmark out to indicate that we have resumed. 164 */ 165 ASSERT3U(zb->zb_object, <=, td->td_resume->zb_object); 166 if (bcmp(zb, td->td_resume, sizeof (*zb)) == 0) { 167 bzero(td->td_resume, sizeof (*zb)); 168 if (td->td_flags & TRAVERSE_POST) 169 return (RESUME_SKIP_CHILDREN); 170 } 171 } 172 return (RESUME_SKIP_NONE); 173 } 174 175 static void 176 traverse_pause(traverse_data_t *td, const zbookmark_t *zb) 177 { 178 ASSERT(td->td_resume != NULL); 179 ASSERT0(zb->zb_level); 180 bcopy(zb, td->td_resume, sizeof (*td->td_resume)); 181 } 182 183 static void 184 traverse_prefetch_metadata(traverse_data_t *td, 185 arc_buf_t *pbuf, const blkptr_t *bp, const zbookmark_t *zb) 186 { 187 uint32_t flags = ARC_NOWAIT | ARC_PREFETCH; 188 189 if (!(td->td_flags & TRAVERSE_PREFETCH_METADATA)) 190 return; 191 /* 192 * If we are in the process of resuming, don't prefetch, because 193 * some children will not be needed (and in fact may have already 194 * been freed). 195 */ 196 if (td->td_resume != NULL && !ZB_IS_ZERO(td->td_resume)) 197 return; 198 if (BP_IS_HOLE(bp) || bp->blk_birth <= td->td_min_txg) 199 return; 200 if (BP_GET_LEVEL(bp) == 0 && BP_GET_TYPE(bp) != DMU_OT_DNODE) 201 return; 202 203 (void) arc_read(NULL, td->td_spa, bp, 204 pbuf, NULL, NULL, ZIO_PRIORITY_ASYNC_READ, 205 ZIO_FLAG_CANFAIL, &flags, zb); 206 } 207 208 static int 209 traverse_visitbp(traverse_data_t *td, const dnode_phys_t *dnp, 210 arc_buf_t *pbuf, const blkptr_t *bp, const zbookmark_t *zb) 211 { 212 zbookmark_t czb; 213 int err = 0, lasterr = 0; 214 arc_buf_t *buf = NULL; 215 prefetch_data_t *pd = td->td_pfd; 216 boolean_t hard = td->td_flags & TRAVERSE_HARD; 217 boolean_t pause = B_FALSE; 218 219 switch (resume_skip_check(td, dnp, zb)) { 220 case RESUME_SKIP_ALL: 221 return (0); 222 case RESUME_SKIP_CHILDREN: 223 goto post; 224 case RESUME_SKIP_NONE: 225 break; 226 default: 227 ASSERT(0); 228 } 229 230 if (BP_IS_HOLE(bp)) { 231 err = td->td_func(td->td_spa, NULL, NULL, pbuf, zb, dnp, 232 td->td_arg); 233 return (err); 234 } 235 236 if (bp->blk_birth <= td->td_min_txg) 237 return (0); 238 239 if (pd && !pd->pd_exited && 240 ((pd->pd_flags & TRAVERSE_PREFETCH_DATA) || 241 BP_GET_TYPE(bp) == DMU_OT_DNODE || BP_GET_LEVEL(bp) > 0)) { 242 mutex_enter(&pd->pd_mtx); 243 ASSERT(pd->pd_blks_fetched >= 0); 244 while (pd->pd_blks_fetched == 0 && !pd->pd_exited) 245 cv_wait(&pd->pd_cv, &pd->pd_mtx); 246 pd->pd_blks_fetched--; 247 cv_broadcast(&pd->pd_cv); 248 mutex_exit(&pd->pd_mtx); 249 } 250 251 if (td->td_flags & TRAVERSE_PRE) { 252 err = td->td_func(td->td_spa, NULL, bp, pbuf, zb, dnp, 253 td->td_arg); 254 if (err == TRAVERSE_VISIT_NO_CHILDREN) 255 return (0); 256 if (err == ERESTART) 257 pause = B_TRUE; /* handle pausing at a common point */ 258 if (err != 0) 259 goto post; 260 } 261 262 if (BP_GET_LEVEL(bp) > 0) { 263 uint32_t flags = ARC_WAIT; 264 int i; 265 blkptr_t *cbp; 266 int epb = BP_GET_LSIZE(bp) >> SPA_BLKPTRSHIFT; 267 268 err = dsl_read(NULL, td->td_spa, bp, pbuf, 269 arc_getbuf_func, &buf, 270 ZIO_PRIORITY_ASYNC_READ, ZIO_FLAG_CANFAIL, &flags, zb); 271 if (err) 272 return (err); 273 cbp = buf->b_data; 274 275 for (i = 0; i < epb; i++) { 276 SET_BOOKMARK(&czb, zb->zb_objset, zb->zb_object, 277 zb->zb_level - 1, 278 zb->zb_blkid * epb + i); 279 traverse_prefetch_metadata(td, buf, &cbp[i], &czb); 280 } 281 282 /* recursively visitbp() blocks below this */ 283 for (i = 0; i < epb; i++) { 284 SET_BOOKMARK(&czb, zb->zb_objset, zb->zb_object, 285 zb->zb_level - 1, 286 zb->zb_blkid * epb + i); 287 err = traverse_visitbp(td, dnp, buf, &cbp[i], &czb); 288 if (err) { 289 if (!hard) 290 break; 291 lasterr = err; 292 } 293 } 294 } else if (BP_GET_TYPE(bp) == DMU_OT_DNODE) { 295 uint32_t flags = ARC_WAIT; 296 int i; 297 int epb = BP_GET_LSIZE(bp) >> DNODE_SHIFT; 298 299 err = dsl_read(NULL, td->td_spa, bp, pbuf, 300 arc_getbuf_func, &buf, 301 ZIO_PRIORITY_ASYNC_READ, ZIO_FLAG_CANFAIL, &flags, zb); 302 if (err) 303 return (err); 304 dnp = buf->b_data; 305 306 for (i = 0; i < epb; i++) { 307 prefetch_dnode_metadata(td, &dnp[i], buf, zb->zb_objset, 308 zb->zb_blkid * epb + i); 309 } 310 311 /* recursively visitbp() blocks below this */ 312 for (i = 0; i < epb; i++) { 313 err = traverse_dnode(td, &dnp[i], buf, zb->zb_objset, 314 zb->zb_blkid * epb + i); 315 if (err) { 316 if (!hard) 317 break; 318 lasterr = err; 319 } 320 } 321 } else if (BP_GET_TYPE(bp) == DMU_OT_OBJSET) { 322 uint32_t flags = ARC_WAIT; 323 objset_phys_t *osp; 324 dnode_phys_t *dnp; 325 326 err = dsl_read_nolock(NULL, td->td_spa, bp, 327 arc_getbuf_func, &buf, 328 ZIO_PRIORITY_ASYNC_READ, ZIO_FLAG_CANFAIL, &flags, zb); 329 if (err) 330 return (err); 331 332 osp = buf->b_data; 333 dnp = &osp->os_meta_dnode; 334 prefetch_dnode_metadata(td, dnp, buf, zb->zb_objset, 335 DMU_META_DNODE_OBJECT); 336 if (arc_buf_size(buf) >= sizeof (objset_phys_t)) { 337 prefetch_dnode_metadata(td, &osp->os_userused_dnode, 338 buf, zb->zb_objset, DMU_USERUSED_OBJECT); 339 prefetch_dnode_metadata(td, &osp->os_groupused_dnode, 340 buf, zb->zb_objset, DMU_USERUSED_OBJECT); 341 } 342 343 err = traverse_dnode(td, dnp, buf, zb->zb_objset, 344 DMU_META_DNODE_OBJECT); 345 if (err && hard) { 346 lasterr = err; 347 err = 0; 348 } 349 if (err == 0 && arc_buf_size(buf) >= sizeof (objset_phys_t)) { 350 dnp = &osp->os_userused_dnode; 351 err = traverse_dnode(td, dnp, buf, zb->zb_objset, 352 DMU_USERUSED_OBJECT); 353 } 354 if (err && hard) { 355 lasterr = err; 356 err = 0; 357 } 358 if (err == 0 && arc_buf_size(buf) >= sizeof (objset_phys_t)) { 359 dnp = &osp->os_groupused_dnode; 360 err = traverse_dnode(td, dnp, buf, zb->zb_objset, 361 DMU_GROUPUSED_OBJECT); 362 } 363 } 364 365 if (buf) 366 (void) arc_buf_remove_ref(buf, &buf); 367 368 post: 369 if (err == 0 && lasterr == 0 && (td->td_flags & TRAVERSE_POST)) { 370 err = td->td_func(td->td_spa, NULL, bp, pbuf, zb, dnp, 371 td->td_arg); 372 if (err == ERESTART) 373 pause = B_TRUE; 374 } 375 376 if (pause && td->td_resume != NULL) { 377 ASSERT3U(err, ==, ERESTART); 378 ASSERT(!hard); 379 traverse_pause(td, zb); 380 } 381 382 return (err != 0 ? err : lasterr); 383 } 384 385 static void 386 prefetch_dnode_metadata(traverse_data_t *td, const dnode_phys_t *dnp, 387 arc_buf_t *buf, uint64_t objset, uint64_t object) 388 { 389 int j; 390 zbookmark_t czb; 391 392 for (j = 0; j < dnp->dn_nblkptr; j++) { 393 SET_BOOKMARK(&czb, objset, object, dnp->dn_nlevels - 1, j); 394 traverse_prefetch_metadata(td, buf, &dnp->dn_blkptr[j], &czb); 395 } 396 397 if (dnp->dn_flags & DNODE_FLAG_SPILL_BLKPTR) { 398 SET_BOOKMARK(&czb, objset, object, 0, DMU_SPILL_BLKID); 399 traverse_prefetch_metadata(td, buf, &dnp->dn_spill, &czb); 400 } 401 } 402 403 static int 404 traverse_dnode(traverse_data_t *td, const dnode_phys_t *dnp, 405 arc_buf_t *buf, uint64_t objset, uint64_t object) 406 { 407 int j, err = 0, lasterr = 0; 408 zbookmark_t czb; 409 boolean_t hard = (td->td_flags & TRAVERSE_HARD); 410 411 for (j = 0; j < dnp->dn_nblkptr; j++) { 412 SET_BOOKMARK(&czb, objset, object, dnp->dn_nlevels - 1, j); 413 err = traverse_visitbp(td, dnp, buf, &dnp->dn_blkptr[j], &czb); 414 if (err) { 415 if (!hard) 416 break; 417 lasterr = err; 418 } 419 } 420 421 if (dnp->dn_flags & DNODE_FLAG_SPILL_BLKPTR) { 422 SET_BOOKMARK(&czb, objset, object, 0, DMU_SPILL_BLKID); 423 err = traverse_visitbp(td, dnp, buf, &dnp->dn_spill, &czb); 424 if (err) { 425 if (!hard) 426 return (err); 427 lasterr = err; 428 } 429 } 430 return (err != 0 ? err : lasterr); 431 } 432 433 /* ARGSUSED */ 434 static int 435 traverse_prefetcher(spa_t *spa, zilog_t *zilog, const blkptr_t *bp, 436 arc_buf_t *pbuf, const zbookmark_t *zb, const dnode_phys_t *dnp, 437 void *arg) 438 { 439 prefetch_data_t *pfd = arg; 440 uint32_t aflags = ARC_NOWAIT | ARC_PREFETCH; 441 442 ASSERT(pfd->pd_blks_fetched >= 0); 443 if (pfd->pd_cancel) 444 return (EINTR); 445 446 if (bp == NULL || !((pfd->pd_flags & TRAVERSE_PREFETCH_DATA) || 447 BP_GET_TYPE(bp) == DMU_OT_DNODE || BP_GET_LEVEL(bp) > 0) || 448 BP_GET_TYPE(bp) == DMU_OT_INTENT_LOG) 449 return (0); 450 451 mutex_enter(&pfd->pd_mtx); 452 while (!pfd->pd_cancel && pfd->pd_blks_fetched >= pfd->pd_blks_max) 453 cv_wait(&pfd->pd_cv, &pfd->pd_mtx); 454 pfd->pd_blks_fetched++; 455 cv_broadcast(&pfd->pd_cv); 456 mutex_exit(&pfd->pd_mtx); 457 458 (void) dsl_read(NULL, spa, bp, pbuf, NULL, NULL, 459 ZIO_PRIORITY_ASYNC_READ, 460 ZIO_FLAG_CANFAIL | ZIO_FLAG_SPECULATIVE, 461 &aflags, zb); 462 463 return (0); 464 } 465 466 static void 467 traverse_prefetch_thread(void *arg) 468 { 469 traverse_data_t *td_main = arg; 470 traverse_data_t td = *td_main; 471 zbookmark_t czb; 472 473 td.td_func = traverse_prefetcher; 474 td.td_arg = td_main->td_pfd; 475 td.td_pfd = NULL; 476 477 SET_BOOKMARK(&czb, td.td_objset, 478 ZB_ROOT_OBJECT, ZB_ROOT_LEVEL, ZB_ROOT_BLKID); 479 (void) traverse_visitbp(&td, NULL, NULL, td.td_rootbp, &czb); 480 481 mutex_enter(&td_main->td_pfd->pd_mtx); 482 td_main->td_pfd->pd_exited = B_TRUE; 483 cv_broadcast(&td_main->td_pfd->pd_cv); 484 mutex_exit(&td_main->td_pfd->pd_mtx); 485 } 486 487 /* 488 * NB: dataset must not be changing on-disk (eg, is a snapshot or we are 489 * in syncing context). 490 */ 491 static int 492 traverse_impl(spa_t *spa, dsl_dataset_t *ds, uint64_t objset, blkptr_t *rootbp, 493 uint64_t txg_start, zbookmark_t *resume, int flags, 494 blkptr_cb_t func, void *arg) 495 { 496 traverse_data_t td; 497 prefetch_data_t pd = { 0 }; 498 zbookmark_t czb; 499 int err; 500 501 ASSERT(ds == NULL || objset == ds->ds_object); 502 ASSERT(!(flags & TRAVERSE_PRE) || !(flags & TRAVERSE_POST)); 503 504 /* 505 * The data prefetching mechanism (the prefetch thread) is incompatible 506 * with resuming from a bookmark. 507 */ 508 ASSERT(resume == NULL || !(flags & TRAVERSE_PREFETCH_DATA)); 509 510 td.td_spa = spa; 511 td.td_objset = objset; 512 td.td_rootbp = rootbp; 513 td.td_min_txg = txg_start; 514 td.td_resume = resume; 515 td.td_func = func; 516 td.td_arg = arg; 517 td.td_pfd = &pd; 518 td.td_flags = flags; 519 520 pd.pd_blks_max = zfs_pd_blks_max; 521 pd.pd_flags = flags; 522 mutex_init(&pd.pd_mtx, NULL, MUTEX_DEFAULT, NULL); 523 cv_init(&pd.pd_cv, NULL, CV_DEFAULT, NULL); 524 525 /* See comment on ZIL traversal in dsl_scan_visitds. */ 526 if (ds != NULL && !dsl_dataset_is_snapshot(ds)) { 527 objset_t *os; 528 529 err = dmu_objset_from_ds(ds, &os); 530 if (err) 531 return (err); 532 533 traverse_zil(&td, &os->os_zil_header); 534 } 535 536 if (!(flags & TRAVERSE_PREFETCH_DATA) || 537 0 == taskq_dispatch(system_taskq, traverse_prefetch_thread, 538 &td, TQ_NOQUEUE)) 539 pd.pd_exited = B_TRUE; 540 541 SET_BOOKMARK(&czb, td.td_objset, 542 ZB_ROOT_OBJECT, ZB_ROOT_LEVEL, ZB_ROOT_BLKID); 543 err = traverse_visitbp(&td, NULL, NULL, rootbp, &czb); 544 545 mutex_enter(&pd.pd_mtx); 546 pd.pd_cancel = B_TRUE; 547 cv_broadcast(&pd.pd_cv); 548 while (!pd.pd_exited) 549 cv_wait(&pd.pd_cv, &pd.pd_mtx); 550 mutex_exit(&pd.pd_mtx); 551 552 mutex_destroy(&pd.pd_mtx); 553 cv_destroy(&pd.pd_cv); 554 555 return (err); 556 } 557 558 /* 559 * NB: dataset must not be changing on-disk (eg, is a snapshot or we are 560 * in syncing context). 561 */ 562 int 563 traverse_dataset(dsl_dataset_t *ds, uint64_t txg_start, int flags, 564 blkptr_cb_t func, void *arg) 565 { 566 return (traverse_impl(ds->ds_dir->dd_pool->dp_spa, ds, ds->ds_object, 567 &ds->ds_phys->ds_bp, txg_start, NULL, flags, func, arg)); 568 } 569 570 int 571 traverse_dataset_destroyed(spa_t *spa, blkptr_t *blkptr, 572 uint64_t txg_start, zbookmark_t *resume, int flags, 573 blkptr_cb_t func, void *arg) 574 { 575 return (traverse_impl(spa, NULL, ZB_DESTROYED_OBJSET, 576 blkptr, txg_start, resume, flags, func, arg)); 577 } 578 579 /* 580 * NB: pool must not be changing on-disk (eg, from zdb or sync context). 581 */ 582 int 583 traverse_pool(spa_t *spa, uint64_t txg_start, int flags, 584 blkptr_cb_t func, void *arg) 585 { 586 int err, lasterr = 0; 587 uint64_t obj; 588 dsl_pool_t *dp = spa_get_dsl(spa); 589 objset_t *mos = dp->dp_meta_objset; 590 boolean_t hard = (flags & TRAVERSE_HARD); 591 592 /* visit the MOS */ 593 err = traverse_impl(spa, NULL, 0, spa_get_rootblkptr(spa), 594 txg_start, NULL, flags, func, arg); 595 if (err) 596 return (err); 597 598 /* visit each dataset */ 599 for (obj = 1; err == 0 || (err != ESRCH && hard); 600 err = dmu_object_next(mos, &obj, FALSE, txg_start)) { 601 dmu_object_info_t doi; 602 603 err = dmu_object_info(mos, obj, &doi); 604 if (err) { 605 if (!hard) 606 return (err); 607 lasterr = err; 608 continue; 609 } 610 611 if (doi.doi_type == DMU_OT_DSL_DATASET) { 612 dsl_dataset_t *ds; 613 uint64_t txg = txg_start; 614 615 rw_enter(&dp->dp_config_rwlock, RW_READER); 616 err = dsl_dataset_hold_obj(dp, obj, FTAG, &ds); 617 rw_exit(&dp->dp_config_rwlock); 618 if (err) { 619 if (!hard) 620 return (err); 621 lasterr = err; 622 continue; 623 } 624 if (ds->ds_phys->ds_prev_snap_txg > txg) 625 txg = ds->ds_phys->ds_prev_snap_txg; 626 err = traverse_dataset(ds, txg, flags, func, arg); 627 dsl_dataset_rele(ds, FTAG); 628 if (err) { 629 if (!hard) 630 return (err); 631 lasterr = err; 632 } 633 } 634 } 635 if (err == ESRCH) 636 err = 0; 637 return (err != 0 ? err : lasterr); 638 } 639