/* * CDDL HEADER START * * The contents of this file are subject to the terms of the * Common Development and Distribution License (the "License"). * You may not use this file except in compliance with the License. * * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE * or http://www.opensolaris.org/os/licensing. * See the License for the specific language governing permissions * and limitations under the License. * * When distributing Covered Code, include this CDDL HEADER in each * file and include the License file at usr/src/OPENSOLARIS.LICENSE. * If applicable, add the following below this CDDL HEADER, with the * fields enclosed by brackets "[]" replaced with your own identifying * information: Portions Copyright [yyyy] [name of copyright owner] * * CDDL HEADER END */ /* * Copyright (c) 2005, 2010, Oracle and/or its affiliates. All rights reserved. */ #include <sys/zfs_context.h> #include <sys/dbuf.h> #include <sys/dnode.h> #include <sys/dmu.h> #include <sys/dmu_tx.h> #include <sys/dmu_objset.h> #include <sys/dsl_dataset.h> #include <sys/spa.h> static void dnode_increase_indirection(dnode_t *dn, dmu_tx_t *tx) { dmu_buf_impl_t *db; int txgoff = tx->tx_txg & TXG_MASK; int nblkptr = dn->dn_phys->dn_nblkptr; int old_toplvl = dn->dn_phys->dn_nlevels - 1; int new_level = dn->dn_next_nlevels[txgoff]; int i; rw_enter(&dn->dn_struct_rwlock, RW_WRITER); /* this dnode can't be paged out because it's dirty */ ASSERT(dn->dn_phys->dn_type != DMU_OT_NONE); ASSERT(RW_WRITE_HELD(&dn->dn_struct_rwlock)); ASSERT(new_level > 1 && dn->dn_phys->dn_nlevels > 0); db = dbuf_hold_level(dn, dn->dn_phys->dn_nlevels, 0, FTAG); ASSERT(db != NULL); dn->dn_phys->dn_nlevels = new_level; dprintf("os=%p obj=%llu, increase to %d\n", dn->dn_objset, dn->dn_object, dn->dn_phys->dn_nlevels); /* check for existing blkptrs in the dnode */ for (i = 0; i < nblkptr; i++) if (!BP_IS_HOLE(&dn->dn_phys->dn_blkptr[i])) break; if (i != nblkptr) { /* transfer dnode's block pointers to new indirect block */ (void) dbuf_read(db, NULL, DB_RF_MUST_SUCCEED|DB_RF_HAVESTRUCT); ASSERT(db->db.db_data); ASSERT(arc_released(db->db_buf)); ASSERT3U(sizeof (blkptr_t) * nblkptr, <=, db->db.db_size); bcopy(dn->dn_phys->dn_blkptr, db->db.db_data, sizeof (blkptr_t) * nblkptr); arc_buf_freeze(db->db_buf); } /* set dbuf's parent pointers to new indirect buf */ for (i = 0; i < nblkptr; i++) { dmu_buf_impl_t *child = dbuf_find(dn, old_toplvl, i); if (child == NULL) continue; #ifdef DEBUG DB_DNODE_ENTER(child); ASSERT3P(DB_DNODE(child), ==, dn); DB_DNODE_EXIT(child); #endif /* DEBUG */ if (child->db_parent && child->db_parent != dn->dn_dbuf) { ASSERT(child->db_parent->db_level == db->db_level); ASSERT(child->db_blkptr != &dn->dn_phys->dn_blkptr[child->db_blkid]); mutex_exit(&child->db_mtx); continue; } ASSERT(child->db_parent == NULL || child->db_parent == dn->dn_dbuf); child->db_parent = db; dbuf_add_ref(db, child); if (db->db.db_data) child->db_blkptr = (blkptr_t *)db->db.db_data + i; else child->db_blkptr = NULL; dprintf_dbuf_bp(child, child->db_blkptr, "changed db_blkptr to new indirect %s", ""); mutex_exit(&child->db_mtx); } bzero(dn->dn_phys->dn_blkptr, sizeof (blkptr_t) * nblkptr); dbuf_rele(db, FTAG); rw_exit(&dn->dn_struct_rwlock); } static int free_blocks(dnode_t *dn, blkptr_t *bp, int num, dmu_tx_t *tx) { dsl_dataset_t *ds = dn->dn_objset->os_dsl_dataset; uint64_t bytesfreed = 0; int i, blocks_freed = 0; dprintf("ds=%p obj=%llx num=%d\n", ds, dn->dn_object, num); for (i = 0; i < num; i++, bp++) { if (BP_IS_HOLE(bp)) continue; bytesfreed += dsl_dataset_block_kill(ds, bp, tx, B_FALSE); ASSERT3U(bytesfreed, <=, DN_USED_BYTES(dn->dn_phys)); bzero(bp, sizeof (blkptr_t)); blocks_freed += 1; } dnode_diduse_space(dn, -bytesfreed); return (blocks_freed); } #ifdef ZFS_DEBUG static void free_verify(dmu_buf_impl_t *db, uint64_t start, uint64_t end, dmu_tx_t *tx) { int off, num; int i, err, epbs; uint64_t txg = tx->tx_txg; dnode_t *dn; DB_DNODE_ENTER(db); dn = DB_DNODE(db); epbs = dn->dn_phys->dn_indblkshift - SPA_BLKPTRSHIFT; off = start - (db->db_blkid * 1<<epbs); num = end - start + 1; ASSERT3U(off, >=, 0); ASSERT3U(num, >=, 0); ASSERT3U(db->db_level, >, 0); ASSERT3U(db->db.db_size, ==, 1 << dn->dn_phys->dn_indblkshift); ASSERT3U(off+num, <=, db->db.db_size >> SPA_BLKPTRSHIFT); ASSERT(db->db_blkptr != NULL); for (i = off; i < off+num; i++) { uint64_t *buf; dmu_buf_impl_t *child; dbuf_dirty_record_t *dr; int j; ASSERT(db->db_level == 1); rw_enter(&dn->dn_struct_rwlock, RW_READER); err = dbuf_hold_impl(dn, db->db_level-1, (db->db_blkid << epbs) + i, TRUE, FTAG, &child); rw_exit(&dn->dn_struct_rwlock); if (err == ENOENT) continue; ASSERT(err == 0); ASSERT(child->db_level == 0); dr = child->db_last_dirty; while (dr && dr->dr_txg > txg) dr = dr->dr_next; ASSERT(dr == NULL || dr->dr_txg == txg); /* data_old better be zeroed */ if (dr) { buf = dr->dt.dl.dr_data->b_data; for (j = 0; j < child->db.db_size >> 3; j++) { if (buf[j] != 0) { panic("freed data not zero: " "child=%p i=%d off=%d num=%d\n", (void *)child, i, off, num); } } } /* * db_data better be zeroed unless it's dirty in a * future txg. */ mutex_enter(&child->db_mtx); buf = child->db.db_data; if (buf != NULL && child->db_state != DB_FILL && child->db_last_dirty == NULL) { for (j = 0; j < child->db.db_size >> 3; j++) { if (buf[j] != 0) { panic("freed data not zero: " "child=%p i=%d off=%d num=%d\n", (void *)child, i, off, num); } } } mutex_exit(&child->db_mtx); dbuf_rele(child, FTAG); } DB_DNODE_EXIT(db); } #endif #define ALL -1 static int free_children(dmu_buf_impl_t *db, uint64_t blkid, uint64_t nblks, int trunc, dmu_tx_t *tx) { dnode_t *dn; blkptr_t *bp; dmu_buf_impl_t *subdb; uint64_t start, end, dbstart, dbend, i; int epbs, shift, err; int all = TRUE; int blocks_freed = 0; /* * There is a small possibility that this block will not be cached: * 1 - if level > 1 and there are no children with level <= 1 * 2 - if we didn't get a dirty hold (because this block had just * finished being written -- and so had no holds), and then this * block got evicted before we got here. */ if (db->db_state != DB_CACHED) (void) dbuf_read(db, NULL, DB_RF_MUST_SUCCEED); dbuf_release_bp(db); bp = (blkptr_t *)db->db.db_data; DB_DNODE_ENTER(db); dn = DB_DNODE(db); epbs = dn->dn_phys->dn_indblkshift - SPA_BLKPTRSHIFT; shift = (db->db_level - 1) * epbs; dbstart = db->db_blkid << epbs; start = blkid >> shift; if (dbstart < start) { bp += start - dbstart; all = FALSE; } else { start = dbstart; } dbend = ((db->db_blkid + 1) << epbs) - 1; end = (blkid + nblks - 1) >> shift; if (dbend <= end) end = dbend; else if (all) all = trunc; ASSERT3U(start, <=, end); if (db->db_level == 1) { FREE_VERIFY(db, start, end, tx); blocks_freed = free_blocks(dn, bp, end-start+1, tx); arc_buf_freeze(db->db_buf); ASSERT(all || blocks_freed == 0 || db->db_last_dirty); DB_DNODE_EXIT(db); return (all ? ALL : blocks_freed); } for (i = start; i <= end; i++, bp++) { if (BP_IS_HOLE(bp)) continue; rw_enter(&dn->dn_struct_rwlock, RW_READER); err = dbuf_hold_impl(dn, db->db_level-1, i, TRUE, FTAG, &subdb); ASSERT3U(err, ==, 0); rw_exit(&dn->dn_struct_rwlock); if (free_children(subdb, blkid, nblks, trunc, tx) == ALL) { ASSERT3P(subdb->db_blkptr, ==, bp); blocks_freed += free_blocks(dn, bp, 1, tx); } else { all = FALSE; } dbuf_rele(subdb, FTAG); } DB_DNODE_EXIT(db); arc_buf_freeze(db->db_buf); #ifdef ZFS_DEBUG bp -= (end-start)+1; for (i = start; i <= end; i++, bp++) { if (i == start && blkid != 0) continue; else if (i == end && !trunc) continue; ASSERT3U(bp->blk_birth, ==, 0); } #endif ASSERT(all || blocks_freed == 0 || db->db_last_dirty); return (all ? ALL : blocks_freed); } /* * free_range: Traverse the indicated range of the provided file * and "free" all the blocks contained there. */ static void dnode_sync_free_range(dnode_t *dn, uint64_t blkid, uint64_t nblks, dmu_tx_t *tx) { blkptr_t *bp = dn->dn_phys->dn_blkptr; dmu_buf_impl_t *db; int trunc, start, end, shift, i, err; int dnlevel = dn->dn_phys->dn_nlevels; if (blkid > dn->dn_phys->dn_maxblkid) return; ASSERT(dn->dn_phys->dn_maxblkid < UINT64_MAX); trunc = blkid + nblks > dn->dn_phys->dn_maxblkid; if (trunc) nblks = dn->dn_phys->dn_maxblkid - blkid + 1; /* There are no indirect blocks in the object */ if (dnlevel == 1) { if (blkid >= dn->dn_phys->dn_nblkptr) { /* this range was never made persistent */ return; } ASSERT3U(blkid + nblks, <=, dn->dn_phys->dn_nblkptr); (void) free_blocks(dn, bp + blkid, nblks, tx); if (trunc) { ASSERTV(uint64_t off = (dn->dn_phys->dn_maxblkid + 1) * (dn->dn_phys->dn_datablkszsec<<SPA_MINBLOCKSHIFT)); dn->dn_phys->dn_maxblkid = (blkid ? blkid - 1 : 0); ASSERT(off < dn->dn_phys->dn_maxblkid || dn->dn_phys->dn_maxblkid == 0 || dnode_next_offset(dn, 0, &off, 1, 1, 0) != 0); } return; } shift = (dnlevel - 1) * (dn->dn_phys->dn_indblkshift - SPA_BLKPTRSHIFT); start = blkid >> shift; ASSERT(start < dn->dn_phys->dn_nblkptr); end = (blkid + nblks - 1) >> shift; bp += start; for (i = start; i <= end; i++, bp++) { if (BP_IS_HOLE(bp)) continue; rw_enter(&dn->dn_struct_rwlock, RW_READER); err = dbuf_hold_impl(dn, dnlevel-1, i, TRUE, FTAG, &db); ASSERT3U(err, ==, 0); rw_exit(&dn->dn_struct_rwlock); if (free_children(db, blkid, nblks, trunc, tx) == ALL) { ASSERT3P(db->db_blkptr, ==, bp); (void) free_blocks(dn, bp, 1, tx); } dbuf_rele(db, FTAG); } if (trunc) { ASSERTV(uint64_t off = (dn->dn_phys->dn_maxblkid + 1) * (dn->dn_phys->dn_datablkszsec << SPA_MINBLOCKSHIFT)); dn->dn_phys->dn_maxblkid = (blkid ? blkid - 1 : 0); ASSERT(off < dn->dn_phys->dn_maxblkid || dn->dn_phys->dn_maxblkid == 0 || dnode_next_offset(dn, 0, &off, 1, 1, 0) != 0); } } /* * Try to kick all the dnodes dbufs out of the cache... */ void dnode_evict_dbufs(dnode_t *dn) { int progress; int pass = 0; do { dmu_buf_impl_t *db, marker; int evicting = FALSE; progress = FALSE; mutex_enter(&dn->dn_dbufs_mtx); list_insert_tail(&dn->dn_dbufs, &marker); db = list_head(&dn->dn_dbufs); for (; db != ▮ db = list_head(&dn->dn_dbufs)) { list_remove(&dn->dn_dbufs, db); list_insert_tail(&dn->dn_dbufs, db); #ifdef DEBUG DB_DNODE_ENTER(db); ASSERT3P(DB_DNODE(db), ==, dn); DB_DNODE_EXIT(db); #endif /* DEBUG */ mutex_enter(&db->db_mtx); if (db->db_state == DB_EVICTING) { progress = TRUE; evicting = TRUE; mutex_exit(&db->db_mtx); } else if (refcount_is_zero(&db->db_holds)) { progress = TRUE; dbuf_clear(db); /* exits db_mtx for us */ } else { mutex_exit(&db->db_mtx); } } list_remove(&dn->dn_dbufs, &marker); /* * NB: we need to drop dn_dbufs_mtx between passes so * that any DB_EVICTING dbufs can make progress. * Ideally, we would have some cv we could wait on, but * since we don't, just wait a bit to give the other * thread a chance to run. */ mutex_exit(&dn->dn_dbufs_mtx); if (evicting) delay(1); pass++; if ((pass % 100) == 0) dprintf("Exceeded %d passes evicting dbufs\n", pass); } while (progress); if (pass >= 100) dprintf("Required %d passes to evict dbufs\n", pass); rw_enter(&dn->dn_struct_rwlock, RW_WRITER); if (dn->dn_bonus && refcount_is_zero(&dn->dn_bonus->db_holds)) { mutex_enter(&dn->dn_bonus->db_mtx); dbuf_evict(dn->dn_bonus); dn->dn_bonus = NULL; } rw_exit(&dn->dn_struct_rwlock); } static void dnode_undirty_dbufs(list_t *list) { dbuf_dirty_record_t *dr; while ((dr = list_head(list))) { dmu_buf_impl_t *db = dr->dr_dbuf; uint64_t txg = dr->dr_txg; if (db->db_level != 0) dnode_undirty_dbufs(&dr->dt.di.dr_children); mutex_enter(&db->db_mtx); /* XXX - use dbuf_undirty()? */ list_remove(list, dr); ASSERT(db->db_last_dirty == dr); db->db_last_dirty = NULL; db->db_dirtycnt -= 1; if (db->db_level == 0) { ASSERT(db->db_blkid == DMU_BONUS_BLKID || dr->dt.dl.dr_data == db->db_buf); dbuf_unoverride(dr); } kmem_free(dr, sizeof (dbuf_dirty_record_t)); dbuf_rele_and_unlock(db, (void *)(uintptr_t)txg); } } static void dnode_sync_free(dnode_t *dn, dmu_tx_t *tx) { int txgoff = tx->tx_txg & TXG_MASK; ASSERT(dmu_tx_is_syncing(tx)); /* * Our contents should have been freed in dnode_sync() by the * free range record inserted by the caller of dnode_free(). */ ASSERT3U(DN_USED_BYTES(dn->dn_phys), ==, 0); ASSERT(BP_IS_HOLE(dn->dn_phys->dn_blkptr)); dnode_undirty_dbufs(&dn->dn_dirty_records[txgoff]); dnode_evict_dbufs(dn); ASSERT3P(list_head(&dn->dn_dbufs), ==, NULL); /* * XXX - It would be nice to assert this, but we may still * have residual holds from async evictions from the arc... * * zfs_obj_to_path() also depends on this being * commented out. * * ASSERT3U(refcount_count(&dn->dn_holds), ==, 1); */ /* Undirty next bits */ dn->dn_next_nlevels[txgoff] = 0; dn->dn_next_indblkshift[txgoff] = 0; dn->dn_next_blksz[txgoff] = 0; /* ASSERT(blkptrs are zero); */ ASSERT(dn->dn_phys->dn_type != DMU_OT_NONE); ASSERT(dn->dn_type != DMU_OT_NONE); ASSERT(dn->dn_free_txg > 0); if (dn->dn_allocated_txg != dn->dn_free_txg) dbuf_will_dirty(dn->dn_dbuf, tx); bzero(dn->dn_phys, sizeof (dnode_phys_t)); mutex_enter(&dn->dn_mtx); dn->dn_type = DMU_OT_NONE; dn->dn_maxblkid = 0; dn->dn_allocated_txg = 0; dn->dn_free_txg = 0; dn->dn_have_spill = B_FALSE; mutex_exit(&dn->dn_mtx); ASSERT(dn->dn_object != DMU_META_DNODE_OBJECT); dnode_rele(dn, (void *)(uintptr_t)tx->tx_txg); /* * Now that we've released our hold, the dnode may * be evicted, so we musn't access it. */ } /* * Write out the dnode's dirty buffers. */ void dnode_sync(dnode_t *dn, dmu_tx_t *tx) { free_range_t *rp; dnode_phys_t *dnp = dn->dn_phys; int txgoff = tx->tx_txg & TXG_MASK; list_t *list = &dn->dn_dirty_records[txgoff]; boolean_t kill_spill = B_FALSE; ASSERTV(static const dnode_phys_t zerodn = { 0 }); ASSERT(dmu_tx_is_syncing(tx)); ASSERT(dnp->dn_type != DMU_OT_NONE || dn->dn_allocated_txg); ASSERT(dnp->dn_type != DMU_OT_NONE || bcmp(dnp, &zerodn, DNODE_SIZE) == 0); DNODE_VERIFY(dn); ASSERT(dn->dn_dbuf == NULL || arc_released(dn->dn_dbuf->db_buf)); if (dmu_objset_userused_enabled(dn->dn_objset) && !DMU_OBJECT_IS_SPECIAL(dn->dn_object)) { mutex_enter(&dn->dn_mtx); dn->dn_oldused = DN_USED_BYTES(dn->dn_phys); dn->dn_oldflags = dn->dn_phys->dn_flags; dn->dn_phys->dn_flags |= DNODE_FLAG_USERUSED_ACCOUNTED; mutex_exit(&dn->dn_mtx); dmu_objset_userquota_get_ids(dn, B_FALSE, tx); } else { /* Once we account for it, we should always account for it. */ ASSERT(!(dn->dn_phys->dn_flags & DNODE_FLAG_USERUSED_ACCOUNTED)); } mutex_enter(&dn->dn_mtx); if (dn->dn_allocated_txg == tx->tx_txg) { /* The dnode is newly allocated or reallocated */ if (dnp->dn_type == DMU_OT_NONE) { /* this is a first alloc, not a realloc */ dnp->dn_nlevels = 1; dnp->dn_nblkptr = dn->dn_nblkptr; } dnp->dn_type = dn->dn_type; dnp->dn_bonustype = dn->dn_bonustype; dnp->dn_bonuslen = dn->dn_bonuslen; } ASSERT(dnp->dn_nlevels > 1 || BP_IS_HOLE(&dnp->dn_blkptr[0]) || BP_GET_LSIZE(&dnp->dn_blkptr[0]) == dnp->dn_datablkszsec << SPA_MINBLOCKSHIFT); if (dn->dn_next_blksz[txgoff]) { ASSERT(P2PHASE(dn->dn_next_blksz[txgoff], SPA_MINBLOCKSIZE) == 0); ASSERT(BP_IS_HOLE(&dnp->dn_blkptr[0]) || dn->dn_maxblkid == 0 || list_head(list) != NULL || avl_last(&dn->dn_ranges[txgoff]) || dn->dn_next_blksz[txgoff] >> SPA_MINBLOCKSHIFT == dnp->dn_datablkszsec); dnp->dn_datablkszsec = dn->dn_next_blksz[txgoff] >> SPA_MINBLOCKSHIFT; dn->dn_next_blksz[txgoff] = 0; } if (dn->dn_next_bonuslen[txgoff]) { if (dn->dn_next_bonuslen[txgoff] == DN_ZERO_BONUSLEN) dnp->dn_bonuslen = 0; else dnp->dn_bonuslen = dn->dn_next_bonuslen[txgoff]; ASSERT(dnp->dn_bonuslen <= DN_MAX_BONUSLEN); dn->dn_next_bonuslen[txgoff] = 0; } if (dn->dn_next_bonustype[txgoff]) { ASSERT(dn->dn_next_bonustype[txgoff] < DMU_OT_NUMTYPES); dnp->dn_bonustype = dn->dn_next_bonustype[txgoff]; dn->dn_next_bonustype[txgoff] = 0; } /* * We will either remove a spill block when a file is being removed * or we have been asked to remove it. */ if (dn->dn_rm_spillblk[txgoff] || ((dnp->dn_flags & DNODE_FLAG_SPILL_BLKPTR) && dn->dn_free_txg > 0 && dn->dn_free_txg <= tx->tx_txg)) { if ((dnp->dn_flags & DNODE_FLAG_SPILL_BLKPTR)) kill_spill = B_TRUE; dn->dn_rm_spillblk[txgoff] = 0; } if (dn->dn_next_indblkshift[txgoff]) { ASSERT(dnp->dn_nlevels == 1); dnp->dn_indblkshift = dn->dn_next_indblkshift[txgoff]; dn->dn_next_indblkshift[txgoff] = 0; } /* * Just take the live (open-context) values for checksum and compress. * Strictly speaking it's a future leak, but nothing bad happens if we * start using the new checksum or compress algorithm a little early. */ dnp->dn_checksum = dn->dn_checksum; dnp->dn_compress = dn->dn_compress; mutex_exit(&dn->dn_mtx); if (kill_spill) { (void) free_blocks(dn, &dn->dn_phys->dn_spill, 1, tx); mutex_enter(&dn->dn_mtx); dnp->dn_flags &= ~DNODE_FLAG_SPILL_BLKPTR; mutex_exit(&dn->dn_mtx); } /* process all the "freed" ranges in the file */ while ((rp = avl_last(&dn->dn_ranges[txgoff]))) { dnode_sync_free_range(dn, rp->fr_blkid, rp->fr_nblks, tx); /* grab the mutex so we don't race with dnode_block_freed() */ mutex_enter(&dn->dn_mtx); avl_remove(&dn->dn_ranges[txgoff], rp); mutex_exit(&dn->dn_mtx); kmem_free(rp, sizeof (free_range_t)); } if (dn->dn_free_txg > 0 && dn->dn_free_txg <= tx->tx_txg) { dnode_sync_free(dn, tx); return; } if (dn->dn_next_nblkptr[txgoff]) { /* this should only happen on a realloc */ ASSERT(dn->dn_allocated_txg == tx->tx_txg); if (dn->dn_next_nblkptr[txgoff] > dnp->dn_nblkptr) { /* zero the new blkptrs we are gaining */ bzero(dnp->dn_blkptr + dnp->dn_nblkptr, sizeof (blkptr_t) * (dn->dn_next_nblkptr[txgoff] - dnp->dn_nblkptr)); #ifdef ZFS_DEBUG } else { int i; ASSERT(dn->dn_next_nblkptr[txgoff] < dnp->dn_nblkptr); /* the blkptrs we are losing better be unallocated */ for (i = dn->dn_next_nblkptr[txgoff]; i < dnp->dn_nblkptr; i++) ASSERT(BP_IS_HOLE(&dnp->dn_blkptr[i])); #endif } mutex_enter(&dn->dn_mtx); dnp->dn_nblkptr = dn->dn_next_nblkptr[txgoff]; dn->dn_next_nblkptr[txgoff] = 0; mutex_exit(&dn->dn_mtx); } if (dn->dn_next_nlevels[txgoff]) { dnode_increase_indirection(dn, tx); dn->dn_next_nlevels[txgoff] = 0; } dbuf_sync_list(list, tx); if (!DMU_OBJECT_IS_SPECIAL(dn->dn_object)) { ASSERT3P(list_head(list), ==, NULL); dnode_rele(dn, (void *)(uintptr_t)tx->tx_txg); } /* * Although we have dropped our reference to the dnode, it * can't be evicted until its written, and we haven't yet * initiated the IO for the dnode's dbuf. */ }