--- a/usr/src/uts/common/fs/zfs/dmu_send.c	Wed Jan 28 12:09:40 2009 -0800
+++ b/usr/src/uts/common/fs/zfs/dmu_send.c	Wed Jan 28 15:32:27 2009 -0700
@@ -19,7 +19,7 @@
  * CDDL HEADER END
  */
 /*
- * Copyright 2008 Sun Microsystems, Inc.  All rights reserved.
+ * Copyright 2009 Sun Microsystems, Inc.  All rights reserved.
  * Use is subject to license terms.
  */
 
@@ -816,10 +816,11 @@
 		/* currently allocated, want to be allocated */
 		dmu_tx_hold_bonus(tx, drro->drr_object);
 		/*
-		 * We may change blocksize, so need to
-		 * hold_write
+		 * We may change blocksize and delete old content,
+		 * so need to hold_write and hold_free.
 		 */
 		dmu_tx_hold_write(tx, drro->drr_object, 0, 1);
+		dmu_tx_hold_free(tx, drro->drr_object, 0, DMU_OBJECT_END);
 		err = dmu_tx_assign(tx, TXG_WAIT);
 		if (err) {
 			dmu_tx_abort(tx);

--- a/usr/src/uts/common/fs/zfs/dnode.c	Wed Jan 28 12:09:40 2009 -0800
+++ b/usr/src/uts/common/fs/zfs/dnode.c	Wed Jan 28 15:32:27 2009 -0700
@@ -417,7 +417,7 @@
 dnode_reallocate(dnode_t *dn, dmu_object_type_t ot, int blocksize,
     dmu_object_type_t bonustype, int bonuslen, dmu_tx_t *tx)
 {
-	int i, old_nblkptr;
+	int i, nblkptr;
 	dmu_buf_impl_t *db = NULL;
 
 	ASSERT3U(blocksize, >=, SPA_MINBLOCKSIZE);
@@ -447,6 +447,8 @@
 		dnode_free_range(dn, 0, -1ULL, tx);
 	}
 
+	nblkptr = 1 + ((DN_MAX_BONUSLEN - bonuslen) >> SPA_BLKPTRSHIFT);
+
 	/* change blocksize */
 	rw_enter(&dn->dn_struct_rwlock, RW_WRITER);
 	if (blocksize != dn->dn_datablksz &&
@@ -459,6 +461,8 @@
 	dnode_setdirty(dn, tx);
 	dn->dn_next_bonuslen[tx->tx_txg&TXG_MASK] = bonuslen;
 	dn->dn_next_blksz[tx->tx_txg&TXG_MASK] = blocksize;
+	if (dn->dn_nblkptr != nblkptr)
+		dn->dn_next_nblkptr[tx->tx_txg&TXG_MASK] = nblkptr;
 	rw_exit(&dn->dn_struct_rwlock);
 	if (db)
 		dbuf_rele(db, FTAG);
@@ -468,19 +472,15 @@
 
 	/* change bonus size and type */
 	mutex_enter(&dn->dn_mtx);
-	old_nblkptr = dn->dn_nblkptr;
 	dn->dn_bonustype = bonustype;
 	dn->dn_bonuslen = bonuslen;
-	dn->dn_nblkptr = 1 + ((DN_MAX_BONUSLEN - bonuslen) >> SPA_BLKPTRSHIFT);
+	dn->dn_nblkptr = nblkptr;
 	dn->dn_checksum = ZIO_CHECKSUM_INHERIT;
 	dn->dn_compress = ZIO_COMPRESS_INHERIT;
 	ASSERT3U(dn->dn_nblkptr, <=, DN_MAX_NBLKPTR);
 
-	/* XXX - for now, we can't make nblkptr smaller */
-	ASSERT3U(dn->dn_nblkptr, >=, old_nblkptr);
-
-	/* fix up the bonus db_size if dn_nblkptr has changed */
-	if (dn->dn_bonus && dn->dn_bonuslen != old_nblkptr) {
+	/* fix up the bonus db_size */
+	if (dn->dn_bonus) {
 		dn->dn_bonus->db.db_size =
 		    DN_MAX_BONUSLEN - (dn->dn_nblkptr-1) * sizeof (blkptr_t);
 		ASSERT(dn->dn_bonuslen <= dn->dn_bonus->db.db_size);

--- a/usr/src/uts/common/fs/zfs/dnode_sync.c	Wed Jan 28 12:09:40 2009 -0800
+++ b/usr/src/uts/common/fs/zfs/dnode_sync.c	Wed Jan 28 15:32:27 2009 -0700
@@ -19,12 +19,10 @@
  * CDDL HEADER END
  */
 /*
- * Copyright 2008 Sun Microsystems, Inc.  All rights reserved.
+ * Copyright 2009 Sun Microsystems, Inc.  All rights reserved.
  * Use is subject to license terms.
  */
 
-#pragma ident	"%Z%%M%	%I%	%E% SMI"
-
 #include <sys/zfs_context.h>
 #include <sys/dbuf.h>
 #include <sys/dnode.h>
@@ -532,18 +530,12 @@
 			/* XXX shouldn't the phys already be zeroed? */
 			bzero(dnp, DNODE_CORE_SIZE);
 			dnp->dn_nlevels = 1;
+			dnp->dn_nblkptr = dn->dn_nblkptr;
 		}
 
-		if (dn->dn_nblkptr > dnp->dn_nblkptr) {
-			/* zero the new blkptrs we are gaining */
-			bzero(dnp->dn_blkptr + dnp->dn_nblkptr,
-			    sizeof (blkptr_t) *
-			    (dn->dn_nblkptr - dnp->dn_nblkptr));
-		}
 		dnp->dn_type = dn->dn_type;
 		dnp->dn_bonustype = dn->dn_bonustype;
 		dnp->dn_bonuslen = dn->dn_bonuslen;
-		dnp->dn_nblkptr = dn->dn_nblkptr;
 	}
 
 	ASSERT(dnp->dn_nlevels > 1 ||
@@ -603,6 +595,30 @@
 		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;

--- a/usr/src/uts/common/fs/zfs/sys/dnode.h	Wed Jan 28 12:09:40 2009 -0800
+++ b/usr/src/uts/common/fs/zfs/sys/dnode.h	Wed Jan 28 15:32:27 2009 -0700
@@ -19,7 +19,7 @@
  * CDDL HEADER END
  */
 /*
- * Copyright 2008 Sun Microsystems, Inc.  All rights reserved.
+ * Copyright 2009 Sun Microsystems, Inc.  All rights reserved.
  * Use is subject to license terms.
  */
 
@@ -160,6 +160,7 @@
 	uint16_t dn_datablkszsec;	/* in 512b sectors */
 	uint32_t dn_datablksz;		/* in bytes */
 	uint64_t dn_maxblkid;
+	uint8_t dn_next_nblkptr[TXG_SIZE];
 	uint8_t dn_next_nlevels[TXG_SIZE];
 	uint8_t dn_next_indblkshift[TXG_SIZE];
 	uint16_t dn_next_bonuslen[TXG_SIZE];