4370 avoid transmitting holes during zfs send

4371 DMU code clean up
Reviewed by: Matthew Ahrens <mahrens@delphix.com>
Reviewed by: George Wilson <george.wilson@delphix.com>
Reviewed by: Christopher Siden <christopher.siden@delphix.com>
Reviewed by: Josef 'Jeff' Sipek <jeffpc@josefsipek.net>
Approved by: Garrett D'Amore <garrett@damore.org>

39 files changed, 702 insertions, 411 deletions

diff --git a/usr/src/cmd/mdb/common/modules/zfs/zfs.c b/usr/src/cmd/mdb/common/modules/zfs/zfs.c
index 255656a9b7..16c0a175f1 100644
--- a/usr/src/cmd/mdb/common/modules/zfs/zfs.c
+++ b/usr/src/cmd/mdb/common/modules/zfs/zfs.c
@@ -378,7 +378,8 @@ blkptr(uintptr_t addr, uint_t flags, int argc, const mdb_arg_t *argv)
 	enum_lookup(compress, sizeof (compress), compress_enum,
 	    BP_GET_COMPRESS(bp), "ZIO_COMPRESS_");
 
-	SPRINTF_BLKPTR(mdb_snprintf, '\n', buf, bp, type, checksum, compress);
+	SNPRINTF_BLKPTR(mdb_snprintf, '\n', buf, sizeof (buf), bp, type,
+	    checksum, compress);
 
 	mdb_printf("%s\n", buf);
 
diff --git a/usr/src/cmd/zdb/zdb.c b/usr/src/cmd/zdb/zdb.c
index 1723342ee7..a61cae3805 100644
--- a/usr/src/cmd/zdb/zdb.c
+++ b/usr/src/cmd/zdb/zdb.c
@@ -764,7 +764,7 @@ dump_dde(const ddt_t *ddt, const ddt_entry_t *dde, uint64_t index)
 		if (ddp->ddp_phys_birth == 0)
 			continue;
 		ddt_bp_create(ddt->ddt_checksum, ddk, ddp, &blk);
-		sprintf_blkptr(blkbuf, &blk);
+		snprintf_blkptr(blkbuf, sizeof (blkbuf), &blk);
 		(void) printf("index %llx refcnt %llu %s %s\n",
 		    (u_longlong_t)index, (u_longlong_t)ddp->ddp_refcnt,
 		    types[p], blkbuf);
@@ -1022,31 +1022,39 @@ blkid2offset(const dnode_phys_t *dnp, const blkptr_t *bp, const zbookmark_t *zb)
 }
 
 static void
-sprintf_blkptr_compact(char *blkbuf, const blkptr_t *bp)
+snprintf_blkptr_compact(char *blkbuf, size_t buflen, const blkptr_t *bp)
 {
 	const dva_t *dva = bp->blk_dva;
 	int ndvas = dump_opt['d'] > 5 ? BP_GET_NDVAS(bp) : 1;
 
 	if (dump_opt['b'] >= 6) {
-		sprintf_blkptr(blkbuf, bp);
+		snprintf_blkptr(blkbuf, buflen, bp);
 		return;
 	}
 
 	blkbuf[0] = '\0';
 
 	for (int i = 0; i < ndvas; i++)
-		(void) sprintf(blkbuf + strlen(blkbuf), "%llu:%llx:%llx ",
+		(void) snprintf(blkbuf + strlen(blkbuf),
+		    buflen - strlen(blkbuf), "%llu:%llx:%llx ",
 		    (u_longlong_t)DVA_GET_VDEV(&dva[i]),
 		    (u_longlong_t)DVA_GET_OFFSET(&dva[i]),
 		    (u_longlong_t)DVA_GET_ASIZE(&dva[i]));
 
-	(void) sprintf(blkbuf + strlen(blkbuf),
-	    "%llxL/%llxP F=%llu B=%llu/%llu",
-	    (u_longlong_t)BP_GET_LSIZE(bp),
-	    (u_longlong_t)BP_GET_PSIZE(bp),
-	    (u_longlong_t)bp->blk_fill,
-	    (u_longlong_t)bp->blk_birth,
-	    (u_longlong_t)BP_PHYSICAL_BIRTH(bp));
+	if (BP_IS_HOLE(bp)) {
+		(void) snprintf(blkbuf + strlen(blkbuf),
+		    buflen - strlen(blkbuf), "B=%llu",
+		    (u_longlong_t)bp->blk_birth);
+	} else {
+		(void) snprintf(blkbuf + strlen(blkbuf),
+		    buflen - strlen(blkbuf),
+		    "%llxL/%llxP F=%llu B=%llu/%llu",
+		    (u_longlong_t)BP_GET_LSIZE(bp),
+		    (u_longlong_t)BP_GET_PSIZE(bp),
+		    (u_longlong_t)bp->blk_fill,
+		    (u_longlong_t)bp->blk_birth,
+		    (u_longlong_t)BP_PHYSICAL_BIRTH(bp));
+	}
 }
 
 static void
@@ -1071,7 +1079,7 @@ print_indirect(blkptr_t *bp, const zbookmark_t *zb,
 		}
 	}
 
-	sprintf_blkptr_compact(blkbuf, bp);
+	snprintf_blkptr_compact(blkbuf, sizeof (blkbuf), bp);
 	(void) printf("%s\n", blkbuf);
 }
 
@@ -1086,7 +1094,7 @@ visit_indirect(spa_t *spa, const dnode_phys_t *dnp,
 
 	print_indirect(bp, zb, dnp);
 
-	if (BP_GET_LEVEL(bp) > 0) {
+	if (BP_GET_LEVEL(bp) > 0 && !BP_IS_HOLE(bp)) {
 		uint32_t flags = ARC_WAIT;
 		int i;
 		blkptr_t *cbp;
@@ -1211,7 +1219,7 @@ dump_dsl_dataset(objset_t *os, uint64_t object, void *data, size_t size)
 	zdb_nicenum(ds->ds_compressed_bytes, compressed);
 	zdb_nicenum(ds->ds_uncompressed_bytes, uncompressed);
 	zdb_nicenum(ds->ds_unique_bytes, unique);
-	sprintf_blkptr(blkbuf, &ds->ds_bp);
+	snprintf_blkptr(blkbuf, sizeof (blkbuf), &ds->ds_bp);
 
 	(void) printf("\t\tdir_obj = %llu\n",
 	    (u_longlong_t)ds->ds_dir_obj);
@@ -1256,7 +1264,7 @@ dump_bptree_cb(void *arg, const blkptr_t *bp, dmu_tx_t *tx)
 	char blkbuf[BP_SPRINTF_LEN];
 
 	if (bp->blk_birth != 0) {
-		sprintf_blkptr(blkbuf, bp);
+		snprintf_blkptr(blkbuf, sizeof (blkbuf), bp);
 		(void) printf("\t%s\n", blkbuf);
 	}
 	return (0);
@@ -1294,7 +1302,7 @@ dump_bpobj_cb(void *arg, const blkptr_t *bp, dmu_tx_t *tx)
 	char blkbuf[BP_SPRINTF_LEN];
 
 	ASSERT(bp->blk_birth != 0);
-	sprintf_blkptr_compact(blkbuf, bp);
+	snprintf_blkptr_compact(blkbuf, sizeof (blkbuf), bp);
 	(void) printf("\t%s\n", blkbuf);
 	return (0);
 }
@@ -1793,8 +1801,9 @@ dump_dir(objset_t *os)
 	zdb_nicenum(refdbytes, numbuf);
 
 	if (verbosity >= 4) {
-		(void) sprintf(blkbuf, ", rootbp ");
-		(void) sprintf_blkptr(blkbuf + strlen(blkbuf), os->os_rootbp);
+		(void) snprintf(blkbuf, sizeof (blkbuf), ", rootbp ");
+		(void) snprintf_blkptr(blkbuf + strlen(blkbuf),
+		    sizeof (blkbuf) - strlen(blkbuf), os->os_rootbp);
 	} else {
 		blkbuf[0] = '\0';
 	}
@@ -1824,7 +1833,7 @@ dump_dir(objset_t *os)
 	if (verbosity < 2)
 		return;
 
-	if (os->os_rootbp->blk_birth == 0)
+	if (BP_IS_HOLE(os->os_rootbp))
 		return;
 
 	dump_object(os, 0, verbosity, &print_header);
@@ -1865,7 +1874,7 @@ dump_uberblock(uberblock_t *ub, const char *header, const char *footer)
 	    (u_longlong_t)ub->ub_timestamp, asctime(localtime(&timestamp)));
 	if (dump_opt['u'] >= 3) {
 		char blkbuf[BP_SPRINTF_LEN];
-		sprintf_blkptr(blkbuf, &ub->ub_rootbp);
+		snprintf_blkptr(blkbuf, sizeof (blkbuf), &ub->ub_rootbp);
 		(void) printf("\trootbp = %s\n", blkbuf);
 	}
 	(void) printf(footer ? footer : "");
@@ -2202,7 +2211,7 @@ zdb_blkptr_done(zio_t *zio)
 		zcb->zcb_errors[ioerr]++;
 
 		if (dump_opt['b'] >= 2)
-			sprintf_blkptr(blkbuf, bp);
+			snprintf_blkptr(blkbuf, sizeof (blkbuf), bp);
 		else
 			blkbuf[0] = '\0';
 
@@ -2224,11 +2233,22 @@ zdb_blkptr_cb(spa_t *spa, zilog_t *zilog, const blkptr_t *bp,
     const zbookmark_t *zb, const dnode_phys_t *dnp, void *arg)
 {
 	zdb_cb_t *zcb = arg;
-	char blkbuf[BP_SPRINTF_LEN];
 	dmu_object_type_t type;
 	boolean_t is_metadata;
 
-	if (bp == NULL)
+	if (dump_opt['b'] >= 5 && bp->blk_birth > 0) {
+		char blkbuf[BP_SPRINTF_LEN];
+		snprintf_blkptr(blkbuf, sizeof (blkbuf), bp);
+		(void) printf("objset %llu object %llu "
+		    "level %lld offset 0x%llx %s\n",
+		    (u_longlong_t)zb->zb_objset,
+		    (u_longlong_t)zb->zb_object,
+		    (longlong_t)zb->zb_level,
+		    (u_longlong_t)blkid2offset(dnp, bp, zb),
+		    blkbuf);
+	}
+
+	if (BP_IS_HOLE(bp))
 		return (0);
 
 	type = BP_GET_TYPE(bp);
@@ -2259,17 +2279,6 @@ zdb_blkptr_cb(spa_t *spa, zilog_t *zilog, const blkptr_t *bp,
 
 	zcb->zcb_readfails = 0;
 
-	if (dump_opt['b'] >= 5) {
-		sprintf_blkptr(blkbuf, bp);
-		(void) printf("objset %llu object %llu "
-		    "level %lld offset 0x%llx %s\n",
-		    (u_longlong_t)zb->zb_objset,
-		    (u_longlong_t)zb->zb_object,
-		    (longlong_t)zb->zb_level,
-		    (u_longlong_t)blkid2offset(dnp, bp, zb),
-		    blkbuf);
-	}
-
 	if (dump_opt['b'] < 5 && isatty(STDERR_FILENO) &&
 	    gethrtime() > zcb->zcb_lastprint + NANOSEC) {
 		uint64_t now = gethrtime();
@@ -2426,7 +2435,7 @@ count_block_cb(void *arg, const blkptr_t *bp, dmu_tx_t *tx)
 
 	if (dump_opt['b'] >= 5) {
 		char blkbuf[BP_SPRINTF_LEN];
-		sprintf_blkptr(blkbuf, bp);
+		snprintf_blkptr(blkbuf, sizeof (blkbuf), bp);
 		(void) printf("[%s] %s\n",
 		    "deferred free", blkbuf);
 	}
@@ -2673,7 +2682,7 @@ zdb_ddt_add_cb(spa_t *spa, zilog_t *zilog, const blkptr_t *bp,
 	avl_index_t where;
 	zdb_ddt_entry_t *zdde, zdde_search;
 
-	if (bp == NULL)
+	if (BP_IS_HOLE(bp))
 		return (0);
 
 	if (dump_opt['S'] > 1 && zb->zb_level == ZB_ROOT_LEVEL) {
@@ -2840,7 +2849,7 @@ zdb_print_blkptr(blkptr_t *bp, int flags)
 	if (flags & ZDB_FLAG_BSWAP)
 		byteswap_uint64_array((void *)bp, sizeof (blkptr_t));
 
-	sprintf_blkptr(blkbuf, bp);
+	snprintf_blkptr(blkbuf, sizeof (blkbuf), bp);
 	(void) printf("%s\n", blkbuf);
 }
 
diff --git a/usr/src/cmd/zdb/zdb_il.c b/usr/src/cmd/zdb/zdb_il.c
index a0ed985f52..17f7ad3e8c 100644
--- a/usr/src/cmd/zdb/zdb_il.c
+++ b/usr/src/cmd/zdb/zdb_il.c
@@ -24,6 +24,10 @@
  */
 
 /*
+ * Copyright (c) 2013 by Delphix. All rights reserved.
+ */
+
+/*
  * Print intent log header and statistics.
  */
 
@@ -47,7 +51,7 @@ print_log_bp(const blkptr_t *bp, const char *prefix)
 {
 	char blkbuf[BP_SPRINTF_LEN];
 
-	sprintf_blkptr(blkbuf, bp);
+	snprintf_blkptr(blkbuf, sizeof (blkbuf), bp);
 	(void) printf("%s%s\n", prefix, blkbuf);
 }
 
@@ -132,6 +136,7 @@ zil_prt_rec_write(zilog_t *zilog, int txtype, lr_write_t *lr)
 
 	if (lr->lr_common.lrc_reclen == sizeof (lr_write_t)) {
 		(void) printf("%shas blkptr, %s\n", prefix,
+		    !BP_IS_HOLE(bp) &&
 		    bp->blk_birth >= spa_first_txg(zilog->zl_spa) ?
 		    "will claim" : "won't claim");
 		print_log_bp(bp, prefix);
@@ -139,8 +144,6 @@ zil_prt_rec_write(zilog_t *zilog, int txtype, lr_write_t *lr)
 		if (BP_IS_HOLE(bp)) {
 			(void) printf("\t\t\tLSIZE 0x%llx\n",
 			    (u_longlong_t)BP_GET_LSIZE(bp));
-		}
-		if (bp->blk_birth == 0) {
 			bzero(buf, sizeof (buf));
 			(void) printf("%s<hole>\n", prefix);
 			return;
@@ -313,7 +316,8 @@ print_log_block(zilog_t *zilog, blkptr_t *bp, void *arg, uint64_t claim_txg)
 
 	if (verbose >= 5) {
 		(void) strcpy(blkbuf, ", ");
-		sprintf_blkptr(blkbuf + strlen(blkbuf), bp);
+		snprintf_blkptr(blkbuf + strlen(blkbuf),
+		    sizeof (blkbuf) - strlen(blkbuf), bp);
 	} else {
 		blkbuf[0] = '\0';
 	}
@@ -361,7 +365,7 @@ dump_intent_log(zilog_t *zilog)
 	int verbose = MAX(dump_opt['d'], dump_opt['i']);
 	int i;
 
-	if (zh->zh_log.blk_birth == 0 || verbose < 1)
+	if (BP_IS_HOLE(&zh->zh_log) || verbose < 1)
 		return;
 
 	(void) printf("\n    ZIL header: claim_txg %llu, "
diff --git a/usr/src/cmd/zhack/zhack.c b/usr/src/cmd/zhack/zhack.c
index 1d8002343e..c0ed974363 100644
--- a/usr/src/cmd/zhack/zhack.c
+++ b/usr/src/cmd/zhack/zhack.c
@@ -277,6 +277,9 @@ zhack_do_feature_stat(int argc, char **argv)
 	dump_obj(os, spa->spa_feat_for_read_obj, "for_read");
 	dump_obj(os, spa->spa_feat_for_write_obj, "for_write");
 	dump_obj(os, spa->spa_feat_desc_obj, "descriptions");
+	if (spa_feature_is_active(spa, SPA_FEATURE_ENABLED_TXG)) {
+		dump_obj(os, spa->spa_feat_enabled_txg_obj, "enabled_txg");
+	}
 	dump_mos(spa);
 
 	spa_close(spa, FTAG);
@@ -313,7 +316,9 @@ zhack_do_feature_enable(int argc, char **argv)
 	feature.fi_uname = "zhack";
 	feature.fi_mos = B_FALSE;
 	feature.fi_can_readonly = B_FALSE;
+	feature.fi_activate_on_enable = B_FALSE;
 	feature.fi_depends = nodeps;
+	feature.fi_feature = SPA_FEATURE_NONE;
 
 	optind = 1;
 	while ((c = getopt(argc, argv, "rmd:")) != -1) {
@@ -371,7 +376,7 @@ feature_incr_sync(void *arg, dmu_tx_t *tx)
 	zfeature_info_t *feature = arg;
 	uint64_t refcount;
 
-	VERIFY0(feature_get_refcount(spa, feature, &refcount));
+	VERIFY0(feature_get_refcount_from_disk(spa, feature, &refcount));
 	feature_sync(spa, feature, refcount + 1, tx);
 	spa_history_log_internal(spa, "zhack feature incr", tx,
 	    "guid=%s", feature->fi_guid);
@@ -384,7 +389,7 @@ feature_decr_sync(void *arg, dmu_tx_t *tx)
 	zfeature_info_t *feature = arg;
 	uint64_t refcount;
 
-	VERIFY0(feature_get_refcount(spa, feature, &refcount));
+	VERIFY0(feature_get_refcount_from_disk(spa, feature, &refcount));
 	feature_sync(spa, feature, refcount - 1, tx);
 	spa_history_log_internal(spa, "zhack feature decr", tx,
 	    "guid=%s", feature->fi_guid);
@@ -411,6 +416,7 @@ zhack_do_feature_ref(int argc, char **argv)
 	feature.fi_mos = B_FALSE;
 	feature.fi_desc = NULL;
 	feature.fi_depends = nodeps;
+	feature.fi_feature = SPA_FEATURE_NONE;
 
 	optind = 1;
 	while ((c = getopt(argc, argv, "md")) != -1) {
@@ -459,8 +465,8 @@ zhack_do_feature_ref(int argc, char **argv)
 
 	if (decr) {
 		uint64_t count;
-		if (feature_get_refcount(spa, &feature, &count) == 0 &&
-		    count != 0) {
+		if (feature_get_refcount_from_disk(spa, &feature,
+		    &count) == 0 && count != 0) {
 			fatal(spa, FTAG, "feature refcount already 0: %s",
 			    feature.fi_guid);
 		}
diff --git a/usr/src/common/zfs/zfeature_common.c b/usr/src/common/zfs/zfeature_common.c
index 175f8a51c2..2b9418b598 100644
--- a/usr/src/common/zfs/zfeature_common.c
+++ b/usr/src/common/zfs/zfeature_common.c
@@ -115,10 +115,21 @@ zfeature_lookup_name(const char *name, spa_feature_t *res)
 	return (ENOENT);
 }
 
+boolean_t
+zfeature_depends_on(spa_feature_t fid, spa_feature_t check) {
+	zfeature_info_t *feature = &spa_feature_table[fid];
+
+	for (int i = 0; feature->fi_depends[i] != SPA_FEATURE_NONE; i++) {
+		if (feature->fi_depends[i] == check)
+			return (B_TRUE);
+	}
+	return (B_FALSE);
+}
+
 static void
 zfeature_register(spa_feature_t fid, const char *guid, const char *name,
     const char *desc, boolean_t readonly, boolean_t mos,
-    const spa_feature_t *deps)
+    boolean_t activate_on_enable, const spa_feature_t *deps)
 {
 	zfeature_info_t *feature = &spa_feature_table[fid];
 	static spa_feature_t nodeps[] = { SPA_FEATURE_NONE };
@@ -138,6 +149,7 @@ zfeature_register(spa_feature_t fid, const char *guid, const char *name,
 	feature->fi_desc = desc;
 	feature->fi_can_readonly = readonly;
 	feature->fi_mos = mos;
+	feature->fi_activate_on_enable = activate_on_enable;
 	feature->fi_depends = deps;
 }
 
@@ -146,21 +158,43 @@ zpool_feature_init(void)
 {
 	zfeature_register(SPA_FEATURE_ASYNC_DESTROY,
 	    "com.delphix:async_destroy", "async_destroy",
-	    "Destroy filesystems asynchronously.", B_TRUE, B_FALSE, NULL);
+	    "Destroy filesystems asynchronously.", B_TRUE, B_FALSE,
+	    B_FALSE, NULL);
+
 	zfeature_register(SPA_FEATURE_EMPTY_BPOBJ,
 	    "com.delphix:empty_bpobj", "empty_bpobj",
-	    "Snapshots use less space.", B_TRUE, B_FALSE, NULL);
+	    "Snapshots use less space.", B_TRUE, B_FALSE,
+	    B_FALSE, NULL);
+
 	zfeature_register(SPA_FEATURE_LZ4_COMPRESS,
 	    "org.illumos:lz4_compress", "lz4_compress",
-	    "LZ4 compression algorithm support.", B_FALSE, B_FALSE, NULL);
+	    "LZ4 compression algorithm support.", B_FALSE, B_FALSE,
+	    B_FALSE, NULL);
+
 	zfeature_register(SPA_FEATURE_MULTI_VDEV_CRASH_DUMP,
 	    "com.joyent:multi_vdev_crash_dump", "multi_vdev_crash_dump",
-	    "Crash dumps to multiple vdev pools.", B_FALSE, B_FALSE, NULL);
+	    "Crash dumps to multiple vdev pools.", B_FALSE, B_FALSE,
+	    B_FALSE, NULL);
+
 	zfeature_register(SPA_FEATURE_SPACEMAP_HISTOGRAM,
 	    "com.delphix:spacemap_histogram", "spacemap_histogram",
-	    "Spacemaps maintain space histograms.", B_TRUE, B_FALSE, NULL);
+	    "Spacemaps maintain space histograms.", B_TRUE, B_FALSE,
+	    B_FALSE, NULL);
+
+	zfeature_register(SPA_FEATURE_ENABLED_TXG,
+	    "com.delphix:enabled_txg", "enabled_txg",
+	    "Record txg at which a feature is enabled", B_TRUE, B_FALSE,
+	    B_FALSE, NULL);
+
+	static spa_feature_t hole_birth_deps[] = { SPA_FEATURE_ENABLED_TXG,
+	    SPA_FEATURE_NONE };
+	zfeature_register(SPA_FEATURE_HOLE_BIRTH,
+	    "com.delphix:hole_birth", "hole_birth",
+	    "Retain hole birth txg for more precise zfs send",
+	    B_FALSE, B_TRUE, B_TRUE, hole_birth_deps);
+
 	zfeature_register(SPA_FEATURE_EXTENSIBLE_DATASET,
 	    "com.delphix:extensible_dataset", "extensible_dataset",
 	    "Enhanced dataset functionality, used by other features.",
-	    B_FALSE, B_FALSE, NULL);
+	    B_FALSE, B_FALSE, B_FALSE, NULL);
 }
diff --git a/usr/src/common/zfs/zfeature_common.h b/usr/src/common/zfs/zfeature_common.h
index 861f1db0fd..7d23493037 100644
--- a/usr/src/common/zfs/zfeature_common.h
+++ b/usr/src/common/zfs/zfeature_common.h
@@ -45,10 +45,14 @@ typedef enum spa_feature {
 	SPA_FEATURE_LZ4_COMPRESS,
 	SPA_FEATURE_MULTI_VDEV_CRASH_DUMP,
 	SPA_FEATURE_SPACEMAP_HISTOGRAM,
+	SPA_FEATURE_ENABLED_TXG,
+	SPA_FEATURE_HOLE_BIRTH,
 	SPA_FEATURE_EXTENSIBLE_DATASET,
 	SPA_FEATURES
 } spa_feature_t;
 
+#define	SPA_FEATURE_DISABLED	(-1ULL)
+
 typedef struct zfeature_info {
 	spa_feature_t fi_feature;
 	const char *fi_uname;	/* User-facing feature name */
@@ -56,6 +60,8 @@ typedef struct zfeature_info {
 	const char *fi_desc;	/* Feature description */
 	boolean_t fi_can_readonly; /* Can open pool readonly w/o support? */
 	boolean_t fi_mos;	/* Is the feature necessary to read the MOS? */
+	/* Activate this feature at the same time it is enabled */
+	boolean_t fi_activate_on_enable;
 	/* array of dependencies, terminated by SPA_FEATURE_NONE */
 	const spa_feature_t *fi_depends;
 } zfeature_info_t;
@@ -70,6 +76,7 @@ extern boolean_t zfeature_is_valid_guid(const char *);
 
 extern boolean_t zfeature_is_supported(const char *);
 extern int zfeature_lookup_name(const char *name, spa_feature_t *res);
+extern boolean_t zfeature_depends_on(spa_feature_t fid, spa_feature_t check);
 
 extern void zpool_feature_init(void);
 
diff --git a/usr/src/grub/capability b/usr/src/grub/capability
index 822546819d..964cbe9306 100644
--- a/usr/src/grub/capability
+++ b/usr/src/grub/capability
@@ -19,7 +19,7 @@
 # CDDL HEADER END
 #
 # Copyright (c) 2010, Oracle and/or its affiliates. All rights reserved.
-# Copyright (c) 2012 by Delphix. All rights reserved.
+# Copyright (c) 2013 by Delphix. All rights reserved.
 #
 # This file defines the current capabilities of GRUB over and above that
 # supported by the standard distribution
@@ -29,7 +29,7 @@
 # GRUB necessitating that the boot blocks be reinstalled for that fix or
 # enhancement to take effect.
 #
-VERSION=22
+VERSION=23
 dboot
 xVM
 zfs
diff --git a/usr/src/grub/grub-0.97/stage2/fsys_zfs.c b/usr/src/grub/grub-0.97/stage2/fsys_zfs.c
index 8a3b177443..950f3ce880 100644
--- a/usr/src/grub/grub-0.97/stage2/fsys_zfs.c
+++ b/usr/src/grub/grub-0.97/stage2/fsys_zfs.c
@@ -330,7 +330,7 @@ zio_read_gang(blkptr_t *bp, dva_t *dva, void *buf, char *stack)
 	}
 
 	for (i = 0; i < SPA_GBH_NBLKPTRS; i++) {
-		if (zio_gb->zg_blkptr[i].blk_birth == 0)
+		if (BP_IS_HOLE(&zio_gb->zg_blkptr[i]))
 			continue;
 
 		if (zio_read_data(&zio_gb->zg_blkptr[i], buf, stack))
@@ -966,6 +966,7 @@ get_default_bootfsobj(dnode_phys_t *mosmdn, uint64_t *obj, char *stack)
  */
 static const char *spa_feature_names[] = {
 	"org.illumos:lz4_compress",
+	"com.delphix:hole_birth",
 	"com.delphix:extensible_dataset",
 	NULL
 };
diff --git a/usr/src/grub/grub-0.97/stage2/zfs-include/spa.h b/usr/src/grub/grub-0.97/stage2/zfs-include/spa.h
index 4cb53c2d51..8d53ad6866 100644
--- a/usr/src/grub/grub-0.97/stage2/zfs-include/spa.h
+++ b/usr/src/grub/grub-0.97/stage2/zfs-include/spa.h
@@ -23,7 +23,7 @@
  */
 
 /*
- * Copyright (c) 2012 by Delphix. All rights reserved.
+ * Copyright (c) 2013 by Delphix. All rights reserved.
  */
 
 #ifndef _SYS_SPA_H
@@ -175,9 +175,10 @@ typedef struct blkptr {
  * Macros to get and set fields in a bp or DVA.
  */
 #define	DVA_GET_ASIZE(dva)	\
-	BF64_GET_SB((dva)->dva_word[0], 0, 24, SPA_MINBLOCKSHIFT, 0)
+	BF64_GET_SB((dva)->dva_word[0], 0, SPA_ASIZEBITS, SPA_MINBLOCKSHIFT, 0)
 #define	DVA_SET_ASIZE(dva, x)	\
-	BF64_SET_SB((dva)->dva_word[0], 0, 24, SPA_MINBLOCKSHIFT, 0, x)
+	BF64_SET_SB((dva)->dva_word[0], 0, SPA_ASIZEBITS, \
+	SPA_MINBLOCKSHIFT, 0, x)
 
 #define	DVA_GET_GRID(dva)	BF64_GET((dva)->dva_word[0], 24, 8)
 #define	DVA_SET_GRID(dva, x)	BF64_SET((dva)->dva_word[0], 24, 8, x)
@@ -194,14 +195,14 @@ typedef struct blkptr {
 #define	DVA_SET_GANG(dva, x)	BF64_SET((dva)->dva_word[1], 63, 1, x)
 
 #define	BP_GET_LSIZE(bp)	\
-	BF64_GET_SB((bp)->blk_prop, 0, 16, SPA_MINBLOCKSHIFT, 1)
+	BF64_GET_SB((bp)->blk_prop, 0, SPA_LSIZEBITS, SPA_MINBLOCKSHIFT, 1)
 #define	BP_SET_LSIZE(bp, x)	\
-	BF64_SET_SB((bp)->blk_prop, 0, 16, SPA_MINBLOCKSHIFT, 1, x)
+	BF64_SET_SB((bp)->blk_prop, 0, SPA_LSIZEBITS, SPA_MINBLOCKSHIFT, 1, x)
 
 #define	BP_GET_PSIZE(bp)	\
-	BF64_GET_SB((bp)->blk_prop, 16, 16, SPA_MINBLOCKSHIFT, 1)
+	BF64_GET_SB((bp)->blk_prop, 16, SPA_PSIZEBITS, SPA_MINBLOCKSHIFT, 1)
 #define	BP_SET_PSIZE(bp, x)	\
-	BF64_SET_SB((bp)->blk_prop, 16, 16, SPA_MINBLOCKSHIFT, 1, x)
+	BF64_SET_SB((bp)->blk_prop, 16, SPA_PSIZEBITS, SPA_MINBLOCKSHIFT, 1, x)
 
 #define	BP_GET_COMPRESS(bp)		BF64_GET((bp)->blk_prop, 32, 8)
 #define	BP_SET_COMPRESS(bp, x)		BF64_SET((bp)->blk_prop, 32, 8, x)
@@ -215,13 +216,10 @@ typedef struct blkptr {
 #define	BP_GET_LEVEL(bp)		BF64_GET((bp)->blk_prop, 56, 5)
 #define	BP_SET_LEVEL(bp, x)		BF64_SET((bp)->blk_prop, 56, 5, x)
 
-#define	BP_GET_PROP_BIT_61(bp)		BF64_GET((bp)->blk_prop, 61, 1)
-#define	BP_SET_PROP_BIT_61(bp, x)	BF64_SET((bp)->blk_prop, 61, 1, x)
-
 #define	BP_GET_DEDUP(bp)		BF64_GET((bp)->blk_prop, 62, 1)
 #define	BP_SET_DEDUP(bp, x)		BF64_SET((bp)->blk_prop, 62, 1, x)
 
-#define	BP_GET_BYTEORDER(bp)		(0 - BF64_GET((bp)->blk_prop, 63, 1))
+#define	BP_GET_BYTEORDER(bp)		BF64_GET((bp)->blk_prop, 63, 1)
 #define	BP_SET_BYTEORDER(bp, x)		BF64_SET((bp)->blk_prop, 63, 1, x)
 
 #define	BP_PHYSICAL_BIRTH(bp)		\
@@ -246,11 +244,6 @@ typedef struct blkptr {
 	!!DVA_GET_ASIZE(&(bp)->blk_dva[1]) + \
 	!!DVA_GET_ASIZE(&(bp)->blk_dva[2]))
 
-#define	BP_COUNT_GANG(bp)	\
-	(DVA_GET_GANG(&(bp)->blk_dva[0]) + \
-	DVA_GET_GANG(&(bp)->blk_dva[1]) + \
-	DVA_GET_GANG(&(bp)->blk_dva[2]))
-
 #define	DVA_EQUAL(dva1, dva2)	\
 	((dva1)->dva_word[1] == (dva2)->dva_word[1] && \
 	(dva1)->dva_word[0] == (dva2)->dva_word[0])
@@ -279,7 +272,9 @@ typedef struct blkptr {
 
 #define	BP_IDENTITY(bp)		(&(bp)->blk_dva[0])
 #define	BP_IS_GANG(bp)		DVA_GET_GANG(BP_IDENTITY(bp))
-#define	BP_IS_HOLE(bp)		((bp)->blk_birth == 0)
+#define	DVA_IS_EMPTY(dva)	((dva)->dva_word[0] == 0ULL &&	\
+				(dva)->dva_word[1] == 0ULL)
+#define	BP_IS_HOLE(bp)		DVA_IS_EMPTY(BP_IDENTITY(bp))
 
 /* BP_IS_RAIDZ(bp) assumes no block compression */
 #define	BP_IS_RAIDZ(bp)		(DVA_GET_ASIZE(&(bp)->blk_dva[0]) > \
@@ -302,14 +297,10 @@ typedef struct blkptr {
 	ZIO_SET_CHECKSUM(&(bp)->blk_cksum, 0, 0, 0, 0);	\
 }
 
-/*
- * Note: the byteorder is either 0 or -1, both of which are palindromes.
- * This simplifies the endianness handling a bit.
- */
 #ifdef _BIG_ENDIAN
 #define	ZFS_HOST_BYTEORDER	(0ULL)
 #else
-#define	ZFS_HOST_BYTEORDER	(-1ULL)
+#define	ZFS_HOST_BYTEORDER	(1ULL)
 #endif
 
 #define	BP_SHOULD_BYTESWAP(bp)	(BP_GET_BYTEORDER(bp) != ZFS_HOST_BYTEORDER)
diff --git a/usr/src/man/man5/zpool-features.5 b/usr/src/man/man5/zpool-features.5
index 33088b38a9..4df496d0ad 100644
--- a/usr/src/man/man5/zpool-features.5
+++ b/usr/src/man/man5/zpool-features.5
@@ -295,5 +295,70 @@ this feature are destroyed.
 
 .RE
 
+.sp
+.ne 2
+.na
+\fB\fBenabled_txg\fR\fR
+.ad
+.RS 4n
+.TS
+l l .
+GUID	com.delphix:enabled_txg
+READ\-ONLY COMPATIBLE	yes
+DEPENDENCIES	none
+.TE
+
+Once this feature is enabled ZFS records the transaction group number
+in which new features are enabled. This has no user-visible impact,
+but other features may depend on this feature.
+
+This feature becomes \fBactive\fR as soon as it is enabled and will
+never return to being \fBenabled\fB.
+
+.RE
+
+.sp
+.ne 2
+.na
+\fB\fBhole_birth\fR\fR
+.ad
+.RS 4n
+.TS
+l l .
+GUID	com.delphix:hole_birth
+READ\-ONLY COMPATIBLE	no
+DEPENDENCIES	enabled_txg
+.TE
+
+This feature improves performance of incremental sends ("zfs send -i")
+and receives for objects with many holes. The most common case of
+hole-filled objects is zvols.
+
+An incremental send stream from snapshot \fBA\fR to snapshot \fBB\fR
+contains information about every block that changed between \fBA\fR and
+\fBB\fR. Blocks which did not change between those snapshots can be
+identified and omitted from the stream using a piece of metadata called
+the 'block birth time', but birth times are not recorded for holes (blocks
+filled only with zeroes). Since holes created after \fBA\fR cannot be
+distinguished from holes created before \fBA\fR, information about every
+hole in the entire filesystem or zvol is included in the send stream.
+
+For workloads where holes are rare this is not a problem. However, when
+incrementally replicating filesystems or zvols with many holes (for
+example a zvol formatted with another filesystem) a lot of time will
+be spent sending and receiving unnecessary information about holes that
+already exist on the receiving side.
+
+Once the \fBhole_birth\fR feature has been enabled the block birth times
+of all new holes will be recorded. Incremental sends between snapshots
+created after this feature is enabled will use this new metadata to avoid
+sending information about holes that already exist on the receiving side.
+
+This feature becomes \fBactive\fR as soon as it is enabled and will
+never return to being \fBenabled\fB.
+
+.RE
+
+
 .SH "SEE ALSO"
 \fBzpool\fR(1M)
diff --git a/usr/src/test/zfs-tests/tests/functional/cli_root/zpool_get/zpool_get.cfg b/usr/src/test/zfs-tests/tests/functional/cli_root/zpool_get/zpool_get.cfg
index 0cd3b4f2ab..86fe4ba80c 100644
--- a/usr/src/test/zfs-tests/tests/functional/cli_root/zpool_get/zpool_get.cfg
+++ b/usr/src/test/zfs-tests/tests/functional/cli_root/zpool_get/zpool_get.cfg
@@ -25,7 +25,7 @@
 #
 
 #
-# Copyright (c) 2012 by Delphix. All rights reserved.
+# Copyright (c) 2013 by Delphix. All rights reserved.
 #
 
 # Set the expected properties of zpool
@@ -34,4 +34,5 @@ typeset -a properties=("size" "capacity" "altroot" "health" "guid" "version"
     "free" "allocated" "readonly" "comment" "expandsize" "freeing" "failmode"
     "listsnapshots" "autoexpand" "feature@async_destroy" "feature@empty_bpobj"
     "feature@lz4_compress" "feature@multi_vdev_crash_dump"
-    "feature@spacemap_histogram" "feature@extensible_dataset")
+    "feature@spacemap_histogram" "feature@enabled_txg" "feature@hole_birth"
+    "feature@extensible_dataset")
diff --git a/usr/src/uts/common/fs/zfs/arc.c b/usr/src/uts/common/fs/zfs/arc.c
index c5fe8f934f..67e8c1b041 100644
--- a/usr/src/uts/common/fs/zfs/arc.c
+++ b/usr/src/uts/common/fs/zfs/arc.c
@@ -727,7 +727,7 @@ buf_hash(uint64_t spa, const dva_t *dva, uint64_t birth)
 #define	BUF_EMPTY(buf)						\
 	((buf)->b_dva.dva_word[0] == 0 &&			\
 	(buf)->b_dva.dva_word[1] == 0 &&			\
-	(buf)->b_birth == 0)
+	(buf)->b_cksum0 == 0)
 
 #define	BUF_EQUAL(spa, dva, birth, buf)				\
 	((buf)->b_dva.dva_word[0] == (dva)->dva_word[0]) &&	\
@@ -3509,9 +3509,13 @@ arc_write_done(zio_t *zio)
 	ASSERT(hdr->b_acb == NULL);
 
 	if (zio->io_error == 0) {
-		hdr->b_dva = *BP_IDENTITY(zio->io_bp);
-		hdr->b_birth = BP_PHYSICAL_BIRTH(zio->io_bp);
-		hdr->b_cksum0 = zio->io_bp->blk_cksum.zc_word[0];
+		if (BP_IS_HOLE(zio->io_bp)) {
+			buf_discard_identity(hdr);
+		} else {
+			hdr->b_dva = *BP_IDENTITY(zio->io_bp);
+			hdr->b_birth = BP_PHYSICAL_BIRTH(zio->io_bp);
+			hdr->b_cksum0 = zio->io_bp->blk_cksum.zc_word[0];
+		}
 	} else {
 		ASSERT(BUF_EMPTY(hdr));
 	}
diff --git a/usr/src/uts/common/fs/zfs/bptree.c b/usr/src/uts/common/fs/zfs/bptree.c
index a0c90cc4d9..f70f23c698 100644
--- a/usr/src/uts/common/fs/zfs/bptree.c
+++ b/usr/src/uts/common/fs/zfs/bptree.c
@@ -20,7 +20,7 @@
  */
 
 /*
- * Copyright (c) 2012 by Delphix. All rights reserved.
+ * Copyright (c) 2013 by Delphix. All rights reserved.
  */
 
 #include <sys/arc.h>
@@ -141,7 +141,7 @@ bptree_visit_cb(spa_t *spa, zilog_t *zilog, const blkptr_t *bp,
 	int err;
 	struct bptree_args *ba = arg;
 
-	if (bp == NULL)
+	if (BP_IS_HOLE(bp))
 		return (0);
 
 	err = ba->ba_func(ba->ba_arg, bp, ba->ba_tx);
diff --git a/usr/src/uts/common/fs/zfs/dbuf.c b/usr/src/uts/common/fs/zfs/dbuf.c
index 86498c9d63..ed1808dae7 100644
--- a/usr/src/uts/common/fs/zfs/dbuf.c
+++ b/usr/src/uts/common/fs/zfs/dbuf.c
@@ -455,10 +455,9 @@ dbuf_loan_arcbuf(dmu_buf_impl_t *db)
 	mutex_enter(&db->db_mtx);
 	if (arc_released(db->db_buf) || refcount_count(&db->db_holds) > 1) {
 		int blksz = db->db.db_size;
-		spa_t *spa;
+		spa_t *spa = db->db_objset->os_spa;
 
 		mutex_exit(&db->db_mtx);
-		DB_GET_SPA(&spa, db);
 		abuf = arc_loan_buf(spa, blksz);
 		bcopy(db->db.db_data, abuf->b_data, blksz);
 	} else {
@@ -519,7 +518,6 @@ static void
 dbuf_read_impl(dmu_buf_impl_t *db, zio_t *zio, uint32_t *flags)
 {
 	dnode_t *dn;
-	spa_t *spa;
 	zbookmark_t zb;
 	uint32_t aflags = ARC_NOWAIT;
 
@@ -559,9 +557,9 @@ dbuf_read_impl(dmu_buf_impl_t *db, zio_t *zio, uint32_t *flags)
 	    BP_IS_HOLE(db->db_blkptr)))) {
 		arc_buf_contents_t type = DBUF_GET_BUFC_TYPE(db);
 
-		dbuf_set_data(db, arc_buf_alloc(dn->dn_objset->os_spa,
-		    db->db.db_size, db, type));
 		DB_DNODE_EXIT(db);
+		dbuf_set_data(db, arc_buf_alloc(db->db_objset->os_spa,
+		    db->db.db_size, db, type));
 		bzero(db->db.db_data, db->db.db_size);
 		db->db_state = DB_CACHED;
 		*flags |= DB_RF_CACHED;
@@ -569,7 +567,6 @@ dbuf_read_impl(dmu_buf_impl_t *db, zio_t *zio, uint32_t *flags)
 		return;
 	}
 
-	spa = dn->dn_objset->os_spa;
 	DB_DNODE_EXIT(db);
 
 	db->db_state = DB_READ;
@@ -586,7 +583,7 @@ dbuf_read_impl(dmu_buf_impl_t *db, zio_t *zio, uint32_t *flags)
 
 	dbuf_add_ref(db, NULL);
 
-	(void) arc_read(zio, spa, db->db_blkptr,
+	(void) arc_read(zio, db->db_objset->os_spa, db->db_blkptr,
 	    dbuf_read_done, db, ZIO_PRIORITY_SYNC_READ,
 	    (*flags & DB_RF_CANFAIL) ? ZIO_FLAG_CANFAIL : ZIO_FLAG_MUSTSUCCEED,
 	    &aflags, &zb);
@@ -598,8 +595,8 @@ int
 dbuf_read(dmu_buf_impl_t *db, zio_t *zio, uint32_t flags)
 {
 	int err = 0;
-	int havepzio = (zio != NULL);
-	int prefetch;
+	boolean_t havepzio = (zio != NULL);
+	boolean_t prefetch;
 	dnode_t *dn;
 
 	/*
@@ -694,11 +691,10 @@ dbuf_noread(dmu_buf_impl_t *db)
 		cv_wait(&db->db_changed, &db->db_mtx);
 	if (db->db_state == DB_UNCACHED) {
 		arc_buf_contents_t type = DBUF_GET_BUFC_TYPE(db);
-		spa_t *spa;
+		spa_t *spa = db->db_objset->os_spa;
 
 		ASSERT(db->db_buf == NULL);
 		ASSERT(db->db.db_data == NULL);
-		DB_GET_SPA(&spa, db);
 		dbuf_set_data(db, arc_buf_alloc(spa, db->db.db_size, db, type));
 		db->db_state = DB_FILL;
 	} else if (db->db_state == DB_NOFILL) {
@@ -753,9 +749,8 @@ dbuf_fix_old_data(dmu_buf_impl_t *db, uint64_t txg)
 	} else if (refcount_count(&db->db_holds) > db->db_dirtycnt) {
 		int size = db->db.db_size;
 		arc_buf_contents_t type = DBUF_GET_BUFC_TYPE(db);
-		spa_t *spa;
+		spa_t *spa = db->db_objset->os_spa;
 
-		DB_GET_SPA(&spa, db);
 		dr->dt.dl.dr_data = arc_buf_alloc(spa, size, db, type);
 		bcopy(db->db.db_data, dr->dt.dl.dr_data->b_data, size);
 	} else {
@@ -781,12 +776,9 @@ dbuf_unoverride(dbuf_dirty_record_t *dr)
 	ASSERT(db->db_data_pending != dr);
 
 	/* free this block */
-	if (!BP_IS_HOLE(bp) && !dr->dt.dl.dr_nopwrite) {
-		spa_t *spa;
+	if (!BP_IS_HOLE(bp) && !dr->dt.dl.dr_nopwrite)
+		zio_free(db->db_objset->os_spa, txg, bp);
 
-		DB_GET_SPA(&spa, db);
-		zio_free(spa, txg, bp);
-	}
 	dr->dt.dl.dr_override_state = DR_NOT_OVERRIDDEN;
 	dr->dt.dl.dr_nopwrite = B_FALSE;
 
@@ -804,9 +796,7 @@ dbuf_unoverride(dbuf_dirty_record_t *dr)
 /*
  * Evict (if its unreferenced) or clear (if its referenced) any level-0
  * data blocks in the free range, so that any future readers will find
- * empty blocks.  Also, if we happen across any level-1 dbufs in the
- * range that have not already been marked dirty, mark them dirty so
- * they stay in memory.
+ * empty blocks.
  *
  * This is a no-op if the dataset is in the middle of an incremental
  * receive; see comment below for details.
@@ -816,14 +806,9 @@ dbuf_free_range(dnode_t *dn, uint64_t start, uint64_t end, dmu_tx_t *tx)
 {
 	dmu_buf_impl_t *db, *db_next;
 	uint64_t txg = tx->tx_txg;
-	int epbs = dn->dn_indblkshift - SPA_BLKPTRSHIFT;
-	uint64_t first_l1 = start >> epbs;
-	uint64_t last_l1 = end >> epbs;
 
-	if (end > dn->dn_maxblkid && (end != DMU_SPILL_BLKID)) {
+	if (end > dn->dn_maxblkid && (end != DMU_SPILL_BLKID))
 		end = dn->dn_maxblkid;
-		last_l1 = end >> epbs;
-	}
 	dprintf_dnode(dn, "start=%llu end=%llu\n", start, end);
 
 	mutex_enter(&dn->dn_dbufs_mtx);
@@ -846,23 +831,8 @@ dbuf_free_range(dnode_t *dn, uint64_t start, uint64_t end, dmu_tx_t *tx)
 		db_next = list_next(&dn->dn_dbufs, db);
 		ASSERT(db->db_blkid != DMU_BONUS_BLKID);
 
-		if (db->db_level == 1 &&
-		    db->db_blkid >= first_l1 && db->db_blkid <= last_l1) {
-			mutex_enter(&db->db_mtx);
-			if (db->db_last_dirty &&
-			    db->db_last_dirty->dr_txg < txg) {
-				dbuf_add_ref(db, FTAG);
-				mutex_exit(&db->db_mtx);
-				dbuf_will_dirty(db, tx);
-				dbuf_rele(db, FTAG);
-			} else {
-				mutex_exit(&db->db_mtx);
-			}
-		}
-
 		if (db->db_level != 0)
 			continue;
-		dprintf_dbuf(db, "found buf %s\n", "");
 		if (db->db_blkid < start || db->db_blkid > end)
 			continue;
 
@@ -939,24 +909,29 @@ dbuf_block_freeable(dmu_buf_impl_t *db)
 	 * We don't need any locking to protect db_blkptr:
 	 * If it's syncing, then db_last_dirty will be set
 	 * so we'll ignore db_blkptr.
+	 *
+	 * This logic ensures that only block births for
+	 * filled blocks are considered.
 	 */
 	ASSERT(MUTEX_HELD(&db->db_mtx));
-	if (db->db_last_dirty)
+	if (db->db_last_dirty && (db->db_blkptr == NULL ||
+	    !BP_IS_HOLE(db->db_blkptr))) {
 		birth_txg = db->db_last_dirty->dr_txg;
-	else if (db->db_blkptr)
+	} else if (db->db_blkptr != NULL && !BP_IS_HOLE(db->db_blkptr)) {
 		birth_txg = db->db_blkptr->blk_birth;
+	}
 
 	/*
-	 * If we don't exist or are in a snapshot, we can't be freed.
+	 * If this block don't exist or is in a snapshot, it can't be freed.
 	 * Don't pass the bp to dsl_dataset_block_freeable() since we
 	 * are holding the db_mtx lock and might deadlock if we are
 	 * prefetching a dedup-ed block.
 	 */
-	if (birth_txg)
+	if (birth_txg != 0)
 		return (ds == NULL ||
 		    dsl_dataset_block_freeable(ds, NULL, birth_txg));
 	else
-		return (FALSE);
+		return (B_FALSE);
 }
 
 void
@@ -976,7 +951,7 @@ dbuf_new_size(dmu_buf_impl_t *db, int size, dmu_tx_t *tx)
 	ASSERT(RW_WRITE_HELD(&dn->dn_struct_rwlock));
 
 	/*
-	 * This call to dbuf_will_dirty() with the dn_struct_rwlock held
+	 * This call to dmu_buf_will_dirty() with the dn_struct_rwlock held
 	 * is OK, because there can be no other references to the db
 	 * when we are changing its size, so no concurrent DB_FILL can
 	 * be happening.
@@ -985,7 +960,7 @@ dbuf_new_size(dmu_buf_impl_t *db, int size, dmu_tx_t *tx)
 	 * XXX we should be doing a dbuf_read, checking the return
 	 * value and returning that up to our callers
 	 */
-	dbuf_will_dirty(db, tx);
+	dmu_buf_will_dirty(&db->db, tx);
 
 	/* create the data buffer for the new block */
 	buf = arc_buf_alloc(dn->dn_objset->os_spa, size, db, type);
@@ -1015,9 +990,8 @@ dbuf_new_size(dmu_buf_impl_t *db, int size, dmu_tx_t *tx)
 void
 dbuf_release_bp(dmu_buf_impl_t *db)
 {
-	objset_t *os;
+	objset_t *os = db->db_objset;
 
-	DB_GET_OBJSET(&os, db);
 	ASSERT(dsl_pool_sync_context(dmu_objset_pool(os)));
 	ASSERT(arc_released(os->os_phys_buf) ||
 	    list_link_active(&os->os_dsl_dataset->ds_synced_link));
@@ -1391,10 +1365,10 @@ dbuf_undirty(dmu_buf_impl_t *db, dmu_tx_t *tx)
 	return (B_FALSE);
 }
 
-#pragma weak dmu_buf_will_dirty = dbuf_will_dirty
 void
-dbuf_will_dirty(dmu_buf_impl_t *db, dmu_tx_t *tx)
+dmu_buf_will_dirty(dmu_buf_t *db_fake, dmu_tx_t *tx)
 {
+	dmu_buf_impl_t *db = (dmu_buf_impl_t *)db_fake;
 	int rf = DB_RF_MUST_SUCCEED | DB_RF_NOPREFETCH;
 
 	ASSERT(tx->tx_txg != 0);
@@ -1517,7 +1491,7 @@ dbuf_assign_arcbuf(dmu_buf_impl_t *db, arc_buf_t *buf, dmu_tx_t *tx)
 	db->db_state = DB_FILL;
 	mutex_exit(&db->db_mtx);
 	(void) dbuf_dirty(db, tx);
-	dbuf_fill_done(db, tx);
+	dmu_buf_fill_done(&db->db, tx);
 }
 
 /*
@@ -2022,7 +1996,6 @@ dbuf_add_ref(dmu_buf_impl_t *db, void *tag)
  * Without that, the dbuf_rele() could lead to a dnode_rele() followed by the
  * dnode's parent dbuf evicting its dnode handles.
  */
-#pragma weak dmu_buf_rele = dbuf_rele
 void
 dbuf_rele(dmu_buf_impl_t *db, void *tag)
 {
@@ -2030,6 +2003,12 @@ dbuf_rele(dmu_buf_impl_t *db, void *tag)
 	dbuf_rele_and_unlock(db, tag);
 }
 
+void
+dmu_buf_rele(dmu_buf_t *db, void *tag)
+{
+	dbuf_rele((dmu_buf_impl_t *)db, tag);
+}
+
 /*
  * dbuf_rele() for an already-locked dbuf.  This is necessary to allow
  * db_dirtycnt and db_holds to be updated atomically.
@@ -2476,18 +2455,14 @@ dbuf_write_ready(zio_t *zio, arc_buf_t *buf, void *vdb)
 	dnode_diduse_space(dn, delta - zio->io_prev_space_delta);
 	zio->io_prev_space_delta = delta;
 
-	if (BP_IS_HOLE(bp)) {
-		ASSERT(bp->blk_fill == 0);
-		DB_DNODE_EXIT(db);
-		return;
+	if (bp->blk_birth != 0) {
+		ASSERT((db->db_blkid != DMU_SPILL_BLKID &&
+		    BP_GET_TYPE(bp) == dn->dn_type) ||
+		    (db->db_blkid == DMU_SPILL_BLKID &&
+		    BP_GET_TYPE(bp) == dn->dn_bonustype));
+		ASSERT(BP_GET_LEVEL(bp) == db->db_level);
 	}
 
-	ASSERT((db->db_blkid != DMU_SPILL_BLKID &&
-	    BP_GET_TYPE(bp) == dn->dn_type) ||
-	    (db->db_blkid == DMU_SPILL_BLKID &&
-	    BP_GET_TYPE(bp) == dn->dn_bonustype));
-	ASSERT(BP_GET_LEVEL(bp) == db->db_level);
-
 	mutex_enter(&db->db_mtx);
 
 #ifdef ZFS_DEBUG
@@ -2513,7 +2488,11 @@ dbuf_write_ready(zio_t *zio, arc_buf_t *buf, void *vdb)
 					fill++;
 			}
 		} else {
-			fill = 1;
+			if (BP_IS_HOLE(bp)) {
+				fill = 0;
+			} else {
+				fill = 1;
+			}
 		}
 	} else {
 		blkptr_t *ibp = db->db.db_data;
@@ -2568,9 +2547,10 @@ static void
 dbuf_write_done(zio_t *zio, arc_buf_t *buf, void *vdb)
 {
 	dmu_buf_impl_t *db = vdb;
-	blkptr_t *bp = zio->io_bp;
 	blkptr_t *bp_orig = &zio->io_bp_orig;
-	uint64_t txg = zio->io_txg;
+	blkptr_t *bp = db->db_blkptr;
+	objset_t *os = db->db_objset;
+	dmu_tx_t *tx = os->os_synctx;
 	dbuf_dirty_record_t **drp, *dr;
 
 	ASSERT0(zio->io_error);
@@ -2583,14 +2563,7 @@ dbuf_write_done(zio_t *zio, arc_buf_t *buf, void *vdb)
 	if (zio->io_flags & (ZIO_FLAG_IO_REWRITE | ZIO_FLAG_NOPWRITE)) {
 		ASSERT(BP_EQUAL(bp, bp_orig));
 	} else {
-		objset_t *os;
-		dsl_dataset_t *ds;
-		dmu_tx_t *tx;
-
-		DB_GET_OBJSET(&os, db);
-		ds = os->os_dsl_dataset;
-		tx = os->os_synctx;
-
+		dsl_dataset_t *ds = os->os_dsl_dataset;
 		(void) dsl_dataset_block_kill(ds, bp_orig, tx, B_TRUE);
 		dsl_dataset_block_born(ds, bp, tx);
 	}
@@ -2603,7 +2576,6 @@ dbuf_write_done(zio_t *zio, arc_buf_t *buf, void *vdb)
 	while ((dr = *drp) != db->db_data_pending)
 		drp = &dr->dr_next;
 	ASSERT(!list_link_active(&dr->dr_dirty_node));
-	ASSERT(dr->dr_txg == txg);
 	ASSERT(dr->dr_dbuf == db);
 	ASSERT(dr->dr_next == NULL);
 	*drp = dr->dr_next;
@@ -2637,14 +2609,14 @@ dbuf_write_done(zio_t *zio, arc_buf_t *buf, void *vdb)
 		DB_DNODE_ENTER(db);
 		dn = DB_DNODE(db);
 		ASSERT(list_head(&dr->dt.di.dr_children) == NULL);
-		ASSERT3U(db->db.db_size, ==, 1<<dn->dn_phys->dn_indblkshift);
+		ASSERT3U(db->db.db_size, ==, 1 << dn->dn_phys->dn_indblkshift);
 		if (!BP_IS_HOLE(db->db_blkptr)) {
 			int epbs =
 			    dn->dn_phys->dn_indblkshift - SPA_BLKPTRSHIFT;
+			ASSERT3U(db->db_blkid, <=,
+			    dn->dn_phys->dn_maxblkid >> (db->db_level * epbs));
 			ASSERT3U(BP_GET_LSIZE(db->db_blkptr), ==,
 			    db->db.db_size);
-			ASSERT3U(dn->dn_phys->dn_maxblkid
-			    >> (db->db_level * epbs), >=, db->db_blkid);
 			arc_set_callback(db->db_buf, dbuf_do_evict, db);
 		}
 		DB_DNODE_EXIT(db);
@@ -2657,8 +2629,7 @@ dbuf_write_done(zio_t *zio, arc_buf_t *buf, void *vdb)
 	ASSERT(db->db_dirtycnt > 0);
 	db->db_dirtycnt -= 1;
 	db->db_data_pending = NULL;
-
-	dbuf_rele_and_unlock(db, (void *)(uintptr_t)txg);
+	dbuf_rele_and_unlock(db, (void *)(uintptr_t)tx->tx_txg);
 }
 
 static void
diff --git a/usr/src/uts/common/fs/zfs/ddt.c b/usr/src/uts/common/fs/zfs/ddt.c
index be88ec05a2..ccf7fdc0c5 100644
--- a/usr/src/uts/common/fs/zfs/ddt.c
+++ b/usr/src/uts/common/fs/zfs/ddt.c
@@ -111,12 +111,12 @@ ddt_object_load(ddt_t *ddt, enum ddt_type type, enum ddt_class class)
 	error = zap_lookup(ddt->ddt_os, DMU_POOL_DIRECTORY_OBJECT, name,
 	    sizeof (uint64_t), 1, &ddt->ddt_object[type][class]);
 
-	if (error)
+	if (error != 0)
 		return (error);
 
-	error = zap_lookup(ddt->ddt_os, ddt->ddt_spa->spa_ddt_stat_object, name,
+	VERIFY0(zap_lookup(ddt->ddt_os, ddt->ddt_spa->spa_ddt_stat_object, name,
 	    sizeof (uint64_t), sizeof (ddt_histogram_t) / sizeof (uint64_t),
-	    &ddt->ddt_histogram[type][class]);
+	    &ddt->ddt_histogram[type][class]));
 
 	/*
 	 * Seed the cached statistics.
@@ -127,8 +127,7 @@ ddt_object_load(ddt_t *ddt, enum ddt_type type, enum ddt_class class)
 	ddo->ddo_dspace = doi.doi_physical_blocks_512 << 9;
 	ddo->ddo_mspace = doi.doi_fill_count * doi.doi_data_block_size;
 
-	ASSERT(error == 0);
-	return (error);
+	return (0);
 }
 
 static void
@@ -581,7 +580,10 @@ ddt_compress(void *src, uchar_t *dst, size_t s_len, size_t d_len)
 		bcopy(src, dst, s_len);
 	}
 
-	*version = (ZFS_HOST_BYTEORDER & DDT_COMPRESS_BYTEORDER_MASK) | cpfunc;
+	*version = cpfunc;
+	/* CONSTCOND */
+	if (ZFS_HOST_BYTEORDER)
+		*version |= DDT_COMPRESS_BYTEORDER_MASK;
 
 	return (c_len + 1);
 }
@@ -598,7 +600,8 @@ ddt_decompress(uchar_t *src, void *dst, size_t s_len, size_t d_len)
 	else
 		bcopy(src, dst, d_len);
 
-	if ((version ^ ZFS_HOST_BYTEORDER) & DDT_COMPRESS_BYTEORDER_MASK)
+	if (((version & DDT_COMPRESS_BYTEORDER_MASK) != 0) !=
+	    (ZFS_HOST_BYTEORDER != 0))
 		byteswap_uint64_array(dst, d_len);
 }
 
diff --git a/usr/src/uts/common/fs/zfs/dmu.c b/usr/src/uts/common/fs/zfs/dmu.c
index 428e74102a..11d79b41da 100644
--- a/usr/src/uts/common/fs/zfs/dmu.c
+++ b/usr/src/uts/common/fs/zfs/dmu.c
@@ -680,7 +680,7 @@ dmu_free_long_range(objset_t *os, uint64_t object,
 	 * will take the fast path, and (b) dnode_reallocate() can verify
 	 * that the entire file has been freed.
 	 */
-	if (offset == 0 && length == DMU_OBJECT_END)
+	if (err == 0 && offset == 0 && length == DMU_OBJECT_END)
 		dn->dn_maxblkid = 0;
 
 	dnode_rele(dn, FTAG);
@@ -1184,10 +1184,8 @@ arc_buf_t *
 dmu_request_arcbuf(dmu_buf_t *handle, int size)
 {
 	dmu_buf_impl_t *db = (dmu_buf_impl_t *)handle;
-	spa_t *spa;
 
-	DB_GET_SPA(&spa, db);
-	return (arc_loan_buf(spa, size));
+	return (arc_loan_buf(db->db_objset->os_spa, size));
 }
 
 /*
diff --git a/usr/src/uts/common/fs/zfs/dmu_diff.c b/usr/src/uts/common/fs/zfs/dmu_diff.c
index a2cb2fc8d8..8d7385539f 100644
--- a/usr/src/uts/common/fs/zfs/dmu_diff.c
+++ b/usr/src/uts/common/fs/zfs/dmu_diff.c
@@ -118,7 +118,7 @@ diff_cb(spa_t *spa, zilog_t *zilog, const blkptr_t *bp,
 	if (zb->zb_object != DMU_META_DNODE_OBJECT)
 		return (0);
 
-	if (bp == NULL) {
+	if (BP_IS_HOLE(bp)) {
 		uint64_t span = DBP_SPAN(dnp, zb->zb_level);
 		uint64_t dnobj = (zb->zb_blkid * span) >> DNODE_SHIFT;
 
diff --git a/usr/src/uts/common/fs/zfs/dmu_send.c b/usr/src/uts/common/fs/zfs/dmu_send.c
index ca58e84a0f..2d78c16cd5 100644
--- a/usr/src/uts/common/fs/zfs/dmu_send.c
+++ b/usr/src/uts/common/fs/zfs/dmu_send.c
@@ -356,11 +356,12 @@ backup_cb(spa_t *spa, zilog_t *zilog, const blkptr_t *bp,
 	if (zb->zb_object != DMU_META_DNODE_OBJECT &&
 	    DMU_OBJECT_IS_SPECIAL(zb->zb_object)) {
 		return (0);
-	} else if (bp == NULL && zb->zb_object == DMU_META_DNODE_OBJECT) {
+	} else if (BP_IS_HOLE(bp) &&
+	    zb->zb_object == DMU_META_DNODE_OBJECT) {
 		uint64_t span = BP_SPAN(dnp, zb->zb_level);
 		uint64_t dnobj = (zb->zb_blkid * span) >> DNODE_SHIFT;
 		err = dump_freeobjects(dsp, dnobj, span >> DNODE_SHIFT);
-	} else if (bp == NULL) {
+	} else if (BP_IS_HOLE(bp)) {
 		uint64_t span = BP_SPAN(dnp, zb->zb_level);
 		err = dump_free(dsp, zb->zb_object, zb->zb_blkid * span, span);
 	} else if (zb->zb_level > 0 || type == DMU_OT_OBJSET) {
diff --git a/usr/src/uts/common/fs/zfs/dmu_traverse.c b/usr/src/uts/common/fs/zfs/dmu_traverse.c
index aa9a485f55..68bcac4884 100644
--- a/usr/src/uts/common/fs/zfs/dmu_traverse.c
+++ b/usr/src/uts/common/fs/zfs/dmu_traverse.c
@@ -36,6 +36,7 @@
 #include <sys/sa.h>
 #include <sys/sa_impl.h>
 #include <sys/callb.h>
+#include <sys/zfeature.h>
 
 int zfs_pd_blks_max = 100;
 
@@ -72,7 +73,7 @@ traverse_zil_block(zilog_t *zilog, blkptr_t *bp, void *arg, uint64_t claim_txg)
 	traverse_data_t *td = arg;
 	zbookmark_t zb;
 
-	if (bp->blk_birth == 0)
+	if (BP_IS_HOLE(bp))
 		return (0);
 
 	if (claim_txg == 0 && bp->blk_birth >= spa_first_txg(td->td_spa))
@@ -96,7 +97,7 @@ traverse_zil_record(zilog_t *zilog, lr_t *lrc, void *arg, uint64_t claim_txg)
 		blkptr_t *bp = &lr->lr_blkptr;
 		zbookmark_t zb;
 
-		if (bp->blk_birth == 0)
+		if (BP_IS_HOLE(bp))
 			return (0);
 
 		if (claim_txg == 0 || bp->blk_birth < claim_txg)
@@ -226,14 +227,35 @@ traverse_visitbp(traverse_data_t *td, const dnode_phys_t *dnp,
 		ASSERT(0);
 	}
 
+	if (bp->blk_birth == 0) {
+		if (spa_feature_is_active(td->td_spa, SPA_FEATURE_HOLE_BIRTH)) {
+			/*
+			 * Since this block has a birth time of 0 it must be a
+			 * hole created before the SPA_FEATURE_HOLE_BIRTH
+			 * feature was enabled.  If SPA_FEATURE_HOLE_BIRTH
+			 * was enabled before the min_txg for this traveral we
+			 * know the hole must have been created before the
+			 * min_txg for this traveral, so we can skip it. If
+			 * SPA_FEATURE_HOLE_BIRTH was enabled after the min_txg
+			 * for this traveral we cannot tell if the hole was
+			 * created before or after the min_txg for this
+			 * traversal, so we cannot skip it.
+			 */
+			uint64_t hole_birth_enabled_txg;
+			VERIFY(spa_feature_enabled_txg(td->td_spa,
+			    SPA_FEATURE_HOLE_BIRTH, &hole_birth_enabled_txg));
+			if (hole_birth_enabled_txg < td->td_min_txg)
+				return (0);
+		}
+	} else if (bp->blk_birth <= td->td_min_txg) {
+		return (0);
+	}
+
 	if (BP_IS_HOLE(bp)) {
-		err = td->td_func(td->td_spa, NULL, NULL, zb, dnp, td->td_arg);
+		err = td->td_func(td->td_spa, NULL, bp, zb, dnp, td->td_arg);
 		return (err);
 	}
 
-	if (bp->blk_birth <= td->td_min_txg)
-		return (0);
-
 	if (pd && !pd->pd_exited &&
 	    ((pd->pd_flags & TRAVERSE_PREFETCH_DATA) ||
 	    BP_GET_TYPE(bp) == DMU_OT_DNODE || BP_GET_LEVEL(bp) > 0)) {
@@ -436,7 +458,8 @@ traverse_prefetcher(spa_t *spa, zilog_t *zilog, const blkptr_t *bp,
 	if (pfd->pd_cancel)
 		return (SET_ERROR(EINTR));
 
-	if (bp == NULL || !((pfd->pd_flags & TRAVERSE_PREFETCH_DATA) ||
+	if (BP_IS_HOLE(bp) ||
+	    !((pfd->pd_flags & TRAVERSE_PREFETCH_DATA) ||
 	    BP_GET_TYPE(bp) == DMU_OT_DNODE || BP_GET_LEVEL(bp) > 0) ||
 	    BP_GET_TYPE(bp) == DMU_OT_INTENT_LOG)
 		return (0);
diff --git a/usr/src/uts/common/fs/zfs/dnode.c b/usr/src/uts/common/fs/zfs/dnode.c
index d1295d55ac..b02854f4d2 100644
--- a/usr/src/uts/common/fs/zfs/dnode.c
+++ b/usr/src/uts/common/fs/zfs/dnode.c
@@ -1544,7 +1544,13 @@ dnode_free_range(dnode_t *dn, uint64_t off, uint64_t len, dmu_tx_t *tx)
 	} else {
 		ASSERT(dn->dn_maxblkid == 0);
 		if (off == 0 && len >= blksz) {
-			/* Freeing the whole block; fast-track this request */
+			/*
+			 * Freeing the whole block; fast-track this request.
+			 * Note that we won't dirty any indirect blocks,
+			 * which is fine because we will be freeing the entire
+			 * file and thus all indirect blocks will be freed
+			 * by free_children().
+			 */
 			blkid = 0;
 			nblks = 1;
 			goto done;
@@ -1571,7 +1577,7 @@ dnode_free_range(dnode_t *dn, uint64_t off, uint64_t len, dmu_tx_t *tx)
 			if (db->db_last_dirty ||
 			    (db->db_blkptr && !BP_IS_HOLE(db->db_blkptr))) {
 				rw_exit(&dn->dn_struct_rwlock);
-				dbuf_will_dirty(db, tx);
+				dmu_buf_will_dirty(&db->db, tx);
 				rw_enter(&dn->dn_struct_rwlock, RW_WRITER);
 				data = db->db.db_data;
 				bzero(data + blkoff, head);
@@ -1607,7 +1613,7 @@ dnode_free_range(dnode_t *dn, uint64_t off, uint64_t len, dmu_tx_t *tx)
 			if (db->db_last_dirty ||
 			    (db->db_blkptr && !BP_IS_HOLE(db->db_blkptr))) {
 				rw_exit(&dn->dn_struct_rwlock);
-				dbuf_will_dirty(db, tx);
+				dmu_buf_will_dirty(&db->db, tx);
 				rw_enter(&dn->dn_struct_rwlock, RW_WRITER);
 				bzero(db->db.db_data, tail);
 			}
@@ -1628,18 +1634,18 @@ dnode_free_range(dnode_t *dn, uint64_t off, uint64_t len, dmu_tx_t *tx)
 		nblks += 1;
 
 	/*
-	 * Read in and mark all the level-1 indirects dirty,
-	 * so that they will stay in memory until syncing phase.
-	 * Always dirty the first and last indirect to make sure
-	 * we dirty all the partial indirects.
+	 * Dirty the first and last indirect blocks, as they (and/or their
+	 * parents) will need to be written out if they were only
+	 * partially freed.  Interior indirect blocks will be themselves freed,
+	 * by free_children(), so they need not be dirtied.  Note that these
+	 * interior blocks have already been prefetched by dmu_tx_hold_free().
 	 */
 	if (dn->dn_nlevels > 1) {
-		uint64_t i, first, last;
-		int shift = epbs + dn->dn_datablkshift;
+		uint64_t first, last;
 
 		first = blkid >> epbs;
 		if (db = dbuf_hold_level(dn, 1, first, FTAG)) {
-			dbuf_will_dirty(db, tx);
+			dmu_buf_will_dirty(&db->db, tx);
 			dbuf_rele(db, FTAG);
 		}
 		if (trunc)
@@ -1647,26 +1653,11 @@ dnode_free_range(dnode_t *dn, uint64_t off, uint64_t len, dmu_tx_t *tx)
 		else
 			last = (blkid + nblks - 1) >> epbs;
 		if (last > first && (db = dbuf_hold_level(dn, 1, last, FTAG))) {
-			dbuf_will_dirty(db, tx);
+			dmu_buf_will_dirty(&db->db, tx);
 			dbuf_rele(db, FTAG);
 		}
-		for (i = first + 1; i < last; i++) {
-			uint64_t ibyte = i << shift;
-			int err;
-
-			err = dnode_next_offset(dn,
-			    DNODE_FIND_HAVELOCK, &ibyte, 1, 1, 0);
-			i = ibyte >> shift;
-			if (err == ESRCH || i >= last)
-				break;
-			ASSERT(err == 0);
-			db = dbuf_hold_level(dn, 1, i, FTAG);
-			if (db) {
-				dbuf_will_dirty(db, tx);
-				dbuf_rele(db, FTAG);
-			}
-		}
 	}
+
 done:
 	/*
 	 * Add this range to the dnode range list.
@@ -1694,8 +1685,6 @@ done:
 	dbuf_free_range(dn, blkid, blkid + nblks - 1, tx);
 	dnode_setdirty(dn, tx);
 out:
-	if (trunc && dn->dn_maxblkid >= (off >> blkshift))
-		dn->dn_maxblkid = (off >> blkshift ? (off >> blkshift) - 1 : 0);
 
 	rw_exit(&dn->dn_struct_rwlock);
 }
@@ -1872,8 +1861,10 @@ dnode_next_offset_level(dnode_t *dn, int flags, uint64_t *offset,
 		data = db->db.db_data;
 	}
 
-	if (db && txg &&
-	    (db->db_blkptr == NULL || db->db_blkptr->blk_birth <= txg)) {
+
+	if (db != NULL && txg != 0 && (db->db_blkptr == NULL ||
+	    db->db_blkptr->blk_birth <= txg ||
+	    BP_IS_HOLE(db->db_blkptr))) {
 		/*
 		 * This can only happen when we are searching up the tree
 		 * and these conditions mean that we need to keep climbing.
diff --git a/usr/src/uts/common/fs/zfs/dnode_sync.c b/usr/src/uts/common/fs/zfs/dnode_sync.c
index b9f2ea9ad8..d3d114f075 100644
--- a/usr/src/uts/common/fs/zfs/dnode_sync.c
+++ b/usr/src/uts/common/fs/zfs/dnode_sync.c
@@ -32,6 +32,7 @@
 #include <sys/dmu_objset.h>
 #include <sys/dsl_dataset.h>
 #include <sys/spa.h>
+#include <sys/zfeature.h>
 
 static void
 dnode_increase_indirection(dnode_t *dn, dmu_tx_t *tx)
@@ -112,26 +113,44 @@ dnode_increase_indirection(dnode_t *dn, dmu_tx_t *tx)
 	rw_exit(&dn->dn_struct_rwlock);
 }
 
-static int
+static void
 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++) {
+	for (int 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));
+
+		/*
+		 * Save some useful information on the holes being
+		 * punched, including logical size, type, and indirection
+		 * level. Retaining birth time enables detection of when
+		 * holes are punched for reducing the number of free
+		 * records transmitted during a zfs send.
+		 */
+
+		uint64_t lsize = BP_GET_LSIZE(bp);
+		dmu_object_type_t type = BP_GET_TYPE(bp);
+		uint64_t lvl = BP_GET_LEVEL(bp);
+
 		bzero(bp, sizeof (blkptr_t));
-		blocks_freed += 1;
+
+		if (spa_feature_is_active(dn->dn_objset->os_spa,
+		    SPA_FEATURE_HOLE_BIRTH)) {
+			BP_SET_LSIZE(bp, lsize);
+			BP_SET_TYPE(bp, type);
+			BP_SET_LEVEL(bp, lvl);
+			BP_SET_BIRTH(bp, dmu_tx_get_txg(tx), 0);
+		}
 	}
 	dnode_diduse_space(dn, -bytesfreed);
-	return (blocks_freed);
 }
 
 #ifdef ZFS_DEBUG
@@ -215,30 +234,27 @@ free_verify(dmu_buf_impl_t *db, uint64_t start, uint64_t end, dmu_tx_t *tx)
 
 #define	ALL -1
 
-static int
-free_children(dmu_buf_impl_t *db, uint64_t blkid, uint64_t nblks, int trunc,
+static void
+free_children(dmu_buf_impl_t *db, uint64_t blkid, uint64_t nblks,
     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;
+	int epbs, shift;
 
 	/*
 	 * 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.
+	 *   2 - if this block was evicted since we read it from
+	 *	 dmu_tx_hold_free().
 	 */
 	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;
+	bp = db->db.db_data;
 
 	DB_DNODE_ENTER(db);
 	dn = DB_DNODE(db);
@@ -248,7 +264,6 @@ free_children(dmu_buf_impl_t *db, uint64_t blkid, uint64_t nblks, int trunc,
 	start = blkid >> shift;
 	if (dbstart < start) {
 		bp += start - dbstart;
-		all = FALSE;
 	} else {
 		start = dbstart;
 	}
@@ -256,49 +271,46 @@ free_children(dmu_buf_impl_t *db, uint64_t blkid, uint64_t nblks, int trunc,
 	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);
+		free_blocks(dn, bp, end-start+1, tx);
+	} else {
+		for (i = start; i <= end; i++, bp++) {
+			if (BP_IS_HOLE(bp))
+				continue;
+			rw_enter(&dn->dn_struct_rwlock, RW_READER);
+			VERIFY0(dbuf_hold_impl(dn, db->db_level - 1,
+			    i, B_TRUE, FTAG, &subdb));
+			rw_exit(&dn->dn_struct_rwlock);
+			ASSERT3P(bp, ==, subdb->db_blkptr);
+
+			free_children(subdb, blkid, nblks, tx);
+			dbuf_rele(subdb, FTAG);
+		}
 	}
 
-	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);
-		ASSERT0(err);
-		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);
+	/* If this whole block is free, free ourself too. */
+	for (i = 0, bp = db->db.db_data; i < 1 << epbs; i++, bp++) {
+		if (!BP_IS_HOLE(bp))
+			break;
+	}
+	if (i == 1 << epbs) {
+		/* didn't find any non-holes */
+		bzero(db->db.db_data, db->db.db_size);
+		free_blocks(dn, db->db_blkptr, 1, tx);
+	} else {
+		/*
+		 * Partial block free; must be marked dirty so that it
+		 * will be written out.
+		 */
+		ASSERT(db->db_dirtycnt > 0);
 	}
+
 	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;
-		ASSERT0(bp->blk_birth);
-	}
-#endif
-	ASSERT(all || blocks_freed == 0 || db->db_last_dirty);
-	return (all ? ALL : blocks_freed);
 }
 
 /*
@@ -306,20 +318,21 @@ free_children(dmu_buf_impl_t *db, uint64_t blkid, uint64_t nblks, int trunc,
  * 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)
+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;
+	boolean_t trunc = B_FALSE;
 
 	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)
+	if (blkid + nblks > dn->dn_phys->dn_maxblkid) {
 		nblks = dn->dn_phys->dn_maxblkid - blkid + 1;
+		trunc = B_TRUE;
+	}
 
 	/* There are no indirect blocks in the object */
 	if (dnlevel == 1) {
@@ -328,41 +341,35 @@ dnode_sync_free_range(dnode_t *dn, uint64_t blkid, uint64_t nblks, dmu_tx_t *tx)
 			return;
 		}
 		ASSERT3U(blkid + nblks, <=, dn->dn_phys->dn_nblkptr);
-		(void) free_blocks(dn, bp + blkid, nblks, tx);
-		if (trunc) {
-			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);
-		ASSERT0(err);
-		rw_exit(&dn->dn_struct_rwlock);
+		free_blocks(dn, bp + blkid, nblks, tx);
+	} else {
+		int shift = (dnlevel - 1) *
+		    (dn->dn_phys->dn_indblkshift - SPA_BLKPTRSHIFT);
+		int start = blkid >> shift;
+		int end = (blkid + nblks - 1) >> shift;
+		dmu_buf_impl_t *db;
+
+		ASSERT(start < dn->dn_phys->dn_nblkptr);
+		bp += start;
+		for (int i = start; i <= end; i++, bp++) {
+			if (BP_IS_HOLE(bp))
+				continue;
+			rw_enter(&dn->dn_struct_rwlock, RW_READER);
+			VERIFY0(dbuf_hold_impl(dn, dnlevel - 1, i,
+			    TRUE, FTAG, &db));
+			rw_exit(&dn->dn_struct_rwlock);
+
+			free_children(db, blkid, nblks, tx);
+			dbuf_rele(db, FTAG);
 
-		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) {
+		dn->dn_phys->dn_maxblkid = blkid == 0 ? 0 : blkid - 1;
+
 		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);
@@ -500,7 +507,7 @@ dnode_sync_free(dnode_t *dn, dmu_tx_t *tx)
 
 	ASSERT(dn->dn_free_txg > 0);
 	if (dn->dn_allocated_txg != dn->dn_free_txg)
-		dbuf_will_dirty(dn->dn_dbuf, tx);
+		dmu_buf_will_dirty(&dn->dn_dbuf->db, tx);
 	bzero(dn->dn_phys, sizeof (dnode_phys_t));
 
 	mutex_enter(&dn->dn_mtx);
@@ -607,13 +614,15 @@ dnode_sync(dnode_t *dn, dmu_tx_t *tx)
 		dn->dn_next_bonustype[txgoff] = 0;
 	}
 
+	boolean_t freeing_dnode = dn->dn_free_txg > 0 &&
+	    dn->dn_free_txg <= tx->tx_txg;
+
 	/*
 	 * 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)) {
+	    ((dnp->dn_flags & DNODE_FLAG_SPILL_BLKPTR) && freeing_dnode)) {
 		if ((dnp->dn_flags & DNODE_FLAG_SPILL_BLKPTR))
 			kill_spill = B_TRUE;
 		dn->dn_rm_spillblk[txgoff] = 0;
@@ -636,7 +645,7 @@ dnode_sync(dnode_t *dn, dmu_tx_t *tx)
 	mutex_exit(&dn->dn_mtx);
 
 	if (kill_spill) {
-		(void) free_blocks(dn, &dn->dn_phys->dn_spill, 1, tx);
+		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);
@@ -652,7 +661,7 @@ dnode_sync(dnode_t *dn, dmu_tx_t *tx)
 		kmem_free(rp, sizeof (free_range_t));
 	}
 
-	if (dn->dn_free_txg > 0 && dn->dn_free_txg <= tx->tx_txg) {
+	if (freeing_dnode) {
 		dnode_sync_free(dn, tx);
 		return;
 	}
diff --git a/usr/src/uts/common/fs/zfs/dsl_dataset.c b/usr/src/uts/common/fs/zfs/dsl_dataset.c
index 2db6c88b2e..74395d3077 100644
--- a/usr/src/uts/common/fs/zfs/dsl_dataset.c
+++ b/usr/src/uts/common/fs/zfs/dsl_dataset.c
@@ -119,17 +119,16 @@ int
 dsl_dataset_block_kill(dsl_dataset_t *ds, const blkptr_t *bp, dmu_tx_t *tx,
     boolean_t async)
 {
+	int used = bp_get_dsize_sync(tx->tx_pool->dp_spa, bp);
+	int compressed = BP_GET_PSIZE(bp);
+	int uncompressed = BP_GET_UCSIZE(bp);
+
 	if (BP_IS_HOLE(bp))
 		return (0);
 
 	ASSERT(dmu_tx_is_syncing(tx));
 	ASSERT(bp->blk_birth <= tx->tx_txg);
 
-	int used = bp_get_dsize_sync(tx->tx_pool->dp_spa, bp);
-	int compressed = BP_GET_PSIZE(bp);
-	int uncompressed = BP_GET_UCSIZE(bp);
-
-	ASSERT(used > 0);
 	if (ds == NULL) {
 		dsl_free(tx->tx_pool, tx->tx_txg, bp);
 		dsl_pool_mos_diduse_space(tx->tx_pool,
@@ -227,7 +226,8 @@ boolean_t
 dsl_dataset_block_freeable(dsl_dataset_t *ds, const blkptr_t *bp,
     uint64_t blk_birth)
 {
-	if (blk_birth <= dsl_dataset_prev_snap_txg(ds))
+	if (blk_birth <= dsl_dataset_prev_snap_txg(ds) ||
+	    (bp != NULL && BP_IS_HOLE(bp)))
 		return (B_FALSE);
 
 	ddt_prefetch(dsl_dataset_get_spa(ds), bp);
diff --git a/usr/src/uts/common/fs/zfs/dsl_destroy.c b/usr/src/uts/common/fs/zfs/dsl_destroy.c
index 047fc63e69..6f75b0df41 100644
--- a/usr/src/uts/common/fs/zfs/dsl_destroy.c
+++ b/usr/src/uts/common/fs/zfs/dsl_destroy.c
@@ -144,6 +144,8 @@ process_old_cb(void *arg, const blkptr_t *bp, dmu_tx_t *tx)
 	struct process_old_arg *poa = arg;
 	dsl_pool_t *dp = poa->ds->ds_dir->dd_pool;
 
+	ASSERT(!BP_IS_HOLE(bp));
+
 	if (bp->blk_birth <= poa->ds->ds_phys->ds_prev_snap_txg) {
 		dsl_deadlist_insert(&poa->ds->ds_deadlist, bp, tx);
 		if (poa->ds_prev && !poa->after_branch_point &&
@@ -536,7 +538,7 @@ kill_blkptr(spa_t *spa, zilog_t *zilog, const blkptr_t *bp,
 	struct killarg *ka = arg;
 	dmu_tx_t *tx = ka->tx;
 
-	if (bp == NULL)
+	if (BP_IS_HOLE(bp))
 		return (0);
 
 	if (zb->zb_level == ZB_ZIL_LEVEL) {
diff --git a/usr/src/uts/common/fs/zfs/dsl_scan.c b/usr/src/uts/common/fs/zfs/dsl_scan.c
index 050eccac22..ee8f65cf7a 100644
--- a/usr/src/uts/common/fs/zfs/dsl_scan.c
+++ b/usr/src/uts/common/fs/zfs/dsl_scan.c
@@ -450,7 +450,7 @@ dsl_scan_zil_block(zilog_t *zilog, blkptr_t *bp, void *arg, uint64_t claim_txg)
 	zil_header_t *zh = zsa->zsa_zh;
 	zbookmark_t zb;
 
-	if (bp->blk_birth <= scn->scn_phys.scn_cur_min_txg)
+	if (BP_IS_HOLE(bp) || bp->blk_birth <= scn->scn_phys.scn_cur_min_txg)
 		return (0);
 
 	/*
@@ -482,7 +482,8 @@ dsl_scan_zil_record(zilog_t *zilog, lr_t *lrc, void *arg, uint64_t claim_txg)
 		blkptr_t *bp = &lr->lr_blkptr;
 		zbookmark_t zb;
 
-		if (bp->blk_birth <= scn->scn_phys.scn_cur_min_txg)
+		if (BP_IS_HOLE(bp) ||
+		    bp->blk_birth <= scn->scn_phys.scn_cur_min_txg)
 			return (0);
 
 		/*
@@ -734,7 +735,7 @@ dsl_scan_visitbp(blkptr_t *bp, const zbookmark_t *zb,
 	if (dsl_scan_check_resume(scn, dnp, zb))
 		return;
 
-	if (bp->blk_birth == 0)
+	if (BP_IS_HOLE(bp))
 		return;
 
 	scn->scn_visited_this_txg++;
diff --git a/usr/src/uts/common/fs/zfs/spa.c b/usr/src/uts/common/fs/zfs/spa.c
index 58aa56ef4d..6f155e8ca9 100644
--- a/usr/src/uts/common/fs/zfs/spa.c
+++ b/usr/src/uts/common/fs/zfs/spa.c
@@ -1827,7 +1827,7 @@ static int
 spa_load_verify_cb(spa_t *spa, zilog_t *zilog, const blkptr_t *bp,
     const zbookmark_t *zb, const dnode_phys_t *dnp, void *arg)
 {
-	if (bp != NULL) {
+	if (!BP_IS_HOLE(bp)) {
 		zio_t *rio = arg;
 		size_t size = BP_GET_PSIZE(bp);
 		void *data = zio_data_buf_alloc(size);
@@ -2351,6 +2351,33 @@ spa_load_impl(spa_t *spa, uint64_t pool_guid, nvlist_t *config,
 			return (spa_vdev_err(rvd, VDEV_AUX_UNSUP_FEAT,
 			    ENOTSUP));
 		}
+
+		/*
+		 * Load refcounts for ZFS features from disk into an in-memory
+		 * cache during SPA initialization.
+		 */
+		for (spa_feature_t i = 0; i < SPA_FEATURES; i++) {
+			uint64_t refcount;
+
+			error = feature_get_refcount_from_disk(spa,
+			    &spa_feature_table[i], &refcount);
+			if (error == 0) {
+				spa->spa_feat_refcount_cache[i] = refcount;
+			} else if (error == ENOTSUP) {
+				spa->spa_feat_refcount_cache[i] =
+				    SPA_FEATURE_DISABLED;
+			} else {
+				return (spa_vdev_err(rvd,
+				    VDEV_AUX_CORRUPT_DATA, EIO));
+			}
+		}
+	}
+
+	if (spa_feature_is_active(spa, SPA_FEATURE_ENABLED_TXG)) {
+		if (spa_dir_prop(spa, DMU_POOL_FEATURE_ENABLED_TXG,
+		    &spa->spa_feat_enabled_txg_obj) != 0) {
+			return (spa_vdev_err(rvd, VDEV_AUX_CORRUPT_DATA, EIO));
+		}
 	}
 
 	spa->spa_is_initializing = B_TRUE;
@@ -5777,7 +5804,7 @@ spa_sync_nvlist(spa_t *spa, uint64_t obj, nvlist_t *nv, dmu_tx_t *tx)
 
 	/*
 	 * Write full (SPA_CONFIG_BLOCKSIZE) blocks of configuration
-	 * information.  This avoids the dbuf_will_dirty() path and
+	 * information.  This avoids the dmu_buf_will_dirty() path and
 	 * saves us a pre-read to get data we don't actually care about.
 	 */
 	bufsize = P2ROUNDUP((uint64_t)nvsize, SPA_CONFIG_BLOCKSIZE);
diff --git a/usr/src/uts/common/fs/zfs/spa_misc.c b/usr/src/uts/common/fs/zfs/spa_misc.c
index 9f217f7051..928497ca87 100644
--- a/usr/src/uts/common/fs/zfs/spa_misc.c
+++ b/usr/src/uts/common/fs/zfs/spa_misc.c
@@ -586,6 +586,15 @@ spa_add(const char *name, nvlist_t *config, const char *altroot)
 
 	spa->spa_debug = ((zfs_flags & ZFS_DEBUG_SPA) != 0);
 
+	/*
+	 * As a pool is being created, treat all features as disabled by
+	 * setting SPA_FEATURE_DISABLED for all entries in the feature
+	 * refcount cache.
+	 */
+	for (int i = 0; i < SPA_FEATURES; i++) {
+		spa->spa_feat_refcount_cache[i] = SPA_FEATURE_DISABLED;
+	}
+
 	return (spa);
 }
 
@@ -1141,11 +1150,19 @@ spa_vdev_state_exit(spa_t *spa, vdev_t *vd, int error)
  */
 
 void
-spa_activate_mos_feature(spa_t *spa, const char *feature)
+spa_activate_mos_feature(spa_t *spa, const char *feature, dmu_tx_t *tx)
 {
 	if (!nvlist_exists(spa->spa_label_features, feature)) {
 		fnvlist_add_boolean(spa->spa_label_features, feature);
-		vdev_config_dirty(spa->spa_root_vdev);
+		/*
+		 * When we are creating the pool (tx_txg==TXG_INITIAL), we can't
+		 * dirty the vdev config because lock SCL_CONFIG is not held.
+		 * Thankfully, in this case we don't need to dirty the config
+		 * because it will be written out anyway when we finish
+		 * creating the pool.
+		 */
+		if (tx->tx_txg != TXG_INITIAL)
+			vdev_config_dirty(spa->spa_root_vdev);
 	}
 }
 
@@ -1304,7 +1321,7 @@ spa_generate_guid(spa_t *spa)
 }
 
 void
-sprintf_blkptr(char *buf, const blkptr_t *bp)
+snprintf_blkptr(char *buf, size_t buflen, const blkptr_t *bp)
 {
 	char type[256];
 	char *checksum = NULL;
@@ -1326,7 +1343,8 @@ sprintf_blkptr(char *buf, const blkptr_t *bp)
 		compress = zio_compress_table[BP_GET_COMPRESS(bp)].ci_name;
 	}
 
-	SPRINTF_BLKPTR(snprintf, ' ', buf, bp, type, checksum, compress);
+	SNPRINTF_BLKPTR(snprintf, ' ', buf, buflen, bp, type, checksum,
+	    compress);
 }
 
 void
diff --git a/usr/src/uts/common/fs/zfs/sys/dbuf.h b/usr/src/uts/common/fs/zfs/sys/dbuf.h
index b8f5eeb725..207834dfd4 100644
--- a/usr/src/uts/common/fs/zfs/sys/dbuf.h
+++ b/usr/src/uts/common/fs/zfs/sys/dbuf.h
@@ -268,8 +268,6 @@ void dbuf_rele_and_unlock(dmu_buf_impl_t *db, void *tag);
 dmu_buf_impl_t *dbuf_find(struct dnode *dn, uint8_t level, uint64_t blkid);
 
 int dbuf_read(dmu_buf_impl_t *db, zio_t *zio, uint32_t flags);
-void dbuf_will_dirty(dmu_buf_impl_t *db, dmu_tx_t *tx);
-void dbuf_fill_done(dmu_buf_impl_t *db, dmu_tx_t *tx);
 void dmu_buf_will_not_fill(dmu_buf_t *db, dmu_tx_t *tx);
 void dmu_buf_will_fill(dmu_buf_t *db, dmu_tx_t *tx);
 void dmu_buf_fill_done(dmu_buf_t *db, dmu_tx_t *tx);
@@ -295,20 +293,6 @@ void dbuf_new_size(dmu_buf_impl_t *db, int size, dmu_tx_t *tx);
 #define	DB_DNODE_ENTER(_db)	(zrl_add(&DB_DNODE_LOCK(_db)))
 #define	DB_DNODE_EXIT(_db)	(zrl_remove(&DB_DNODE_LOCK(_db)))
 #define	DB_DNODE_HELD(_db)	(!zrl_is_zero(&DB_DNODE_LOCK(_db)))
-#define	DB_GET_SPA(_spa_p, _db) {		\
-	dnode_t *__dn;				\
-	DB_DNODE_ENTER(_db);			\
-	__dn = DB_DNODE(_db);			\
-	*(_spa_p) = __dn->dn_objset->os_spa;	\
-	DB_DNODE_EXIT(_db);			\
-}
-#define	DB_GET_OBJSET(_os_p, _db) {		\
-	dnode_t *__dn;				\
-	DB_DNODE_ENTER(_db);			\
-	__dn = DB_DNODE(_db);			\
-	*(_os_p) = __dn->dn_objset;		\
-	DB_DNODE_EXIT(_db);			\
-}
 
 void dbuf_init(void);
 void dbuf_fini(void);
@@ -358,7 +342,7 @@ _NOTE(CONSTCOND) } while (0)
 #define	dprintf_dbuf_bp(db, bp, fmt, ...) do {			\
 	if (zfs_flags & ZFS_DEBUG_DPRINTF) {			\
 	char *__blkbuf = kmem_alloc(BP_SPRINTF_LEN, KM_SLEEP);	\
-	sprintf_blkptr(__blkbuf, bp);				\
+	snprintf_blkptr(__blkbuf, BP_SPRINTF_LEN, bp);		\
 	dprintf_dbuf(db, fmt " %s\n", __VA_ARGS__, __blkbuf);	\
 	kmem_free(__blkbuf, BP_SPRINTF_LEN);			\
 	}							\
diff --git a/usr/src/uts/common/fs/zfs/sys/dmu.h b/usr/src/uts/common/fs/zfs/sys/dmu.h
index 1d1c385f38..dcc56376be 100644
--- a/usr/src/uts/common/fs/zfs/sys/dmu.h
+++ b/usr/src/uts/common/fs/zfs/sys/dmu.h
@@ -293,6 +293,7 @@ typedef void dmu_buf_evict_func_t(struct dmu_buf *db, void *user_ptr);
 #define	DMU_POOL_FEATURES_FOR_WRITE	"features_for_write"
 #define	DMU_POOL_FEATURES_FOR_READ	"features_for_read"
 #define	DMU_POOL_FEATURE_DESCRIPTIONS	"feature_descriptions"
+#define	DMU_POOL_FEATURE_ENABLED_TXG	"feature_enabled_txg"
 #define	DMU_POOL_ROOT_DATASET		"root_dataset"
 #define	DMU_POOL_SYNC_BPOBJ		"sync_bplist"
 #define	DMU_POOL_ERRLOG_SCRUB		"errlog_scrub"
diff --git a/usr/src/uts/common/fs/zfs/sys/spa.h b/usr/src/uts/common/fs/zfs/sys/spa.h
index aed3d4806c..c76dc0fbad 100644
--- a/usr/src/uts/common/fs/zfs/sys/spa.h
+++ b/usr/src/uts/common/fs/zfs/sys/spa.h
@@ -20,7 +20,7 @@
  */
 /*
  * Copyright (c) 2005, 2010, Oracle and/or its affiliates. All rights reserved.
- * Copyright (c) 2012 by Delphix. All rights reserved.
+ * Copyright (c) 2013 by Delphix. All rights reserved.
  * Copyright 2011 Nexenta Systems, Inc.  All rights reserved.
  */
 
@@ -65,20 +65,33 @@ struct dsl_dataset;
 #define	BF32_GET(x, low, len)		BF32_DECODE(x, low, len)
 #define	BF64_GET(x, low, len)		BF64_DECODE(x, low, len)
 
-#define	BF32_SET(x, low, len, val)	\
-	((x) ^= BF32_ENCODE((x >> low) ^ (val), low, len))
-#define	BF64_SET(x, low, len, val)	\
-	((x) ^= BF64_ENCODE((x >> low) ^ (val), low, len))
+#define	BF32_SET(x, low, len, val) do { \
+	ASSERT3U(val, <, 1U << (len)); \
+	ASSERT3U(low + len, <=, 32); \
+	(x) ^= BF32_ENCODE((x >> low) ^ (val), low, len); \
+_NOTE(CONSTCOND) } while (0)
+
+#define	BF64_SET(x, low, len, val) do { \
+	ASSERT3U(val, <, 1ULL << (len)); \
+	ASSERT3U(low + len, <=, 64); \
+	((x) ^= BF64_ENCODE((x >> low) ^ (val), low, len)); \
+_NOTE(CONSTCOND) } while (0)
 
 #define	BF32_GET_SB(x, low, len, shift, bias)	\
 	((BF32_GET(x, low, len) + (bias)) << (shift))
 #define	BF64_GET_SB(x, low, len, shift, bias)	\
 	((BF64_GET(x, low, len) + (bias)) << (shift))
 
-#define	BF32_SET_SB(x, low, len, shift, bias, val)	\
-	BF32_SET(x, low, len, ((val) >> (shift)) - (bias))
-#define	BF64_SET_SB(x, low, len, shift, bias, val)	\
-	BF64_SET(x, low, len, ((val) >> (shift)) - (bias))
+#define	BF32_SET_SB(x, low, len, shift, bias, val) do { \
+	ASSERT(IS_P2ALIGNED(val, 1U << shift)); \
+	ASSERT3S((val) >> (shift), >=, bias); \
+	BF32_SET(x, low, len, ((val) >> (shift)) - (bias)); \
+_NOTE(CONSTCOND) } while (0)
+#define	BF64_SET_SB(x, low, len, shift, bias, val) do { \
+	ASSERT(IS_P2ALIGNED(val, 1ULL << shift)); \
+	ASSERT3S((val) >> (shift), >=, bias); \
+	BF64_SET(x, low, len, ((val) >> (shift)) - (bias)); \
+_NOTE(CONSTCOND) } while (0)
 
 /*
  * We currently support nine block sizes, from 512 bytes to 128K.
@@ -186,6 +199,15 @@ typedef struct zio_cksum {
 #define	SPA_BLKPTRSHIFT	7		/* blkptr_t is 128 bytes	*/
 #define	SPA_DVAS_PER_BP	3		/* Number of DVAs in a bp	*/
 
+/*
+ * A block is a hole when it has either 1) never been written to, or
+ * 2) is zero-filled. In both cases, ZFS can return all zeroes for all reads
+ * without physically allocating disk space. Holes are represented in the
+ * blkptr_t structure by zeroed blk_dva. Correct checking for holes is
+ * done through the BP_IS_HOLE macro. For holes, the logical size, level,
+ * DMU object type, and birth times are all also stored for holes that
+ * were written to at some point (i.e. were punched after having been filled).
+ */
 typedef struct blkptr {
 	dva_t		blk_dva[SPA_DVAS_PER_BP]; /* Data Virtual Addresses */
 	uint64_t	blk_prop;	/* size, compression, type, etc	    */
@@ -200,9 +222,10 @@ typedef struct blkptr {
  * Macros to get and set fields in a bp or DVA.
  */
 #define	DVA_GET_ASIZE(dva)	\
-	BF64_GET_SB((dva)->dva_word[0], 0, 24, SPA_MINBLOCKSHIFT, 0)
+	BF64_GET_SB((dva)->dva_word[0], 0, SPA_ASIZEBITS, SPA_MINBLOCKSHIFT, 0)
 #define	DVA_SET_ASIZE(dva, x)	\
-	BF64_SET_SB((dva)->dva_word[0], 0, 24, SPA_MINBLOCKSHIFT, 0, x)
+	BF64_SET_SB((dva)->dva_word[0], 0, SPA_ASIZEBITS, \
+	SPA_MINBLOCKSHIFT, 0, x)
 
 #define	DVA_GET_GRID(dva)	BF64_GET((dva)->dva_word[0], 24, 8)
 #define	DVA_SET_GRID(dva, x)	BF64_SET((dva)->dva_word[0], 24, 8, x)
@@ -219,14 +242,14 @@ typedef struct blkptr {
 #define	DVA_SET_GANG(dva, x)	BF64_SET((dva)->dva_word[1], 63, 1, x)
 
 #define	BP_GET_LSIZE(bp)	\
-	BF64_GET_SB((bp)->blk_prop, 0, 16, SPA_MINBLOCKSHIFT, 1)
+	BF64_GET_SB((bp)->blk_prop, 0, SPA_LSIZEBITS, SPA_MINBLOCKSHIFT, 1)
 #define	BP_SET_LSIZE(bp, x)	\
-	BF64_SET_SB((bp)->blk_prop, 0, 16, SPA_MINBLOCKSHIFT, 1, x)
+	BF64_SET_SB((bp)->blk_prop, 0, SPA_LSIZEBITS, SPA_MINBLOCKSHIFT, 1, x)
 
 #define	BP_GET_PSIZE(bp)	\
-	BF64_GET_SB((bp)->blk_prop, 16, 16, SPA_MINBLOCKSHIFT, 1)
+	BF64_GET_SB((bp)->blk_prop, 16, SPA_PSIZEBITS, SPA_MINBLOCKSHIFT, 1)
 #define	BP_SET_PSIZE(bp, x)	\
-	BF64_SET_SB((bp)->blk_prop, 16, 16, SPA_MINBLOCKSHIFT, 1, x)
+	BF64_SET_SB((bp)->blk_prop, 16, SPA_PSIZEBITS, SPA_MINBLOCKSHIFT, 1, x)
 
 #define	BP_GET_COMPRESS(bp)		BF64_GET((bp)->blk_prop, 32, 8)
 #define	BP_SET_COMPRESS(bp, x)		BF64_SET((bp)->blk_prop, 32, 8, x)
@@ -246,7 +269,7 @@ typedef struct blkptr {
 #define	BP_GET_DEDUP(bp)		BF64_GET((bp)->blk_prop, 62, 1)
 #define	BP_SET_DEDUP(bp, x)		BF64_SET((bp)->blk_prop, 62, 1, x)
 
-#define	BP_GET_BYTEORDER(bp)		(0 - BF64_GET((bp)->blk_prop, 63, 1))
+#define	BP_GET_BYTEORDER(bp)		BF64_GET((bp)->blk_prop, 63, 1)
 #define	BP_SET_BYTEORDER(bp, x)		BF64_SET((bp)->blk_prop, 63, 1, x)
 
 #define	BP_PHYSICAL_BIRTH(bp)		\
@@ -304,7 +327,9 @@ typedef struct blkptr {
 
 #define	BP_IDENTITY(bp)		(&(bp)->blk_dva[0])
 #define	BP_IS_GANG(bp)		DVA_GET_GANG(BP_IDENTITY(bp))
-#define	BP_IS_HOLE(bp)		((bp)->blk_birth == 0)
+#define	DVA_IS_EMPTY(dva)	((dva)->dva_word[0] == 0ULL &&	\
+				(dva)->dva_word[1] == 0ULL)
+#define	BP_IS_HOLE(bp)		DVA_IS_EMPTY(BP_IDENTITY(bp))
 
 /* BP_IS_RAIDZ(bp) assumes no block compression */
 #define	BP_IS_RAIDZ(bp)		(DVA_GET_ASIZE(&(bp)->blk_dva[0]) > \
@@ -327,14 +352,10 @@ typedef struct blkptr {
 	ZIO_SET_CHECKSUM(&(bp)->blk_cksum, 0, 0, 0, 0);	\
 }
 
-/*
- * Note: the byteorder is either 0 or -1, both of which are palindromes.
- * This simplifies the endianness handling a bit.
- */
 #ifdef _BIG_ENDIAN
 #define	ZFS_HOST_BYTEORDER	(0ULL)
 #else
-#define	ZFS_HOST_BYTEORDER	(-1ULL)
+#define	ZFS_HOST_BYTEORDER	(1ULL)
 #endif
 
 #define	BP_SHOULD_BYTESWAP(bp)	(BP_GET_BYTEORDER(bp) != ZFS_HOST_BYTEORDER)
@@ -346,18 +367,22 @@ typedef struct blkptr {
  * 'func' is either snprintf() or mdb_snprintf().
  * 'ws' (whitespace) can be ' ' for single-line format, '\n' for multi-line.
  */
-#define	SPRINTF_BLKPTR(func, ws, buf, bp, type, checksum, compress)	\
+#define	SNPRINTF_BLKPTR(func, ws, buf, size, bp, type, checksum, compress) \
 {									\
 	static const char *copyname[] =					\
 	    { "zero", "single", "double", "triple" };			\
-	int size = BP_SPRINTF_LEN;					\
 	int len = 0;							\
 	int copies = 0;							\
 									\
 	if (bp == NULL) {						\
-		len = func(buf + len, size - len, "<NULL>");		\
+		len += func(buf + len, size - len, "<NULL>");		\
 	} else if (BP_IS_HOLE(bp)) {					\
-		len = func(buf + len, size - len, "<hole>");		\
+		len += func(buf + len, size - len, "<hole>");		\
+		if (bp->blk_birth > 0) {				\
+			len += func(buf + len, size - len,		\
+			    " birth=%lluL",				\
+			    (u_longlong_t)bp->blk_birth);		\
+		}							\
 	} else {							\
 		for (int d = 0; d < BP_GET_NDVAS(bp); d++) {		\
 			const dva_t *dva = &bp->blk_dva[d];		\
@@ -599,7 +624,8 @@ extern objset_t *spa_meta_objset(spa_t *spa);
 extern uint64_t spa_deadman_synctime(spa_t *spa);
 
 /* Miscellaneous support routines */
-extern void spa_activate_mos_feature(spa_t *spa, const char *feature);
+extern void spa_activate_mos_feature(spa_t *spa, const char *feature,
+    dmu_tx_t *tx);
 extern void spa_deactivate_mos_feature(spa_t *spa, const char *feature);
 extern int spa_rename(const char *oldname, const char *newname);
 extern spa_t *spa_by_guid(uint64_t pool_guid, uint64_t device_guid);
@@ -608,7 +634,7 @@ extern char *spa_strdup(const char *);
 extern void spa_strfree(char *);
 extern uint64_t spa_get_random(uint64_t range);
 extern uint64_t spa_generate_guid(spa_t *spa);
-extern void sprintf_blkptr(char *buf, const blkptr_t *bp);
+extern void snprintf_blkptr(char *buf, size_t buflen, const blkptr_t *bp);
 extern void spa_freeze(spa_t *spa);
 extern int spa_change_guid(spa_t *spa);
 extern void spa_upgrade(spa_t *spa, uint64_t version);
@@ -676,9 +702,9 @@ extern void spa_event_notify(spa_t *spa, vdev_t *vdev, const char *name);
 
 #ifdef ZFS_DEBUG
 #define	dprintf_bp(bp, fmt, ...) do {				\
-	if (zfs_flags & ZFS_DEBUG_DPRINTF) { 			\
+	if (zfs_flags & ZFS_DEBUG_DPRINTF) {			\
 	char *__blkbuf = kmem_alloc(BP_SPRINTF_LEN, KM_SLEEP);	\
-	sprintf_blkptr(__blkbuf, (bp));				\
+	snprintf_blkptr(__blkbuf, BP_SPRINTF_LEN, (bp));	\
 	dprintf(fmt " %s\n", __VA_ARGS__, __blkbuf);		\
 	kmem_free(__blkbuf, BP_SPRINTF_LEN);			\
 	} \
diff --git a/usr/src/uts/common/fs/zfs/sys/spa_impl.h b/usr/src/uts/common/fs/zfs/sys/spa_impl.h
index e9e67bbcac..40f447e9ef 100644
--- a/usr/src/uts/common/fs/zfs/sys/spa_impl.h
+++ b/usr/src/uts/common/fs/zfs/sys/spa_impl.h
@@ -38,6 +38,7 @@
 #include <sys/refcount.h>
 #include <sys/bplist.h>
 #include <sys/bpobj.h>
+#include <zfeature_common.h>
 
 #ifdef	__cplusplus
 extern "C" {
@@ -232,6 +233,9 @@ struct spa {
 	uint64_t	spa_feat_for_write_obj;	/* required to write to pool */
 	uint64_t	spa_feat_for_read_obj;	/* required to read from pool */
 	uint64_t	spa_feat_desc_obj;	/* Feature descriptions */
+	uint64_t	spa_feat_enabled_txg_obj; /* Feature enabled txg */
+	/* cache feature refcounts */
+	uint64_t	spa_feat_refcount_cache[SPA_FEATURES];
 	cyclic_id_t	spa_deadman_cycid;	/* cyclic id */
 	uint64_t	spa_deadman_calls;	/* number of deadman calls */
 	hrtime_t	spa_sync_starttime;	/* starting time fo spa_sync */
diff --git a/usr/src/uts/common/fs/zfs/sys/vdev.h b/usr/src/uts/common/fs/zfs/sys/vdev.h
index 5a7836612b..043ba6dd3b 100644
--- a/usr/src/uts/common/fs/zfs/sys/vdev.h
+++ b/usr/src/uts/common/fs/zfs/sys/vdev.h
@@ -21,7 +21,7 @@
 
 /*
  * Copyright (c) 2005, 2010, Oracle and/or its affiliates. All rights reserved.
- * Copyright (c) 2012 by Delphix. All rights reserved.
+ * Copyright (c) 2013 by Delphix. All rights reserved.
  */
 
 #ifndef _SYS_VDEV_H
@@ -110,7 +110,7 @@ extern boolean_t vdev_accessible(vdev_t *vd, zio_t *zio);
 
 extern void vdev_cache_init(vdev_t *vd);
 extern void vdev_cache_fini(vdev_t *vd);
-extern int vdev_cache_read(zio_t *zio);
+extern boolean_t vdev_cache_read(zio_t *zio);
 extern void vdev_cache_write(zio_t *zio);
 extern void vdev_cache_purge(vdev_t *vd);
 
diff --git a/usr/src/uts/common/fs/zfs/sys/zfeature.h b/usr/src/uts/common/fs/zfs/sys/zfeature.h
index c2ca63f7ca..5abde149a6 100644
--- a/usr/src/uts/common/fs/zfs/sys/zfeature.h
+++ b/usr/src/uts/common/fs/zfs/sys/zfeature.h
@@ -34,6 +34,10 @@
 extern "C" {
 #endif
 
+#define	VALID_FEATURE_FID(fid)	((fid) >= 0 && (fid) < SPA_FEATURES)
+#define	VALID_FEATURE_OR_NONE(fid)	((fid) == SPA_FEATURE_NONE ||	\
+    VALID_FEATURE_FID(fid))
+
 struct spa;
 struct dmu_tx;
 struct objset;
@@ -45,6 +49,8 @@ extern void spa_feature_incr(struct spa *, spa_feature_t, struct dmu_tx *);
 extern void spa_feature_decr(struct spa *, spa_feature_t, struct dmu_tx *);
 extern boolean_t spa_feature_is_enabled(struct spa *, spa_feature_t);
 extern boolean_t spa_feature_is_active(struct spa *, spa_feature_t);
+extern boolean_t spa_feature_enabled_txg(spa_t *spa, spa_feature_t fid,
+    uint64_t *txg);
 extern uint64_t spa_feature_refcount(spa_t *, spa_feature_t, uint64_t);
 extern boolean_t spa_features_check(spa_t *, boolean_t, nvlist_t *, nvlist_t *);
 
@@ -53,6 +59,8 @@ extern boolean_t spa_features_check(spa_t *, boolean_t, nvlist_t *, nvlist_t *);
  * use the above interfaces.
  */
 extern int feature_get_refcount(struct spa *, zfeature_info_t *, uint64_t *);
+extern int feature_get_refcount_from_disk(spa_t *spa, zfeature_info_t *feature,
+    uint64_t *res);
 extern void feature_enable_sync(struct spa *, zfeature_info_t *,
     struct dmu_tx *);
 extern void feature_sync(struct spa *, zfeature_info_t *, uint64_t,
diff --git a/usr/src/uts/common/fs/zfs/vdev_cache.c b/usr/src/uts/common/fs/zfs/vdev_cache.c
index 800641e61f..678c4e40ea 100644
--- a/usr/src/uts/common/fs/zfs/vdev_cache.c
+++ b/usr/src/uts/common/fs/zfs/vdev_cache.c
@@ -248,9 +248,9 @@ vdev_cache_fill(zio_t *fio)
 }
 
 /*
- * Read data from the cache.  Returns 0 on cache hit, errno on a miss.
+ * Read data from the cache.  Returns B_TRUE cache hit, B_FALSE on miss.
  */
-int
+boolean_t
 vdev_cache_read(zio_t *zio)
 {
 	vdev_cache_t *vc = &zio->io_vd->vdev_cache;
@@ -262,16 +262,16 @@ vdev_cache_read(zio_t *zio)
 	ASSERT(zio->io_type == ZIO_TYPE_READ);
 
 	if (zio->io_flags & ZIO_FLAG_DONT_CACHE)
-		return (SET_ERROR(EINVAL));
+		return (B_FALSE);
 
 	if (zio->io_size > zfs_vdev_cache_max)
-		return (SET_ERROR(EOVERFLOW));
+		return (B_FALSE);
 
 	/*
 	 * If the I/O straddles two or more cache blocks, don't cache it.
 	 */
 	if (P2BOUNDARY(zio->io_offset, zio->io_size, VCBS))
-		return (SET_ERROR(EXDEV));
+		return (B_FALSE);
 
 	ASSERT(cache_phase + zio->io_size <= VCBS);
 
@@ -283,7 +283,7 @@ vdev_cache_read(zio_t *zio)
 	if (ve != NULL) {
 		if (ve->ve_missed_update) {
 			mutex_exit(&vc->vc_lock);
-			return (SET_ERROR(ESTALE));
+			return (B_FALSE);
 		}
 
 		if ((fio = ve->ve_fill_io) != NULL) {
@@ -291,7 +291,7 @@ vdev_cache_read(zio_t *zio)
 			zio_add_child(zio, fio);
 			mutex_exit(&vc->vc_lock);
 			VDCSTAT_BUMP(vdc_stat_delegations);
-			return (0);
+			return (B_TRUE);
 		}
 
 		vdev_cache_hit(vc, ve, zio);
@@ -299,14 +299,14 @@ vdev_cache_read(zio_t *zio)
 
 		mutex_exit(&vc->vc_lock);
 		VDCSTAT_BUMP(vdc_stat_hits);
-		return (0);
+		return (B_TRUE);
 	}
 
 	ve = vdev_cache_allocate(zio);
 
 	if (ve == NULL) {
 		mutex_exit(&vc->vc_lock);
-		return (SET_ERROR(ENOMEM));
+		return (B_FALSE);
 	}
 
 	fio = zio_vdev_delegated_io(zio->io_vd, cache_offset,
@@ -321,7 +321,7 @@ vdev_cache_read(zio_t *zio)
 	zio_nowait(fio);
 	VDCSTAT_BUMP(vdc_stat_misses);
 
-	return (0);
+	return (B_TRUE);
 }
 
 /*
diff --git a/usr/src/uts/common/fs/zfs/vdev_disk.c b/usr/src/uts/common/fs/zfs/vdev_disk.c
index 5cc9d9f226..22e376d3ea 100644
--- a/usr/src/uts/common/fs/zfs/vdev_disk.c
+++ b/usr/src/uts/common/fs/zfs/vdev_disk.c
@@ -262,8 +262,6 @@ vdev_disk_get_space(vdev_t *vd, uint64_t capacity, uint_t blksz)
 	    FKIOCTL, kcred, NULL) == 0) {
 		uint64_t efi_altern_lba = LE_64(efi->efi_gpt_AlternateLBA);
 
-		zfs_dbgmsg("vdev %s, capacity %llu, altern lba %llu",
-		    vd->vdev_path, capacity, efi_altern_lba);
 		if (capacity > efi_altern_lba)
 			avail_space = (capacity - efi_altern_lba) * blksz;
 	}
diff --git a/usr/src/uts/common/fs/zfs/zfeature.c b/usr/src/uts/common/fs/zfs/zfeature.c
index 62a88714e0..e69fcd3730 100644
--- a/usr/src/uts/common/fs/zfs/zfeature.c
+++ b/usr/src/uts/common/fs/zfs/zfeature.c
@@ -216,6 +216,8 @@ spa_features_check(spa_t *spa, boolean_t for_write,
 }
 
 /*
+ * Use an in-memory cache of feature refcounts for quick retrieval.
+ *
  * Note: well-designed features will not need to use this; they should
  * use spa_feature_is_enabled() and spa_feature_is_active() instead.
  * However, this is non-static for zdb and zhack.
@@ -223,6 +225,24 @@ spa_features_check(spa_t *spa, boolean_t for_write,
 int
 feature_get_refcount(spa_t *spa, zfeature_info_t *feature, uint64_t *res)
 {
+	ASSERT(VALID_FEATURE_FID(feature->fi_feature));
+	if (spa->spa_feat_refcount_cache[feature->fi_feature] ==
+	    SPA_FEATURE_DISABLED) {
+		return (SET_ERROR(ENOTSUP));
+	}
+	*res = spa->spa_feat_refcount_cache[feature->fi_feature];
+	return (0);
+}
+
+/*
+ * Note: well-designed features will not need to use this; they should
+ * use spa_feature_is_enabled() and spa_feature_is_active() instead.
+ * However, this is non-static for zdb and zhack.
+ */
+int
+feature_get_refcount_from_disk(spa_t *spa, zfeature_info_t *feature,
+    uint64_t *res)
+{
 	int err;
 	uint64_t refcount;
 	uint64_t zapobj = feature->fi_can_readonly ?
@@ -247,6 +267,26 @@ feature_get_refcount(spa_t *spa, zfeature_info_t *feature, uint64_t *res)
 	return (0);
 }
 
+
+static int
+feature_get_enabled_txg(spa_t *spa, zfeature_info_t *feature, uint64_t *res) {
+	uint64_t enabled_txg_obj = spa->spa_feat_enabled_txg_obj;
+
+	ASSERT(zfeature_depends_on(feature->fi_feature,
+	    SPA_FEATURE_ENABLED_TXG));
+
+	if (!spa_feature_is_enabled(spa, feature->fi_feature)) {
+		return (SET_ERROR(ENOTSUP));
+	}
+
+	ASSERT(enabled_txg_obj != 0);
+
+	VERIFY0(zap_lookup(spa->spa_meta_objset, spa->spa_feat_enabled_txg_obj,
+	    feature->fi_guid, sizeof (uint64_t), 1, res));
+
+	return (0);
+}
+
 /*
  * This function is non-static for zhack; it should otherwise not be used
  * outside this file.
@@ -255,16 +295,31 @@ void
 feature_sync(spa_t *spa, zfeature_info_t *feature, uint64_t refcount,
     dmu_tx_t *tx)
 {
+	ASSERT(VALID_FEATURE_OR_NONE(feature->fi_feature));
 	uint64_t zapobj = feature->fi_can_readonly ?
 	    spa->spa_feat_for_write_obj : spa->spa_feat_for_read_obj;
 
 	VERIFY0(zap_update(spa->spa_meta_objset, zapobj, feature->fi_guid,
 	    sizeof (uint64_t), 1, &refcount, tx));
 
+	/*
+	 * feature_sync is called directly from zhack, allowing the
+	 * creation of arbitrary features whose fi_feature field may
+	 * be greater than SPA_FEATURES. When called from zhack, the
+	 * zfeature_info_t object's fi_feature field will be set to
+	 * SPA_FEATURE_NONE.
+	 */
+	if (feature->fi_feature != SPA_FEATURE_NONE) {
+		uint64_t *refcount_cache =
+		    &spa->spa_feat_refcount_cache[feature->fi_feature];
+		VERIFY3U(*refcount_cache, ==,
+		    atomic_swap_64(refcount_cache, refcount));
+	}
+
 	if (refcount == 0)
 		spa_deactivate_mos_feature(spa, feature->fi_guid);
 	else if (feature->fi_mos)
-		spa_activate_mos_feature(spa, feature->fi_guid);
+		spa_activate_mos_feature(spa, feature->fi_guid, tx);
 }
 
 /*
@@ -274,6 +329,7 @@ feature_sync(spa_t *spa, zfeature_info_t *feature, uint64_t refcount,
 void
 feature_enable_sync(spa_t *spa, zfeature_info_t *feature, dmu_tx_t *tx)
 {
+	uint64_t initial_refcount = feature->fi_activate_on_enable ? 1 : 0;
 	uint64_t zapobj = feature->fi_can_readonly ?
 	    spa->spa_feat_for_write_obj : spa->spa_feat_for_read_obj;
 
@@ -293,7 +349,24 @@ feature_enable_sync(spa_t *spa, zfeature_info_t *feature, dmu_tx_t *tx)
 	VERIFY0(zap_update(spa->spa_meta_objset, spa->spa_feat_desc_obj,
 	    feature->fi_guid, 1, strlen(feature->fi_desc) + 1,
 	    feature->fi_desc, tx));
-	feature_sync(spa, feature, 0, tx);
+
+	feature_sync(spa, feature, initial_refcount, tx);
+
+	if (spa_feature_is_enabled(spa, SPA_FEATURE_ENABLED_TXG)) {
+		uint64_t enabling_txg = dmu_tx_get_txg(tx);
+
+		if (spa->spa_feat_enabled_txg_obj == 0ULL) {
+			spa->spa_feat_enabled_txg_obj =
+			    zap_create_link(spa->spa_meta_objset,
+			    DMU_OTN_ZAP_METADATA, DMU_POOL_DIRECTORY_OBJECT,
+			    DMU_POOL_FEATURE_ENABLED_TXG, tx);
+		}
+		spa_feature_incr(spa, SPA_FEATURE_ENABLED_TXG, tx);
+
+		VERIFY0(zap_add(spa->spa_meta_objset,
+		    spa->spa_feat_enabled_txg_obj, feature->fi_guid,
+		    sizeof (uint64_t), 1, &enabling_txg, tx));
+	}
 }
 
 static void
@@ -305,15 +378,14 @@ feature_do_action(spa_t *spa, spa_feature_t fid, feature_action_t action,
 	uint64_t zapobj = feature->fi_can_readonly ?
 	    spa->spa_feat_for_write_obj : spa->spa_feat_for_read_obj;
 
-	ASSERT3U(fid, <, SPA_FEATURES);
+	ASSERT(VALID_FEATURE_FID(fid));
 	ASSERT(0 != zapobj);
 	ASSERT(zfeature_is_valid_guid(feature->fi_guid));
 
 	ASSERT(dmu_tx_is_syncing(tx));
 	ASSERT3U(spa_version(spa), >=, SPA_VERSION_FEATURES);
 
-	VERIFY0(zap_lookup(spa->spa_meta_objset, zapobj, feature->fi_guid,
-	    sizeof (uint64_t), 1, &refcount));
+	VERIFY3U(feature_get_refcount(spa, feature, &refcount), !=, ENOTSUP);
 
 	switch (action) {
 	case FEATURE_ACTION_INCR:
@@ -360,7 +432,7 @@ void
 spa_feature_enable(spa_t *spa, spa_feature_t fid, dmu_tx_t *tx)
 {
 	ASSERT3U(spa_version(spa), >=, SPA_VERSION_FEATURES);
-	ASSERT3U(fid, <, SPA_FEATURES);
+	ASSERT(VALID_FEATURE_FID(fid));
 	feature_enable_sync(spa, &spa_feature_table[fid], tx);
 }
 
@@ -382,7 +454,7 @@ spa_feature_is_enabled(spa_t *spa, spa_feature_t fid)
 	int err;
 	uint64_t refcount;
 
-	ASSERT3U(fid, <, SPA_FEATURES);
+	ASSERT(VALID_FEATURE_FID(fid));
 	if (spa_version(spa) < SPA_VERSION_FEATURES)
 		return (B_FALSE);
 
@@ -397,7 +469,7 @@ spa_feature_is_active(spa_t *spa, spa_feature_t fid)
 	int err;
 	uint64_t refcount;
 
-	ASSERT3U(fid, <, SPA_FEATURES);
+	ASSERT(VALID_FEATURE_FID(fid));
 	if (spa_version(spa) < SPA_VERSION_FEATURES)
 		return (B_FALSE);
 
@@ -405,3 +477,26 @@ spa_feature_is_active(spa_t *spa, spa_feature_t fid)
 	ASSERT(err == 0 || err == ENOTSUP);
 	return (err == 0 && refcount > 0);
 }
+
+/*
+ * For the feature specified by fid (which must depend on
+ * SPA_FEATURE_ENABLED_TXG), return the TXG at which it was enabled in the
+ * OUT txg argument.
+ *
+ * Returns B_TRUE if the feature is enabled, in which case txg will be filled
+ * with the transaction group in which the specified feature was enabled.
+ * Returns B_FALSE otherwise (i.e. if the feature is not enabled).
+ */
+boolean_t
+spa_feature_enabled_txg(spa_t *spa, spa_feature_t fid, uint64_t *txg) {
+	int err;
+
+	ASSERT(VALID_FEATURE_FID(fid));
+	if (spa_version(spa) < SPA_VERSION_FEATURES)
+		return (B_FALSE);
+
+	err = feature_get_enabled_txg(spa, &spa_feature_table[fid], txg);
+	ASSERT(err == 0 || err == ENOTSUP);
+
+	return (err == 0);
+}
diff --git a/usr/src/uts/common/fs/zfs/zfs_znode.c b/usr/src/uts/common/fs/zfs/zfs_znode.c
index 3a3eee52be..d441faf96d 100644
--- a/usr/src/uts/common/fs/zfs/zfs_znode.c
+++ b/usr/src/uts/common/fs/zfs/zfs_znode.c
@@ -769,7 +769,6 @@ zfs_mknode(znode_t *dzp, vattr_t *vap, dmu_tx_t *tx, cred_t *cr,
 	dmu_buf_t	*db;
 	timestruc_t	now;
 	uint64_t	gen, obj;
-	int		err;
 	int		bonuslen;
 	sa_handle_t	*sa_hdl;
 	dmu_object_type_t obj_type;
@@ -804,10 +803,9 @@ zfs_mknode(znode_t *dzp, vattr_t *vap, dmu_tx_t *tx, cred_t *cr,
 	 */
 	if (vap->va_type == VDIR) {
 		if (zfsvfs->z_replay) {
-			err = zap_create_claim_norm(zfsvfs->z_os, obj,
+			VERIFY0(zap_create_claim_norm(zfsvfs->z_os, obj,
 			    zfsvfs->z_norm, DMU_OT_DIRECTORY_CONTENTS,
-			    obj_type, bonuslen, tx);
-			ASSERT0(err);
+			    obj_type, bonuslen, tx));
 		} else {
 			obj = zap_create_norm(zfsvfs->z_os,
 			    zfsvfs->z_norm, DMU_OT_DIRECTORY_CONTENTS,
@@ -815,10 +813,9 @@ zfs_mknode(znode_t *dzp, vattr_t *vap, dmu_tx_t *tx, cred_t *cr,
 		}
 	} else {
 		if (zfsvfs->z_replay) {
-			err = dmu_object_claim(zfsvfs->z_os, obj,
+			VERIFY0(dmu_object_claim(zfsvfs->z_os, obj,
 			    DMU_OT_PLAIN_FILE_CONTENTS, 0,
-			    obj_type, bonuslen, tx);
-			ASSERT0(err);
+			    obj_type, bonuslen, tx));
 		} else {
 			obj = dmu_object_alloc(zfsvfs->z_os,
 			    DMU_OT_PLAIN_FILE_CONTENTS, 0,
@@ -999,8 +996,7 @@ zfs_mknode(znode_t *dzp, vattr_t *vap, dmu_tx_t *tx, cred_t *cr,
 
 	if (obj_type == DMU_OT_ZNODE ||
 	    acl_ids->z_aclp->z_version < ZFS_ACL_VERSION_FUID) {
-		err = zfs_aclset_common(*zpp, acl_ids->z_aclp, cr, tx);
-		ASSERT0(err);
+		VERIFY0(zfs_aclset_common(*zpp, acl_ids->z_aclp, cr, tx));
 	}
 	ZFS_OBJ_HOLD_EXIT(zfsvfs, obj);
 }
diff --git a/usr/src/uts/common/fs/zfs/zil.c b/usr/src/uts/common/fs/zfs/zil.c
index 5de969af7d..17b22a0c8f 100644
--- a/usr/src/uts/common/fs/zfs/zil.c
+++ b/usr/src/uts/common/fs/zfs/zil.c
@@ -371,7 +371,8 @@ zil_claim_log_block(zilog_t *zilog, blkptr_t *bp, void *tx, uint64_t first_txg)
 	 * Claim log block if not already committed and not already claimed.
 	 * If tx == NULL, just verify that the block is claimable.
 	 */
-	if (bp->blk_birth < first_txg || zil_bp_tree_add(zilog, bp) != 0)
+	if (BP_IS_HOLE(bp) || bp->blk_birth < first_txg ||
+	    zil_bp_tree_add(zilog, bp) != 0)
 		return (0);
 
 	return (zio_wait(zio_claim(NULL, zilog->zl_spa,
@@ -421,7 +422,8 @@ zil_free_log_record(zilog_t *zilog, lr_t *lrc, void *tx, uint64_t claim_txg)
 	 * If we previously claimed it, we need to free it.
 	 */
 	if (claim_txg != 0 && lrc->lrc_txtype == TX_WRITE &&
-	    bp->blk_birth >= claim_txg && zil_bp_tree_add(zilog, bp) == 0)
+	    bp->blk_birth >= claim_txg && zil_bp_tree_add(zilog, bp) == 0 &&
+	    !BP_IS_HOLE(bp))
 		zio_free(zilog->zl_spa, dmu_tx_get_txg(tx), bp);
 
 	return (0);
diff --git a/usr/src/uts/common/fs/zfs/zio.c b/usr/src/uts/common/fs/zfs/zio.c
index 71bd86dba7..1c8765ff94 100644
--- a/usr/src/uts/common/fs/zfs/zio.c
+++ b/usr/src/uts/common/fs/zfs/zio.c
@@ -36,6 +36,7 @@
 #include <sys/dmu_objset.h>
 #include <sys/arc.h>
 #include <sys/ddt.h>
+#include <sys/zfeature.h>
 
 /*
  * ==========================================================================
@@ -1022,7 +1023,7 @@ zio_write_bp_init(zio_t *zio)
 		BP_ZERO(bp);
 	}
 
-	if (bp->blk_birth == zio->io_txg) {
+	if (!BP_IS_HOLE(bp) && bp->blk_birth == zio->io_txg) {
 		/*
 		 * We're rewriting an existing block, which means we're
 		 * working on behalf of spa_sync().  For spa_sync() to
@@ -1066,7 +1067,8 @@ zio_write_bp_init(zio_t *zio)
 	 * spa_sync() to allocate new blocks, but force rewrites after that.
 	 * There should only be a handful of blocks after pass 1 in any case.
 	 */
-	if (bp->blk_birth == zio->io_txg && BP_GET_PSIZE(bp) == psize &&
+	if (!BP_IS_HOLE(bp) && bp->blk_birth == zio->io_txg &&
+	    BP_GET_PSIZE(bp) == psize &&
 	    pass >= zfs_sync_pass_rewrite) {
 		ASSERT(psize != 0);
 		enum zio_stage gang_stages = zio->io_pipeline & ZIO_GANG_STAGES;
@@ -1078,15 +1080,22 @@ zio_write_bp_init(zio_t *zio)
 	}
 
 	if (psize == 0) {
+		if (zio->io_bp_orig.blk_birth != 0 &&
+		    spa_feature_is_active(spa, SPA_FEATURE_HOLE_BIRTH)) {
+			BP_SET_LSIZE(bp, lsize);
+			BP_SET_TYPE(bp, zp->zp_type);
+			BP_SET_LEVEL(bp, zp->zp_level);
+			BP_SET_BIRTH(bp, zio->io_txg, 0);
+		}
 		zio->io_pipeline = ZIO_INTERLOCK_PIPELINE;
 	} else {
 		ASSERT(zp->zp_checksum != ZIO_CHECKSUM_GANG_HEADER);
 		BP_SET_LSIZE(bp, lsize);
+		BP_SET_TYPE(bp, zp->zp_type);
+		BP_SET_LEVEL(bp, zp->zp_level);
 		BP_SET_PSIZE(bp, psize);
 		BP_SET_COMPRESS(bp, compress);
 		BP_SET_CHECKSUM(bp, zp->zp_checksum);
-		BP_SET_TYPE(bp, zp->zp_type);
-		BP_SET_LEVEL(bp, zp->zp_level);
 		BP_SET_DEDUP(bp, zp->zp_dedup);
 		BP_SET_BYTEORDER(bp, ZFS_HOST_BYTEORDER);
 		if (zp->zp_dedup) {
@@ -2484,7 +2493,7 @@ zio_vdev_io_start(zio_t *zio)
 	if (vd->vdev_ops->vdev_op_leaf &&
 	    (zio->io_type == ZIO_TYPE_READ || zio->io_type == ZIO_TYPE_WRITE)) {
 
-		if (zio->io_type == ZIO_TYPE_READ && vdev_cache_read(zio) == 0)
+		if (zio->io_type == ZIO_TYPE_READ && vdev_cache_read(zio))
 			return (ZIO_PIPELINE_CONTINUE);
 
 		if ((zio = vdev_queue_io(zio)) == NULL)
diff --git a/usr/src/uts/common/fs/zfs/zvol.c b/usr/src/uts/common/fs/zfs/zvol.c
index 2984eeef4b..36ccbe0049 100644
--- a/usr/src/uts/common/fs/zfs/zvol.c
+++ b/usr/src/uts/common/fs/zfs/zvol.c
@@ -250,7 +250,8 @@ zvol_map_block(spa_t *spa, zilog_t *zilog, const blkptr_t *bp,
 	zvol_extent_t *ze;
 	int bs = ma->ma_zv->zv_volblocksize;
 
-	if (bp == NULL || zb->zb_object != ZVOL_OBJ || zb->zb_level != 0)
+	if (BP_IS_HOLE(bp) ||
+	    zb->zb_object != ZVOL_OBJ || zb->zb_level != 0)
 		return (0);
 
 	VERIFY3U(ma->ma_blks, ==, zb->zb_blkid);