--- /dev/null	Mon May 21 13:12:48 2012
+++ new/usr/src/uts/common/fs/zfs/bptree.c	Mon May 21 13:12:48 2012
@@ -0,0 +1,224 @@
+/*
+ * CDDL HEADER START
+ *
+ * The contents of this file are subject to the terms of the
+ * Common Development and Distribution License (the "License").
+ * You may not use this file except in compliance with the License.
+ *
+ * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
+ * or http://www.opensolaris.org/os/licensing.
+ * See the License for the specific language governing permissions
+ * and limitations under the License.
+ *
+ * When distributing Covered Code, include this CDDL HEADER in each
+ * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
+ * If applicable, add the following below this CDDL HEADER, with the
+ * fields enclosed by brackets "[]" replaced with your own identifying
+ * information: Portions Copyright [yyyy] [name of copyright owner]
+ *
+ * CDDL HEADER END
+ */
+
+/*
+ * Copyright (c) 2012 by Delphix. All rights reserved.
+ */
+
+#include <sys/arc.h>
+#include <sys/bptree.h>
+#include <sys/dmu.h>
+#include <sys/dmu_objset.h>
+#include <sys/dmu_tx.h>
+#include <sys/dmu_traverse.h>
+#include <sys/dsl_dataset.h>
+#include <sys/dsl_dir.h>
+#include <sys/dsl_pool.h>
+#include <sys/dnode.h>
+#include <sys/refcount.h>
+#include <sys/spa.h>
+
+/*
+ * A bptree is a queue of root block pointers from destroyed datasets. When a
+ * dataset is destroyed its root block pointer is put on the end of the pool's
+ * bptree queue so the dataset's blocks can be freed asynchronously by
+ * dsl_scan_sync. This allows the delete operation to finish without traversing
+ * all the dataset's blocks.
+ *
+ * Note that while bt_begin and bt_end are only ever incremented in this code
+ * they are effectively reset to 0 every time the entire bptree is freed because
+ * the bptree's object is destroyed and re-created.
+ */
+
+struct bptree_args {
+	bptree_phys_t *ba_phys;	/* data in bonus buffer, dirtied if freeing */
+	boolean_t ba_free;	/* true if freeing during traversal */
+
+	bptree_itor_t *ba_func;	/* function to call for each blockpointer */
+	void *ba_arg;		/* caller supplied argument to ba_func */
+	dmu_tx_t *ba_tx;	/* caller supplied tx, NULL if not freeing */
+} bptree_args_t;
+
+uint64_t
+bptree_alloc(objset_t *os, dmu_tx_t *tx)
+{
+	uint64_t obj;
+	dmu_buf_t *db;
+	bptree_phys_t *bt;
+
+	obj = dmu_object_alloc(os, DMU_OTN_UINT64_METADATA,
+	    SPA_MAXBLOCKSIZE, DMU_OTN_UINT64_METADATA,
+	    sizeof (bptree_phys_t), tx);
+
+	/*
+	 * Bonus buffer contents are already initialized to 0, but for
+	 * readability we make it explicit.
+	 */
+	VERIFY3U(0, ==, dmu_bonus_hold(os, obj, FTAG, &db));
+	dmu_buf_will_dirty(db, tx);
+	bt = db->db_data;
+	bt->bt_begin = 0;
+	bt->bt_end = 0;
+	bt->bt_bytes = 0;
+	bt->bt_comp = 0;
+	bt->bt_uncomp = 0;
+	dmu_buf_rele(db, FTAG);
+
+	return (obj);
+}
+
+int
+bptree_free(objset_t *os, uint64_t obj, dmu_tx_t *tx)
+{
+	dmu_buf_t *db;
+	bptree_phys_t *bt;
+
+	VERIFY3U(0, ==, dmu_bonus_hold(os, obj, FTAG, &db));
+	bt = db->db_data;
+	ASSERT3U(bt->bt_begin, ==, bt->bt_end);
+	ASSERT3U(bt->bt_bytes, ==, 0);
+	ASSERT3U(bt->bt_comp, ==, 0);
+	ASSERT3U(bt->bt_uncomp, ==, 0);
+	dmu_buf_rele(db, FTAG);
+
+	return (dmu_object_free(os, obj, tx));
+}
+
+void
+bptree_add(objset_t *os, uint64_t obj, blkptr_t *bp, uint64_t birth_txg,
+    uint64_t bytes, uint64_t comp, uint64_t uncomp, dmu_tx_t *tx)
+{
+	dmu_buf_t *db;
+	bptree_phys_t *bt;
+	bptree_entry_phys_t bte;
+
+	/*
+	 * bptree objects are in the pool mos, therefore they can only be
+	 * modified in syncing context. Furthermore, this is only modified
+	 * by the sync thread, so no locking is necessary.
+	 */
+	ASSERT(dmu_tx_is_syncing(tx));
+
+	VERIFY3U(0, ==, dmu_bonus_hold(os, obj, FTAG, &db));
+	bt = db->db_data;
+
+	bte.be_birth_txg = birth_txg;
+	bte.be_bp = *bp;
+	bzero(&bte.be_zb, sizeof (bte.be_zb));
+	dmu_write(os, obj, bt->bt_end * sizeof (bte), sizeof (bte), &bte, tx);
+
+	dmu_buf_will_dirty(db, tx);
+	bt->bt_end++;
+	bt->bt_bytes += bytes;
+	bt->bt_comp += comp;
+	bt->bt_uncomp += uncomp;
+	dmu_buf_rele(db, FTAG);
+}
+
+/* ARGSUSED */
+static int
+bptree_visit_cb(spa_t *spa, zilog_t *zilog, const blkptr_t *bp, arc_buf_t *pbuf,
+    const zbookmark_t *zb, const dnode_phys_t *dnp, void *arg)
+{
+	int err;
+	struct bptree_args *ba = arg;
+
+	if (bp == NULL)
+		return (0);
+
+	err = ba->ba_func(ba->ba_arg, bp, ba->ba_tx);
+	if (err == 0 && ba->ba_free) {
+		ba->ba_phys->bt_bytes -= bp_get_dsize_sync(spa, bp);
+		ba->ba_phys->bt_comp -= BP_GET_PSIZE(bp);
+		ba->ba_phys->bt_uncomp -= BP_GET_UCSIZE(bp);
+	}
+	return (err);
+}
+
+int
+bptree_iterate(objset_t *os, uint64_t obj, boolean_t free, bptree_itor_t func,
+    void *arg, dmu_tx_t *tx)
+{
+	int err;
+	uint64_t i;
+	dmu_buf_t *db;
+	struct bptree_args ba;
+
+	ASSERT(!free || dmu_tx_is_syncing(tx));
+
+	err = dmu_bonus_hold(os, obj, FTAG, &db);
+	if (err != 0)
+		return (err);
+
+	if (free)
+		dmu_buf_will_dirty(db, tx);
+
+	ba.ba_phys = db->db_data;
+	ba.ba_free = free;
+	ba.ba_func = func;
+	ba.ba_arg = arg;
+	ba.ba_tx = tx;
+
+	err = 0;
+	for (i = ba.ba_phys->bt_begin; i < ba.ba_phys->bt_end; i++) {
+		bptree_entry_phys_t bte;
+
+		ASSERT(!free || i == ba.ba_phys->bt_begin);
+
+		err = dmu_read(os, obj, i * sizeof (bte), sizeof (bte),
+		    &bte, DMU_READ_NO_PREFETCH);
+		if (err != 0)
+			break;
+
+		err = traverse_dataset_destroyed(os->os_spa, &bte.be_bp,
+		    bte.be_birth_txg, &bte.be_zb, TRAVERSE_POST,
+		    bptree_visit_cb, &ba);
+		if (free) {
+			ASSERT(err == 0 || err == ERESTART);
+			if (err != 0) {
+				/* save bookmark for future resume */
+				ASSERT3U(bte.be_zb.zb_objset, ==,
+				    ZB_DESTROYED_OBJSET);
+				ASSERT3U(bte.be_zb.zb_level, ==, 0);
+				dmu_write(os, obj, i * sizeof (bte),
+				    sizeof (bte), &bte, tx);
+				break;
+			} else {
+				ba.ba_phys->bt_begin++;
+				(void) dmu_free_range(os, obj,
+				    i * sizeof (bte), sizeof (bte), tx);
+			}
+		}
+	}
+
+	ASSERT(!free || err != 0 || ba.ba_phys->bt_begin == ba.ba_phys->bt_end);
+
+	/* if all blocks are free there should be no used space */
+	if (ba.ba_phys->bt_begin == ba.ba_phys->bt_end) {
+		ASSERT3U(ba.ba_phys->bt_bytes, ==, 0);
+		ASSERT3U(ba.ba_phys->bt_comp, ==, 0);
+		ASSERT3U(ba.ba_phys->bt_uncomp, ==, 0);
+	}
+
+	dmu_buf_rele(db, FTAG);
+
+	return (err);
+}
