+ * Directly assign a provided arc buf to a given dbuf if it's not referenced
+ * by anybody except our caller. Otherwise copy arcbuf's contents to dbuf.
+ */
+void
+dbuf_assign_arcbuf(dmu_buf_impl_t *db, arc_buf_t *buf, dmu_tx_t *tx)
+{
+ ASSERT(!refcount_is_zero(&db->db_holds));
+ ASSERT(db->db_dnode->dn_object != DMU_META_DNODE_OBJECT);
+ ASSERT(db->db_blkid != DB_BONUS_BLKID);
+ ASSERT(db->db_level == 0);
+ ASSERT(DBUF_GET_BUFC_TYPE(db) == ARC_BUFC_DATA);
+ ASSERT(buf != NULL);
+ ASSERT(arc_buf_size(buf) == db->db.db_size);
+ ASSERT(tx->tx_txg != 0);
+
+ arc_return_buf(buf, db);
+ ASSERT(arc_released(buf));
+
+ mutex_enter(&db->db_mtx);
+
+ while (db->db_state == DB_READ || db->db_state == DB_FILL)
+ cv_wait(&db->db_changed, &db->db_mtx);
+
+ ASSERT(db->db_state == DB_CACHED || db->db_state == DB_UNCACHED);
+
+ if (db->db_state == DB_CACHED &&
+ refcount_count(&db->db_holds) - 1 > db->db_dirtycnt) {
+ mutex_exit(&db->db_mtx);
+ (void) dbuf_dirty(db, tx);
+ bcopy(buf->b_data, db->db.db_data, db->db.db_size);
+ VERIFY(arc_buf_remove_ref(buf, db) == 1);
+ return;
+ }
+
+ if (db->db_state == DB_CACHED) {
+ dbuf_dirty_record_t *dr = db->db_last_dirty;
+
+ ASSERT(db->db_buf != NULL);
+ if (dr != NULL && dr->dr_txg == tx->tx_txg) {
+ ASSERT(dr->dt.dl.dr_data == db->db_buf);
+ if (!arc_released(db->db_buf)) {
+ ASSERT(dr->dt.dl.dr_override_state ==
+ DR_OVERRIDDEN);
+ arc_release(db->db_buf, db);
+ }
+ dr->dt.dl.dr_data = buf;
+ VERIFY(arc_buf_remove_ref(db->db_buf, db) == 1);
+ } else if (dr == NULL || dr->dt.dl.dr_data != db->db_buf) {
+ arc_release(db->db_buf, db);
+ VERIFY(arc_buf_remove_ref(db->db_buf, db) == 1);
+ }
+ db->db_buf = NULL;
+ }
+ ASSERT(db->db_buf == NULL);
+ dbuf_set_data(db, buf);
+ db->db_state = DB_FILL;
+ mutex_exit(&db->db_mtx);
+ (void) dbuf_dirty(db, tx);
+ dbuf_fill_done(db, tx);
+}
+
+/*