diff --git a/Makefile b/Makefile
index fc0ecb3..450c7d7 100644
--- a/Makefile
+++ b/Makefile
@@ -7,7 +7,9 @@ SOURCE=\
 	endian_utils.cc \
 	error_set.cc \
 	hex_dump.cc \
+	human_readable_format.cc \
 	metadata.cc \
+	metadata_dump.cc \
 	metadata_disk_structures.cc \
 	space_map_disk.cc \
 	transaction_manager.cc
diff --git a/block.tcc b/block.tcc
index b5b66f1..19eb18f 100644
--- a/block.tcc
+++ b/block.tcc
@@ -57,7 +57,8 @@ block_manager<BlockSize>::block_manager(std::string const &path, block_address n
 	  superblock_count_(0),
 	  ordinary_count_(0)
 {
-	fd_ = ::open(path.c_str(), O_RDWR | O_CREAT, 0666);
+	//fd_ = ::open(path.c_str(), O_RDWR | O_CREAT, 0666);
+	fd_ = ::open(path.c_str(), O_RDONLY, 0666);
 	if (fd_ < 0)
 		throw std::runtime_error("couldn't open file");
 }
diff --git a/btree.h b/btree.h
index 722cb25..40f1c60 100644
--- a/btree.h
+++ b/btree.h
@@ -332,12 +332,14 @@ namespace persistent_data {
 
 			// The bool return values indicate whether the walk
 			// should be continued into sub trees of the node (true == continue).
-			virtual bool visit_internal(unsigned level, boost::optional<uint64_t> key,
+			virtual bool visit_internal(unsigned level, bool sub_root, boost::optional<uint64_t> key,
 						    internal_node const &n) = 0;
-			virtual bool visit_internal_leaf(unsigned level, boost::optional<uint64_t> key,
+			virtual bool visit_internal_leaf(unsigned level, bool sub_root, boost::optional<uint64_t> key,
 							 internal_node const &n) = 0;
-			virtual bool visit_leaf(unsigned level, boost::optional<uint64_t> key,
+			virtual bool visit_leaf(unsigned level, bool sub_root, boost::optional<uint64_t> key,
 						leaf_node const &n) = 0;
+
+			virtual void visit_complete() {}
 		};
 
 		// Walks the tree in depth first order
@@ -366,7 +368,7 @@ namespace persistent_data {
 				int *index);
 
 		void walk_tree(typename visitor::ptr visitor,
-			       unsigned level, boost::optional<uint64_t> key,
+			       unsigned level, bool root, boost::optional<uint64_t> key,
 			       block_address b) const;
 
 		typename persistent_data::transaction_manager::ptr tm_;
diff --git a/btree.tcc b/btree.tcc
index 97d1978..fed0d1a 100644
--- a/btree.tcc
+++ b/btree.tcc
@@ -599,14 +599,16 @@ template <unsigned Levels, typename ValueTraits>
 void
 btree<Levels, ValueTraits>::visit(typename visitor::ptr visitor) const
 {
-	walk_tree(visitor, 0, boost::optional<uint64_t>(), root_);
+	walk_tree(visitor, 0, true, boost::optional<uint64_t>(), root_);
+	visitor->visit_complete();
 }
 
 template <unsigned Levels, typename ValueTraits>
 void
 btree<Levels, ValueTraits>::
 walk_tree(typename visitor::ptr visitor,
-	  unsigned level, boost::optional<uint64_t> key,
+	  unsigned level, bool sub_root,
+	  boost::optional<uint64_t> key,
 	  block_address b) const
 {
 	using namespace btree_detail;
@@ -614,18 +616,18 @@ walk_tree(typename visitor::ptr visitor,
 	read_ref blk = tm_->read_lock(b);
 	internal_node o = to_node<uint64_traits>(blk);
 	if (o.get_type() == INTERNAL) {
-		if (visitor->visit_internal(level, key, o))
+		if (visitor->visit_internal(level, sub_root, key, o))
 			for (unsigned i = 0; i < o.get_nr_entries(); i++)
-				walk_tree(visitor, level, o.key_at(i), o.value_at(i));
+				walk_tree(visitor, level, false, o.key_at(i), o.value_at(i));
 
 	} else if (level < Levels - 1) {
-		if (visitor->visit_internal_leaf(level, key, o))
+		if (visitor->visit_internal_leaf(level, sub_root, key, o))
 			for (unsigned i = 0; i < o.get_nr_entries(); i++)
-				walk_tree(visitor, level + 1, boost::optional<uint64_t>(), o.value_at(i));
+				walk_tree(visitor, level + 1, true, boost::optional<uint64_t>(o.key_at(i)), o.value_at(i));
 
 	} else {
 		leaf_node ov = to_node<ValueTraits>(blk);
-		visitor->visit_leaf(level, key, ov);
+		visitor->visit_leaf(level, sub_root, key, ov);
 	}
 }
 
diff --git a/btree_checker.h b/btree_checker.h
index 4e238df..3c0f028 100644
--- a/btree_checker.h
+++ b/btree_checker.h
@@ -75,6 +75,7 @@ namespace persistent_data {
 		}
 
 		bool visit_internal(unsigned level,
+				    bool sub_root,
 				    optional<uint64_t> key,
 				    btree_detail::node_ref<uint64_traits> const &n) {
 			if (already_visited(n))
@@ -94,6 +95,7 @@ namespace persistent_data {
 		}
 
 		bool visit_internal_leaf(unsigned level,
+					 bool sub_root,
 					 optional<uint64_t> key,
 					 btree_detail::node_ref<uint64_traits> const &n) {
 			if (already_visited(n))
@@ -115,6 +117,7 @@ namespace persistent_data {
 		}
 
 		bool visit_leaf(unsigned level,
+				bool sub_root,
 				optional<uint64_t> key,
 				btree_detail::node_ref<ValueTraits> const &n) {
 			if (already_visited(n))
diff --git a/emitter.h b/emitter.h
new file mode 100644
index 0000000..f8aee5f
--- /dev/null
+++ b/emitter.h
@@ -0,0 +1,53 @@
+#ifndef EMITTER_H
+#define EMITTER_H
+
+#include <boost/shared_ptr.hpp>
+#include <string>
+#include <stdint.h>
+
+//----------------------------------------------------------------
+
+namespace thin_provisioning {
+
+	//------------------------------------------------
+	// Here's a little grammar for how this all hangs together:
+	//
+	// superblock := <uuid> <time> <trans_id> <data_block_size> device*
+	// device := <dev id> <transaction id> <creation time> <snap time> <binding>
+        // binding := (<identifier> | <mapping>)*
+	// mapping := range_map | single_map
+	// range_map := <origin_begin> <origin_end> <data_begin>
+	// single_map := <origin> <data>
+	// named_mapping := <identifier> <mapping>
+	//------------------------------------------------
+	class emitter {
+	public:
+		typedef boost::shared_ptr<emitter> ptr;
+
+		virtual ~emitter() {}
+
+		virtual void begin_superblock(std::string const &uuid,
+					      uint64_t time,
+					      uint64_t trans_id,
+					      uint32_t data_block_size) = 0;
+		virtual void end_superblock() = 0;
+
+		virtual void begin_device(uint32_t dev_id,
+					  uint64_t mapped_blocks,
+					  uint64_t trans_id,
+					  uint64_t creation_time,
+					  uint64_t snap_time) = 0;
+		virtual void end_device() = 0;
+
+		virtual void begin_named_mapping(std::string const &name) = 0;
+		virtual void end_named_mapping() = 0;
+
+		virtual void identifier(std::string const &name) = 0;
+		virtual void range_map(uint64_t origin_begin, uint64_t data_begin, uint64_t len) = 0;
+		virtual void single_map(uint64_t origin_block, uint64_t ddata_block) = 0;
+	};
+}
+
+//----------------------------------------------------------------
+
+#endif
diff --git a/human_readable_format.cc b/human_readable_format.cc
new file mode 100644
index 0000000..5fb279d
--- /dev/null
+++ b/human_readable_format.cc
@@ -0,0 +1,89 @@
+#include "human_readable_format.h"
+
+#include <iostream>
+
+using namespace std;
+using namespace thin_provisioning;
+
+//----------------------------------------------------------------
+
+namespace {
+	class hr_emitter : public emitter {
+	public:
+		hr_emitter(ostream &out)
+			: out_(out) {
+		}
+
+		void begin_superblock(string const &uuid,
+				      uint64_t time,
+				      uint64_t trans_id,
+				      uint32_t data_block_size) {
+			out_ << "begin superblock: " << uuid
+			     << ", " << time
+			     << ", " << trans_id
+			     << ", " << data_block_size
+			     << endl;
+		}
+
+		void end_superblock() {
+			out_ << "end superblock" << endl;
+		}
+
+		void begin_device(uint32_t dev_id,
+				  uint64_t mapped_blocks,
+				  uint64_t trans_id,
+				  uint64_t creation_time,
+				  uint64_t snap_time) {
+			out_ << "device: " << dev_id << endl
+			     << "mapped_blocks: " << mapped_blocks << endl
+			     << "transaction: " << trans_id << endl
+			     << "creation time: " << creation_time << endl
+			     << "snap time: " << snap_time << endl;
+		}
+
+		void end_device() {
+			out_ << endl;
+		}
+
+		void begin_named_mapping(string const &name) {
+			out_ << "begin named mapping"
+			     << endl;
+		}
+
+		void end_named_mapping() {
+			out_ << "end named mapping"
+			     << endl;
+		}
+
+		void identifier(string const &name) {
+			out_ << "identifier: " << name << endl;
+		}
+
+		void range_map(uint64_t origin_begin, uint64_t data_begin, uint64_t len) {
+			out_ << "    (" << origin_begin
+			     << ".." << origin_begin + len - 1
+			     << ") -> (" << data_begin
+			     << ".." << data_begin + len - 1
+			     << ")" << endl;
+		}
+
+		void single_map(uint64_t origin_block, uint64_t data_block) {
+			out_ << "    " << origin_block
+			     << " -> " << data_block
+			     << endl;
+		}
+
+	private:
+		ostream &out_;
+	};
+}
+
+//----------------------------------------------------------------
+
+thin_provisioning::emitter::ptr
+thin_provisioning::create_human_readable_emitter(ostream &out)
+{
+	return emitter::ptr(new hr_emitter(out));
+}
+
+//----------------------------------------------------------------
diff --git a/human_readable_format.h b/human_readable_format.h
new file mode 100644
index 0000000..925ee42
--- /dev/null
+++ b/human_readable_format.h
@@ -0,0 +1,16 @@
+#ifndef HUMAN_READABLE_H
+#define HUMAN_READABLE_H
+
+#include "emitter.h"
+
+#include <iosfwd>
+
+//----------------------------------------------------------------
+
+namespace thin_provisioning {
+	emitter::ptr create_human_readable_emitter(std::ostream &out);
+}
+
+//----------------------------------------------------------------
+
+#endif
diff --git a/metadata.cc b/metadata.cc
index 80f42bb..41443ab 100644
--- a/metadata.cc
+++ b/metadata.cc
@@ -105,10 +105,11 @@ namespace {
 		// Sharing can only occur in level 1 nodes.
 		// FIXME: not true once we start having held roots.
 		bool visit_internal_leaf(unsigned level,
+					 bool sub_root,
 					 optional<uint64_t> key,
 					 btree_detail::node_ref<uint64_traits> const &n) {
 
-			bool r = btree_checker<2, block_traits>::visit_internal_leaf(level, key, n);
+			bool r = btree_checker<2, block_traits>::visit_internal_leaf(level, sub_root, key, n);
 			if (!r && level == 0) {
 				throw runtime_error("unexpected sharing in level 0 of mapping tree.");
 			}
@@ -120,9 +121,10 @@ namespace {
 		}
 
 		bool visit_leaf(unsigned level,
+				bool sub_root,
 				optional<uint64_t> key,
 				btree_detail::node_ref<block_traits> const &n) {
-			bool r = btree_checker<2, block_traits>::visit_leaf(level, key, n);
+			bool r = btree_checker<2, block_traits>::visit_leaf(level, sub_root, key, n);
 
 			if (r)
 				for (unsigned i = 0; i < n.get_nr_entries(); i++)
@@ -149,9 +151,10 @@ namespace {
 		}
 
 		bool visit_leaf(unsigned level,
+				bool sub_root,
 				optional<uint64_t> key,
 				btree_detail::node_ref<device_details_traits> const &n) {
-			bool r = btree_checker<1, device_details_traits>::visit_leaf(level, key, n);
+			bool r = btree_checker<1, device_details_traits>::visit_leaf(level, sub_root, key, n);
 
 			if (r)
 				for (unsigned i = 0; i < n.get_nr_entries(); i++)
diff --git a/metadata_dump.cc b/metadata_dump.cc
new file mode 100644
index 0000000..ae24a15
--- /dev/null
+++ b/metadata_dump.cc
@@ -0,0 +1,153 @@
+#include "metadata.h"
+
+#include "human_readable_format.h"
+
+using namespace persistent_data;
+using namespace thin_provisioning;
+
+//----------------------------------------------------------------
+
+namespace {
+	class mappings_extractor : public btree<2, block_traits>::visitor {
+	public:
+		typedef boost::shared_ptr<mappings_extractor> ptr;
+
+		mappings_extractor(uint64_t dev_id, emitter::ptr e,
+				   space_map::ptr md_sm, space_map::ptr data_sm)
+			: dev_id_(dev_id),
+			  e_(e),
+			  md_sm_(md_sm),
+			  data_sm_(data_sm),
+			  in_range_(false) {
+		}
+
+		bool visit_internal(unsigned level, bool sub_root, boost::optional<uint64_t> key,
+				    btree_detail::node_ref<uint64_traits> const &n) {
+			return (sub_root && key) ? (*key == dev_id_) : true;
+		}
+
+		bool visit_internal_leaf(unsigned level, bool sub_root, boost::optional<uint64_t> key,
+					 btree_detail::node_ref<uint64_traits> const &n) {
+			return true;
+		}
+
+		bool visit_leaf(unsigned level, bool sub_root, boost::optional<uint64_t> maybe_key,
+				btree_detail::node_ref<block_traits> const &n) {
+			for (unsigned i = 0; i < n.get_nr_entries(); i++) {
+				add_mapping(n.key_at(i), n.value_at(i).block_);
+			}
+
+			return true;
+		}
+
+
+		void visit_complete() {
+			end_mapping();
+		}
+
+	private:
+		void start_mapping(uint64_t origin_block, uint64_t dest_block) {
+			origin_start_ = origin_block;
+			dest_start_ = dest_block;
+			len_ = 1;
+			in_range_ = true;
+		}
+
+		void end_mapping() {
+			if (in_range_) {
+				if (len_ == 1)
+					e_->single_map(origin_start_, dest_start_);
+				else
+					e_->range_map(origin_start_, dest_start_, len_);
+
+				in_range_ = false;
+			}
+		}
+
+		void add_mapping(uint64_t origin_block, uint64_t dest_block) {
+			if (!in_range_)
+				start_mapping(origin_block, dest_block);
+
+			else if (origin_block == origin_start_ + len_ &&
+				 dest_block == dest_start_ + len_)
+				len_++;
+
+			else {
+				end_mapping();
+				start_mapping(origin_block, dest_block);
+			}
+		}
+
+		uint64_t dev_id_;
+		emitter::ptr e_;
+		space_map::ptr md_sm_;
+		space_map::ptr data_sm_;
+
+		bool in_range_;
+		uint64_t origin_start_, dest_start_, len_;
+
+	};
+
+	class details_extractor : public btree<1, device_details_traits>::visitor {
+	public:
+		typedef boost::shared_ptr<details_extractor> ptr;
+
+		details_extractor() {
+		}
+
+		bool visit_internal(unsigned level, bool sub_root, boost::optional<uint64_t> key,
+				    btree_detail::node_ref<uint64_traits> const &n) {
+			return true;
+		}
+
+		bool visit_internal_leaf(unsigned level, bool sub_root, boost::optional<uint64_t> key,
+					 btree_detail::node_ref<uint64_traits> const &n) {
+			return true;
+		}
+
+		bool visit_leaf(unsigned level, bool sub_root, boost::optional<uint64_t> maybe_key,
+				btree_detail::node_ref<device_details_traits> const &n) {
+			for (unsigned i = 0; i < n.get_nr_entries(); i++)
+				devices_.insert(make_pair(n.key_at(i), n.value_at(i)));
+
+			return true;
+		}
+
+		map<uint64_t, device_details> const &get_devices() const {
+			return devices_;
+		}
+
+	private:
+		map<uint64_t, device_details> devices_;
+	};
+}
+
+void
+metadata::dump()
+{
+	emitter::ptr e = create_human_readable_emitter(cout);
+
+	details_extractor::ptr de(new details_extractor);
+
+	details_.visit(de);
+	map<uint64_t, device_details> const &devs = de->get_devices();
+
+	map<uint64_t, device_details>::const_iterator it, end = devs.end();
+	for (it = devs.begin(); it != end; ++it) {
+		uint64_t dev_id = it->first;
+		device_details const &dd = it->second;
+
+		e->begin_device(dev_id,
+				dd.mapped_blocks_,
+				dd.transaction_id_,
+				dd.creation_time_,
+				dd.snapshotted_time_);
+
+		mappings_extractor::ptr me(new mappings_extractor(dev_id, e, metadata_sm_, data_sm_));
+		mappings_.visit(me);
+
+		e->end_device();
+	}
+}
+
+//----------------------------------------------------------------
diff --git a/space_map_disk.cc b/space_map_disk.cc
index 59fc67b..74cb2b9 100644
--- a/space_map_disk.cc
+++ b/space_map_disk.cc
@@ -321,9 +321,10 @@ namespace {
 		}
 
 		bool visit_leaf(unsigned level,
+				bool sub_root,
 				optional<uint64_t> key,
 				btree_detail::node_ref<index_entry_traits> const &n) {
-			bool r = btree_checker<1, index_entry_traits>::visit_leaf(level, key, n);
+			bool r = btree_checker<1, index_entry_traits>::visit_leaf(level, sub_root, key, n);
 			if (!r)
 				return r;
 
diff --git a/thin_dump.cc b/thin_dump.cc
index accbe69..52929dd 100644
--- a/thin_dump.cc
+++ b/thin_dump.cc
@@ -12,7 +12,7 @@ namespace {
 	void dump(string const &path) {
 		metadata md(path);
 		//human_readable::ptr emitter(new human_readable);
-		// md.dump();
+		md.dump();
 	}
 
 	void usage(string const &cmd) {