diff --git a/Makefile.in b/Makefile.in
index ea2bdca..949e30a 100644
--- a/Makefile.in
+++ b/Makefile.in
@@ -126,10 +126,14 @@ TOOLS_SOURCE=\
 	thin-provisioning/thin_trim.cc
 
 DEVTOOLS_SOURCE=\
+	base/command_interpreter.cc \
+	base/output_formatter.cc \
+	caching/cache_debug.cc \
 	caching/devel_commands.cc \
 	era/devel_commands.cc \
 	thin-provisioning/damage_generator.cc \
 	thin-provisioning/devel_commands.cc \
+	thin-provisioning/thin_debug.cc \
 	thin-provisioning/thin_generate_damage.cc \
 	thin-provisioning/thin_generate_mappings.cc \
 	thin-provisioning/thin_generate_metadata.cc \
diff --git a/base/command_interpreter.cc b/base/command_interpreter.cc
new file mode 100644
index 0000000..ce7bd97
--- /dev/null
+++ b/base/command_interpreter.cc
@@ -0,0 +1,88 @@
+#include "base/command_interpreter.h"
+
+using namespace dbg;
+using namespace std;
+
+//----------------------------------------------------------------
+
+namespace {
+	class command_interpreter_impl : public command_interpreter {
+	public:
+		typedef std::shared_ptr<command_interpreter> ptr;
+
+		command_interpreter_impl(std::istream &in, std::ostream &out)
+			: in_(in),
+			  out_(out),
+			  exit_(false) {
+		}
+
+		void register_command(std::string const &str, command::ptr cmd) {
+			commands_.insert(make_pair(str, cmd));
+		}
+
+		void enter_main_loop() {
+			while (!exit_)
+				do_once();
+		}
+
+		void exit_main_loop() {
+			exit_ = true;
+		}
+
+	private:
+		void do_once();
+
+		std::istream &in_;
+		std::ostream &out_;
+		std::map <std::string, command::ptr> commands_;
+		bool exit_;
+	};
+
+	//--------------------------------
+
+	strings read_input(std::istream &in)
+	{
+		using namespace boost::algorithm;
+
+		std::string input;
+		getline(in, input);
+
+		strings toks;
+		split(toks, input, is_any_of(" \t"), token_compress_on);
+
+		return toks;
+	}
+}
+
+//----------------------------------------------------------------
+
+void command_interpreter_impl::do_once()
+{
+	if (in_.eof())
+		throw runtime_error("input closed");
+
+	out_ << "> ";
+	strings args = read_input(in_);
+
+	std::map<std::string, command::ptr>::iterator it;
+	it = commands_.find(args[0]);
+	if (it == commands_.end())
+		out_ << "Unrecognised command" << endl;
+	else {
+		try {
+			it->second->exec(args, out_);
+		} catch (std::exception &e) {
+			cerr << e.what() << endl;
+		}
+	}
+}
+
+//----------------------------------------------------------------
+
+command_interpreter::ptr
+dbg::create_command_interpreter(std::istream &in, std::ostream &out)
+{
+	return command_interpreter::ptr(new command_interpreter_impl(in, out));
+}
+
+//----------------------------------------------------------------
diff --git a/base/command_interpreter.h b/base/command_interpreter.h
new file mode 100644
index 0000000..b0646d9
--- /dev/null
+++ b/base/command_interpreter.h
@@ -0,0 +1,40 @@
+#ifndef DBG_COMMAND_INTERPRETER
+#define DBG_COMMAND_INTERPRETER
+
+#include <boost/algorithm/string/classification.hpp>
+#include <boost/algorithm/string/split.hpp>
+
+#include <iostream>
+#include <map>
+#include <string>
+#include <vector>
+
+//----------------------------------------------------------------
+
+namespace dbg {
+	typedef std::vector<std::string> strings;
+
+	class command {
+	public:
+		typedef std::shared_ptr<command> ptr;
+
+		virtual ~command() {}
+		virtual void exec(strings const &args, std::ostream &out) = 0;
+	};
+
+	class command_interpreter {
+	public:
+		typedef std::shared_ptr<command_interpreter> ptr;
+
+		virtual void register_command(std::string const &str, command::ptr cmd) = 0;
+		virtual void enter_main_loop() = 0;
+		virtual void exit_main_loop() = 0;
+	};
+
+	command_interpreter::ptr
+	create_command_interpreter(std::istream &in, std::ostream &out);
+}
+
+//----------------------------------------------------------------
+
+#endif
diff --git a/base/output_formatter.cc b/base/output_formatter.cc
new file mode 100644
index 0000000..c62058f
--- /dev/null
+++ b/base/output_formatter.cc
@@ -0,0 +1,86 @@
+#include <string>
+
+#include "base/output_formatter.h"
+
+using namespace dbg;
+using namespace std;
+
+//----------------------------------------------------------------
+
+namespace {
+	class abstract_formatter : public formatter {
+		typedef boost::optional<std::string> maybe_string;
+
+		void field(std::string const &name, std::string const &value) {
+			fields_.push_back(field_type(name, value));
+		}
+
+		void child(std::string const &name, formatter::ptr t) {
+			children_.push_back(field_type(name, t));
+		}
+
+	protected:
+		typedef boost::variant<std::string, ptr> value;
+		typedef boost::tuple<std::string, value> field_type;
+
+		std::vector<field_type> fields_;
+		std::vector<field_type> children_;
+	};
+
+	class xml_formatter : public abstract_formatter {
+	public:
+		void output(std::ostream &out, int depth = 0,
+			    boost::optional<std::string> name = boost::none);
+	};
+
+	void indent(int depth, std::ostream &out) {
+		for (int i = 0; i < depth * 2; i++)
+			out << ' ';
+	}
+}
+
+//----------------------------------------------------------------
+
+void xml_formatter::output(std::ostream &out,
+			   int depth,
+			   boost::optional<std::string> name) {
+	indent(depth, out);
+	out << "<fields";
+	if (name && (*name).length())
+		out << " id=\"" << *name << "\"";
+
+	/* output non-child fields */
+	std::vector<field_type>::const_iterator it;
+	for (it = fields_.begin(); it != fields_.end(); ++it) {
+		if (string const *s = boost::get<string>(&it->get<1>())) {
+			out << " " << it->get<0>() << "=\"" << *s << "\"";
+		}
+	}
+
+	if (children_.size() == 0) {
+		out << " />" << endl;
+		return;
+	}
+
+	/* output child fields */
+	out << ">" << endl;
+	for (it = children_.begin(); it != children_.end(); ++it) {
+		if (!boost::get<string>(&it->get<1>())) {
+			formatter::ptr f = boost::get<formatter::ptr>(it->get<1>());
+			f->output(out, depth + 1, it->get<0>());
+		}
+	}
+
+	indent(depth, out);
+	out << "</fields>" << endl;
+}
+
+//----------------------------------------------------------------
+
+formatter::ptr
+dbg::create_xml_formatter()
+{
+	return formatter::ptr(new xml_formatter());
+}
+
+//----------------------------------------------------------------
diff --git a/base/output_formatter.h b/base/output_formatter.h
new file mode 100644
index 0000000..2cc4bc5
--- /dev/null
+++ b/base/output_formatter.h
@@ -0,0 +1,37 @@
+#ifndef DBG_OUTPUT_FORMATTER_H
+#define DBG_OUTPUT_FORMATTER_H
+
+#include <boost/lexical_cast.hpp>
+#include <boost/optional.hpp>
+#include <boost/tuple/tuple.hpp>
+#include <boost/variant.hpp>
+
+#include <vector>
+#include <string>
+
+//----------------------------------------------------------------
+
+namespace dbg {
+	class formatter {
+	public:
+		typedef std::shared_ptr<formatter> ptr;
+
+		virtual ~formatter() {}
+		virtual void field(std::string const &name, std::string const &value) = 0;
+		virtual void child(std::string const &name, formatter::ptr t) = 0;
+		virtual void output(std::ostream &out, int depth = 0,
+				    boost::optional<std::string> name = boost::none) = 0;
+	};
+
+	template <typename T>
+	void
+	field(formatter &t, std::string const &name, T const &value) {
+		t.field(name, boost::lexical_cast<std::string>(value));
+	}
+
+	formatter::ptr create_xml_formatter();
+}
+
+//----------------------------------------------------------------
+
+#endif
diff --git a/caching/cache_debug.cc b/caching/cache_debug.cc
new file mode 100644
index 0000000..1053560
--- /dev/null
+++ b/caching/cache_debug.cc
@@ -0,0 +1,331 @@
+// Copyright (C) 2012 Red Hat, Inc. All rights reserved.
+//
+// This file is part of the thin-provisioning-tools source.
+//
+// thin-provisioning-tools is free software: you can redistribute it
+// and/or modify it under the terms of the GNU General Public License
+// as published by the Free Software Foundation, either version 3 of
+// the License, or (at your option) any later version.
+//
+// thin-provisioning-tools is distributed in the hope that it will be
+// useful, but WITHOUT ANY WARRANTY; without even the implied warranty
+// of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License along
+// with thin-provisioning-tools.  If not, see
+// <http://www.gnu.org/licenses/>.
+
+#include <boost/lexical_cast.hpp>
+#include <getopt.h>
+#include <iostream>
+#include <string>
+
+#include "base/command_interpreter.h"
+#include "base/output_formatter.h"
+#include "persistent-data/file_utils.h"
+#include "persistent-data/data-structures/btree.h"
+#include "persistent-data/data-structures/simple_traits.h"
+#include "persistent-data/space-maps/disk_structures.h"
+#include "caching/commands.h"
+#include "caching/metadata.h"
+#include "version.h"
+
+using namespace dbg;
+using namespace persistent_data;
+using namespace std;
+using namespace caching;
+
+//----------------------------------------------------------------
+
+namespace {
+	class hello : public dbg::command {
+		virtual void exec(strings const &args, ostream &out) {
+			out << "Hello, world!" << endl;
+		}
+	};
+
+	class help : public dbg::command {
+		virtual void exec(strings const &args, ostream &out) {
+			out << "Commands:" << endl
+			    << "  superblock" << endl
+			    << "  mapping_node <block# of tree node for mappings>" << endl
+			    << "  mapping_array <block# of array block for mappings>" << endl
+			    << "  exit" << endl;
+		}
+	};
+
+	class exit_handler : public dbg::command {
+	public:
+		exit_handler(command_interpreter::ptr interpreter)
+			: interpreter_(interpreter) {
+		}
+
+		virtual void exec(strings const &args, ostream &out) {
+			out << "Goodbye!" << endl;
+			interpreter_->exit_main_loop();
+		}
+
+		command_interpreter::ptr interpreter_;
+	};
+
+	class sm_root_show_traits : public persistent_data::sm_disk_detail::sm_root_traits {
+	public:
+		static void show(formatter::ptr f, string const &key,
+				 persistent_data::sm_disk_detail::sm_root const &value) {
+			field(*f, "nr_blocks", value.nr_blocks_);
+			field(*f, "nr_allocated", value.nr_allocated_);
+			field(*f, "bitmap_root", value.bitmap_root_);
+			field(*f, "ref_count_root", value.ref_count_root_);
+		}
+	};
+
+	class show_superblock : public dbg::command {
+	public:
+		explicit show_superblock(metadata::ptr md)
+			: md_(md) {
+		}
+
+		virtual void exec(strings const &args, ostream &out) {
+			formatter::ptr f = create_xml_formatter();
+			ostringstream version;
+
+			superblock const &sb = md_->sb_;
+
+			field(*f, "csum", sb.csum);
+			field(*f, "flags", sb.flags.encode());
+			field(*f, "blocknr", sb.blocknr);
+			field(*f, "uuid", sb.uuid); // FIXME: delimit, and handle non-printable chars
+			field(*f, "magic", sb.magic);
+			field(*f, "version", sb.version);
+			field(*f, "policy_name", reinterpret_cast<char const*>(sb.policy_name));
+			version << sb.policy_version[0] << "."
+				<< sb.policy_version[1] << "."
+				<< sb.policy_version[2];
+			field(*f, "policy_version", version.str().c_str());
+			field(*f, "policy_hint_size", sb.policy_hint_size);
+
+			sm_disk_detail::sm_root_disk const *d;
+			sm_disk_detail::sm_root v;
+			{
+				d = reinterpret_cast<sm_disk_detail::sm_root_disk const *>(sb.metadata_space_map_root);
+				sm_disk_detail::sm_root_traits::unpack(*d, v);
+				formatter::ptr f2 = create_xml_formatter();
+				sm_root_show_traits::show(f2, "value", v);
+				f->child("metadata_space_map_root", f2);
+			}
+
+			field(*f, "mapping_root", sb.mapping_root);
+			if (sb.version >= 2)
+				field(*f, "dirty_root", *sb.dirty_root);
+			field(*f, "hint_root", sb.hint_root);
+			field(*f, "discard_root", sb.discard_root);
+			field(*f, "discard_block_size", sb.discard_block_size);
+			field(*f, "discard_nr_blocks", sb.discard_nr_blocks);
+			field(*f, "data_block_size", sb.data_block_size);
+			field(*f, "metadata_block_size", sb.metadata_block_size);
+			field(*f, "cache_blocks", sb.cache_blocks);
+			field(*f, "compat_flags", sb.compat_flags);
+			field(*f, "compat_ro_flags", sb.compat_ro_flags);
+			field(*f, "incompat_flags", sb.incompat_flags);
+			field(*f, "read_hits", sb.read_hits);
+			field(*f, "read_misses", sb.read_misses);
+			field(*f, "write_hits", sb.write_hits);
+			field(*f, "write_misses", sb.write_misses);
+
+			f->output(out, 0);
+		}
+
+	private:
+		metadata::ptr md_;
+	};
+
+	class uint64_show_traits : public uint64_traits {
+	public:
+		static void show(formatter::ptr f, string const &key, uint64_t const &value) {
+			field(*f, key, boost::lexical_cast<string>(value));
+		}
+	};
+
+	// FIXME: Expose the array ValueTraits parameter or not?
+	//	  Since the block_traits isn't related to the ValueTraits.
+	class block_show_traits : public persistent_data::array<caching::mapping_traits>::block_traits {
+	public:
+		static void show(formatter::ptr f, string const &key, block_address const &value) {
+			field(*f, "block", value);
+		}
+	};
+
+	class mapping_show_traits : public caching::mapping_traits {
+	public:
+		static void show(formatter::ptr f, string const &key, caching::mapping const &value) {
+			field(*f, "oblock", value.oblock_);
+			field(*f, "flags", value.flags_);
+		}
+	};
+
+	template <typename ValueTraits>
+	class show_btree_node : public dbg::command {
+	public:
+		explicit show_btree_node(metadata::ptr md)
+			: md_(md) {
+		}
+
+		virtual void exec(strings const &args, ostream &out) {
+			using namespace persistent_data::btree_detail;
+
+			if (args.size() != 2)
+				throw runtime_error("incorrect number of arguments");
+
+			block_address block = boost::lexical_cast<block_address>(args[1]);
+			block_manager::read_ref rr = md_->tm_->read_lock(block);
+
+			node_ref<uint64_show_traits> n = btree_detail::to_node<uint64_show_traits>(rr);
+			if (n.get_type() == INTERNAL)
+				show_node<uint64_show_traits>(n, out);
+			else {
+				node_ref<ValueTraits> n = btree_detail::to_node<ValueTraits>(rr);
+				show_node<ValueTraits>(n, out);
+			}
+		}
+
+	private:
+		template <typename VT>
+		void show_node(node_ref<VT> n, ostream &out) {
+			formatter::ptr f = create_xml_formatter();
+
+			field(*f, "csum", n.get_checksum());
+			field(*f, "blocknr", n.get_location());
+			field(*f, "type", n.get_type() == INTERNAL ? "internal" : "leaf");
+			field(*f, "nr_entries", n.get_nr_entries());
+			field(*f, "max_entries", n.get_max_entries());
+			field(*f, "value_size", n.get_value_size());
+
+			for (unsigned i = 0; i < n.get_nr_entries(); i++) {
+				formatter::ptr f2 = create_xml_formatter();
+				field(*f2, "key", n.key_at(i));
+				VT::show(f2, "value", n.value_at(i));
+				f->child("child", f2);
+			}
+
+			f->output(out, 0);
+		}
+
+		metadata::ptr md_;
+	};
+
+	template <typename ValueTraits>
+	class show_array_block : public dbg::command {
+		typedef array_block<ValueTraits, block_manager::read_ref> rblock;
+	public:
+		explicit show_array_block(metadata::ptr md)
+			: md_(md) {
+		}
+
+		virtual void exec(strings const& args, ostream &out) {
+			if (args.size() != 2)
+				throw runtime_error("incorrect number of arguments");
+
+			block_address block = boost::lexical_cast<block_address>(args[1]);
+			block_manager::read_ref rr = md_->tm_->read_lock(block);
+
+			rblock b(rr, typename ValueTraits::ref_counter());
+			show_array_entries(b, out);
+		}
+
+	private:
+		void show_array_entries(rblock const& b, ostream &out) {
+			formatter::ptr f = create_xml_formatter();
+			uint32_t nr_entries = b.nr_entries();
+
+			field(*f, "max_entries", b.max_entries());
+			field(*f, "nr_entries", nr_entries);
+			field(*f, "value_size", b.value_size());
+
+			for (unsigned i = 0; i < nr_entries; i++) {
+				formatter::ptr f2 = create_xml_formatter();
+				field(*f2, "index", i);
+				ValueTraits::show(f2, "value", b.get(i));
+				f->child("child", f2);
+			}
+
+			f->output(out, 0);
+		}
+
+		metadata::ptr md_;
+	};
+
+	//--------------------------------
+
+	int debug(string const &path) {
+		using dbg::command;
+
+		try {
+			block_manager::ptr bm = open_bm(path, block_manager::READ_ONLY);
+			metadata::ptr md(new metadata(bm));
+			command_interpreter::ptr interp = create_command_interpreter(cin, cout);
+			interp->register_command("hello", command::ptr(new hello));
+			interp->register_command("superblock", command::ptr(new show_superblock(md)));
+			interp->register_command("mapping_node", command::ptr(new show_btree_node<block_show_traits>(md)));
+			interp->register_command("mapping_array", command::ptr(new show_array_block<mapping_show_traits>(md)));
+			interp->register_command("help", command::ptr(new help));
+			interp->register_command("exit", command::ptr(new exit_handler(interp)));
+			interp->enter_main_loop();
+
+		} catch (std::exception &e) {
+			cerr << e.what();
+			return 1;
+		}
+
+		return 0;
+	}
+}
+
+//----------------------------------------------------------------
+
+cache_debug_cmd::cache_debug_cmd()
+	: command("cache_debug")
+{
+}
+
+void
+cache_debug_cmd::usage(std::ostream &out) const
+{
+	out << "Usage: " << get_name() << " {device|file}" << endl
+	    << "Options:" << endl
+	    << "  {-h|--help}" << endl
+	    << "  {-V|--version}" << endl;
+}
+
+int
+cache_debug_cmd::run(int argc, char **argv)
+{
+	int c;
+	const char shortopts[] = "hV";
+	const struct option longopts[] = {
+		{ "help", no_argument, NULL, 'h'},
+		{ "version", no_argument, NULL, 'V'},
+		{ NULL, no_argument, NULL, 0 }
+	};
+
+	while ((c = getopt_long(argc, argv, shortopts, longopts, NULL)) != -1) {
+		switch(c) {
+		case 'h':
+			usage(cout);
+			return 0;
+
+		case 'V':
+			cerr << THIN_PROVISIONING_TOOLS_VERSION << endl;
+			return 0;
+		}
+	}
+
+	if (argc == optind) {
+		usage(cerr);
+		exit(1);
+	}
+
+	return debug(argv[optind]);
+}
+
+//----------------------------------------------------------------
diff --git a/caching/commands.h b/caching/commands.h
index b0546ab..04deac9 100644
--- a/caching/commands.h
+++ b/caching/commands.h
@@ -70,6 +70,18 @@ namespace caching {
 		virtual int run(int argc, char **argv);
 	};
 
+	//------------------------------------------------------
+
+	class cache_debug_cmd : public base::command {
+	public:
+		cache_debug_cmd();
+
+		virtual void usage(std::ostream &out) const;
+		virtual int run(int argc, char **argv);
+	};
+
+	//------------------------------------------------------
+
 	void register_cache_commands(base::application &app);
 }
 
diff --git a/caching/devel_commands.cc b/caching/devel_commands.cc
index 21a1188..c63a68d 100644
--- a/caching/devel_commands.cc
+++ b/caching/devel_commands.cc
@@ -8,6 +8,7 @@ using namespace caching;
 void
 caching::register_cache_commands(application &app)
 {
+	app.add_cmd(command::ptr(new cache_debug_cmd));
 }
 
 //----------------------------------------------------------------
diff --git a/thin-provisioning/commands.h b/thin-provisioning/commands.h
index 0f603ae..2067970 100644
--- a/thin-provisioning/commands.h
+++ b/thin-provisioning/commands.h
@@ -73,6 +73,13 @@ namespace thin_provisioning {
 
 	//------------------------------------------------------
 
+	class thin_debug_cmd : public base::command {
+	public:
+		thin_debug_cmd();
+		virtual void usage(std::ostream &out) const;
+		virtual int run(int argc, char **argv);
+	};
+
 	class thin_generate_damage_cmd : public base::command {
 	public:
 		thin_generate_damage_cmd();
@@ -94,6 +101,13 @@ namespace thin_provisioning {
 		virtual int run(int argc, char **argv);
 	};
 
+	class thin_journal_cmd : public base::command {
+	public:
+		thin_journal_cmd();
+		virtual void usage(std::ostream &out) const;
+		virtual int run(int argc, char **argv);
+	};
+
 	class thin_ll_dump_cmd : public base::command {
 	public:
 		thin_ll_dump_cmd();
@@ -140,13 +154,6 @@ namespace thin_provisioning {
 		virtual int run(int argc, char **argv);
 	};
 
-	class thin_journal_cmd : public base::command {
-	public:
-		thin_journal_cmd();
-		virtual void usage(std::ostream &out) const;
-		virtual int run(int argc, char **argv);
-	};
-
 	void register_thin_commands(base::application &app);
 }
 
diff --git a/thin-provisioning/devel_commands.cc b/thin-provisioning/devel_commands.cc
index 7a12297..e0f0ae5 100644
--- a/thin-provisioning/devel_commands.cc
+++ b/thin-provisioning/devel_commands.cc
@@ -8,6 +8,7 @@ using namespace thin_provisioning;
 void
 thin_provisioning::register_thin_commands(base::application &app)
 {
+	app.add_cmd(command::ptr(new thin_debug_cmd()));
 	app.add_cmd(command::ptr(new thin_generate_damage_cmd()));
 	app.add_cmd(command::ptr(new thin_generate_mappings_cmd()));
 	app.add_cmd(command::ptr(new thin_generate_metadata_cmd()));
diff --git a/thin-provisioning/thin_debug.cc b/thin-provisioning/thin_debug.cc
index 48ad544..e458d7d 100644
--- a/thin-provisioning/thin_debug.cc
+++ b/thin-provisioning/thin_debug.cc
@@ -16,227 +16,174 @@
 // with thin-provisioning-tools.  If not, see
 // <http://www.gnu.org/licenses/>.
 
-#include <boost/algorithm/string/classification.hpp>
-#include <boost/algorithm/string/split.hpp>
 #include <boost/lexical_cast.hpp>
-#include <boost/tuple/tuple.hpp>
-#include <boost/variant.hpp>
 #include <getopt.h>
 #include <iostream>
-#include <libgen.h>
-#include <map>
 #include <string>
-#include <vector>
 
+#include "base/command_interpreter.h"
+#include "base/math_utils.h"
+#include "base/output_formatter.h"
 #include "persistent-data/data-structures/btree.h"
+#include "persistent-data/data-structures/simple_traits.h"
+#include "persistent-data/file_utils.h"
+#include "persistent-data/space-maps/disk_structures.h"
+#include "thin-provisioning/commands.h"
 #include "thin-provisioning/metadata.h"
-#include "thin-provisioning/metadata_checker.h"
+#include "thin-provisioning/superblock.h"
 #include "version.h"
 
-using namespace boost;
+using namespace dbg;
 using namespace persistent_data;
 using namespace std;
 using namespace thin_provisioning;
 
 namespace {
-	typedef vector<string> strings;
-
-	class formatter {
-	public:
-		typedef shared_ptr<formatter> ptr;
-
-		virtual ~formatter() {}
-
-		typedef optional<string> maybe_string;
-
-		void field(string const &name, string const &value) {
-			fields_.push_back(field_type(name, value));
-		}
-
-		void child(string const &name, formatter::ptr t) {
-			fields_.push_back(field_type(name, t));
-		}
-
-		virtual void output(ostream &out, int depth = 0) = 0;
-
-	protected:
-		typedef variant<string, ptr> value;
-		typedef tuple<string, value> field_type;
-
-		vector<field_type> fields_;
-	};
-
-	template <typename T>
-	void
-	field(formatter &t, string const &name, T const &value) {
-		t.field(name, lexical_cast<string>(value));
-	}
-
-	//--------------------------------
-
-	class xml_formatter : public formatter {
-	public:
-		virtual void output(ostream &out, int depth)  {
-			indent(depth, out);
-			out << "<fields>" << endl;
-			vector<field_type>::const_iterator it;
-			for (it = fields_.begin(); it != fields_.end(); ++it) {
-				if (string const *s = get<string>(&it->get<1>())) {
-					indent(depth + 1, out);
-					out << "<field key=\""
-					    << it->get<0>()
-					    << "\" value=\""
-					    << *s
-					    << "\"/>"
-					    << endl;
-
-				} else {
-					formatter::ptr f = get<formatter::ptr>(it->get<1>());
-					f->output(out, depth + 1);
-				}
-			}
-
-			indent(depth, out);
-			out << "</fields>" << endl;
-		}
-
-	private:
-		void indent(int depth, ostream &out) const {
-			for (int i = 0; i < depth * 2; i++)
-				out << ' ';
-		}
-	};
-
-	//--------------------------------
-
-	class command {
-	public:
-		typedef std::shared_ptr<command> ptr;
-
-		virtual ~command() {}
-		virtual void exec(strings const &args, ostream &out) = 0;
-	};
-
-	class command_interpreter {
-	public:
-		command_interpreter(istream &in, ostream &out)
-			: in_(in),
-			  out_(out) {
-		}
-
-		void register_command(string const &str, command::ptr cmd) {
-			commands_.insert(make_pair(str, cmd));
-		}
-
-		void enter_main_loop() {
-			while (true)
-				do_once();
-		}
-
-	private:
-		strings read_input() {
-			using namespace boost::algorithm;
-
-			string input;
-			getline(in_, input);
-
-			strings toks;
-			split(toks, input, is_any_of(" \t"), token_compress_on);
-
-			return toks;
-		}
-
-		void do_once() {
-			if (in_.eof())
-				throw runtime_error("input closed");
-
-			out_ << "> ";
-			strings args = read_input();
-
-			map<string, command::ptr>::iterator it;
-			it = commands_.find(args[0]);
-			if (it == commands_.end())
-				out_ << "Unrecognised command" << endl;
-			else
-				it->second->exec(args, out_);
-		}
-
-		istream &in_;
-		ostream &out_;
-		map <string, command::ptr> commands_;
-	};
-
-	//--------------------------------
-
-	class hello : public command {
+	class hello : public dbg::command {
 		virtual void exec(strings const &args, ostream &out) {
 			out << "Hello, world!" << endl;
 		}
 	};
 
-	class show_superblock : public command {
+	class help : public dbg::command {
+		virtual void exec(strings const &args, ostream &out) {
+			out << "Commands:" << endl
+			    << "  superblock" << endl
+			    << "  m1_node <block# of top-level mapping tree node>" << endl
+			    << "  m2_node <block# of bottom-level mapping tree node>" << endl
+			    << "  detail_node <block# of device details tree node>" << endl
+			    << "  index_block <block# of metadata space map root>" << endl
+			    << "  index_node <block# of data space map node>" << endl
+			    << "  exit" << endl;
+		}
+	};
+
+	class exit_handler : public dbg::command {
+	public:
+		exit_handler(command_interpreter::ptr interpreter)
+			: interpreter_(interpreter) {
+		}
+
+		virtual void exec(strings const &args, ostream &out) {
+			out << "Goodbye!" << endl;
+			interpreter_->exit_main_loop();
+		}
+
+		command_interpreter::ptr interpreter_;
+	};
+
+	class sm_root_show_traits : public persistent_data::sm_disk_detail::sm_root_traits {
+	public:
+		static void show(formatter::ptr f, string const &key,
+				 persistent_data::sm_disk_detail::sm_root const &value) {
+			field(*f, "nr_blocks", value.nr_blocks_);
+			field(*f, "nr_allocated", value.nr_allocated_);
+			field(*f, "bitmap_root", value.bitmap_root_);
+			field(*f, "ref_count_root", value.ref_count_root_);
+		}
+	};
+
+	class show_superblock : public dbg::command {
 	public:
 		explicit show_superblock(metadata::ptr md)
 			: md_(md) {
 		}
 
 		virtual void exec(strings const &args, ostream &out) {
-			xml_formatter f;
+			formatter::ptr f = create_xml_formatter();
 
-			superblock const &sb = md_->sb_;
+			thin_provisioning::superblock_detail::superblock const &sb = md_->sb_;
 
-			field(f, "csum", sb.csum_);
-			field(f, "flags", sb.flags_);
-			field(f, "blocknr", sb.blocknr_);
-			field(f, "uuid", sb.uuid_); // FIXME: delimit, and handle non-printable chars
-			field(f, "magic", sb.magic_);
-			field(f, "version", sb.version_);
-			field(f, "time", sb.time_);
-			field(f, "trans id", sb.trans_id_);
-			field(f, "metadata snap", sb.metadata_snap_);
-			field(f, "data mapping root", sb.data_mapping_root_);
-			field(f, "device details root", sb.device_details_root_);
-			field(f, "data block size", sb.data_block_size_);
-			field(f, "metadata block size", sb.metadata_block_size_);
-			field(f, "metadata nr blocks", sb.metadata_nr_blocks_);
-			field(f, "compat flags", sb.compat_flags_);
-			field(f, "compat ro flags", sb.compat_ro_flags_);
-			field(f, "incompat flags", sb.incompat_flags_);
+			field(*f, "csum", sb.csum_);
+			field(*f, "flags", sb.flags_);
+			field(*f, "blocknr", sb.blocknr_);
+			field(*f, "uuid", sb.uuid_); // FIXME: delimit, and handle non-printable chars
+			field(*f, "magic", sb.magic_);
+			field(*f, "version", sb.version_);
+			field(*f, "time", sb.time_);
+			field(*f, "trans_id", sb.trans_id_);
+			field(*f, "metadata_snap", sb.metadata_snap_);
 
-			f.output(out, 0);
+			sm_disk_detail::sm_root_disk const *d;
+			sm_disk_detail::sm_root v;
+			{
+				d = reinterpret_cast<sm_disk_detail::sm_root_disk const *>(sb.metadata_space_map_root_);
+				sm_disk_detail::sm_root_traits::unpack(*d, v);
+				formatter::ptr f2 = create_xml_formatter();
+				sm_root_show_traits::show(f2, "value", v);
+				f->child("metadata_space_map_root", f2);
+			}
+			{
+				d = reinterpret_cast<sm_disk_detail::sm_root_disk const *>(sb.data_space_map_root_);
+				sm_disk_detail::sm_root_traits::unpack(*d, v);
+				formatter::ptr f2 = create_xml_formatter();
+				sm_root_show_traits::show(f2, "value", v);
+				f->child("data_space_map_root", f2);
+			}
+
+			field(*f, "data_mapping_root", sb.data_mapping_root_);
+			field(*f, "device_details_root", sb.device_details_root_);
+			field(*f, "data_block_size", sb.data_block_size_);
+			field(*f, "metadata_block_size", sb.metadata_block_size_);
+			field(*f, "metadata_nr_blocks", sb.metadata_nr_blocks_);
+			field(*f, "compat_flags", sb.compat_flags_);
+			field(*f, "compat_ro_flags", sb.compat_ro_flags_);
+			field(*f, "incompat_flags", sb.incompat_flags_);
+
+			f->output(out, 0);
 		}
 
 	private:
 		metadata::ptr md_;
 	};
 
-	class device_details_show_traits : public device_details_traits {
+	class device_details_show_traits : public thin_provisioning::device_tree_detail::device_details_traits {
 	public:
-		static void show(formatter &f, string const &key, device_details const &value) {
-			field(f, "mapped blocks", value.mapped_blocks_);
-			field(f, "transaction id", value.transaction_id_);
-			field(f, "creation time", value.creation_time_);
-			field(f, "snap time", value.snapshotted_time_);
+		typedef thin_provisioning::device_tree_detail::device_details_traits value_trait;
+
+		static void show(formatter::ptr f, string const &key,
+				 thin_provisioning::device_tree_detail::device_details const &value) {
+			field(*f, "mapped_blocks", value.mapped_blocks_);
+			field(*f, "transaction_id", value.transaction_id_);
+			field(*f, "creation_time", value.creation_time_);
+			field(*f, "snap_time", value.snapshotted_time_);
 		}
 	};
 
 	class uint64_show_traits : public uint64_traits {
 	public:
-		static void show(formatter &f, string const &key, uint64_t const &value) {
-			field(f, key, lexical_cast<string>(value));
+		typedef uint64_traits value_trait;
+
+		static void show(formatter::ptr f, string const &key, uint64_t const &value) {
+			field(*f, key, boost::lexical_cast<string>(value));
 		}
 	};
 
-	class block_show_traits : public block_traits {
+	class block_show_traits : public thin_provisioning::mapping_tree_detail::block_traits {
 	public:
-		static void show(formatter &f, string const &key, block_time const &value) {
-			field(f, "block", value.block_);
-			field(f, "time", value.time_);
+		typedef thin_provisioning::mapping_tree_detail::block_traits value_trait;
+
+		static void show(formatter::ptr f, string const &key,
+				 thin_provisioning::mapping_tree_detail::block_time const &value) {
+			field(*f, "block", value.block_);
+			field(*f, "time", value.time_);
 		}
 	};
 
-	template <typename ValueTraits>
-	class show_btree_node : public command {
+	class index_entry_show_traits : public persistent_data::sm_disk_detail::index_entry_traits {
+	public:
+		typedef persistent_data::sm_disk_detail::index_entry_traits value_trait;
+
+		static void show(formatter::ptr f, string const &key,
+				 persistent_data::sm_disk_detail::index_entry const &value) {
+			field(*f, "blocknr", value.blocknr_);
+			field(*f, "nr_free", value.nr_free_);
+			field(*f, "none_free_before", value.none_free_before_);
+		}
+	};
+
+	template <typename ShowTraits>
+	class show_btree_node : public dbg::command {
 	public:
 		explicit show_btree_node(metadata::ptr md)
 			: md_(md) {
@@ -248,98 +195,165 @@ namespace {
 			if (args.size() != 2)
 				throw runtime_error("incorrect number of arguments");
 
-			block_address block = lexical_cast<block_address>(args[1]);
-			block_manager<>::read_ref rr = md_->tm_->read_lock(block);
+			block_address block = boost::lexical_cast<block_address>(args[1]);
+			block_manager::read_ref rr = md_->tm_->read_lock(block);
 
-			node_ref<uint64_show_traits> n = btree_detail::to_node<uint64_show_traits>(rr);
+			node_ref<uint64_show_traits::value_trait> n = btree_detail::to_node<uint64_show_traits::value_trait>(rr);
 			if (n.get_type() == INTERNAL)
 				show_node<uint64_show_traits>(n, out);
 			else {
-				node_ref<ValueTraits> n = btree_detail::to_node<ValueTraits>(rr);
-				show_node<ValueTraits>(n, out);
+				node_ref<typename ShowTraits::value_trait> n = btree_detail::to_node<typename ShowTraits::value_trait>(rr);
+				show_node<ShowTraits>(n, out);
 			}
 		}
 
 	private:
-		template <typename VT>
-		void show_node(node_ref<VT> n, ostream &out) {
-			xml_formatter f;
+		template <typename ST>
+		void show_node(node_ref<typename ST::value_trait> n, ostream &out) {
+			formatter::ptr f = create_xml_formatter();
 
-			field(f, "csum", n.get_checksum());
-			field(f, "blocknr", n.get_location());
-			field(f, "type", n.get_type() == INTERNAL ? "internal" : "leaf");
-			field(f, "nr entries", n.get_nr_entries());
-			field(f, "max entries", n.get_max_entries());
-			field(f, "value size", n.get_value_size());
+			field(*f, "csum", n.get_checksum());
+			field(*f, "blocknr", n.get_block_nr());
+			field(*f, "type", n.get_type() == INTERNAL ? "internal" : "leaf");
+			field(*f, "nr_entries", n.get_nr_entries());
+			field(*f, "max_entries", n.get_max_entries());
+			field(*f, "value_size", n.get_value_size());
 
 			for (unsigned i = 0; i < n.get_nr_entries(); i++) {
-				formatter::ptr f2(new xml_formatter);
+				formatter::ptr f2 = create_xml_formatter();
 				field(*f2, "key", n.key_at(i));
-				VT::show(*f2, "value", n.value_at(i));
-				f.child("child", f2);
+				ST::show(f2, "value", n.value_at(i));
+				f->child(boost::lexical_cast<string>(i), f2);
 			}
 
-			f.output(out, 0);
+			f->output(out, 0);
 		}
 
 		metadata::ptr md_;
 	};
 
+	class show_index_block : public dbg::command {
+	public:
+		explicit show_index_block(metadata::ptr md)
+			: md_(md) {
+		}
+
+		virtual void exec(strings const &args, ostream &out) {
+			if (args.size() != 2)
+				throw runtime_error("incorrect number of arguments");
+
+			// manually load metadata_index, without using index_validator()
+			block_address block = boost::lexical_cast<block_address>(args[1]);
+			block_manager::read_ref rr = md_->tm_->read_lock(block);
+
+			sm_disk_detail::sm_root_disk const *d =
+				reinterpret_cast<sm_disk_detail::sm_root_disk const *>(md_->sb_.metadata_space_map_root_);
+			sm_disk_detail::sm_root v;
+			sm_disk_detail::sm_root_traits::unpack(*d, v);
+			block_address nr_indexes = base::div_up<block_address>(v.nr_blocks_, ENTRIES_PER_BLOCK);
+
+			sm_disk_detail::metadata_index const *mdi =
+				reinterpret_cast<sm_disk_detail::metadata_index const *>(rr.data());
+			show_metadata_index(mdi, nr_indexes, out);
+		}
+
+	private:
+		void show_metadata_index(sm_disk_detail::metadata_index const *mdi, block_address nr_indexes, ostream &out) {
+			formatter::ptr f = create_xml_formatter();
+			field(*f, "csum", to_cpu<uint32_t>(mdi->csum_));
+			field(*f, "padding", to_cpu<uint32_t>(mdi->padding_));
+			field(*f, "blocknr", to_cpu<uint64_t>(mdi->blocknr_));
+
+			sm_disk_detail::index_entry ie;
+			for (block_address i = 0; i < nr_indexes; i++) {
+				sm_disk_detail::index_entry_traits::unpack(*(mdi->index + i), ie);
+				formatter::ptr f2 = create_xml_formatter();
+				index_entry_show_traits::show(f2, "value", ie);
+				f->child(boost::lexical_cast<string>(i), f2);
+			}
+			f->output(out, 0);
+		}
+
+		unsigned const ENTRIES_PER_BLOCK = (MD_BLOCK_SIZE - sizeof(persistent_data::sm_disk_detail::bitmap_header)) * 4;
+		metadata::ptr md_;
+	};
+
 	//--------------------------------
 
-	int debug(string const &path) {
+	int debug_(string const &path, bool ignore_metadata_sm) {
+		using dbg::command;
+
 		try {
-			metadata::ptr md(new metadata(path, metadata::OPEN));
-			command_interpreter interp(cin, cout);
-			interp.register_command("hello", command::ptr(new hello));
-			interp.register_command("superblock", command::ptr(new show_superblock(md)));
-			interp.register_command("m1_node", command::ptr(new show_btree_node<uint64_show_traits>(md)));
-			interp.register_command("m2_node", command::ptr(new show_btree_node<block_show_traits>(md)));
-			interp.register_command("detail_node", command::ptr(new show_btree_node<device_details_show_traits>(md)));
-			interp.enter_main_loop();
+			block_manager::ptr bm = open_bm(path, block_manager::READ_ONLY, 1);
+			metadata::ptr md(new metadata(bm, false));
+			command_interpreter::ptr interp = create_command_interpreter(cin, cout);
+			interp->register_command("hello", command::ptr(new hello));
+			interp->register_command("superblock", command::ptr(new show_superblock(md)));
+			interp->register_command("m1_node", command::ptr(new show_btree_node<uint64_show_traits>(md)));
+			interp->register_command("m2_node", command::ptr(new show_btree_node<block_show_traits>(md)));
+			interp->register_command("detail_node", command::ptr(new show_btree_node<device_details_show_traits>(md)));
+			interp->register_command("index_block", command::ptr(new show_index_block(md)));
+			interp->register_command("index_node", command::ptr(new show_btree_node<index_entry_show_traits>(md)));
+			interp->register_command("help", command::ptr(new help));
+			interp->register_command("exit", command::ptr(new exit_handler(interp)));
+			interp->enter_main_loop();
 
 		} catch (std::exception &e) {
-			cerr << e.what();
+			cerr << e.what() << endl;
 			return 1;
 		}
 
 		return 0;
 	}
-
-	void usage(string const &cmd) {
-		cerr << "Usage: " << cmd << " {device|file}" << endl
-		     << "Options:" << endl
-		     << "  {-h|--help}" << endl
-		     << "  {-V|--version}" << endl;
-	}
 }
 
-int main(int argc, char **argv)
+thin_debug_cmd::thin_debug_cmd()
+	: command("thin_debug")
+{
+}
+
+void
+thin_debug_cmd::usage(std::ostream &out) const
+{
+	out << "Usage: " << get_name() << " {device|file}" << endl
+	    << "Options:" << endl
+	    << "  {-h|--help}" << endl
+	    << "  {-V|--version}" << endl;
+}
+
+int
+thin_debug_cmd::run(int argc, char **argv)
 {
 	int c;
 	const char shortopts[] = "hV";
 	const struct option longopts[] = {
 		{ "help", no_argument, NULL, 'h'},
 		{ "version", no_argument, NULL, 'V'},
+		{ "ignore-metadata-sm", no_argument, NULL, 1},
 		{ NULL, no_argument, NULL, 0 }
 	};
+	bool ignore_metadata_sm = false;
 
 	while ((c = getopt_long(argc, argv, shortopts, longopts, NULL)) != -1) {
 		switch(c) {
 		case 'h':
-			usage(basename(argv[0]));
+			usage(cout);
 			return 0;
 
 		case 'V':
 			cerr << THIN_PROVISIONING_TOOLS_VERSION << endl;
 			return 0;
+
+		case 1:
+			ignore_metadata_sm = true;
+			break;
 		}
 	}
 
 	if (argc == optind) {
-		usage(basename(argv[0]));
+		usage(cerr);
 		exit(1);
 	}
 
-	return debug(argv[optind]);
+	return debug_(argv[optind], ignore_metadata_sm);
 }