diff --git a/persistent-data/cache.h b/persistent-data/cache.h
new file mode 100644
index 0000000..b13e864
--- /dev/null
+++ b/persistent-data/cache.h
@@ -0,0 +1,270 @@
+// Copyright (C) 2011 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/>.
+
+#ifndef CACHE_H
+#define CACHE_H
+
+#include "deleter.h"
+
+#include <boost/intrusive/circular_list_algorithms.hpp>
+#include <boost/intrusive/rbtree_algorithms.hpp>
+#include <boost/optional.hpp>
+#include <list>
+#include <map>
+#include <memory>
+#include <stdexcept>
+
+//----------------------------------------------------------------
+
+namespace base {
+	// ValueTraits needs to define value_type, key_type and a get_key()
+	// static function.  Commonly you will want value_type to be a
+	// shared_ptr, with any teardown specific stuff in the destructor.
+	template <typename ValueTraits>
+	class cache {
+	public:
+		typedef typename ValueTraits::value_type value_type;
+		typedef typename ValueTraits::key_type key_type;
+
+		cache(unsigned max_entries);
+		~cache();
+
+		void insert(value_type const &v);
+
+		boost::optional<value_type> get(key_type const &k);
+		void put(value_type const &k);
+
+		template <typename T>
+		void iterate_unheld(T fn) const;
+
+	private:
+		void make_space();
+
+		struct value_entry {
+			// FIXME: this means the cached object must have a
+			// default constructor also, which is a shame.
+			// so we can construct the headers.
+			value_entry()
+				: ref_count_(1) {
+			}
+
+			explicit value_entry(value_type v)
+				: ref_count_(1),
+				  v_(v) {
+			}
+
+			struct {
+				value_entry *next_, *prev_;
+			} lru_;
+
+			struct {
+				value_entry *parent_, *left_, *right_;
+				int color_;
+			} lookup_;
+
+			unsigned ref_count_;
+			value_type v_;
+		};
+
+		struct value_ptr_cmp {
+			bool operator() (value_entry const *lhs, value_entry const *rhs) {
+				key_type k1 = ValueTraits::get_key(lhs->v_);
+				key_type k2 = ValueTraits::get_key(rhs->v_);
+
+				return k1 < k2;
+			}
+		};
+
+		struct key_value_ptr_cmp {
+			bool operator() (key_type const &k1, value_entry const *rhs) {
+				key_type k2 = ValueTraits::get_key(rhs->v_);
+				return k1 < k2;
+			}
+
+			bool operator() (value_entry const *lhs, key_type const &k2) {
+				key_type k1 = ValueTraits::get_key(lhs->v_);
+				return k1 < k2;
+			}
+
+		};
+
+		struct list_node_traits {
+			typedef value_entry node;
+			typedef value_entry *node_ptr;
+			typedef const value_entry *const_node_ptr;
+
+			static node_ptr get_next(const_node_ptr n) {
+				return n->lru_.next_;
+			}
+
+			static void set_next(node_ptr n, node_ptr next) {
+				n->lru_.next_ = next;
+			}
+
+			static node_ptr get_previous(const_node_ptr n) {
+				return n->lru_.prev_;
+			}
+
+			static void set_previous(node_ptr n, node_ptr prev) {
+				n->lru_.prev_ = prev;
+			}
+		};
+
+		struct rbtree_node_traits {
+			typedef value_entry node;
+			typedef value_entry *node_ptr;
+			typedef const value_entry * const_node_ptr;
+			typedef int color;
+
+			static node_ptr get_parent(const_node_ptr n) {
+				return n->lookup_.parent_;
+			}
+
+			static void set_parent(node_ptr n, node_ptr parent) {
+				n->lookup_.parent_ = parent;
+			}
+
+			static node_ptr get_left(const_node_ptr n) {
+				return n->lookup_.left_;
+			}
+
+			static void set_left(node_ptr n, node_ptr left) {
+				n->lookup_.left_ = left;
+			}
+
+			static node_ptr get_right(const_node_ptr n) {
+				return n->lookup_.right_;
+			}
+
+			static void set_right(node_ptr n, node_ptr right) {
+				n->lookup_.right_ = right;
+			}
+
+			static int get_color(const_node_ptr n) {
+				return n->lookup_.color_;
+			}
+
+			static void set_color(node_ptr n, color c) {
+				n->lookup_.color_ = c;
+			}
+
+			static color red() {
+				return 0;
+			}
+
+			static color black() {
+				return 1;
+			}
+		};
+
+		typedef boost::intrusive::circular_list_algorithms<list_node_traits> lru_algo;
+		typedef boost::intrusive::rbtree_algorithms<rbtree_node_traits> lookup_algo;
+
+		unsigned max_entries_;
+		unsigned current_entries_;
+
+		value_entry lru_header_;
+		value_entry lookup_header_;
+	};
+
+	template <typename ValueTraits>
+	cache<ValueTraits>::cache(unsigned max_entries)
+		: max_entries_(max_entries),
+		  current_entries_(0) {
+		lru_algo::init_header(&lru_header_);
+		lookup_algo::init_header(&lookup_header_);
+	}
+
+	template <typename ValueTraits>
+	cache<ValueTraits>::~cache() {
+		utils::deleter<value_entry> d;
+		lookup_algo::clear_and_dispose(&lookup_header_, d);
+	}
+
+	template <typename ValueTraits>
+	void
+	cache<ValueTraits>::insert(value_type const &v) {
+		make_space();
+
+		std::auto_ptr<value_entry> node(new value_entry(v));
+		value_ptr_cmp cmp;
+		lookup_algo::insert_equal(&lookup_header_, &lookup_header_, node.get(), cmp);
+		node.release();
+		current_entries_++;
+	}
+
+	template <typename ValueTraits>
+	boost::optional<typename ValueTraits::value_type>
+	cache<ValueTraits>::get(key_type const &k) {
+		key_value_ptr_cmp cmp;
+		value_entry *node = lookup_algo::find(&lookup_header_, k, cmp);
+		if (node == &lookup_header_)
+			return boost::optional<value_type>();
+
+		if (!node->ref_count_++)
+			lru_algo::unlink(node);
+		return boost::optional<value_type>(node->v_);
+	}
+
+	template <typename ValueTraits>
+	void
+	cache<ValueTraits>::put(value_type const &v) {
+		// FIXME: the lookup will go once we use a proper hook
+		key_value_ptr_cmp cmp;
+		key_type k = ValueTraits::get_key(v);
+		value_entry *node = lookup_algo::find(&lookup_header_, k, cmp);
+		if (node == &lookup_header_)
+			throw std::runtime_error("invalid put");
+
+		if (node->ref_count_ == 0)
+			throw std::runtime_error("invalid put");
+
+		if (!--node->ref_count_)
+			lru_algo::link_after(&lru_header_, node);
+	}
+
+	template <typename ValueTraits>
+	void
+	cache<ValueTraits>::make_space() {
+		if (current_entries_ == max_entries_) {
+			value_entry *node = lru_header_.lru_.prev_;
+			if (node == &lru_header_)
+				throw std::runtime_error("cache full");
+
+			lru_algo::unlink(node);
+			lookup_algo::unlink(node);
+			delete node;
+			current_entries_--;
+		}
+	}
+
+	template <typename ValueTraits>
+	template <typename T>
+	void
+	cache<ValueTraits>::iterate_unheld(T fn) const {
+		value_entry *n = lru_header_.lru_.next_;
+		while (n != &lru_header_) {
+			fn(n->v_);
+			n = n->lru_.next_;
+		}
+	}
+}
+
+//----------------------------------------------------------------
+
+#endif