diff --git a/lib/lru_cache.c b/lib/lru_cache.c
new file mode 100644
index 0000000..270de9d
--- /dev/null
+++ b/lib/lru_cache.c
@@ -0,0 +1,560 @@
+/*
+   lru_cache.c
+
+   This file is part of DRBD by Philipp Reisner and Lars Ellenberg.
+
+   Copyright (C) 2003-2008, LINBIT Information Technologies GmbH.
+   Copyright (C) 2003-2008, Philipp Reisner <philipp.reisner@linbit.com>.
+   Copyright (C) 2003-2008, Lars Ellenberg <lars.ellenberg@linbit.com>.
+
+   drbd 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 2, or (at your option)
+   any later version.
+
+   drbd 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 drbd; see the file COPYING.  If not, write to
+   the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.
+
+ */
+
+#include <linux/module.h>
+#include <linux/bitops.h>
+#include <linux/slab.h>
+#include <linux/string.h> /* for memset */
+#include <linux/seq_file.h> /* for seq_printf */
+#include <linux/lru_cache.h>
+
+MODULE_AUTHOR("Philipp Reisner <phil@linbit.com>, "
+	      "Lars Ellenberg <lars@linbit.com>");
+MODULE_DESCRIPTION("lru_cache - Track sets of hot objects");
+MODULE_LICENSE("GPL");
+
+/* this is developers aid only.
+ * it catches concurrent access (lack of locking on the users part) */
+#define PARANOIA_ENTRY() do {		\
+	BUG_ON(!lc);			\
+	BUG_ON(!lc->nr_elements);	\
+	BUG_ON(test_and_set_bit(__LC_PARANOIA, &lc->flags)); \
+} while (0)
+
+#define RETURN(x...)     do { \
+	clear_bit(__LC_PARANOIA, &lc->flags); \
+	smp_mb__after_clear_bit(); return x ; } while (0)
+
+/* BUG() if e is not one of the elements tracked by lc */
+#define PARANOIA_LC_ELEMENT(lc, e) do {	\
+	struct lru_cache *lc_ = (lc);	\
+	struct lc_element *e_ = (e);	\
+	unsigned i = e_->lc_index;	\
+	BUG_ON(i >= lc_->nr_elements);	\
+	BUG_ON(lc_->lc_element[i] != e_); } while (0)
+
+/**
+ * lc_create - prepares to track objects in an active set
+ * @name: descriptive name only used in lc_seq_printf_stats and lc_seq_dump_details
+ * @e_count: number of elements allowed to be active simultaneously
+ * @e_size: size of the tracked objects
+ * @e_off: offset to the &struct lc_element member in a tracked object
+ *
+ * Returns a pointer to a newly initialized struct lru_cache on success,
+ * or NULL on (allocation) failure.
+ */
+struct lru_cache *lc_create(const char *name, struct kmem_cache *cache,
+		unsigned e_count, size_t e_size, size_t e_off)
+{
+	struct hlist_head *slot = NULL;
+	struct lc_element **element = NULL;
+	struct lru_cache *lc;
+	struct lc_element *e;
+	unsigned cache_obj_size = kmem_cache_size(cache);
+	unsigned i;
+
+	WARN_ON(cache_obj_size < e_size);
+	if (cache_obj_size < e_size)
+		return NULL;
+
+	/* e_count too big; would probably fail the allocation below anyways.
+	 * for typical use cases, e_count should be few thousand at most. */
+	if (e_count > LC_MAX_ACTIVE)
+		return NULL;
+
+	slot = kzalloc(e_count * sizeof(struct hlist_head*), GFP_KERNEL);
+	if (!slot)
+		goto out_fail;
+	element = kzalloc(e_count * sizeof(struct lc_element *), GFP_KERNEL);
+	if (!element)
+		goto out_fail;
+
+	lc = kzalloc(sizeof(*lc), GFP_KERNEL);
+	if (!lc)
+		goto out_fail;
+
+	INIT_LIST_HEAD(&lc->in_use);
+	INIT_LIST_HEAD(&lc->lru);
+	INIT_LIST_HEAD(&lc->free);
+
+	lc->name = name;
+	lc->element_size = e_size;
+	lc->element_off = e_off;
+	lc->nr_elements = e_count;
+	lc->new_number = LC_FREE;
+	lc->lc_cache = cache;
+	lc->lc_element = element;
+	lc->lc_slot = slot;
+
+	/* preallocate all objects */
+	for (i = 0; i < e_count; i++) {
+		void *p = kmem_cache_alloc(cache, GFP_KERNEL);
+		if (!p)
+			break;
+		memset(p, 0, lc->element_size);
+		e = p + e_off;
+		e->lc_index = i;
+		e->lc_number = LC_FREE;
+		list_add(&e->list, &lc->free);
+		element[i] = e;
+	}
+	if (i == e_count)
+		return lc;
+
+	/* else: could not allocate all elements, give up */
+	for (i--; i; i--) {
+		void *p = element[i];
+		kmem_cache_free(cache, p - e_off);
+	}
+	kfree(lc);
+out_fail:
+	kfree(element);
+	kfree(slot);
+	return NULL;
+}
+
+void lc_free_by_index(struct lru_cache *lc, unsigned i)
+{
+	void *p = lc->lc_element[i];
+	WARN_ON(!p);
+	if (p) {
+		p -= lc->element_off;
+		kmem_cache_free(lc->lc_cache, p);
+	}
+}
+
+/**
+ * lc_destroy - frees memory allocated by lc_create()
+ * @lc: the lru cache to destroy
+ */
+void lc_destroy(struct lru_cache *lc)
+{
+	unsigned i;
+	if (!lc)
+		return;
+	for (i = 0; i < lc->nr_elements; i++)
+		lc_free_by_index(lc, i);
+	kfree(lc->lc_element);
+	kfree(lc->lc_slot);
+	kfree(lc);
+}
+
+/**
+ * lc_reset - does a full reset for @lc and the hash table slots.
+ * @lc: the lru cache to operate on
+ *
+ * It is roughly the equivalent of re-allocating a fresh lru_cache object,
+ * basically a short cut to lc_destroy(lc); lc = lc_create(...);
+ */
+void lc_reset(struct lru_cache *lc)
+{
+	unsigned i;
+
+	INIT_LIST_HEAD(&lc->in_use);
+	INIT_LIST_HEAD(&lc->lru);
+	INIT_LIST_HEAD(&lc->free);
+	lc->used = 0;
+	lc->hits = 0;
+	lc->misses = 0;
+	lc->starving = 0;
+	lc->dirty = 0;
+	lc->changed = 0;
+	lc->flags = 0;
+	lc->changing_element = NULL;
+	lc->new_number = LC_FREE;
+	memset(lc->lc_slot, 0, sizeof(struct hlist_head) * lc->nr_elements);
+
+	for (i = 0; i < lc->nr_elements; i++) {
+		struct lc_element *e = lc->lc_element[i];
+		void *p = e;
+		p -= lc->element_off;
+		memset(p, 0, lc->element_size);
+		/* re-init it */
+		e->lc_index = i;
+		e->lc_number = LC_FREE;
+		list_add(&e->list, &lc->free);
+	}
+}
+
+/**
+ * lc_seq_printf_stats - print stats about @lc into @seq
+ * @seq: the seq_file to print into
+ * @lc: the lru cache to print statistics of
+ */
+size_t lc_seq_printf_stats(struct seq_file *seq, struct lru_cache *lc)
+{
+	/* NOTE:
+	 * total calls to lc_get are
+	 * (starving + hits + misses)
+	 * misses include "dirty" count (update from an other thread in
+	 * progress) and "changed", when this in fact lead to an successful
+	 * update of the cache.
+	 */
+	return seq_printf(seq, "\t%s: used:%u/%u "
+		"hits:%lu misses:%lu starving:%lu dirty:%lu changed:%lu\n",
+		lc->name, lc->used, lc->nr_elements,
+		lc->hits, lc->misses, lc->starving, lc->dirty, lc->changed);
+}
+
+static struct hlist_head *lc_hash_slot(struct lru_cache *lc, unsigned int enr)
+{
+	return  lc->lc_slot + (enr % lc->nr_elements);
+}
+
+
+/**
+ * lc_find - find element by label, if present in the hash table
+ * @lc: The lru_cache object
+ * @enr: element number
+ *
+ * Returns the pointer to an element, if the element with the requested
+ * "label" or element number is present in the hash table,
+ * or NULL if not found. Does not change the refcnt.
+ */
+struct lc_element *lc_find(struct lru_cache *lc, unsigned int enr)
+{
+	struct hlist_node *n;
+	struct lc_element *e;
+
+	BUG_ON(!lc);
+	BUG_ON(!lc->nr_elements);
+	hlist_for_each_entry(e, n, lc_hash_slot(lc, enr), colision) {
+		if (e->lc_number == enr)
+			return e;
+	}
+	return NULL;
+}
+
+/* returned element will be "recycled" immediately */
+static struct lc_element *lc_evict(struct lru_cache *lc)
+{
+	struct list_head  *n;
+	struct lc_element *e;
+
+	if (list_empty(&lc->lru))
+		return NULL;
+
+	n = lc->lru.prev;
+	e = list_entry(n, struct lc_element, list);
+
+	PARANOIA_LC_ELEMENT(lc, e);
+
+	list_del(&e->list);
+	hlist_del(&e->colision);
+	return e;
+}
+
+/**
+ * lc_del - removes an element from the cache
+ * @lc: The lru_cache object
+ * @e: The element to remove
+ *
+ * @e must be unused (refcnt == 0). Moves @e from "lru" to "free" list,
+ * sets @e->enr to %LC_FREE.
+ */
+void lc_del(struct lru_cache *lc, struct lc_element *e)
+{
+	PARANOIA_ENTRY();
+	PARANOIA_LC_ELEMENT(lc, e);
+	BUG_ON(e->refcnt);
+
+	e->lc_number = LC_FREE;
+	hlist_del_init(&e->colision);
+	list_move(&e->list, &lc->free);
+	RETURN();
+}
+
+static struct lc_element *lc_get_unused_element(struct lru_cache *lc)
+{
+	struct list_head *n;
+
+	if (list_empty(&lc->free))
+		return lc_evict(lc);
+
+	n = lc->free.next;
+	list_del(n);
+	return list_entry(n, struct lc_element, list);
+}
+
+static int lc_unused_element_available(struct lru_cache *lc)
+{
+	if (!list_empty(&lc->free))
+		return 1; /* something on the free list */
+	if (!list_empty(&lc->lru))
+		return 1;  /* something to evict */
+
+	return 0;
+}
+
+
+/**
+ * lc_get - get element by label, maybe change the active set
+ * @lc: the lru cache to operate on
+ * @enr: the label to look up
+ *
+ * Finds an element in the cache, increases its usage count,
+ * "touches" and returns it.
+ *
+ * In case the requested number is not present, it needs to be added to the
+ * cache. Therefore it is possible that an other element becomes evicted from
+ * the cache. In either case, the user is notified so he is able to e.g. keep
+ * a persistent log of the cache changes, and therefore the objects in use.
+ *
+ * Return values:
+ *  NULL
+ *     The cache was marked %LC_STARVING,
+ *     or the requested label was not in the active set
+ *     and a changing transaction is still pending (@lc was marked %LC_DIRTY).
+ *     Or no unused or free element could be recycled (@lc will be marked as
+ *     %LC_STARVING, blocking further lc_get() operations).
+ *
+ *  pointer to the element with the REQUESTED element number.
+ *     In this case, it can be used right away
+ *
+ *  pointer to an UNUSED element with some different element number,
+ *          where that different number may also be %LC_FREE.
+ *
+ *          In this case, the cache is marked %LC_DIRTY (blocking further changes),
+ *          and the returned element pointer is removed from the lru list and
+ *          hash collision chains.  The user now should do whatever housekeeping
+ *          is necessary.
+ *          Then he must call lc_changed(lc,element_pointer), to finish
+ *          the change.
+ *
+ * NOTE: The user needs to check the lc_number on EACH use, so he recognizes
+ *       any cache set change.
+ */
+struct lc_element *lc_get(struct lru_cache *lc, unsigned int enr)
+{
+	struct lc_element *e;
+
+	PARANOIA_ENTRY();
+	if (lc->flags & LC_STARVING) {
+		++lc->starving;
+		RETURN(NULL);
+	}
+
+	e = lc_find(lc, enr);
+	if (e) {
+		++lc->hits;
+		if (e->refcnt++ == 0)
+			lc->used++;
+		list_move(&e->list, &lc->in_use); /* Not evictable... */
+		RETURN(e);
+	}
+
+	++lc->misses;
+
+	/* In case there is nothing available and we can not kick out
+	 * the LRU element, we have to wait ...
+	 */
+	if (!lc_unused_element_available(lc)) {
+		__set_bit(__LC_STARVING, &lc->flags);
+		RETURN(NULL);
+	}
+
+	/* it was not present in the active set.
+	 * we are going to recycle an unused (or even "free") element.
+	 * user may need to commit a transaction to record that change.
+	 * we serialize on flags & TF_DIRTY */
+	if (test_and_set_bit(__LC_DIRTY, &lc->flags)) {
+		++lc->dirty;
+		RETURN(NULL);
+	}
+
+	e = lc_get_unused_element(lc);
+	BUG_ON(!e);
+
+	clear_bit(__LC_STARVING, &lc->flags);
+	BUG_ON(++e->refcnt != 1);
+	lc->used++;
+
+	lc->changing_element = e;
+	lc->new_number = enr;
+
+	RETURN(e);
+}
+
+/* similar to lc_get,
+ * but only gets a new reference on an existing element.
+ * you either get the requested element, or NULL.
+ * will be consolidated into one function.
+ */
+struct lc_element *lc_try_get(struct lru_cache *lc, unsigned int enr)
+{
+	struct lc_element *e;
+
+	PARANOIA_ENTRY();
+	if (lc->flags & LC_STARVING) {
+		++lc->starving;
+		RETURN(NULL);
+	}
+
+	e = lc_find(lc, enr);
+	if (e) {
+		++lc->hits;
+		if (e->refcnt++ == 0)
+			lc->used++;
+		list_move(&e->list, &lc->in_use); /* Not evictable... */
+	}
+	RETURN(e);
+}
+
+/**
+ * lc_changed - tell @lc that the change has been recorded
+ * @lc: the lru cache to operate on
+ * @e: the element pending label change
+ */
+void lc_changed(struct lru_cache *lc, struct lc_element *e)
+{
+	PARANOIA_ENTRY();
+	BUG_ON(e != lc->changing_element);
+	PARANOIA_LC_ELEMENT(lc, e);
+	++lc->changed;
+	e->lc_number = lc->new_number;
+	list_add(&e->list, &lc->in_use);
+	hlist_add_head(&e->colision, lc_hash_slot(lc, lc->new_number));
+	lc->changing_element = NULL;
+	lc->new_number = LC_FREE;
+	clear_bit(__LC_DIRTY, &lc->flags);
+	smp_mb__after_clear_bit();
+	RETURN();
+}
+
+
+/**
+ * lc_put - give up refcnt of @e
+ * @lc: the lru cache to operate on
+ * @e: the element to put
+ *
+ * If refcnt reaches zero, the element is moved to the lru list,
+ * and a %LC_STARVING (if set) is cleared.
+ * Returns the new (post-decrement) refcnt.
+ */
+unsigned int lc_put(struct lru_cache *lc, struct lc_element *e)
+{
+	PARANOIA_ENTRY();
+	PARANOIA_LC_ELEMENT(lc, e);
+	BUG_ON(e->refcnt == 0);
+	BUG_ON(e == lc->changing_element);
+	if (--e->refcnt == 0) {
+		/* move it to the front of LRU. */
+		list_move(&e->list, &lc->lru);
+		lc->used--;
+		clear_bit(__LC_STARVING, &lc->flags);
+		smp_mb__after_clear_bit();
+	}
+	RETURN(e->refcnt);
+}
+
+/**
+ * lc_element_by_index
+ * @lc: the lru cache to operate on
+ * @i: the index of the element to return
+ */
+struct lc_element *lc_element_by_index(struct lru_cache *lc, unsigned i)
+{
+	BUG_ON(i >= lc->nr_elements);
+	BUG_ON(lc->lc_element[i] == NULL);
+	BUG_ON(lc->lc_element[i]->lc_index != i);
+	return lc->lc_element[i];
+}
+
+/**
+ * lc_index_of
+ * @lc: the lru cache to operate on
+ * @e: the element to query for its index position in lc->element
+ */
+unsigned int lc_index_of(struct lru_cache *lc, struct lc_element *e)
+{
+	PARANOIA_LC_ELEMENT(lc, e);
+	return e->lc_index;
+}
+
+/**
+ * lc_set - associate index with label
+ * @lc: the lru cache to operate on
+ * @enr: the label to set
+ * @index: the element index to associate label with.
+ *
+ * Used to initialize the active set to some previously recorded state.
+ */
+void lc_set(struct lru_cache *lc, unsigned int enr, int index)
+{
+	struct lc_element *e;
+
+	if (index < 0 || index >= lc->nr_elements)
+		return;
+
+	e = lc_element_by_index(lc, index);
+	e->lc_number = enr;
+
+	hlist_del_init(&e->colision);
+	hlist_add_head(&e->colision, lc_hash_slot(lc, enr));
+	list_move(&e->list, e->refcnt ? &lc->in_use : &lc->lru);
+}
+
+/**
+ * lc_dump - Dump a complete LRU cache to seq in textual form.
+ * @lc: the lru cache to operate on
+ * @seq: the &struct seq_file pointer to seq_printf into
+ * @utext: user supplied "heading" or other info
+ * @detail: function pointer the user may provide to dump further details
+ * of the object the lc_element is embedded in.
+ */
+void lc_seq_dump_details(struct seq_file *seq, struct lru_cache *lc, char *utext,
+	     void (*detail) (struct seq_file *, struct lc_element *))
+{
+	unsigned int nr_elements = lc->nr_elements;
+	struct lc_element *e;
+	int i;
+
+	seq_printf(seq, "\tnn: lc_number refcnt %s\n ", utext);
+	for (i = 0; i < nr_elements; i++) {
+		e = lc_element_by_index(lc, i);
+		if (e->lc_number == LC_FREE) {
+			seq_printf(seq, "\t%2d: FREE\n", i);
+		} else {
+			seq_printf(seq, "\t%2d: %4u %4u    ", i,
+				   e->lc_number, e->refcnt);
+			detail(seq, e);
+		}
+	}
+}
+
+EXPORT_SYMBOL(lc_create);
+EXPORT_SYMBOL(lc_reset);
+EXPORT_SYMBOL(lc_destroy);
+EXPORT_SYMBOL(lc_set);
+EXPORT_SYMBOL(lc_del);
+EXPORT_SYMBOL(lc_try_get);
+EXPORT_SYMBOL(lc_find);
+EXPORT_SYMBOL(lc_get);
+EXPORT_SYMBOL(lc_put);
+EXPORT_SYMBOL(lc_changed);
+EXPORT_SYMBOL(lc_element_by_index);
+EXPORT_SYMBOL(lc_index_of);
+EXPORT_SYMBOL(lc_seq_printf_stats);
+EXPORT_SYMBOL(lc_seq_dump_details);