diff --git a/drivers/md/dm-io.c b/drivers/md/dm-io.c
new file mode 100644
index 0000000..45754bb
--- /dev/null
+++ b/drivers/md/dm-io.c
@@ -0,0 +1,426 @@
+/*
+ * Copyright (C) 2003 Sistina Software
+ *
+ * This file is released under the GPL.
+ */
+
+#include "dm-io.h"
+
+#include <linux/bio.h>
+#include <linux/mempool.h>
+#include <linux/module.h>
+#include <linux/sched.h>
+#include <linux/slab.h>
+
+static struct bio_set *_bios;
+
+/* FIXME: can we shrink this ? */
+struct io {
+	unsigned long error;
+	atomic_t count;
+	struct task_struct *sleeper;
+	io_notify_fn callback;
+	void *context;
+};
+
+/*
+ * io contexts are only dynamically allocated for asynchronous
+ * io.  Since async io is likely to be the majority of io we'll
+ * have the same number of io contexts as buffer heads ! (FIXME:
+ * must reduce this).
+ */
+static unsigned _num_ios;
+static mempool_t *_io_pool;
+
+static void *alloc_io(unsigned int __nocast gfp_mask, void *pool_data)
+{
+	return kmalloc(sizeof(struct io), gfp_mask);
+}
+
+static void free_io(void *element, void *pool_data)
+{
+	kfree(element);
+}
+
+static unsigned int pages_to_ios(unsigned int pages)
+{
+	return 4 * pages;	/* too many ? */
+}
+
+static int resize_pool(unsigned int new_ios)
+{
+	int r = 0;
+
+	if (_io_pool) {
+		if (new_ios == 0) {
+			/* free off the pool */
+			mempool_destroy(_io_pool);
+			_io_pool = NULL;
+			bioset_free(_bios);
+
+		} else {
+			/* resize the pool */
+			r = mempool_resize(_io_pool, new_ios, GFP_KERNEL);
+		}
+
+	} else {
+		/* create new pool */
+		_io_pool = mempool_create(new_ios, alloc_io, free_io, NULL);
+		if (!_io_pool)
+			return -ENOMEM;
+
+		_bios = bioset_create(16, 16, 4);
+		if (!_bios) {
+			mempool_destroy(_io_pool);
+			_io_pool = NULL;
+			return -ENOMEM;
+		}
+	}
+
+	if (!r)
+		_num_ios = new_ios;
+
+	return r;
+}
+
+int dm_io_get(unsigned int num_pages)
+{
+	return resize_pool(_num_ios + pages_to_ios(num_pages));
+}
+
+void dm_io_put(unsigned int num_pages)
+{
+	resize_pool(_num_ios - pages_to_ios(num_pages));
+}
+
+/*-----------------------------------------------------------------
+ * We need to keep track of which region a bio is doing io for.
+ * In order to save a memory allocation we store this the last
+ * bvec which we know is unused (blech).
+ * XXX This is ugly and can OOPS with some configs... find another way.
+ *---------------------------------------------------------------*/
+static inline void bio_set_region(struct bio *bio, unsigned region)
+{
+	bio->bi_io_vec[bio->bi_max_vecs - 1].bv_len = region;
+}
+
+static inline unsigned bio_get_region(struct bio *bio)
+{
+	return bio->bi_io_vec[bio->bi_max_vecs - 1].bv_len;
+}
+
+/*-----------------------------------------------------------------
+ * We need an io object to keep track of the number of bios that
+ * have been dispatched for a particular io.
+ *---------------------------------------------------------------*/
+static void dec_count(struct io *io, unsigned int region, int error)
+{
+	if (error)
+		set_bit(region, &io->error);
+
+	if (atomic_dec_and_test(&io->count)) {
+		if (io->sleeper)
+			wake_up_process(io->sleeper);
+
+		else {
+			int r = io->error;
+			io_notify_fn fn = io->callback;
+			void *context = io->context;
+
+			mempool_free(io, _io_pool);
+			fn(r, context);
+		}
+	}
+}
+
+static int endio(struct bio *bio, unsigned int done, int error)
+{
+	struct io *io = (struct io *) bio->bi_private;
+
+	/* keep going until we've finished */
+	if (bio->bi_size)
+		return 1;
+
+	if (error && bio_data_dir(bio) == READ)
+		zero_fill_bio(bio);
+
+	dec_count(io, bio_get_region(bio), error);
+	bio_put(bio);
+
+	return 0;
+}
+
+/*-----------------------------------------------------------------
+ * These little objects provide an abstraction for getting a new
+ * destination page for io.
+ *---------------------------------------------------------------*/
+struct dpages {
+	void (*get_page)(struct dpages *dp,
+			 struct page **p, unsigned long *len, unsigned *offset);
+	void (*next_page)(struct dpages *dp);
+
+	unsigned context_u;
+	void *context_ptr;
+};
+
+/*
+ * Functions for getting the pages from a list.
+ */
+static void list_get_page(struct dpages *dp,
+		  struct page **p, unsigned long *len, unsigned *offset)
+{
+	unsigned o = dp->context_u;
+	struct page_list *pl = (struct page_list *) dp->context_ptr;
+
+	*p = pl->page;
+	*len = PAGE_SIZE - o;
+	*offset = o;
+}
+
+static void list_next_page(struct dpages *dp)
+{
+	struct page_list *pl = (struct page_list *) dp->context_ptr;
+	dp->context_ptr = pl->next;
+	dp->context_u = 0;
+}
+
+static void list_dp_init(struct dpages *dp, struct page_list *pl, unsigned offset)
+{
+	dp->get_page = list_get_page;
+	dp->next_page = list_next_page;
+	dp->context_u = offset;
+	dp->context_ptr = pl;
+}
+
+/*
+ * Functions for getting the pages from a bvec.
+ */
+static void bvec_get_page(struct dpages *dp,
+		  struct page **p, unsigned long *len, unsigned *offset)
+{
+	struct bio_vec *bvec = (struct bio_vec *) dp->context_ptr;
+	*p = bvec->bv_page;
+	*len = bvec->bv_len;
+	*offset = bvec->bv_offset;
+}
+
+static void bvec_next_page(struct dpages *dp)
+{
+	struct bio_vec *bvec = (struct bio_vec *) dp->context_ptr;
+	dp->context_ptr = bvec + 1;
+}
+
+static void bvec_dp_init(struct dpages *dp, struct bio_vec *bvec)
+{
+	dp->get_page = bvec_get_page;
+	dp->next_page = bvec_next_page;
+	dp->context_ptr = bvec;
+}
+
+static void vm_get_page(struct dpages *dp,
+		 struct page **p, unsigned long *len, unsigned *offset)
+{
+	*p = vmalloc_to_page(dp->context_ptr);
+	*offset = dp->context_u;
+	*len = PAGE_SIZE - dp->context_u;
+}
+
+static void vm_next_page(struct dpages *dp)
+{
+	dp->context_ptr += PAGE_SIZE - dp->context_u;
+	dp->context_u = 0;
+}
+
+static void vm_dp_init(struct dpages *dp, void *data)
+{
+	dp->get_page = vm_get_page;
+	dp->next_page = vm_next_page;
+	dp->context_u = ((unsigned long) data) & (PAGE_SIZE - 1);
+	dp->context_ptr = data;
+}
+
+/*-----------------------------------------------------------------
+ * IO routines that accept a list of pages.
+ *---------------------------------------------------------------*/
+static void do_region(int rw, unsigned int region, struct io_region *where,
+		      struct dpages *dp, struct io *io)
+{
+	struct bio *bio;
+	struct page *page;
+	unsigned long len;
+	unsigned offset;
+	unsigned num_bvecs;
+	sector_t remaining = where->count;
+
+	while (remaining) {
+		/*
+		 * Allocate a suitably sized bio, we add an extra
+		 * bvec for bio_get/set_region().
+		 */
+		num_bvecs = (remaining / (PAGE_SIZE >> 9)) + 2;
+		bio = bio_alloc_bioset(GFP_NOIO, num_bvecs, _bios);
+		bio->bi_sector = where->sector + (where->count - remaining);
+		bio->bi_bdev = where->bdev;
+		bio->bi_end_io = endio;
+		bio->bi_private = io;
+		bio_set_region(bio, region);
+
+		/*
+		 * Try and add as many pages as possible.
+		 */
+		while (remaining) {
+			dp->get_page(dp, &page, &len, &offset);
+			len = min(len, to_bytes(remaining));
+			if (!bio_add_page(bio, page, len, offset))
+				break;
+
+			offset = 0;
+			remaining -= to_sector(len);
+			dp->next_page(dp);
+		}
+
+		atomic_inc(&io->count);
+		submit_bio(rw, bio);
+	}
+}
+
+static void dispatch_io(int rw, unsigned int num_regions,
+			struct io_region *where, struct dpages *dp,
+			struct io *io, int sync)
+{
+	int i;
+	struct dpages old_pages = *dp;
+
+	if (sync)
+		rw |= (1 << BIO_RW_SYNC);
+
+	/*
+	 * For multiple regions we need to be careful to rewind
+	 * the dp object for each call to do_region.
+	 */
+	for (i = 0; i < num_regions; i++) {
+		*dp = old_pages;
+		if (where[i].count)
+			do_region(rw, i, where + i, dp, io);
+	}
+
+	/*
+	 * Drop the extra refence that we were holding to avoid
+	 * the io being completed too early.
+	 */
+	dec_count(io, 0, 0);
+}
+
+static int sync_io(unsigned int num_regions, struct io_region *where,
+	    int rw, struct dpages *dp, unsigned long *error_bits)
+{
+	struct io io;
+
+	if (num_regions > 1 && rw != WRITE) {
+		WARN_ON(1);
+		return -EIO;
+	}
+
+	io.error = 0;
+	atomic_set(&io.count, 1); /* see dispatch_io() */
+	io.sleeper = current;
+
+	dispatch_io(rw, num_regions, where, dp, &io, 1);
+
+	while (1) {
+		set_current_state(TASK_UNINTERRUPTIBLE);
+
+		if (!atomic_read(&io.count) || signal_pending(current))
+			break;
+
+		io_schedule();
+	}
+	set_current_state(TASK_RUNNING);
+
+	if (atomic_read(&io.count))
+		return -EINTR;
+
+	*error_bits = io.error;
+	return io.error ? -EIO : 0;
+}
+
+static int async_io(unsigned int num_regions, struct io_region *where, int rw,
+	     struct dpages *dp, io_notify_fn fn, void *context)
+{
+	struct io *io;
+
+	if (num_regions > 1 && rw != WRITE) {
+		WARN_ON(1);
+		fn(1, context);
+		return -EIO;
+	}
+
+	io = mempool_alloc(_io_pool, GFP_NOIO);
+	io->error = 0;
+	atomic_set(&io->count, 1); /* see dispatch_io() */
+	io->sleeper = NULL;
+	io->callback = fn;
+	io->context = context;
+
+	dispatch_io(rw, num_regions, where, dp, io, 0);
+	return 0;
+}
+
+int dm_io_sync(unsigned int num_regions, struct io_region *where, int rw,
+	       struct page_list *pl, unsigned int offset,
+	       unsigned long *error_bits)
+{
+	struct dpages dp;
+	list_dp_init(&dp, pl, offset);
+	return sync_io(num_regions, where, rw, &dp, error_bits);
+}
+
+int dm_io_sync_bvec(unsigned int num_regions, struct io_region *where, int rw,
+		    struct bio_vec *bvec, unsigned long *error_bits)
+{
+	struct dpages dp;
+	bvec_dp_init(&dp, bvec);
+	return sync_io(num_regions, where, rw, &dp, error_bits);
+}
+
+int dm_io_sync_vm(unsigned int num_regions, struct io_region *where, int rw,
+		  void *data, unsigned long *error_bits)
+{
+	struct dpages dp;
+	vm_dp_init(&dp, data);
+	return sync_io(num_regions, where, rw, &dp, error_bits);
+}
+
+int dm_io_async(unsigned int num_regions, struct io_region *where, int rw,
+		struct page_list *pl, unsigned int offset,
+		io_notify_fn fn, void *context)
+{
+	struct dpages dp;
+	list_dp_init(&dp, pl, offset);
+	return async_io(num_regions, where, rw, &dp, fn, context);
+}
+
+int dm_io_async_bvec(unsigned int num_regions, struct io_region *where, int rw,
+		     struct bio_vec *bvec, io_notify_fn fn, void *context)
+{
+	struct dpages dp;
+	bvec_dp_init(&dp, bvec);
+	return async_io(num_regions, where, rw, &dp, fn, context);
+}
+
+int dm_io_async_vm(unsigned int num_regions, struct io_region *where, int rw,
+		   void *data, io_notify_fn fn, void *context)
+{
+	struct dpages dp;
+	vm_dp_init(&dp, data);
+	return async_io(num_regions, where, rw, &dp, fn, context);
+}
+
+EXPORT_SYMBOL(dm_io_get);
+EXPORT_SYMBOL(dm_io_put);
+EXPORT_SYMBOL(dm_io_sync);
+EXPORT_SYMBOL(dm_io_async);
+EXPORT_SYMBOL(dm_io_sync_bvec);
+EXPORT_SYMBOL(dm_io_async_bvec);
+EXPORT_SYMBOL(dm_io_sync_vm);
+EXPORT_SYMBOL(dm_io_async_vm);