diff --git a/drivers/xen/blkback/blkback.c b/drivers/xen/blkback/blkback.c
new file mode 100644
index 0000000..5b8d50e
--- /dev/null
+++ b/drivers/xen/blkback/blkback.c
@@ -0,0 +1,656 @@
+/******************************************************************************
+ * arch/xen/drivers/blkif/backend/main.c
+ *
+ * Back-end of the driver for virtual block devices. This portion of the
+ * driver exports a 'unified' block-device interface that can be accessed
+ * by any operating system that implements a compatible front end. A
+ * reference front-end implementation can be found in:
+ *  arch/xen/drivers/blkif/frontend
+ *
+ * Copyright (c) 2003-2004, Keir Fraser & Steve Hand
+ * Copyright (c) 2005, Christopher Clark
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License version 2
+ * as published by the Free Software Foundation; or, when distributed
+ * separately from the Linux kernel or incorporated into other
+ * software packages, subject to the following license:
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this source file (the "Software"), to deal in the Software without
+ * restriction, including without limitation the rights to use, copy, modify,
+ * merge, publish, distribute, sublicense, and/or sell copies of the Software,
+ * and to permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
+ * IN THE SOFTWARE.
+ */
+
+#include <linux/spinlock.h>
+#include <linux/kthread.h>
+#include <linux/list.h>
+#include <linux/delay.h>
+#include <xen/balloon.h>
+#include <asm/hypervisor.h>
+#include "common.h"
+
+/*
+ * These are rather arbitrary. They are fairly large because adjacent requests
+ * pulled from a communication ring are quite likely to end up being part of
+ * the same scatter/gather request at the disc.
+ *
+ * ** TRY INCREASING 'blkif_reqs' IF WRITE SPEEDS SEEM TOO LOW **
+ *
+ * This will increase the chances of being able to write whole tracks.
+ * 64 should be enough to keep us competitive with Linux.
+ */
+static int blkif_reqs = 64;
+module_param_named(reqs, blkif_reqs, int, 0);
+MODULE_PARM_DESC(reqs, "Number of blkback requests to allocate");
+
+/* Run-time switchable: /sys/module/blkback/parameters/ */
+static unsigned int log_stats = 0;
+static unsigned int debug_lvl = 0;
+module_param(log_stats, int, 0644);
+module_param(debug_lvl, int, 0644);
+
+/*
+ * Each outstanding request that we've passed to the lower device layers has a
+ * 'pending_req' allocated to it. Each buffer_head that completes decrements
+ * the pendcnt towards zero. When it hits zero, the specified domain has a
+ * response queued for it, with the saved 'id' passed back.
+ */
+typedef struct {
+	blkif_t       *blkif;
+	u64            id;
+	int            nr_pages;
+	atomic_t       pendcnt;
+	unsigned short operation;
+	int            status;
+	struct list_head free_list;
+} pending_req_t;
+
+static pending_req_t *pending_reqs;
+static struct list_head pending_free;
+static DEFINE_SPINLOCK(pending_free_lock);
+static DECLARE_WAIT_QUEUE_HEAD(pending_free_wq);
+
+#define BLKBACK_INVALID_HANDLE (~0)
+
+static struct page **pending_pages;
+static grant_handle_t *pending_grant_handles;
+
+static inline int vaddr_pagenr(pending_req_t *req, int seg)
+{
+	return (req - pending_reqs) * BLKIF_MAX_SEGMENTS_PER_REQUEST + seg;
+}
+
+static inline unsigned long vaddr(pending_req_t *req, int seg)
+{
+	unsigned long pfn = page_to_pfn(pending_pages[vaddr_pagenr(req, seg)]);
+	return (unsigned long)pfn_to_kaddr(pfn);
+}
+
+#define pending_handle(_req, _seg) \
+	(pending_grant_handles[vaddr_pagenr(_req, _seg)])
+
+
+static int do_block_io_op(blkif_t *blkif);
+static void dispatch_rw_block_io(blkif_t *blkif,
+				 blkif_request_t *req,
+				 pending_req_t *pending_req);
+static void make_response(blkif_t *blkif, u64 id,
+			  unsigned short op, int st);
+
+/******************************************************************
+ * misc small helpers
+ */
+static pending_req_t* alloc_req(void)
+{
+	pending_req_t *req = NULL;
+	unsigned long flags;
+
+	spin_lock_irqsave(&pending_free_lock, flags);
+	if (!list_empty(&pending_free)) {
+		req = list_entry(pending_free.next, pending_req_t, free_list);
+		list_del(&req->free_list);
+	}
+	spin_unlock_irqrestore(&pending_free_lock, flags);
+	return req;
+}
+
+static void free_req(pending_req_t *req)
+{
+	unsigned long flags;
+	int was_empty;
+
+	spin_lock_irqsave(&pending_free_lock, flags);
+	was_empty = list_empty(&pending_free);
+	list_add(&req->free_list, &pending_free);
+	spin_unlock_irqrestore(&pending_free_lock, flags);
+	if (was_empty)
+		wake_up(&pending_free_wq);
+}
+
+static void unplug_queue(blkif_t *blkif)
+{
+	if (blkif->plug == NULL)
+		return;
+	if (blkif->plug->unplug_fn)
+		blkif->plug->unplug_fn(blkif->plug);
+	blk_put_queue(blkif->plug);
+	blkif->plug = NULL;
+}
+
+static void plug_queue(blkif_t *blkif, struct block_device *bdev)
+{
+	request_queue_t *q = bdev_get_queue(bdev);
+
+	if (q == blkif->plug)
+		return;
+	unplug_queue(blkif);
+	blk_get_queue(q);
+	blkif->plug = q;
+}
+
+static void fast_flush_area(pending_req_t *req)
+{
+	struct gnttab_unmap_grant_ref unmap[BLKIF_MAX_SEGMENTS_PER_REQUEST];
+	unsigned int i, invcount = 0;
+	grant_handle_t handle;
+	int ret;
+
+	for (i = 0; i < req->nr_pages; i++) {
+		handle = pending_handle(req, i);
+		if (handle == BLKBACK_INVALID_HANDLE)
+			continue;
+		gnttab_set_unmap_op(&unmap[invcount], vaddr(req, i),
+				    GNTMAP_host_map, handle);
+		pending_handle(req, i) = BLKBACK_INVALID_HANDLE;
+		invcount++;
+	}
+
+	ret = HYPERVISOR_grant_table_op(
+		GNTTABOP_unmap_grant_ref, unmap, invcount);
+	BUG_ON(ret);
+}
+
+/******************************************************************
+ * SCHEDULER FUNCTIONS
+ */
+
+static void print_stats(blkif_t *blkif)
+{
+	printk(KERN_DEBUG "%s: oo %3d  |  rd %4d  |  wr %4d  |  br %4d\n",
+	       current->comm, blkif->st_oo_req,
+	       blkif->st_rd_req, blkif->st_wr_req, blkif->st_br_req);
+	blkif->st_print = jiffies + msecs_to_jiffies(10 * 1000);
+	blkif->st_rd_req = 0;
+	blkif->st_wr_req = 0;
+	blkif->st_oo_req = 0;
+}
+
+int blkif_schedule(void *arg)
+{
+	blkif_t *blkif = arg;
+
+	blkif_get(blkif);
+
+	if (debug_lvl)
+		printk(KERN_DEBUG "%s: started\n", current->comm);
+
+	while (!kthread_should_stop()) {
+		if (try_to_freeze())
+			continue;
+
+		wait_event_interruptible(
+			blkif->wq,
+			blkif->waiting_reqs || kthread_should_stop());
+		wait_event_interruptible(
+			pending_free_wq,
+			!list_empty(&pending_free) || kthread_should_stop());
+
+		blkif->waiting_reqs = 0;
+		smp_mb(); /* clear flag *before* checking for work */
+
+		if (do_block_io_op(blkif))
+			blkif->waiting_reqs = 1;
+		unplug_queue(blkif);
+
+		if (log_stats && time_after(jiffies, blkif->st_print))
+			print_stats(blkif);
+	}
+
+	if (log_stats)
+		print_stats(blkif);
+	if (debug_lvl)
+		printk(KERN_DEBUG "%s: exiting\n", current->comm);
+
+	blkif->xenblkd = NULL;
+	blkif_put(blkif);
+
+	return 0;
+}
+
+/******************************************************************
+ * COMPLETION CALLBACK -- Called as bh->b_end_io()
+ */
+
+static void __end_block_io_op(pending_req_t *pending_req, int error)
+{
+	/* An error fails the entire request. */
+	if ((pending_req->operation == BLKIF_OP_WRITE_BARRIER) &&
+	    (error == -EOPNOTSUPP)) {
+		DPRINTK("blkback: write barrier op failed, not supported\n");
+		blkback_barrier(XBT_NIL, pending_req->blkif->be, 0);
+		pending_req->status = BLKIF_RSP_EOPNOTSUPP;
+	} else if (error) {
+		DPRINTK("Buffer not up-to-date at end of operation, "
+			"error=%d\n", error);
+		pending_req->status = BLKIF_RSP_ERROR;
+	}
+
+	if (atomic_dec_and_test(&pending_req->pendcnt)) {
+		fast_flush_area(pending_req);
+		make_response(pending_req->blkif, pending_req->id,
+			      pending_req->operation, pending_req->status);
+		blkif_put(pending_req->blkif);
+		free_req(pending_req);
+	}
+}
+
+static int end_block_io_op(struct bio *bio, unsigned int done, int error)
+{
+	if (bio->bi_size != 0)
+		return 1;
+	__end_block_io_op(bio->bi_private, error);
+	bio_put(bio);
+	return error;
+}
+
+
+/******************************************************************************
+ * NOTIFICATION FROM GUEST OS.
+ */
+
+static void blkif_notify_work(blkif_t *blkif)
+{
+	blkif->waiting_reqs = 1;
+	wake_up(&blkif->wq);
+}
+
+irqreturn_t blkif_be_int(int irq, void *dev_id, struct pt_regs *regs)
+{
+	blkif_notify_work(dev_id);
+	return IRQ_HANDLED;
+}
+
+
+
+/******************************************************************
+ * DOWNWARD CALLS -- These interface with the block-device layer proper.
+ */
+
+static int do_block_io_op(blkif_t *blkif)
+{
+	blkif_back_rings_t *blk_rings = &blkif->blk_rings;
+	blkif_request_t req;
+	pending_req_t *pending_req;
+	RING_IDX rc, rp;
+	int more_to_do = 0;
+
+	rc = blk_rings->common.req_cons;
+	rp = blk_rings->common.sring->req_prod;
+	rmb(); /* Ensure we see queued requests up to 'rp'. */
+
+	while (rc != rp) {
+
+		if (RING_REQUEST_CONS_OVERFLOW(&blk_rings->common, rc))
+			break;
+
+		pending_req = alloc_req();
+		if (NULL == pending_req) {
+			blkif->st_oo_req++;
+			more_to_do = 1;
+			break;
+		}
+
+		if (kthread_should_stop()) {
+			more_to_do = 1;
+			break;
+		}
+
+		switch (blkif->blk_protocol) {
+		case BLKIF_PROTOCOL_NATIVE:
+			memcpy(&req, RING_GET_REQUEST(&blk_rings->native, rc), sizeof(req));
+			break;
+		case BLKIF_PROTOCOL_X86_32:
+			blkif_get_x86_32_req(&req, RING_GET_REQUEST(&blk_rings->x86_32, rc));
+			break;
+		case BLKIF_PROTOCOL_X86_64:
+			blkif_get_x86_64_req(&req, RING_GET_REQUEST(&blk_rings->x86_64, rc));
+			break;
+		default:
+			BUG();
+		}
+		blk_rings->common.req_cons = ++rc; /* before make_response() */
+
+		/* Apply all sanity checks to /private copy/ of request. */
+		barrier();
+
+		switch (req.operation) {
+		case BLKIF_OP_READ:
+			blkif->st_rd_req++;
+			dispatch_rw_block_io(blkif, &req, pending_req);
+			break;
+		case BLKIF_OP_WRITE_BARRIER:
+			blkif->st_br_req++;
+			/* fall through */
+		case BLKIF_OP_WRITE:
+			blkif->st_wr_req++;
+			dispatch_rw_block_io(blkif, &req, pending_req);
+			break;
+		default:
+			/* A good sign something is wrong: sleep for a while to
+			 * avoid excessive CPU consumption by a bad guest. */
+			msleep(1);
+			DPRINTK("error: unknown block io operation [%d]\n",
+				req.operation);
+			make_response(blkif, req.id, req.operation,
+				      BLKIF_RSP_ERROR);
+			free_req(pending_req);
+			break;
+		}
+
+		/* Yield point for this unbounded loop. */
+		cond_resched();
+	}
+
+	return more_to_do;
+}
+
+static void dispatch_rw_block_io(blkif_t *blkif,
+				 blkif_request_t *req,
+				 pending_req_t *pending_req)
+{
+	extern void ll_rw_block(int rw, int nr, struct buffer_head * bhs[]);
+	struct gnttab_map_grant_ref map[BLKIF_MAX_SEGMENTS_PER_REQUEST];
+	struct phys_req preq;
+	struct {
+		unsigned long buf; unsigned int nsec;
+	} seg[BLKIF_MAX_SEGMENTS_PER_REQUEST];
+	unsigned int nseg;
+	struct bio *bio = NULL;
+	int ret, i;
+	int operation;
+
+	switch (req->operation) {
+	case BLKIF_OP_READ:
+		operation = READ;
+		break;
+	case BLKIF_OP_WRITE:
+		operation = WRITE;
+		break;
+	case BLKIF_OP_WRITE_BARRIER:
+		operation = WRITE_BARRIER;
+		break;
+	default:
+		operation = 0; /* make gcc happy */
+		BUG();
+	}
+
+	/* Check that number of segments is sane. */
+	nseg = req->nr_segments;
+	if (unlikely(nseg == 0 && operation != WRITE_BARRIER) ||
+	    unlikely(nseg > BLKIF_MAX_SEGMENTS_PER_REQUEST)) {
+		DPRINTK("Bad number of segments in request (%d)\n", nseg);
+		goto fail_response;
+	}
+
+	preq.dev           = req->handle;
+	preq.sector_number = req->sector_number;
+	preq.nr_sects      = 0;
+
+	pending_req->blkif     = blkif;
+	pending_req->id        = req->id;
+	pending_req->operation = req->operation;
+	pending_req->status    = BLKIF_RSP_OKAY;
+	pending_req->nr_pages  = nseg;
+
+	for (i = 0; i < nseg; i++) {
+		uint32_t flags;
+
+		seg[i].nsec = req->seg[i].last_sect -
+			req->seg[i].first_sect + 1;
+
+		if ((req->seg[i].last_sect >= (PAGE_SIZE >> 9)) ||
+		    (req->seg[i].last_sect < req->seg[i].first_sect))
+			goto fail_response;
+		preq.nr_sects += seg[i].nsec;
+
+		flags = GNTMAP_host_map;
+		if (operation != READ)
+			flags |= GNTMAP_readonly;
+		gnttab_set_map_op(&map[i], vaddr(pending_req, i), flags,
+				  req->seg[i].gref, blkif->domid);
+	}
+
+	ret = HYPERVISOR_grant_table_op(GNTTABOP_map_grant_ref, map, nseg);
+	BUG_ON(ret);
+
+	for (i = 0; i < nseg; i++) {
+		if (unlikely(map[i].status != 0)) {
+			DPRINTK("invalid buffer -- could not remap it\n");
+			map[i].handle = BLKBACK_INVALID_HANDLE;
+			ret |= 1;
+		}
+
+		pending_handle(pending_req, i) = map[i].handle;
+
+		if (ret)
+			continue;
+
+		set_phys_to_machine(__pa(vaddr(
+			pending_req, i)) >> PAGE_SHIFT,
+			FOREIGN_FRAME(map[i].dev_bus_addr >> PAGE_SHIFT));
+		seg[i].buf  = map[i].dev_bus_addr |
+			(req->seg[i].first_sect << 9);
+	}
+
+	if (ret)
+		goto fail_flush;
+
+	if (vbd_translate(&preq, blkif, operation) != 0) {
+		DPRINTK("access denied: %s of [%llu,%llu] on dev=%04x\n",
+			operation == READ ? "read" : "write",
+			preq.sector_number,
+			preq.sector_number + preq.nr_sects, preq.dev);
+		goto fail_flush;
+	}
+
+	plug_queue(blkif, preq.bdev);
+	atomic_set(&pending_req->pendcnt, 1);
+	blkif_get(blkif);
+
+	for (i = 0; i < nseg; i++) {
+		if (((int)preq.sector_number|(int)seg[i].nsec) &
+		    ((bdev_hardsect_size(preq.bdev) >> 9) - 1)) {
+			DPRINTK("Misaligned I/O request from domain %d",
+				blkif->domid);
+			goto fail_put_bio;
+		}
+
+		while ((bio == NULL) ||
+		       (bio_add_page(bio,
+				     virt_to_page(vaddr(pending_req, i)),
+				     seg[i].nsec << 9,
+				     seg[i].buf & ~PAGE_MASK) == 0)) {
+			if (bio) {
+				atomic_inc(&pending_req->pendcnt);
+				submit_bio(operation, bio);
+			}
+
+			bio = bio_alloc(GFP_KERNEL, nseg-i);
+			if (unlikely(bio == NULL))
+				goto fail_put_bio;
+
+			bio->bi_bdev    = preq.bdev;
+			bio->bi_private = pending_req;
+			bio->bi_end_io  = end_block_io_op;
+			bio->bi_sector  = preq.sector_number;
+		}
+
+		preq.sector_number += seg[i].nsec;
+	}
+
+	if (!bio) {
+		BUG_ON(operation != WRITE_BARRIER);
+		bio = bio_alloc(GFP_KERNEL, 0);
+		if (unlikely(bio == NULL))
+			goto fail_put_bio;
+
+		bio->bi_bdev    = preq.bdev;
+		bio->bi_private = pending_req;
+		bio->bi_end_io  = end_block_io_op;
+		bio->bi_sector  = -1;
+	}
+
+	submit_bio(operation, bio);
+
+	if (operation == READ)
+		blkif->st_rd_sect += preq.nr_sects;
+	else if (operation == WRITE || operation == WRITE_BARRIER)
+		blkif->st_wr_sect += preq.nr_sects;
+
+	return;
+
+ fail_flush:
+	fast_flush_area(pending_req);
+ fail_response:
+	make_response(blkif, req->id, req->operation, BLKIF_RSP_ERROR);
+	free_req(pending_req);
+	msleep(1); /* back off a bit */
+	return;
+
+ fail_put_bio:
+	__end_block_io_op(pending_req, -EINVAL);
+	if (bio)
+		bio_put(bio);
+	unplug_queue(blkif);
+	msleep(1); /* back off a bit */
+	return;
+}
+
+
+
+/******************************************************************
+ * MISCELLANEOUS SETUP / TEARDOWN / DEBUGGING
+ */
+
+
+static void make_response(blkif_t *blkif, u64 id,
+			  unsigned short op, int st)
+{
+	blkif_response_t  resp;
+	unsigned long     flags;
+	blkif_back_rings_t *blk_rings = &blkif->blk_rings;
+	int more_to_do = 0;
+	int notify;
+
+	resp.id        = id;
+	resp.operation = op;
+	resp.status    = st;
+
+	spin_lock_irqsave(&blkif->blk_ring_lock, flags);
+	/* Place on the response ring for the relevant domain. */
+	switch (blkif->blk_protocol) {
+	case BLKIF_PROTOCOL_NATIVE:
+		memcpy(RING_GET_RESPONSE(&blk_rings->native, blk_rings->native.rsp_prod_pvt),
+		       &resp, sizeof(resp));
+		break;
+	case BLKIF_PROTOCOL_X86_32:
+		memcpy(RING_GET_RESPONSE(&blk_rings->x86_32, blk_rings->x86_32.rsp_prod_pvt),
+		       &resp, sizeof(resp));
+		break;
+	case BLKIF_PROTOCOL_X86_64:
+		memcpy(RING_GET_RESPONSE(&blk_rings->x86_64, blk_rings->x86_64.rsp_prod_pvt),
+		       &resp, sizeof(resp));
+		break;
+	default:
+		BUG();
+	}
+	blk_rings->common.rsp_prod_pvt++;
+	RING_PUSH_RESPONSES_AND_CHECK_NOTIFY(&blk_rings->common, notify);
+	if (blk_rings->common.rsp_prod_pvt == blk_rings->common.req_cons) {
+		/*
+		 * Tail check for pending requests. Allows frontend to avoid
+		 * notifications if requests are already in flight (lower
+		 * overheads and promotes batching).
+		 */
+		RING_FINAL_CHECK_FOR_REQUESTS(&blk_rings->common, more_to_do);
+
+	} else if (RING_HAS_UNCONSUMED_REQUESTS(&blk_rings->common)) {
+		more_to_do = 1;
+	}
+
+	spin_unlock_irqrestore(&blkif->blk_ring_lock, flags);
+
+	if (more_to_do)
+		blkif_notify_work(blkif);
+	if (notify)
+		notify_remote_via_irq(blkif->irq);
+}
+
+static int __init blkif_init(void)
+{
+	int i, mmap_pages;
+
+	if (!is_running_on_xen())
+		return -ENODEV;
+
+	mmap_pages = blkif_reqs * BLKIF_MAX_SEGMENTS_PER_REQUEST;
+
+	pending_reqs          = kmalloc(sizeof(pending_reqs[0]) *
+					blkif_reqs, GFP_KERNEL);
+	pending_grant_handles = kmalloc(sizeof(pending_grant_handles[0]) *
+					mmap_pages, GFP_KERNEL);
+	pending_pages         = alloc_empty_pages_and_pagevec(mmap_pages);
+
+	if (!pending_reqs || !pending_grant_handles || !pending_pages)
+		goto out_of_memory;
+
+	for (i = 0; i < mmap_pages; i++)
+		pending_grant_handles[i] = BLKBACK_INVALID_HANDLE;
+
+	blkif_interface_init();
+
+	memset(pending_reqs, 0, sizeof(pending_reqs));
+	INIT_LIST_HEAD(&pending_free);
+
+	for (i = 0; i < blkif_reqs; i++)
+		list_add_tail(&pending_reqs[i].free_list, &pending_free);
+
+	blkif_xenbus_init();
+
+	return 0;
+
+ out_of_memory:
+	kfree(pending_reqs);
+	kfree(pending_grant_handles);
+	free_empty_pages_and_pagevec(pending_pages, mmap_pages);
+	printk("%s: out of memory\n", __FUNCTION__);
+	return -ENOMEM;
+}
+
+module_init(blkif_init);
+
+MODULE_LICENSE("Dual BSD/GPL");