diff --git a/drivers/lguest/io.c b/drivers/lguest/io.c
new file mode 100644
index 0000000..06bdba2
--- /dev/null
+++ b/drivers/lguest/io.c
@@ -0,0 +1,399 @@
+/* Simple I/O model for guests, based on shared memory.
+ * Copyright (C) 2006 Rusty Russell IBM Corporation
+ *
+ *  This program 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 of the License, or
+ *  (at your option) any later version.
+ *
+ *  This program 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 this program; if not, write to the Free Software
+ *  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301 USA
+ */
+#include <linux/types.h>
+#include <linux/futex.h>
+#include <linux/jhash.h>
+#include <linux/mm.h>
+#include <linux/highmem.h>
+#include <linux/uaccess.h>
+#include "lg.h"
+
+static struct list_head dma_hash[61];
+
+void lguest_io_init(void)
+{
+	unsigned int i;
+
+	for (i = 0; i < ARRAY_SIZE(dma_hash); i++)
+		INIT_LIST_HEAD(&dma_hash[i]);
+}
+
+/* FIXME: allow multi-page lengths. */
+static int check_dma_list(struct lguest *lg, const struct lguest_dma *dma)
+{
+	unsigned int i;
+
+	for (i = 0; i < LGUEST_MAX_DMA_SECTIONS; i++) {
+		if (!dma->len[i])
+			return 1;
+		if (!lguest_address_ok(lg, dma->addr[i], dma->len[i]))
+			goto kill;
+		if (dma->len[i] > PAGE_SIZE)
+			goto kill;
+		/* We could do over a page, but is it worth it? */
+		if ((dma->addr[i] % PAGE_SIZE) + dma->len[i] > PAGE_SIZE)
+			goto kill;
+	}
+	return 1;
+
+kill:
+	kill_guest(lg, "bad DMA entry: %u@%#lx", dma->len[i], dma->addr[i]);
+	return 0;
+}
+
+static unsigned int hash(const union futex_key *key)
+{
+	return jhash2((u32*)&key->both.word,
+		      (sizeof(key->both.word)+sizeof(key->both.ptr))/4,
+		      key->both.offset)
+		% ARRAY_SIZE(dma_hash);
+}
+
+static inline int key_eq(const union futex_key *a, const union futex_key *b)
+{
+	return (a->both.word == b->both.word
+		&& a->both.ptr == b->both.ptr
+		&& a->both.offset == b->both.offset);
+}
+
+/* Must hold read lock on dmainfo owner's current->mm->mmap_sem */
+static void unlink_dma(struct lguest_dma_info *dmainfo)
+{
+	BUG_ON(!mutex_is_locked(&lguest_lock));
+	dmainfo->interrupt = 0;
+	list_del(&dmainfo->list);
+	drop_futex_key_refs(&dmainfo->key);
+}
+
+static int unbind_dma(struct lguest *lg,
+		      const union futex_key *key,
+		      unsigned long dmas)
+{
+	int i, ret = 0;
+
+	for (i = 0; i < LGUEST_MAX_DMA; i++) {
+		if (key_eq(key, &lg->dma[i].key) && dmas == lg->dma[i].dmas) {
+			unlink_dma(&lg->dma[i]);
+			ret = 1;
+			break;
+		}
+	}
+	return ret;
+}
+
+int bind_dma(struct lguest *lg,
+	     unsigned long ukey, unsigned long dmas, u16 numdmas, u8 interrupt)
+{
+	unsigned int i;
+	int ret = 0;
+	union futex_key key;
+	struct rw_semaphore *fshared = &current->mm->mmap_sem;
+
+	if (interrupt >= LGUEST_IRQS)
+		return 0;
+
+	mutex_lock(&lguest_lock);
+	down_read(fshared);
+	if (get_futex_key((u32 __user *)ukey, fshared, &key) != 0) {
+		kill_guest(lg, "bad dma key %#lx", ukey);
+		goto unlock;
+	}
+	get_futex_key_refs(&key);
+
+	if (interrupt == 0)
+		ret = unbind_dma(lg, &key, dmas);
+	else {
+		for (i = 0; i < LGUEST_MAX_DMA; i++) {
+			if (lg->dma[i].interrupt)
+				continue;
+
+			lg->dma[i].dmas = dmas;
+			lg->dma[i].num_dmas = numdmas;
+			lg->dma[i].next_dma = 0;
+			lg->dma[i].key = key;
+			lg->dma[i].guestid = lg->guestid;
+			lg->dma[i].interrupt = interrupt;
+			list_add(&lg->dma[i].list, &dma_hash[hash(&key)]);
+			ret = 1;
+			goto unlock;
+		}
+	}
+	drop_futex_key_refs(&key);
+unlock:
+ 	up_read(fshared);
+	mutex_unlock(&lguest_lock);
+	return ret;
+}
+
+/* lgread from another guest */
+static int lgread_other(struct lguest *lg,
+			void *buf, u32 addr, unsigned bytes)
+{
+	if (!lguest_address_ok(lg, addr, bytes)
+	    || access_process_vm(lg->tsk, addr, buf, bytes, 0) != bytes) {
+		memset(buf, 0, bytes);
+		kill_guest(lg, "bad address in registered DMA struct");
+		return 0;
+	}
+	return 1;
+}
+
+/* lgwrite to another guest */
+static int lgwrite_other(struct lguest *lg, u32 addr,
+			 const void *buf, unsigned bytes)
+{
+	if (!lguest_address_ok(lg, addr, bytes)
+	    || (access_process_vm(lg->tsk, addr, (void *)buf, bytes, 1)
+		!= bytes)) {
+		kill_guest(lg, "bad address writing to registered DMA");
+		return 0;
+	}
+	return 1;
+}
+
+static u32 copy_data(struct lguest *srclg,
+		     const struct lguest_dma *src,
+		     const struct lguest_dma *dst,
+		     struct page *pages[])
+{
+	unsigned int totlen, si, di, srcoff, dstoff;
+	void *maddr = NULL;
+
+	totlen = 0;
+	si = di = 0;
+	srcoff = dstoff = 0;
+	while (si < LGUEST_MAX_DMA_SECTIONS && src->len[si]
+	       && di < LGUEST_MAX_DMA_SECTIONS && dst->len[di]) {
+		u32 len = min(src->len[si] - srcoff, dst->len[di] - dstoff);
+
+		if (!maddr)
+			maddr = kmap(pages[di]);
+
+		/* FIXME: This is not completely portable, since
+		   archs do different things for copy_to_user_page. */
+		if (copy_from_user(maddr + (dst->addr[di] + dstoff)%PAGE_SIZE,
+				   (void *__user)src->addr[si], len) != 0) {
+			kill_guest(srclg, "bad address in sending DMA");
+			totlen = 0;
+			break;
+		}
+
+		totlen += len;
+		srcoff += len;
+		dstoff += len;
+		if (srcoff == src->len[si]) {
+			si++;
+			srcoff = 0;
+		}
+		if (dstoff == dst->len[di]) {
+			kunmap(pages[di]);
+			maddr = NULL;
+			di++;
+			dstoff = 0;
+		}
+	}
+
+	if (maddr)
+		kunmap(pages[di]);
+
+	return totlen;
+}
+
+/* Src is us, ie. current. */
+static u32 do_dma(struct lguest *srclg, const struct lguest_dma *src,
+		  struct lguest *dstlg, const struct lguest_dma *dst)
+{
+	int i;
+	u32 ret;
+	struct page *pages[LGUEST_MAX_DMA_SECTIONS];
+
+	if (!check_dma_list(dstlg, dst) || !check_dma_list(srclg, src))
+		return 0;
+
+	/* First get the destination pages */
+	for (i = 0; i < LGUEST_MAX_DMA_SECTIONS; i++) {
+		if (dst->len[i] == 0)
+			break;
+		if (get_user_pages(dstlg->tsk, dstlg->mm,
+				   dst->addr[i], 1, 1, 1, pages+i, NULL)
+		    != 1) {
+			kill_guest(dstlg, "Error mapping DMA pages");
+			ret = 0;
+			goto drop_pages;
+		}
+	}
+
+	/* Now copy until we run out of src or dst. */
+	ret = copy_data(srclg, src, dst, pages);
+
+drop_pages:
+	while (--i >= 0)
+		put_page(pages[i]);
+	return ret;
+}
+
+static int dma_transfer(struct lguest *srclg,
+			unsigned long udma,
+			struct lguest_dma_info *dst)
+{
+	struct lguest_dma dst_dma, src_dma;
+	struct lguest *dstlg;
+	u32 i, dma = 0;
+
+	dstlg = &lguests[dst->guestid];
+	/* Get our dma list. */
+	lgread(srclg, &src_dma, udma, sizeof(src_dma));
+
+	/* We can't deadlock against them dmaing to us, because this
+	 * is all under the lguest_lock. */
+	down_read(&dstlg->mm->mmap_sem);
+
+	for (i = 0; i < dst->num_dmas; i++) {
+		dma = (dst->next_dma + i) % dst->num_dmas;
+		if (!lgread_other(dstlg, &dst_dma,
+				  dst->dmas + dma * sizeof(struct lguest_dma),
+				  sizeof(dst_dma))) {
+			goto fail;
+		}
+		if (!dst_dma.used_len)
+			break;
+	}
+	if (i != dst->num_dmas) {
+		unsigned long used_lenp;
+		unsigned int ret;
+
+		ret = do_dma(srclg, &src_dma, dstlg, &dst_dma);
+		/* Put used length in src. */
+		lgwrite_u32(srclg,
+			    udma+offsetof(struct lguest_dma, used_len), ret);
+		if (ret == 0 && src_dma.len[0] != 0)
+			goto fail;
+
+		/* Make sure destination sees contents before length. */
+		wmb();
+		used_lenp = dst->dmas
+			+ dma * sizeof(struct lguest_dma)
+			+ offsetof(struct lguest_dma, used_len);
+		lgwrite_other(dstlg, used_lenp, &ret, sizeof(ret));
+		dst->next_dma++;
+	}
+ 	up_read(&dstlg->mm->mmap_sem);
+
+	/* Do this last so dst doesn't simply sleep on lock. */
+	set_bit(dst->interrupt, dstlg->irqs_pending);
+	wake_up_process(dstlg->tsk);
+	return i == dst->num_dmas;
+
+fail:
+	up_read(&dstlg->mm->mmap_sem);
+	return 0;
+}
+
+void send_dma(struct lguest *lg, unsigned long ukey, unsigned long udma)
+{
+	union futex_key key;
+	int empty = 0;
+	struct rw_semaphore *fshared = &current->mm->mmap_sem;
+
+again:
+	mutex_lock(&lguest_lock);
+	down_read(fshared);
+	if (get_futex_key((u32 __user *)ukey, fshared, &key) != 0) {
+		kill_guest(lg, "bad sending DMA key");
+		goto unlock;
+	}
+	/* Shared mapping?  Look for other guests... */
+	if (key.shared.offset & 1) {
+		struct lguest_dma_info *i;
+		list_for_each_entry(i, &dma_hash[hash(&key)], list) {
+			if (i->guestid == lg->guestid)
+				continue;
+			if (!key_eq(&key, &i->key))
+				continue;
+
+			empty += dma_transfer(lg, udma, i);
+			break;
+		}
+		if (empty == 1) {
+			/* Give any recipients one chance to restock. */
+			up_read(&current->mm->mmap_sem);
+			mutex_unlock(&lguest_lock);
+			empty++;
+			goto again;
+		}
+	} else {
+		/* Private mapping: tell our userspace. */
+		lg->dma_is_pending = 1;
+		lg->pending_dma = udma;
+		lg->pending_key = ukey;
+	}
+unlock:
+	up_read(fshared);
+	mutex_unlock(&lguest_lock);
+}
+
+void release_all_dma(struct lguest *lg)
+{
+	unsigned int i;
+
+	BUG_ON(!mutex_is_locked(&lguest_lock));
+
+	down_read(&lg->mm->mmap_sem);
+	for (i = 0; i < LGUEST_MAX_DMA; i++) {
+		if (lg->dma[i].interrupt)
+			unlink_dma(&lg->dma[i]);
+	}
+	up_read(&lg->mm->mmap_sem);
+}
+
+/* Userspace wants a dma buffer from this guest. */
+unsigned long get_dma_buffer(struct lguest *lg,
+			     unsigned long ukey, unsigned long *interrupt)
+{
+	unsigned long ret = 0;
+	union futex_key key;
+	struct lguest_dma_info *i;
+	struct rw_semaphore *fshared = &current->mm->mmap_sem;
+
+	mutex_lock(&lguest_lock);
+	down_read(fshared);
+	if (get_futex_key((u32 __user *)ukey, fshared, &key) != 0) {
+		kill_guest(lg, "bad registered DMA buffer");
+		goto unlock;
+	}
+	list_for_each_entry(i, &dma_hash[hash(&key)], list) {
+		if (key_eq(&key, &i->key) && i->guestid == lg->guestid) {
+			unsigned int j;
+			for (j = 0; j < i->num_dmas; j++) {
+				struct lguest_dma dma;
+
+				ret = i->dmas + j * sizeof(struct lguest_dma);
+				lgread(lg, &dma, ret, sizeof(dma));
+				if (dma.used_len == 0)
+					break;
+			}
+			*interrupt = i->interrupt;
+			break;
+		}
+	}
+unlock:
+	up_read(fshared);
+	mutex_unlock(&lguest_lock);
+	return ret;
+}
+