[patch 39/43] lguest: This patch gets rid of the old lguest host I/O infrastructure and replaces it with a single hypercall "LHCALL_NOTIFY" which takes an address.

[rusty@rustcorp.com.au]

[-- Attachment #1: new-io-lguest-core-replace-hypercalls.patch --]
[-- Type: text/plain, Size: 34495 bytes --]

The main change is the removal of io.c: that mainly did inter-guest
I/O, which virtio doesn't yet support.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
---
 drivers/lguest/Makefile         |    2 
 drivers/lguest/core.c           |   12 
 drivers/lguest/hypercalls.c     |   26 -
 drivers/lguest/io.c             |  628 ---------------------------------------
 drivers/lguest/lg.h             |   27 -
 drivers/lguest/lguest_user.c    |   39 --
 include/asm-i386/lguest_hcall.h |    3 
 include/linux/lguest_launcher.h |   36 --
 8 files changed, 21 insertions(+), 752 deletions(-)

===================================================================
--- a/drivers/lguest/Makefile
+++ b/drivers/lguest/Makefile
@@ -1,7 +1,7 @@
 # Host requires the other files, which can be a module.
 obj-$(CONFIG_LGUEST)	+= lg.o
 lg-y = core.o hypercalls.o page_tables.o interrupts_and_traps.o \
-	segments.o io.o lguest_user.o
+	segments.o lguest_user.o
 
 lg-$(CONFIG_X86_32) += i386_switcher.o i386_core.o
 
===================================================================
--- a/drivers/lguest/core.c
+++ b/drivers/lguest/core.c
@@ -202,13 +202,12 @@ int run_guest(struct lguest *lg, unsigne
 		if (lg->hcall)
 			do_hypercalls(lg);
 
-		/* It's possible the Guest did a SEND_DMA hypercall to the
+		/* It's possible the Guest did a NOTIFY hypercall to the
 		 * Launcher, in which case we return from the read() now. */
-		if (lg->dma_is_pending) {
-			if (put_user(lg->pending_dma, user) ||
-			    put_user(lg->pending_key, user+1))
+		if (lg->pending_notify) {
+			if (put_user(lg->pending_notify, user))
 				return -EFAULT;
-			return sizeof(unsigned long)*2;
+			return sizeof(lg->pending_notify);
 		}
 
 		/* Check for signals */
@@ -287,9 +286,6 @@ static int __init init(void)
 	err = init_pagetables(switcher_page, SHARED_SWITCHER_PAGES);
 	if (err)
 		goto unmap;
-
-	/* The I/O subsystem needs some things initialized. */
-	lguest_io_init();
 
 	/* We might need to reserve an interrupt vector. */
 	err = init_interrupts();
===================================================================
--- a/drivers/lguest/hypercalls.c
+++ b/drivers/lguest/hypercalls.c
@@ -60,22 +60,9 @@ static void do_hcall(struct lguest *lg, 
 		else
 			guest_pagetable_flush_user(lg);
 		break;
-	case LHCALL_BIND_DMA:
-		/* BIND_DMA really wants four arguments, but it's the only call
-		 * which does.  So the Guest packs the number of buffers and
-		 * the interrupt number into the final argument, and we decode
-		 * it here.  This can legitimately fail, since we currently
-		 * place a limit on the number of DMA pools a Guest can have.
-		 * So we return true or false from this call. */
-		args->arg0 = bind_dma(lg, args->arg1, args->arg2,
-				     args->arg3 >> 8, args->arg3 & 0xFF);
-		break;
 
 	/* All these calls simply pass the arguments through to the right
 	 * routines. */
-	case LHCALL_SEND_DMA:
-		send_dma(lg, args->arg1, args->arg2);
-		break;
 	case LHCALL_NEW_PGTABLE:
 		guest_new_pagetable(lg, args->arg1);
 		break;
@@ -98,6 +85,9 @@ static void do_hcall(struct lguest *lg, 
 	case LHCALL_HALT:
 		/* Similarly, this sets the halted flag for run_guest(). */
 		lg->halted = 1;
+		break;
+	case LHCALL_NOTIFY:
+		lg->pending_notify = args->arg1;
 		break;
 	default:
 		if (lguest_arch_do_hcall(lg, args))
@@ -156,9 +146,9 @@ static void do_async_hcalls(struct lgues
 			break;
 		}
 
- 		/* Stop doing hypercalls if we've just done a DMA to the
-		 * Launcher: it needs to service this first. */
-		if (lg->dma_is_pending)
+ 		/* Stop doing hypercalls if they want to notify the Launcher:
+		 * it needs to service this first. */
+		if (lg->pending_notify)
 			break;
 	}
 }
@@ -220,9 +210,9 @@ void do_hypercalls(struct lguest *lg)
 	do_async_hcalls(lg);
 
 	/* If we stopped reading the hypercall ring because the Guest did a
-	 * SEND_DMA to the Launcher, we want to return now.  Otherwise we do
+	 * NOTIFY to the Launcher, we want to return now.  Otherwise we do
 	 * the hypercall. */
-	if (!lg->dma_is_pending) {
+	if (!lg->pending_notify) {
 		do_hcall(lg, lg->hcall);
 		/* Tricky point: we reset the hcall pointer to mark the
 		 * hypercall as "done".  We use the hcall pointer rather than
===================================================================
--- a/drivers/lguest/io.c
+++ /dev/null
@@ -1,628 +0,0 @@
-/*P:300 The I/O mechanism in lguest is simple yet flexible, allowing the Guest
- * to talk to the Launcher or directly to another Guest.  It uses familiar
- * concepts of DMA and interrupts, plus some neat code stolen from
- * futexes... :*/
-
-/* 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"
-
-/*L:300
- * I/O
- *
- * Getting data in and out of the Guest is quite an art.  There are numerous
- * ways to do it, and they all suck differently.  We try to keep things fairly
- * close to "real" hardware so our Guest's drivers don't look like an alien
- * visitation in the middle of the Linux code, and yet make sure that Guests
- * can talk directly to other Guests, not just the Launcher.
- *
- * To do this, the Guest gives us a key when it binds or sends DMA buffers.
- * The key corresponds to a "physical" address inside the Guest (ie. a virtual
- * address inside the Launcher process).  We don't, however, use this key
- * directly.
- *
- * We want Guests which share memory to be able to DMA to each other: two
- * Launchers can mmap memory the same file, then the Guests can communicate.
- * Fortunately, the futex code provides us with a way to get a "union
- * futex_key" corresponding to the memory lying at a virtual address: if the
- * two processes share memory, the "union futex_key" for that memory will match
- * even if the memory is mapped at different addresses in each.  So we always
- * convert the keys to "union futex_key"s to compare them.
- *
- * Before we dive into this though, we need to look at another set of helper
- * routines used throughout the Host kernel code to access Guest memory.
- :*/
-static struct list_head dma_hash[61];
-
-/* An unfortunate side effect of the Linux double-linked list implementation is
- * that there's no good way to statically initialize an array of linked
- * lists. */
-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;
-}
-
-/*L:330 This is our hash function, using the wonderful Jenkins hash.
- *
- * The futex key is a union with three parts: an unsigned long word, a pointer,
- * and an int "offset".  We could use jhash_2words() which takes three u32s.
- * (Ok, the hash functions are great: the naming sucks though).
- *
- * It's nice to be portable to 64-bit platforms, so we use the more generic
- * jhash2(), which takes an array of u32, the number of u32s, and an initial
- * u32 to roll in.  This is uglier, but breaks down to almost the same code on
- * 32-bit platforms like this one.
- *
- * We want a position in the array, so we modulo ARRAY_SIZE(dma_hash) (ie. 61).
- */
-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);
-}
-
-/* This is a convenience routine to compare two keys.  It's a much bemoaned C
- * weakness that it doesn't allow '==' on structures or unions, so we have to
- * open-code it like this. */
-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);
-}
-
-/*L:360 OK, when we need to actually free up a Guest's DMA array we do several
- * things, so we have a convenient function to do it.
- *
- * The caller must hold a read lock on dmainfo owner's current->mm->mmap_sem
- * for the drop_futex_key_refs(). */
-static void unlink_dma(struct lguest_dma_info *dmainfo)
-{
-	/* You locked this too, right? */
-	BUG_ON(!mutex_is_locked(&lguest_lock));
-	/* This is how we know that the entry is free. */
-	dmainfo->interrupt = 0;
-	/* Remove it from the hash table. */
-	list_del(&dmainfo->list);
-	/* Drop the references we were holding (to the inode or mm). */
-	drop_futex_key_refs(&dmainfo->key);
-}
-
-/*L:350 This is the routine which we call when the Guest asks to unregister a
- * DMA array attached to a given key.  Returns true if the array was found. */
-static int unbind_dma(struct lguest *lg,
-		      const union futex_key *key,
-		      unsigned long dmas)
-{
-	int i, ret = 0;
-
-	/* We don't bother with the hash table, just look through all this
-	 * Guest's DMA arrays. */
-	for (i = 0; i < LGUEST_MAX_DMA; i++) {
-		/* In theory it could have more than one array on the same key,
-		 * or one array on multiple keys, so we check both */
-		if (key_eq(key, &lg->dma[i].key) && dmas == lg->dma[i].dmas) {
-			unlink_dma(&lg->dma[i]);
-			ret = 1;
-			break;
-		}
-	}
-	return ret;
-}
-
-/*L:340 BIND_DMA: this is the hypercall which sets up an array of "struct
- * lguest_dma" for receiving I/O.
- *
- * The Guest wants to bind an array of "struct lguest_dma"s to a particular key
- * to receive input.  This only happens when the Guest is setting up a new
- * device, so it doesn't have to be very fast.
- *
- * It returns 1 on a successful registration (it can fail if we hit the limit
- * of registrations for this Guest).
- */
-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;
-	/* Futex code needs the mmap_sem. */
-	struct rw_semaphore *fshared = &current->mm->mmap_sem;
-
-	/* Invalid interrupt?  (We could kill the guest here). */
-	if (interrupt >= LGUEST_IRQS)
-		return 0;
-
-	/* We need to grab the Big Lguest Lock, because other Guests may be
-	 * trying to look through this Guest's DMAs to send something while
-	 * we're doing this. */
-	mutex_lock(&lguest_lock);
-	down_read(fshared);
-	if (get_futex_key(lg->mem_base + ukey, fshared, &key) != 0) {
-		kill_guest(lg, "bad dma key %#lx", ukey);
-		goto unlock;
-	}
-
-	/* We want to keep this key valid once we drop mmap_sem, so we have to
-	 * hold a reference. */
-	get_futex_key_refs(&key);
-
-	/* If the Guest specified an interrupt of 0, that means they want to
-	 * unregister this array of "struct lguest_dma"s. */
-	if (interrupt == 0)
-		ret = unbind_dma(lg, &key, dmas);
-	else {
-		/* Look through this Guest's dma array for an unused entry. */
-		for (i = 0; i < LGUEST_MAX_DMA; i++) {
-			/* If the interrupt is non-zero, the entry is already
-			 * used. */
-			if (lg->dma[i].interrupt)
-				continue;
-
-			/* OK, a free one!  Fill on our details. */
-			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].owner = lg;
-			lg->dma[i].interrupt = interrupt;
-
-			/* Now we add it to the hash table: the position
-			 * depends on the futex key that we got. */
-			list_add(&lg->dma[i].list, &dma_hash[hash(&key)]);
-			/* Success! */
-			ret = 1;
-			goto unlock;
-		}
-	}
-	/* If we didn't find a slot to put the key in, drop the reference
-	 * again. */
-	drop_futex_key_refs(&key);
-unlock:
-	/* Unlock and out. */
- 	up_read(fshared);
-	mutex_unlock(&lguest_lock);
-	return ret;
-}
-
-/*L:385 Note that our routines to access a different Guest's memory are called
- * lgread_other() and lgwrite_other(): these names emphasize that they are only
- * used when the Guest is *not* the current Guest.
- *
- * The interface for copying from another process's memory is called
- * access_process_vm(), with a final argument of 0 for a read, and 1 for a
- * write.
- *
- * We need lgread_other() to read the destination Guest's "struct lguest_dma"
- * array. */
-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, (unsigned long)lg->mem_base + 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: used to update the destination "used_len" once
- * we've transferred data into the buffer. */
-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, (unsigned long)lg->mem_base + addr,
-				 (void *)buf, bytes, 1) != bytes) {
-		kill_guest(lg, "bad address writing to registered DMA");
-		return 0;
-	}
-	return 1;
-}
-
-/*L:400 This is the generic engine which copies from a source "struct
- * lguest_dma" from this Guest into another Guest's "struct lguest_dma".  The
- * destination Guest's pages have already been mapped, as contained in the
- * pages array.
- *
- * If you're wondering if there's a nice "copy from one process to another"
- * routine, so was I.  But Linux isn't really set up to copy between two
- * unrelated processes, so we have to write it ourselves.
- */
-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;
-
-	/* We return the total length transferred. */
-	totlen = 0;
-
-	/* We keep indexes into the source and destination "struct lguest_dma",
-	 * and an offset within each region. */
-	si = di = 0;
-	srcoff = dstoff = 0;
-
-	/* We loop until the source or destination is exhausted. */
-	while (si < LGUEST_MAX_DMA_SECTIONS && src->len[si]
-	       && di < LGUEST_MAX_DMA_SECTIONS && dst->len[di]) {
-		/* We can only transfer the rest of the src buffer, or as much
-		 * as will fit into the destination buffer. */
-		u32 len = min(src->len[si] - srcoff, dst->len[di] - dstoff);
-
-		/* For systems using "highmem" we need to use kmap() to access
-		 * the page we want.  We often use the same page over and over,
-		 * so rather than kmap() it on every loop, we set the maddr
-		 * pointer to NULL when we need to move to the next
-		 * destination page. */
-		if (!maddr)
-			maddr = kmap(pages[di]);
-
-		/* Copy directly from (this Guest's) source address to the
-		 * destination Guest's kmap()ed buffer.  Note that maddr points
-		 * to the start of the page: we need to add the offset of the
-		 * destination address and offset within the buffer. */
-
-		/* FIXME: This is not completely portable.  I looked at
-		 * copy_to_user_page(), and some arch's seem to need special
-		 * flushes.  x86 is fine. */
-		if (copy_from_user(maddr + (dst->addr[di] + dstoff)%PAGE_SIZE,
-				   srclg->mem_base+src->addr[si], len) != 0) {
-			/* If a copy failed, it's the source's fault. */
-			kill_guest(srclg, "bad address in sending DMA");
-			totlen = 0;
-			break;
-		}
-
-		/* Increment the total and src & dst offsets */
-		totlen += len;
-		srcoff += len;
-		dstoff += len;
-
-		/* Presumably we reached the end of the src or dest buffers: */
-		if (srcoff == src->len[si]) {
-			/* Move to the next buffer at offset 0 */
-			si++;
-			srcoff = 0;
-		}
-		if (dstoff == dst->len[di]) {
-			/* We need to unmap that destination page and reset
-			 * maddr ready for the next one. */
-			kunmap(pages[di]);
-			maddr = NULL;
-			di++;
-			dstoff = 0;
-		}
-	}
-
-	/* If we still had a page mapped at the end, unmap now. */
-	if (maddr)
-		kunmap(pages[di]);
-
-	return totlen;
-}
-
-/*L:390 This is how we transfer a "struct lguest_dma" from the source Guest
- * (the current Guest which called SEND_DMA) to another Guest. */
-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];
-
-	/* We check that both source and destination "struct lguest_dma"s are
-	 * within the bounds of the source and destination Guests */
-	if (!check_dma_list(dstlg, dst) || !check_dma_list(srclg, src))
-		return 0;
-
-	/* We need to map the pages which correspond to each parts of
-	 * destination buffer. */
-	for (i = 0; i < LGUEST_MAX_DMA_SECTIONS; i++) {
-		if (dst->len[i] == 0)
-			break;
-		/* get_user_pages() is a complicated function, especially since
-		 * we only want a single page.  But it works, and returns the
-		 * number of pages.  Note that we're holding the destination's
-		 * mmap_sem, as get_user_pages() requires. */
-		if (get_user_pages(dstlg->tsk, dstlg->mm,
-				   (unsigned long)dstlg->mem_base+dst->addr[i],
-				   1, 1, 1, pages+i, NULL)
-		    != 1) {
-			/* This means the destination gave us a bogus buffer */
-			kill_guest(dstlg, "Error mapping DMA pages");
-			ret = 0;
-			goto drop_pages;
-		}
-	}
-
-	/* Now copy the data 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;
-}
-
-/*L:380 Transferring data from one Guest to another is not as simple as I'd
- * like.  We've found the "struct lguest_dma_info" bound to the same address as
- * the send, we need to copy into it.
- *
- * This function returns true if the destination array was empty. */
-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;
-
-	/* From the "struct lguest_dma_info" we found in the hash, grab the
-	 * Guest. */
-	dstlg = dst->owner;
-	/* Read in the source "struct lguest_dma" handed to SEND_DMA. */
-	lgread(srclg, &src_dma, udma, sizeof(src_dma));
-
-	/* We need the destination's mmap_sem, and we already hold the source's
-	 * mmap_sem for the futex key lookup.  Normally this would suggest that
-	 * we could deadlock if the destination Guest was trying to send to
-	 * this source Guest at the same time, which is another reason that all
-	 * I/O is done under the big lguest_lock. */
-	down_read(&dstlg->mm->mmap_sem);
-
-	/* Look through the destination DMA array for an available buffer. */
-	for (i = 0; i < dst->num_dmas; i++) {
-		/* We keep a "next_dma" pointer which often helps us avoid
-		 * looking at lots of previously-filled entries. */
-		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 we found a buffer, we do the actual data copy. */
-	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 the source "struct lguest_dma"'s used_len
-		 * field.  It's a little tricky to figure out where that is,
-		 * though. */
-		lgwrite_u32(srclg,
-			    udma+offsetof(struct lguest_dma, used_len), ret);
-		/* Tranferring 0 bytes is OK if the source buffer was empty. */
-		if (ret == 0 && src_dma.len[0] != 0)
-			goto fail;
-
-		/* The destination Guest might be running on a different CPU:
-		 * we have to make sure that it will see the "used_len" field
-		 * change to non-zero *after* it sees the data we copied into
-		 * the buffer.  Hence a write memory barrier. */
-		wmb();
-		/* Figuring out where the destination's used_len field for this
-		 * "struct lguest_dma" in the array is also a little ugly. */
-		used_lenp = dst->dmas
-			+ dma * sizeof(struct lguest_dma)
-			+ offsetof(struct lguest_dma, used_len);
-		lgwrite_other(dstlg, used_lenp, &ret, sizeof(ret));
-		/* Move the cursor for next time. */
-		dst->next_dma++;
-	}
- 	up_read(&dstlg->mm->mmap_sem);
-
-	/* We trigger the destination interrupt, even if the destination was
-	 * empty and we didn't transfer anything: this gives them a chance to
-	 * wake up and refill. */
-	set_bit(dst->interrupt, dstlg->irqs_pending);
-	/* Wake up the destination process. */
-	wake_up_process(dstlg->tsk);
-	/* If we passed the last "struct lguest_dma", the receive had no
-	 * buffers left. */
-	return i == dst->num_dmas;
-
-fail:
-	up_read(&dstlg->mm->mmap_sem);
-	return 0;
-}
-
-/*L:370 This is the counter-side to the BIND_DMA hypercall; the SEND_DMA
- * hypercall.  We find out who's listening, and send to them. */
-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);
-	/* Get the futex key for the key the Guest gave us */
-	if (get_futex_key(lg->mem_base + ukey, fshared, &key) != 0) {
-		kill_guest(lg, "bad sending DMA key");
-		goto unlock;
-	}
-	/* Since the key must be a multiple of 4, the futex key uses the lower
-	 * bit of the "offset" field (which would always be 0) to indicate a
-	 * mapping which is shared with other processes (ie. Guests). */
-	if (key.shared.offset & 1) {
-		struct lguest_dma_info *i;
-		/* Look through the hash for other Guests. */
-		list_for_each_entry(i, &dma_hash[hash(&key)], list) {
-			/* Don't send to ourselves (would deadlock). */
-			if (i->owner->mm == lg->mm)
-				continue;
-			if (!key_eq(&key, &i->key))
-				continue;
-
-			/* If dma_transfer() tells us the destination has no
-			 * available buffers, we increment "empty". */
-			empty += dma_transfer(lg, udma, i);
-			break;
-		}
-		/* If the destination is empty, we release our locks and
-		 * give the destination Guest a brief chance to restock. */
-		if (empty == 1) {
-			/* Give any recipients one chance to restock. */
-			up_read(&current->mm->mmap_sem);
-			mutex_unlock(&lguest_lock);
-			/* Next time, we won't try again. */
-			empty++;
-			goto again;
-		}
-	} else {
-		/* Private mapping: Guest is sending to its Launcher.  We set
-		 * the "dma_is_pending" flag so that the main loop will exit
-		 * and the Launcher's read() from /dev/lguest will return. */
-		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);
-}
-
-/*M:007 We only return a single DMA buffer to the Launcher, but it would be
- * more efficient to return a pointer to the entire array of DMA buffers, which
- * it can cache and choose one whenever it wants.
- *
- * Currently the Launcher uses a write to /dev/lguest, and the return value is
- * the address of the DMA structure with the interrupt number placed in
- * dma->used_len.  If we wanted to return the entire array, we need to return
- * the address, array size and interrupt number: this seems to require an
- * ioctl(). :*/
-
-/*L:320 This routine looks for a DMA buffer registered by the Guest on the
- * given key (using the BIND_DMA hypercall). */
-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;
-
-	/* Take the Big Lguest Lock to stop other Guests sending this Guest DMA
-	 * at the same time. */
-	mutex_lock(&lguest_lock);
-	/* To match between Guests sharing the same underlying memory we steal
-	 * code from the futex infrastructure.  This requires that we hold the
-	 * "mmap_sem" for our process (the Launcher), and pass it to the futex
-	 * code. */
-	down_read(fshared);
-
-	/* This can fail if it's not a valid address, or if the address is not
-	 * divisible by 4 (the futex code needs that, we don't really). */
-	if (get_futex_key(lg->mem_base + ukey, fshared, &key) != 0) {
-		kill_guest(lg, "bad registered DMA buffer");
-		goto unlock;
-	}
-	/* Search the hash table for matching entries (the Launcher can only
-	 * send to its own Guest for the moment, so the entry must be for this
-	 * Guest) */
-	list_for_each_entry(i, &dma_hash[hash(&key)], list) {
-		if (key_eq(&key, &i->key) && i->owner == lg) {
-			unsigned int j;
-			/* Look through the registered DMA array for an
-			 * available buffer. */
-			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;
-			}
-			/* Store the interrupt the Guest wants when the buffer
-			 * is used. */
-			*interrupt = i->interrupt;
-			break;
-		}
-	}
-unlock:
-	up_read(fshared);
-	mutex_unlock(&lguest_lock);
-	return ret;
-}
-/*:*/
-
-/*L:410 This really has completed the Launcher.  Not only have we now finished
- * the longest chapter in our journey, but this also means we are over halfway
- * through!
- *
- * Enough prevaricating around the bush: it is time for us to dive into the
- * core of the Host, in "make Host".
- */
===================================================================
--- a/drivers/lguest/lg.h
+++ b/drivers/lguest/lg.h
@@ -6,7 +6,6 @@
 #include <linux/init.h>
 #include <linux/stringify.h>
 #include <linux/binfmts.h>
-#include <linux/futex.h>
 #include <linux/lguest.h>
 #include <linux/lguest_launcher.h>
 #include <linux/wait.h>
@@ -17,17 +16,6 @@
 
 void free_pagetables(void);
 int init_pagetables(struct page **switcher_page, unsigned int pages);
-
-struct lguest_dma_info
-{
-	struct list_head list;
-	union futex_key key;
-	unsigned long dmas;
-	struct lguest *owner;
-	u16 next_dma;
-	u16 num_dmas;
-	u8 interrupt; 	/* 0 when not registered */
-};
 
 struct pgdir
 {
@@ -91,14 +79,10 @@ struct lguest
 	struct task_struct *wake;
 
 	unsigned long noirq_start, noirq_end;
-	int dma_is_pending;
-	unsigned long pending_dma; /* struct lguest_dma */
-	unsigned long pending_key; /* address they're sending to */
+	unsigned long pending_notify; /* pfn from LHCALL_NOTIFY */
 
 	unsigned int stack_pages;
 	u32 tsc_khz;
-
-	struct lguest_dma_info dma[LGUEST_MAX_DMA];
 
 	/* Dead? */
 	const char *dead;
@@ -185,15 +169,6 @@ int lguest_device_init(void);
 int lguest_device_init(void);
 void lguest_device_remove(void);
 
-/* io.c: */
-void lguest_io_init(void);
-int bind_dma(struct lguest *lg,
-	     unsigned long key, unsigned long udma, u16 numdmas, u8 interrupt);
-void send_dma(struct lguest *info, unsigned long key, unsigned long udma);
-void release_all_dma(struct lguest *lg);
-unsigned long get_dma_buffer(struct lguest *lg, unsigned long key,
-			     unsigned long *interrupt);
-
 /* hypercalls.c: */
 void do_hypercalls(struct lguest *lg);
 void write_timestamp(struct lguest *lg);
===================================================================
--- a/drivers/lguest/lguest_user.c
+++ b/drivers/lguest/lguest_user.c
@@ -2,36 +2,11 @@
  * controls and communicates with the Guest.  For example, the first write will
  * tell us the Guest's memory layout, pagetable, entry point and kernel address
  * offset.  A read will run the Guest until something happens, such as a signal
- * or the Guest doing a DMA out to the Launcher.  Writes are also used to get a
- * DMA buffer registered by the Guest and to send the Guest an interrupt. :*/
+ * or the Guest doing a NOTIFY out to the Launcher. :*/
 #include <linux/uaccess.h>
 #include <linux/miscdevice.h>
 #include <linux/fs.h>
 #include "lg.h"
-
-/*L:310 To send DMA into the Guest, the Launcher needs to be able to ask for a
- * DMA buffer.  This is done by writing LHREQ_GETDMA and the key to
- * /dev/lguest. */
-static long user_get_dma(struct lguest *lg, const unsigned long __user *input)
-{
-	unsigned long key, udma, irq;
-
-	/* Fetch the key they wrote to us. */
-	if (get_user(key, input) != 0)
-		return -EFAULT;
-	/* Look for a free Guest DMA buffer bound to that key. */
-	udma = get_dma_buffer(lg, key, &irq);
-	if (!udma)
-		return -ENOENT;
-
-	/* We need to tell the Launcher what interrupt the Guest expects after
-	 * the buffer is filled.  We stash it in udma->used_len. */
-	lgwrite_u32(lg, udma + offsetof(struct lguest_dma, used_len), irq);
-
-	/* The (guest-physical) address of the DMA buffer is returned from
-	 * the write(). */
-	return udma;
-}
 
 /*L:315 To force the Guest to stop running and return to the Launcher, the
  * Waker sets writes LHREQ_BREAK and the value "1" to /dev/lguest.  The
@@ -102,10 +77,10 @@ static ssize_t read(struct file *file, c
 		return len;
 	}
 
-	/* If we returned from read() last time because the Guest sent DMA,
+	/* If we returned from read() last time because the Guest notified,
 	 * clear the flag. */
-	if (lg->dma_is_pending)
-		lg->dma_is_pending = 0;
+	if (lg->pending_notify)
+		lg->pending_notify = 0;
 
 	/* Run the Guest until something interesting happens. */
 	return run_guest(lg, (unsigned long __user *)user);
@@ -216,7 +191,7 @@ unlock:
 /*L:010 The first operation the Launcher does must be a write.  All writes
  * start with a 32 bit number: for the first write this must be
  * LHREQ_INITIALIZE to set up the Guest.  After that the Launcher can use
- * writes of other values to get DMA buffers and send interrupts. */
+ * writes of other values to send interrupts. */
 static ssize_t write(struct file *file, const char __user *in,
 		     size_t size, loff_t *off)
 {
@@ -245,8 +220,6 @@ static ssize_t write(struct file *file, 
 	switch (req) {
 	case LHREQ_INITIALIZE:
 		return initialize(file, input);
-	case LHREQ_GETDMA:
-		return user_get_dma(lg, input);
 	case LHREQ_IRQ:
 		return user_send_irq(lg, input);
 	case LHREQ_BREAK:
@@ -276,8 +249,6 @@ static int close(struct inode *inode, st
 	mutex_lock(&lguest_lock);
 	/* Cancels the hrtimer set via LHCALL_SET_CLOCKEVENT. */
 	hrtimer_cancel(&lg->hrt);
-	/* Free any DMA buffers the Guest had bound. */
-	release_all_dma(lg);
 	/* Free up the shadow page tables for the Guest. */
 	free_guest_pagetable(lg);
 	/* Now all the memory cleanups are done, it's safe to release the
===================================================================
--- a/include/asm-i386/lguest_hcall.h
+++ b/include/asm-i386/lguest_hcall.h
@@ -15,11 +15,10 @@
 #define LHCALL_TS		8
 #define LHCALL_SET_CLOCKEVENT	9
 #define LHCALL_HALT		10
-#define LHCALL_BIND_DMA		12
-#define LHCALL_SEND_DMA		13
 #define LHCALL_SET_PTE		14
 #define LHCALL_SET_PMD		15
 #define LHCALL_LOAD_TLS		16
+#define LHCALL_NOTIFY		17
 
 /*G:031 First, how does our Guest contact the Host to ask for privileged
  * operations?  There are two ways: the direct way is to make a "hypercall",
===================================================================
--- a/include/linux/lguest_launcher.h
+++ b/include/linux/lguest_launcher.h
@@ -9,40 +9,6 @@
 
 /* How many devices?  Assume each one wants up to two dma arrays per device. */
 #define LGUEST_MAX_DEVICES (LGUEST_MAX_DMA/2)
-
-/*D:200
- * Lguest I/O
- *
- * The lguest I/O mechanism is the only way Guests can talk to devices.  There
- * are two hypercalls involved: SEND_DMA for output and BIND_DMA for input.  In
- * each case, "struct lguest_dma" describes the buffer: this contains 16
- * addr/len pairs, and if there are fewer buffer elements the len array is
- * terminated with a 0.
- *
- * I/O is organized by keys: BIND_DMA attaches buffers to a particular key, and
- * SEND_DMA transfers to buffers bound to particular key.  By convention, keys
- * correspond to a physical address within the device's page.  This means that
- * devices will never accidentally end up with the same keys, and allows the
- * Host use The Futex Trick (as we'll see later in our journey).
- *
- * SEND_DMA simply indicates a key to send to, and the physical address of the
- * "struct lguest_dma" to send.  The Host will write the number of bytes
- * transferred into the "struct lguest_dma"'s used_len member.
- *
- * BIND_DMA indicates a key to bind to, a pointer to an array of "struct
- * lguest_dma"s ready for receiving, the size of that array, and an interrupt
- * to trigger when data is received.  The Host will only allow transfers into
- * buffers with a used_len of zero: it then sets used_len to the number of
- * bytes transferred and triggers the interrupt for the Guest to process the
- * new input. */
-struct lguest_dma
-{
-	/* 0 if free to be used, filled by the Host. */
- 	__u32 used_len;
-	__u16 len[LGUEST_MAX_DMA_SECTIONS];
-	unsigned long addr[LGUEST_MAX_DMA_SECTIONS];
-};
-/*:*/
 
 /* Where the Host expects the Guest to SEND_DMA console output to. */
 #define LGUEST_CONSOLE_DMA_KEY 0
@@ -95,7 +61,7 @@ enum lguest_req
 enum lguest_req
 {
 	LHREQ_INITIALIZE, /* + pfnlimit, pgdir, start, pageoffset */
-	LHREQ_GETDMA, /* + addr (returns &lguest_dma, irq in ->used_len) */
+	LHREQ_GETDMA, /* No longer used */
 	LHREQ_IRQ, /* + irq */
 	LHREQ_BREAK, /* + on/off flag (on blocks until someone does off) */
 };

--
   there are those who do and those who hang on and you don't see too
   many doers quoting their contemporaries.  -- Larry McVoy