Update example launcher for virtio

Implements virtio-based console, network and block servers.  The block
server uses a thread so it's async, which is an improvement over the
old synchronous implementation (but a little more complex).

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

1 files changed, 681 insertions, 462 deletions

diff --git a/Documentation/lguest/lguest.c b/Documentation/lguest/lguest.c
index 32c2eaf94c4..7418f852e40 100644
--- a/Documentation/lguest/lguest.c
+++ b/Documentation/lguest/lguest.c
@@ -32,7 +32,9 @@
 #include <termios.h>
 #include <getopt.h>
 #include <zlib.h>
-/*L:110 We can ignore the 28 include files we need for this program, but I do
+#include <assert.h>
+#include <sched.h>
+/*L:110 We can ignore the 30 include files we need for this program, but I do
  * want to draw attention to the use of kernel-style types.
  *
  * As Linus said, "C is a Spartan language, and so should your naming be."  I
@@ -44,6 +46,12 @@ typedef uint32_t u32;
 typedef uint16_t u16;
 typedef uint8_t u8;
 #include "linux/lguest_launcher.h"
+#include "linux/pci_ids.h"
+#include "linux/virtio_config.h"
+#include "linux/virtio_net.h"
+#include "linux/virtio_blk.h"
+#include "linux/virtio_console.h"
+#include "linux/virtio_ring.h"
 #include "asm-x86/e820.h"
 /*:*/
 
@@ -55,6 +63,8 @@ typedef uint8_t u8;
 #endif
 /* We can have up to 256 pages for devices. */
 #define DEVICE_PAGES 256
+/* This fits nicely in a single 4096-byte page. */
+#define VIRTQUEUE_NUM 127
 
 /*L:120 verbose is both a global flag and a macro.  The C preprocessor allows
  * this, and although I wouldn't recommend it, it works quite nicely here. */
@@ -78,8 +88,17 @@ struct device_list
         fd_set infds;
         int max_infd;
 
+        /* Counter to assign interrupt numbers. */
+        unsigned int next_irq;
+
+        /* Counter to print out convenient device numbers. */
+        unsigned int device_num;
+
         /* The descriptor page for the devices. */
-        struct lguest_device_desc *descs;
+        u8 *descpage;
+
+        /* The tail of the last descriptor. */
+        unsigned int desc_used;
 
         /* A single linked list of devices. */
         struct device *dev;
@@ -87,31 +106,88 @@ struct device_list
         struct device **lastdev;
 };
 
+/* The list of Guest devices, based on command line arguments. */
+static struct device_list devices;
+
 /* The device structure describes a single device. */
 struct device
 {
         /* The linked-list pointer. */
         struct device *next;
-        /* The descriptor for this device, as mapped into the Guest. */
+
+        /* The this device's descriptor, as mapped into the Guest. */
         struct lguest_device_desc *desc;
-        /* The memory page(s) of this device, if any.  Also mapped in Guest. */
-        void *mem;
+
+        /* The name of this device, for --verbose. */
+        const char *name;
 
         /* If handle_input is set, it wants to be called when this file
          * descriptor is ready. */
         int fd;
         bool (*handle_input)(int fd, struct device *me);
 
-        /* If handle_output is set, it wants to be called when the Guest sends
-         * DMA to this key. */
-        unsigned long watch_key;
-        u32 (*handle_output)(int fd, const struct iovec *iov,
-                             unsigned int num, struct device *me);
+        /* Any queues attached to this device */
+        struct virtqueue *vq;
 
         /* Device-specific data. */
         void *priv;
 };
 
+/* The virtqueue structure describes a queue attached to a device. */
+struct virtqueue
+{
+        struct virtqueue *next;
+
+        /* Which device owns me. */
+        struct device *dev;
+
+        /* The configuration for this queue. */
+        struct lguest_vqconfig config;
+
+        /* The actual ring of buffers. */
+        struct vring vring;
+
+        /* Last available index we saw. */
+        u16 last_avail_idx;
+
+        /* The routine to call when the Guest pings us. */
+        void (*handle_output)(int fd, struct virtqueue *me);
+};
+
+/* Since guest is UP and we don't run at the same time, we don't need barriers.
+ * But I include them in the code in case others copy it. */
+#define wmb()
+
+/* Convert an iovec element to the given type.
+ *
+ * This is a fairly ugly trick: we need to know the size of the type and
+ * alignment requirement to check the pointer is kosher.  It's also nice to
+ * have the name of the type in case we report failure.
+ *
+ * Typing those three things all the time is cumbersome and error prone, so we
+ * have a macro which sets them all up and passes to the real function. */
+#define convert(iov, type) \
+        ((type *)_convert((iov), sizeof(type), __alignof__(type), #type))
+
+static void *_convert(struct iovec *iov, size_t size, size_t align,
+                      const char *name)
+{
+        if (iov->iov_len != size)
+                errx(1, "Bad iovec size %zu for %s", iov->iov_len, name);
+        if ((unsigned long)iov->iov_base % align != 0)
+                errx(1, "Bad alignment %p for %s", iov->iov_base, name);
+        return iov->iov_base;
+}
+
+/* The virtio configuration space is defined to be little-endian.  x86 is
+ * little-endian too, but it's nice to be explicit so we have these helpers. */
+#define cpu_to_le16(v16) (v16)
+#define cpu_to_le32(v32) (v32)
+#define cpu_to_le64(v64) (v64)
+#define le16_to_cpu(v16) (v16)
+#define le32_to_cpu(v32) (v32)
+#define le64_to_cpu(v32) (v64)
+
 /*L:100 The Launcher code itself takes us out into userspace, that scary place
  * where pointers run wild and free!  Unfortunately, like most userspace
  * programs, it's quite boring (which is why everyone likes to hack on the
@@ -486,11 +562,11 @@ static int tell_kernel(unsigned long pgdir, unsigned long start)
 }
 /*:*/
 
-static void set_fd(int fd, struct device_list *devices)
+static void add_device_fd(int fd)
 {
-        FD_SET(fd, &devices->infds);
-        if (fd > devices->max_infd)
-                devices->max_infd = fd;
+        FD_SET(fd, &devices.infds);
+        if (fd > devices.max_infd)
+                devices.max_infd = fd;
 }
 
 /*L:200
@@ -508,18 +584,18 @@ static void set_fd(int fd, struct device_list *devices)
  *
  * This, of course, is merely a different *kind* of icky.
  */
-static void wake_parent(int pipefd, int lguest_fd, struct device_list *devices)
+static void wake_parent(int pipefd, int lguest_fd)
 {
         /* Add the pipe from the Launcher to the fdset in the device_list, so
          * we watch it, too. */
-        set_fd(pipefd, devices);
+        add_device_fd(pipefd);
 
         for (;;) {
-                fd_set rfds = devices->infds;
+                fd_set rfds = devices.infds;
                 unsigned long args[] = { LHREQ_BREAK, 1 };
 
                 /* Wait until input is ready from one of the devices. */
-                select(devices->max_infd+1, &rfds, NULL, NULL, NULL);
+                select(devices.max_infd+1, &rfds, NULL, NULL, NULL);
                 /* Is it a message from the Launcher? */
                 if (FD_ISSET(pipefd, &rfds)) {
                         int ignorefd;
@@ -530,14 +606,14 @@ static void wake_parent(int pipefd, int lguest_fd, struct device_list *devices)
                         /* Otherwise it's telling us there's a problem with one
                          * of the devices, and we should ignore that file
                          * descriptor from now on. */
-                        FD_CLR(ignorefd, &devices->infds);
+                        FD_CLR(ignorefd, &devices.infds);
                 } else /* Send LHREQ_BREAK command. */
                         write(lguest_fd, args, sizeof(args));
         }
 }
 
 /* This routine just sets up a pipe to the Waker process. */
-static int setup_waker(int lguest_fd, struct device_list *device_list)
+static int setup_waker(int lguest_fd)
 {
         int pipefd[2], child;
 
@@ -551,7 +627,7 @@ static int setup_waker(int lguest_fd, struct device_list *device_list)
         if (child == 0) {
                 /* Close the "writing" end of our copy of the pipe */
                 close(pipefd[1]);
-                wake_parent(pipefd[0], lguest_fd, device_list);
+                wake_parent(pipefd[0], lguest_fd);
         }
         /* Close the reading end of our copy of the pipe. */
         close(pipefd[0]);
@@ -574,7 +650,7 @@ static void *_check_pointer(unsigned long addr, unsigned int size,
         /* We have to separately check addr and addr+size, because size could
          * be huge and addr + size might wrap around. */
         if (addr >= guest_limit || addr + size >= guest_limit)
-                errx(1, "%s:%i: Invalid address %li", __FILE__, line, addr);
+                errx(1, "%s:%i: Invalid address %#lx", __FILE__, line, addr);
         /* We return a pointer for the caller's convenience, now we know it's
          * safe to use. */
         return from_guest_phys(addr);
@@ -582,74 +658,131 @@ static void *_check_pointer(unsigned long addr, unsigned int size,
 /* A macro which transparently hands the line number to the real function. */
 #define check_pointer(addr,size) _check_pointer(addr, size, __LINE__)
 
-/* The Guest has given us the address of a "struct lguest_dma".  We check it's
- * OK and convert it to an iovec (which is a simple array of ptr/size
- * pairs). */
-static u32 *dma2iov(unsigned long dma, struct iovec iov[], unsigned *num)
+/* This simply sets up an iovec array where we can put data to be discarded.
+ * This happens when the Guest doesn't want or can't handle the input: we have
+ * to get rid of it somewhere, and if we bury it in the ceiling space it will
+ * start to smell after a week. */
+static void discard_iovec(struct iovec *iov, unsigned int *num)
 {
-        unsigned int i;
-        struct lguest_dma *udma;
-
-        /* First we make sure that the array memory itself is valid. */
-        udma = check_pointer(dma, sizeof(*udma));
-        /* Now we check each element */
-        for (i = 0; i < LGUEST_MAX_DMA_SECTIONS; i++) {
-                /* A zero length ends the array. */
-                if (!udma->len[i])
-                        break;
+        static char discard_buf[1024];
+        *num = 1;
+        iov->iov_base = discard_buf;
+        iov->iov_len = sizeof(discard_buf);
+}
 
-                iov[i].iov_base = check_pointer(udma->addr[i], udma->len[i]);
-                iov[i].iov_len = udma->len[i];
-        }
-        *num = i;
+/* This function returns the next descriptor in the chain, or vq->vring.num. */
+static unsigned next_desc(struct virtqueue *vq, unsigned int i)
+{
+        unsigned int next;
+
+        /* If this descriptor says it doesn't chain, we're done. */
+        if (!(vq->vring.desc[i].flags & VRING_DESC_F_NEXT))
+                return vq->vring.num;
+
+        /* Check they're not leading us off end of descriptors. */
+        next = vq->vring.desc[i].next;
+        /* Make sure compiler knows to grab that: we don't want it changing! */
+        wmb();
+
+        if (next >= vq->vring.num)
+                errx(1, "Desc next is %u", next);
+
+        return next;
+}
+
+/* This looks in the virtqueue and for the first available buffer, and converts
+ * it to an iovec for convenient access.  Since descriptors consist of some
+ * number of output then some number of input descriptors, it's actually two
+ * iovecs, but we pack them into one and note how many of each there were.
+ *
+ * This function returns the descriptor number found, or vq->vring.num (which
+ * is never a valid descriptor number) if none was found. */
+static unsigned get_vq_desc(struct virtqueue *vq,
+                            struct iovec iov[],
+                            unsigned int *out_num, unsigned int *in_num)
+{
+        unsigned int i, head;
+
+        /* Check it isn't doing very strange things with descriptor numbers. */
+        if ((u16)(vq->vring.avail->idx - vq->last_avail_idx) > vq->vring.num)
+                errx(1, "Guest moved used index from %u to %u",
+                     vq->last_avail_idx, vq->vring.avail->idx);
+
+        /* If there's nothing new since last we looked, return invalid. */
+        if (vq->vring.avail->idx == vq->last_avail_idx)
+                return vq->vring.num;
+
+        /* Grab the next descriptor number they're advertising, and increment
+         * the index we've seen. */
+        head = vq->vring.avail->ring[vq->last_avail_idx++ % vq->vring.num];
+
+        /* If their number is silly, that's a fatal mistake. */
+        if (head >= vq->vring.num)
+                errx(1, "Guest says index %u is available", head);
+
+        /* When we start there are none of either input nor output. */
+        *out_num = *in_num = 0;
+
+        i = head;
+        do {
+                /* Grab the first descriptor, and check it's OK. */
+                iov[*out_num + *in_num].iov_len = vq->vring.desc[i].len;
+                iov[*out_num + *in_num].iov_base
+                        = check_pointer(vq->vring.desc[i].addr,
+                                        vq->vring.desc[i].len);
+                /* If this is an input descriptor, increment that count. */
+                if (vq->vring.desc[i].flags & VRING_DESC_F_WRITE)
+                        (*in_num)++;
+                else {
+                        /* If it's an output descriptor, they're all supposed
+                         * to come before any input descriptors. */
+                        if (*in_num)
+                                errx(1, "Descriptor has out after in");
+                        (*out_num)++;
+                }
+
+                /* If we've got too many, that implies a descriptor loop. */
+                if (*out_num + *in_num > vq->vring.num)
+                        errx(1, "Looped descriptor");
+        } while ((i = next_desc(vq, i)) != vq->vring.num);
 
-        /* We return the pointer to where the caller should write the amount of
-         * the buffer used. */
-        return &udma->used_len;
+        return head;
 }
 
-/* This routine gets a DMA buffer from the Guest for a given key, and converts
- * it to an iovec array.  It returns the interrupt the Guest wants when we're
- * finished, and a pointer to the "used_len" field to fill in. */
-static u32 *get_dma_buffer(int fd, void *key,
-                           struct iovec iov[], unsigned int *num, u32 *irq)
+/* Once we've used one of their buffers, we tell them about it.  We'll then
+ * want to send them an interrupt, using trigger_irq(). */
+static void add_used(struct virtqueue *vq, unsigned int head, int len)
 {
-        unsigned long buf[] = { LHREQ_GETDMA, to_guest_phys(key) };
-        unsigned long udma;
-        u32 *res;
-
-        /* Ask the kernel for a DMA buffer corresponding to this key. */
-        udma = write(fd, buf, sizeof(buf));
-        /* They haven't registered any, or they're all used? */
-        if (udma == (unsigned long)-1)
-                return NULL;
-
-        /* Convert it into our iovec array */
-        res = dma2iov(udma, iov, num);
-        /* The kernel stashes irq in ->used_len to get it out to us. */
-        *irq = *res;
-        /* Return a pointer to ((struct lguest_dma *)udma)->used_len. */
-        return res;
+        struct vring_used_elem *used;
+
+        /* Get a pointer to the next entry in the used ring. */
+        used = &vq->vring.used->ring[vq->vring.used->idx % vq->vring.num];
+        used->id = head;
+        used->len = len;
+        /* Make sure buffer is written before we update index. */
+        wmb();
+        vq->vring.used->idx++;
 }
 
-/* This is a convenient routine to send the Guest an interrupt. */
-static void trigger_irq(int fd, u32 irq)
+/* This actually sends the interrupt for this virtqueue */
+static void trigger_irq(int fd, struct virtqueue *vq)
 {
-        unsigned long buf[] = { LHREQ_IRQ, irq };
+        unsigned long buf[] = { LHREQ_IRQ, vq->config.irq };
+
+        if (vq->vring.avail->flags & VRING_AVAIL_F_NO_INTERRUPT)
+                return;
+
+        /* Send the Guest an interrupt tell them we used something up. */
         if (write(fd, buf, sizeof(buf)) != 0)
-                err(1, "Triggering irq %i", irq);
+                err(1, "Triggering irq %i", vq->config.irq);
 }
 
-/* This simply sets up an iovec array where we can put data to be discarded.
- * This happens when the Guest doesn't want or can't handle the input: we have
- * to get rid of it somewhere, and if we bury it in the ceiling space it will
- * start to smell after a week. */
-static void discard_iovec(struct iovec *iov, unsigned int *num)
+/* And here's the combo meal deal.  Supersize me! */
+static void add_used_and_trigger(int fd, struct virtqueue *vq,
+                                 unsigned int head, int len)
 {
-        static char discard_buf[1024];
-        *num = 1;
-        iov->iov_base = discard_buf;
-        iov->iov_len = sizeof(discard_buf);
+        add_used(vq, head, len);
+        trigger_irq(fd, vq);
 }
 
 /* Here is the input terminal setting we save, and the routine to restore them
@@ -672,38 +805,37 @@ struct console_abort
 /* This is the routine which handles console input (ie. stdin). */
 static bool handle_console_input(int fd, struct device *dev)
 {
-        u32 irq = 0, *lenp;
         int len;
-        unsigned int num;
-        struct iovec iov[LGUEST_MAX_DMA_SECTIONS];
+        unsigned int head, in_num, out_num;
+        struct iovec iov[dev->vq->vring.num];
         struct console_abort *abort = dev->priv;
 
-        /* First we get the console buffer from the Guest.  The key is dev->mem
-         * which was set to 0 in setup_console(). */
-        lenp = get_dma_buffer(fd, dev->mem, iov, &num, &irq);
-        if (!lenp) {
-                /* If it's not ready for input, warn and set up to discard. */
-                warn("console: no dma buffer!");
-                discard_iovec(iov, &num);
-        }
+        /* First we need a console buffer from the Guests's input virtqueue. */
+        head = get_vq_desc(dev->vq, iov, &out_num, &in_num);
+        if (head == dev->vq->vring.num) {
+                /* If they're not ready for input, we warn and set up to
+                 * discard. */
+                warnx("console: no dma buffer!");
+                discard_iovec(iov, &in_num);
+        } else if (out_num)
+                errx(1, "Output buffers in console in queue?");
 
         /* This is why we convert to iovecs: the readv() call uses them, and so
          * it reads straight into the Guest's buffer. */
-        len = readv(dev->fd, iov, num);
+        len = readv(dev->fd, iov, in_num);
         if (len <= 0) {
                 /* This implies that the console is closed, is /dev/null, or
-                 * something went terribly wrong.  We still go through the rest
-                 * of the logic, though, especially the exit handling below. */
+                 * something went terribly wrong. */
                 warnx("Failed to get console input, ignoring console.");
-                len = 0;
+                /* Put the input terminal back and return failure (meaning,
+                 * don't call us again). */
+                restore_term();
+                return false;
         }
 
-        /* If we read the data into the Guest, fill in the length and send the
-         * interrupt. */
-        if (lenp) {
-                *lenp = len;
-                trigger_irq(fd, irq);
-        }
+        /* If we actually read the data into the Guest, tell them about it. */
+        if (head != dev->vq->vring.num)
+                add_used_and_trigger(fd, dev->vq, head, len);
 
         /* Three ^C within one second?  Exit.
          *
@@ -732,202 +864,137 @@ static bool handle_console_input(int fd, struct device *dev)
                 /* Any other key resets the abort counter. */
                 abort->count = 0;
 
-        /* Now, if we didn't read anything, put the input terminal back and
-         * return failure (meaning, don't call us again). */
-        if (!len) {
-                restore_term();
-                return false;
-        }
         /* Everything went OK! */
         return true;
 }
 
-/* Handling console output is much simpler than input. */
-static u32 handle_console_output(int fd, const struct iovec *iov,
-                                 unsigned num, struct device*dev)
+/* Handling output for console is simple: we just get all the output buffers
+ * and write them to stdout. */
+static void handle_console_output(int fd, struct virtqueue *vq)
 {
-        /* Whatever the Guest sends, write it to standard output.  Return the
-         * number of bytes written. */
-        return writev(STDOUT_FILENO, iov, num);
-}
-
-/* Guest->Host network output is also pretty easy. */
-static u32 handle_tun_output(int fd, const struct iovec *iov,
-                             unsigned num, struct device *dev)
-{
-        /* We put a flag in the "priv" pointer of the network device, and set
-         * it as soon as we see output.  We'll see why in handle_tun_input() */
-        *(bool *)dev->priv = true;
-        /* Whatever packet the Guest sent us, write it out to the tun
-         * device. */
-        return writev(dev->fd, iov, num);
+        unsigned int head, out, in;
+        int len;
+        struct iovec iov[vq->vring.num];
+
+        /* Keep getting output buffers from the Guest until we run out. */
+        while ((head = get_vq_desc(vq, iov, &out, &in)) != vq->vring.num) {
+                if (in)
+                        errx(1, "Input buffers in output queue?");
+                len = writev(STDOUT_FILENO, iov, out);
+                add_used_and_trigger(fd, vq, head, len);
+        }
 }
 
-/* This matches the peer_key() in lguest_net.c.  The key for any given slot
- * is the address of the network device's page plus 4 * the slot number. */
-static unsigned long peer_offset(unsigned int peernum)
+/* Handling output for network is also simple: we get all the output buffers
+ * and write them (ignoring the first element) to this device's file descriptor
+ * (stdout). */
+static void handle_net_output(int fd, struct virtqueue *vq)
 {
-        return 4 * peernum;
+        unsigned int head, out, in;
+        int len;
+        struct iovec iov[vq->vring.num];
+
+        /* Keep getting output buffers from the Guest until we run out. */
+        while ((head = get_vq_desc(vq, iov, &out, &in)) != vq->vring.num) {
+                if (in)
+                        errx(1, "Input buffers in output queue?");
+                /* Check header, but otherwise ignore it (we said we supported
+                 * no features). */
+                (void)convert(&iov[0], struct virtio_net_hdr);
+                len = writev(vq->dev->fd, iov+1, out-1);
+                add_used_and_trigger(fd, vq, head, len);
+        }
 }
 
-/* This is where we handle a packet coming in from the tun device */
+/* This is where we handle a packet coming in from the tun device to our
+ * Guest. */
 static bool handle_tun_input(int fd, struct device *dev)
 {
-        u32 irq = 0, *lenp;
+        unsigned int head, in_num, out_num;
         int len;
-        unsigned num;
-        struct iovec iov[LGUEST_MAX_DMA_SECTIONS];
+        struct iovec iov[dev->vq->vring.num];
+        struct virtio_net_hdr *hdr;
 
-        /* First we get a buffer the Guest has bound to its key. */
-        lenp = get_dma_buffer(fd, dev->mem+peer_offset(NET_PEERNUM), iov, &num,
-                              &irq);
-        if (!lenp) {
+        /* First we need a network buffer from the Guests's recv virtqueue. */
+        head = get_vq_desc(dev->vq, iov, &out_num, &in_num);
+        if (head == dev->vq->vring.num) {
                 /* Now, it's expected that if we try to send a packet too
-                 * early, the Guest won't be ready yet.  This is why we set a
-                 * flag when the Guest sends its first packet.  If it's sent a
-                 * packet we assume it should be ready to receive them.
-                 *
-                 * Actually, this is what the status bits in the descriptor are
-                 * for: we should *use* them.  FIXME! */
-                if (*(bool *)dev->priv)
+                 * early, the Guest won't be ready yet.  Wait until the device
+                 * status says it's ready. */
+                /* FIXME: Actually want DRIVER_ACTIVE here. */
+                if (dev->desc->status & VIRTIO_CONFIG_S_DRIVER_OK)
                         warn("network: no dma buffer!");
-                discard_iovec(iov, &num);
-        }
+                discard_iovec(iov, &in_num);
+        } else if (out_num)
+                errx(1, "Output buffers in network recv queue?");
+
+        /* First element is the header: we set it to 0 (no features). */
+        hdr = convert(&iov[0], struct virtio_net_hdr);
+        hdr->flags = 0;
+        hdr->gso_type = VIRTIO_NET_HDR_GSO_NONE;
 
         /* Read the packet from the device directly into the Guest's buffer. */
-        len = readv(dev->fd, iov, num);
+        len = readv(dev->fd, iov+1, in_num-1);
         if (len <= 0)
                 err(1, "reading network");
 
-        /* Write the used_len, and trigger the interrupt for the Guest */
-        if (lenp) {
-                *lenp = len;
-                trigger_irq(fd, irq);
-        }
+        /* If we actually read the data into the Guest, tell them about it. */
+        if (head != dev->vq->vring.num)
+                add_used_and_trigger(fd, dev->vq, head, sizeof(*hdr) + len);
+
         verbose("tun input packet len %i [%02x %02x] (%s)\n", len,
-                ((u8 *)iov[0].iov_base)[0], ((u8 *)iov[0].iov_base)[1],
-                lenp ? "sent" : "discarded");
+                ((u8 *)iov[1].iov_base)[0], ((u8 *)iov[1].iov_base)[1],
+                head != dev->vq->vring.num ? "sent" : "discarded");
+
         /* All good. */
         return true;
 }
 
-/* The last device handling routine is block output: the Guest has sent a DMA
- * to the block device.  It will have placed the command it wants in the
- * "struct lguest_block_page". */
-static u32 handle_block_output(int fd, const struct iovec *iov,
-                               unsigned num, struct device *dev)
-{
-        struct lguest_block_page *p = dev->mem;
-        u32 irq, *lenp;
-        unsigned int len, reply_num;
-        struct iovec reply[LGUEST_MAX_DMA_SECTIONS];
-        off64_t device_len, off = (off64_t)p->sector * 512;
-
-        /* First we extract the device length from the dev->priv pointer. */
-        device_len = *(off64_t *)dev->priv;
-
-        /* We first check that the read or write is within the length of the
-         * block file. */
-        if (off >= device_len)
-                errx(1, "Bad offset %llu vs %llu", off, device_len);
-        /* Move to the right location in the block file.  This shouldn't fail,
-         * but best to check. */
-        if (lseek64(dev->fd, off, SEEK_SET) != off)
-                err(1, "Bad seek to sector %i", p->sector);
-
-        verbose("Block: %s at offset %llu\n", p->type ? "WRITE" : "READ", off);
-
-        /* They were supposed to bind a reply buffer at key equal to the start
-         * of the block device memory.  We need this to tell them when the
-         * request is finished. */
-        lenp = get_dma_buffer(fd, dev->mem, reply, &reply_num, &irq);
-        if (!lenp)
-                err(1, "Block request didn't give us a dma buffer");
-
-        if (p->type) {
-                /* A write request.  The DMA they sent contained the data, so
-                 * write it out. */
-                len = writev(dev->fd, iov, num);
-                /* Grr... Now we know how long the "struct lguest_dma" they
-                 * sent was, we make sure they didn't try to write over the end
-                 * of the block file (possibly extending it). */
-                if (off + len > device_len) {
-                        /* Trim it back to the correct length */
-                        ftruncate64(dev->fd, device_len);
-                        /* Die, bad Guest, die. */
-                        errx(1, "Write past end %llu+%u", off, len);
-                }
-                /* The reply length is 0: we just send back an empty DMA to
-                 * interrupt them and tell them the write is finished. */
-                *lenp = 0;
-        } else {
-                /* A read request.  They sent an empty DMA to start the
-                 * request, and we put the read contents into the reply
-                 * buffer. */
-                len = readv(dev->fd, reply, reply_num);
-                *lenp = len;
-        }
-
-        /* The result is 1 (done), 2 if there was an error (short read or
-         * write). */
-        p->result = 1 + (p->bytes != len);
-        /* Now tell them we've used their reply buffer. */
-        trigger_irq(fd, irq);
-
-        /* We're supposed to return the number of bytes of the output buffer we
-         * used.  But the block device uses the "result" field instead, so we
-         * don't bother. */
-        return 0;
-}
-
-/* This is the generic routine we call when the Guest sends some DMA out. */
-static void handle_output(int fd, unsigned long dma, unsigned long key,
-                          struct device_list *devices)
+/* This is the generic routine we call when the Guest uses LHCALL_NOTIFY. */
+static void handle_output(int fd, unsigned long addr)
 {
         struct device *i;
-        u32 *lenp;
-        struct iovec iov[LGUEST_MAX_DMA_SECTIONS];
-        unsigned num = 0;
-
-        /* Convert the "struct lguest_dma" they're sending to a "struct
-         * iovec". */
-        lenp = dma2iov(dma, iov, &num);
-
-        /* Check each device: if they expect output to this key, tell them to
-         * handle it. */
-        for (i = devices->dev; i; i = i->next) {
-                if (i->handle_output && key == i->watch_key) {
-                        /* We write the result straight into the used_len field
-                         * for them. */
-                        *lenp = i->handle_output(fd, iov, num, i);
-                        return;
+        struct virtqueue *vq;
+
+        /* Check each virtqueue. */
+        for (i = devices.dev; i; i = i->next) {
+                for (vq = i->vq; vq; vq = vq->next) {
+                        if (vq->config.pfn == addr/getpagesize()
+                            && vq->handle_output) {
+                                verbose("Output to %s\n", vq->dev->name);
+                                vq->handle_output(fd, vq);
+                                return;
+                        }
                 }
         }
 
-        /* This can happen: the kernel sends any SEND_DMA which doesn't match
-         * another Guest to us.  It could be that another Guest just left a
-         * network, for example.  But it's unusual. */
-        warnx("Pending dma %p, key %p", (void *)dma, (void *)key);
+        /* Early console write is done using notify on a nul-terminated string
+         * in Guest memory. */
+        if (addr >= guest_limit)
+                errx(1, "Bad NOTIFY %#lx", addr);
+
+        write(STDOUT_FILENO, from_guest_phys(addr),
+              strnlen(from_guest_phys(addr), guest_limit - addr));
 }
 
 /* This is called when the waker wakes us up: check for incoming file
  * descriptors. */
-static void handle_input(int fd, struct device_list *devices)
+static void handle_input(int fd)
 {
         /* select() wants a zeroed timeval to mean "don't wait". */
         struct timeval poll = { .tv_sec = 0, .tv_usec = 0 };
 
         for (;;) {
                 struct device *i;
-                fd_set fds = devices->infds;
+                fd_set fds = devices.infds;
 
                 /* If nothing is ready, we're done. */
-                if (select(devices->max_infd+1, &fds, NULL, NULL, &poll) == 0)
+                if (select(devices.max_infd+1, &fds, NULL, NULL, &poll) == 0)
                         break;
 
                 /* Otherwise, call the device(s) which have readable
                  * file descriptors and a method of handling them.  */
-                for (i = devices->dev; i; i = i->next) {
+                for (i = devices.dev; i; i = i->next) {
                         if (i->handle_input && FD_ISSET(i->fd, &fds)) {
                                 /* If handle_input() returns false, it means we
                                  * should no longer service it.
@@ -936,7 +1003,7 @@ static void handle_input(int fd, struct device_list *devices)
                                         /* Clear it from the set of input file
                                          * descriptors kept at the head of the
                                          * device list. */
-                                        FD_CLR(i->fd, &devices->infds);
+                                        FD_CLR(i->fd, &devices.infds);
                                         /* Tell waker to ignore it too... */
                                         write(waker_fd, &i->fd, sizeof(i->fd));
                                 }
@@ -953,43 +1020,93 @@ static void handle_input(int fd, struct device_list *devices)
  * routines to allocate them.
  *
  * This routine allocates a new "struct lguest_device_desc" from descriptor
- * table in the devices array just above the Guest's normal memory. */
-static struct lguest_device_desc *
-new_dev_desc(struct lguest_device_desc *descs,
-             u16 type, u16 features, u16 num_pages)
+ * table just above the Guest's normal memory.  It returns a pointer to that
+ * descriptor. */
+static struct lguest_device_desc *new_dev_desc(u16 type)
 {
-        unsigned int i;
+        struct lguest_device_desc *d;
 
-        for (i = 0; i < LGUEST_MAX_DEVICES; i++) {
-                if (!descs[i].type) {
-                        descs[i].type = type;
-                        descs[i].features = features;
-                        descs[i].num_pages = num_pages;
-                        /* If they said the device needs memory, we allocate
-                         * that now. */
-                        if (num_pages) {
-                                unsigned long pa;
-                                pa = to_guest_phys(get_pages(num_pages));
-                                descs[i].pfn = pa / getpagesize();
-                        }
-                        return &descs[i];
-                }
-        }
-        errx(1, "too many devices");
+        /* We only have one page for all the descriptors. */
+        if (devices.desc_used + sizeof(*d) > getpagesize())
+                errx(1, "Too many devices");
+
+        /* We don't need to set config_len or status: page is 0 already. */
+        d = (void *)devices.descpage + devices.desc_used;
+        d->type = type;
+        devices.desc_used += sizeof(*d);
+
+        return d;
+}
+
+/* Each device descriptor is followed by some configuration information.
+ * The first byte is a "status" byte for the Guest to report what's happening.
+ * After that are fields: u8 type, u8 len, [... len bytes...].
+ *
+ * This routine adds a new field to an existing device's descriptor.  It only
+ * works for the last device, but that's OK because that's how we use it. */
+static void add_desc_field(struct device *dev, u8 type, u8 len, const void *c)
+{
+        /* This is the last descriptor, right? */
+        assert(devices.descpage + devices.desc_used
+               == (u8 *)(dev->desc + 1) + dev->desc->config_len);
+
+        /* We only have one page of device descriptions. */
+        if (devices.desc_used + 2 + len > getpagesize())
+                errx(1, "Too many devices");
+
+        /* Copy in the new config header: type then length. */
+        devices.descpage[devices.desc_used++] = type;
+        devices.descpage[devices.desc_used++] = len;
+        memcpy(devices.descpage + devices.desc_used, c, len);
+        devices.desc_used += len;
+
+        /* Update the device descriptor length: two byte head then data. */
+        dev->desc->config_len += 2 + len;
+}
+
+/* This routine adds a virtqueue to a device.  We specify how many descriptors
+ * the virtqueue is to have. */
+static void add_virtqueue(struct device *dev, unsigned int num_descs,
+                          void (*handle_output)(int fd, struct virtqueue *me))
+{
+        unsigned int pages;
+        struct virtqueue **i, *vq = malloc(sizeof(*vq));
+        void *p;
+
+        /* First we need some pages for this virtqueue. */
+        pages = (vring_size(num_descs) + getpagesize() - 1) / getpagesize();
+        p = get_pages(pages);
+
+        /* Initialize the configuration. */
+        vq->config.num = num_descs;
+        vq->config.irq = devices.next_irq++;
+        vq->config.pfn = to_guest_phys(p) / getpagesize();
+
+        /* Initialize the vring. */
+        vring_init(&vq->vring, num_descs, p);
+
+        /* Add the configuration information to this device's descriptor. */
+        add_desc_field(dev, VIRTIO_CONFIG_F_VIRTQUEUE,
+                       sizeof(vq->config), &vq->config);
+
+        /* Add to tail of list, so dev->vq is first vq, dev->vq->next is
+         * second.  */
+        for (i = &dev->vq; *i; i = &(*i)->next);
+        *i = vq;
+
+        /* Link virtqueue back to device. */
+        vq->dev = dev;
+
+        /* Set up handler. */
+        vq->handle_output = handle_output;
+        if (!handle_output)
+                vq->vring.used->flags = VRING_USED_F_NO_NOTIFY;
 }
 
-/* This monster routine does all the creation and setup of a new device,
- * including caling new_dev_desc() to allocate the descriptor and device
- * memory. */
-static struct device *new_device(struct device_list *devices,
-                                 u16 type, u16 num_pages, u16 features,
-                                 int fd,
-                                 bool (*handle_input)(int, struct device *),
-                                 unsigned long watch_off,
-                                 u32 (*handle_output)(int,
-                                                      const struct iovec *,
-                                                      unsigned,
-                                                      struct device *))
+/* This routine does all the creation and setup of a new device, including
+ * caling new_dev_desc() to allocate the descriptor and device memory. */
+static struct device *new_device(const char *name, u16 type, int fd,
+                                 bool (*handle_input)(int, struct device *))
 {
         struct device *dev = malloc(sizeof(*dev));
 
@@ -997,27 +1114,25 @@ static struct device *new_device(struct device_list *devices,
          * easier, but the user expects the devices to be arranged on the bus
          * in command-line order.  The first network device on the command line
          * is eth0, the first block device /dev/lgba, etc. */
-        *devices->lastdev = dev;
+        *devices.lastdev = dev;
         dev->next = NULL;
-        devices->lastdev = &dev->next;
+        devices.lastdev = &dev->next;
 
         /* Now we populate the fields one at a time. */
         dev->fd = fd;
         /* If we have an input handler for this file descriptor, then we add it
          * to the device_list's fdset and maxfd. */
         if (handle_input)
-                set_fd(dev->fd, devices);
-        dev->desc = new_dev_desc(devices->descs, type, features, num_pages);
-        dev->mem = from_guest_phys(dev->desc->pfn * getpagesize());
+                add_device_fd(dev->fd);
+        dev->desc = new_dev_desc(type);
         dev->handle_input = handle_input;
-        dev->watch_key = to_guest_phys(dev->mem) + watch_off;
-        dev->handle_output = handle_output;
+        dev->name = name;
         return dev;
 }
 
 /* Our first setup routine is the console.  It's a fairly simple device, but
  * UNIX tty handling makes it uglier than it could be. */
-static void setup_console(struct device_list *devices)
+static void setup_console(void)
 {
         struct device *dev;
 
@@ -1033,127 +1148,38 @@ static void setup_console(struct device_list *devices)
                 atexit(restore_term);
         }
 
-        /* We don't currently require any memory for the console, so we ask for
-         * 0 pages. */
-        dev = new_device(devices, LGUEST_DEVICE_T_CONSOLE, 0, 0,
-                         STDIN_FILENO, handle_console_input,
-                         LGUEST_CONSOLE_DMA_KEY, handle_console_output);
+        dev = new_device("console", VIRTIO_ID_CONSOLE,
+                         STDIN_FILENO, handle_console_input);
         /* We store the console state in dev->priv, and initialize it. */
         dev->priv = malloc(sizeof(struct console_abort));
         ((struct console_abort *)dev->priv)->count = 0;
-        verbose("device %p: console\n",
-                (void *)(dev->desc->pfn * getpagesize()));
-}
 
-/* Setting up a block file is also fairly straightforward. */
-static void setup_block_file(const char *filename, struct device_list *devices)
-{
-        int fd;
-        struct device *dev;
-        off64_t *device_len;
-        struct lguest_block_page *p;
-
-        /* We open with O_LARGEFILE because otherwise we get stuck at 2G.  We
-         * open with O_DIRECT because otherwise our benchmarks go much too
-         * fast. */
-        fd = open_or_die(filename, O_RDWR|O_LARGEFILE|O_DIRECT);
-
-        /* We want one page, and have no input handler (the block file never
-         * has anything interesting to say to us).  Our timing will be quite
-         * random, so it should be a reasonable randomness source. */
-        dev = new_device(devices, LGUEST_DEVICE_T_BLOCK, 1,
-                         LGUEST_DEVICE_F_RANDOMNESS,
-                         fd, NULL, 0, handle_block_output);
-
-        /* We store the device size in the private area */
-        device_len = dev->priv = malloc(sizeof(*device_len));
-        /* This is the safe way of establishing the size of our device: it
-         * might be a normal file or an actual block device like /dev/hdb. */
-        *device_len = lseek64(fd, 0, SEEK_END);
-
-        /* The device memory is a "struct lguest_block_page".  It's zeroed
-         * already, we just need to put in the device size.  Block devices
-         * think in sectors (ie. 512 byte chunks), so we translate here. */
-        p = dev->mem;
-        p->num_sectors = *device_len/512;
-        verbose("device %p: block %i sectors\n",
-                (void *)(dev->desc->pfn * getpagesize()), p->num_sectors);
+        /* The console needs two virtqueues: the input then the output.  We
+         * don't care when they refill the input queue, since we don't hold
+         * data waiting for them.  That's why the input queue's callback is
+         * NULL.  */
+        add_virtqueue(dev, VIRTQUEUE_NUM, NULL);
+        add_virtqueue(dev, VIRTQUEUE_NUM, handle_console_output);
+
+        verbose("device %u: console\n", devices.device_num++);
 }
+/*:*/
 
-/*
- * Network Devices.
+/*M:010 Inter-guest networking is an interesting area.  Simplest is to have a
+ * --sharenet=<name> option which opens or creates a named pipe.  This can be
+ * used to send packets to another guest in a 1:1 manner.
  *
- * Setting up network devices is quite a pain, because we have three types.
- * First, we have the inter-Guest network.  This is a file which is mapped into
- * the address space of the Guests who are on the network.  Because it is a
- * shared mapping, the same page underlies all the devices, and they can send
- * DMA to each other.
+ * More sopisticated is to use one of the tools developed for project like UML
+ * to do networking.
  *
- * Remember from our network driver, the Guest is told what slot in the page it
- * is to use.  We use exclusive fnctl locks to reserve a slot.  If another
- * Guest is using a slot, the lock will fail and we try another.  Because fnctl
- * locks are cleaned up automatically when we die, this cleverly means that our
- * reservation on the slot will vanish if we crash. */
-static unsigned int find_slot(int netfd, const char *filename)
-{
-        struct flock fl;
-
-        fl.l_type = F_WRLCK;
-        fl.l_whence = SEEK_SET;
-        fl.l_len = 1;
-        /* Try a 1 byte lock in each possible position number */
-        for (fl.l_start = 0;
-             fl.l_start < getpagesize()/sizeof(struct lguest_net);
-             fl.l_start++) {
-                /* If we succeed, return the slot number. */
-                if (fcntl(netfd, F_SETLK, &fl) == 0)
-                        return fl.l_start;
-        }
-        errx(1, "No free slots in network file %s", filename);
-}
-
-/* This function sets up the network file */
-static void setup_net_file(const char *filename,
-                           struct device_list *devices)
-{
-        int netfd;
-        struct device *dev;
-
-        /* We don't use open_or_die() here: for friendliness we create the file
-         * if it doesn't already exist. */
-        netfd = open(filename, O_RDWR, 0);
-        if (netfd < 0) {
-                if (errno == ENOENT) {
-                        netfd = open(filename, O_RDWR|O_CREAT, 0600);
-                        if (netfd >= 0) {
-                                /* If we succeeded, initialize the file with a
-                                 * blank page. */
-                                char page[getpagesize()];
-                                memset(page, 0, sizeof(page));
-                                write(netfd, page, sizeof(page));
-                        }
-                }
-                if (netfd < 0)
-                        err(1, "cannot open net file '%s'", filename);
-        }
-
-        /* We need 1 page, and the features indicate the slot to use and that
-         * no checksum is needed.  We never touch this device again; it's
-         * between the Guests on the network, so we don't register input or
-         * output handlers. */
-        dev = new_device(devices, LGUEST_DEVICE_T_NET, 1,
-                         find_slot(netfd, filename)|LGUEST_NET_F_NOCSUM,
-                         -1, NULL, 0, NULL);
-
-        /* Map the shared file. */
-        if (mmap(dev->mem, getpagesize(), PROT_READ|PROT_WRITE,
-                         MAP_FIXED|MAP_SHARED, netfd, 0) != dev->mem)
-                        err(1, "could not mmap '%s'", filename);
-        verbose("device %p: shared net %s, peer %i\n",
-                (void *)(dev->desc->pfn * getpagesize()), filename,
-                dev->desc->features & ~LGUEST_NET_F_NOCSUM);
-}
-/*:*/
+ * Faster is to do virtio bonding in kernel.  Doing this 1:1 would be
+ * completely generic ("here's my vring, attach to your vring") and would work
+ * for any traffic.  Of course, namespace and permissions issues need to be
+ * dealt with.  A more sophisticated "multi-channel" virtio_net.c could hide
+ * multiple inter-guest channels behind one interface, although it would
+ * require some manner of hotplugging new virtio channels.
+ *
+ * Finally, we could implement a virtio network switch in the kernel. :*/
 
 static u32 str2ip(const char *ipaddr)
 {
@@ -1188,7 +1214,7 @@ static void add_to_bridge(int fd, const char *if_name, const char *br_name)
 
 /* This sets up the Host end of the network device with an IP address, brings
  * it up so packets will flow, the copies the MAC address into the hwaddr
- * pointer (in practice, the Host's slot in the network device's memory). */
+ * pointer. */
 static void configure_device(int fd, const char *devname, u32 ipaddr,
                              unsigned char hwaddr[6])
 {
@@ -1214,18 +1240,18 @@ static void configure_device(int fd, const char *devname, u32 ipaddr,
         memcpy(hwaddr, ifr.ifr_hwaddr.sa_data, 6);
 }
 
-/*L:195 The other kind of network is a Host<->Guest network.  This can either
- * use briding or routing, but the principle is the same: it uses the "tun"
- * device to inject packets into the Host as if they came in from a normal
- * network card.  We just shunt packets between the Guest and the tun
- * device. */
-static void setup_tun_net(const char *arg, struct device_list *devices)
+/*L:195 Our network is a Host<->Guest network.  This can either use bridging or
+ * routing, but the principle is the same: it uses the "tun" device to inject
+ * packets into the Host as if they came in from a normal network card.  We
+ * just shunt packets between the Guest and the tun device. */
+static void setup_tun_net(const char *arg)
 {
         struct device *dev;
         struct ifreq ifr;
         int netfd, ipfd;
         u32 ip;
         const char *br_name = NULL;
+        u8 hwaddr[6];
 
         /* We open the /dev/net/tun device and tell it we want a tap device.  A
          * tap device is like a tun device, only somehow different.  To tell
@@ -1241,21 +1267,12 @@ static void setup_tun_net(const char *arg, struct device_list *devices)
          * device: trust us! */
         ioctl(netfd, TUNSETNOCSUM, 1);
 
-        /* We create the net device with 1 page, using the features field of
-         * the descriptor to tell the Guest it is in slot 1 (NET_PEERNUM), and
-         * that the device has fairly random timing.  We do *not* specify
-         * LGUEST_NET_F_NOCSUM: these packets can reach the real world.
-         *
-         * We will put our MAC address is slot 0 for the Guest to see, so
-         * it will send packets to us using the key "peer_offset(0)": */
-        dev = new_device(devices, LGUEST_DEVICE_T_NET, 1,
-                         NET_PEERNUM|LGUEST_DEVICE_F_RANDOMNESS, netfd,
-                         handle_tun_input, peer_offset(0), handle_tun_output);
+        /* First we create a new network device. */
+        dev = new_device("net", VIRTIO_ID_NET, netfd, handle_tun_input);
 
-        /* We keep a flag which says whether we've seen packets come out from
-         * this network device. */
-        dev->priv = malloc(sizeof(bool));
-        *(bool *)dev->priv = false;
+        /* Network devices need a receive and a send queue. */
+        add_virtqueue(dev, VIRTQUEUE_NUM, NULL);
+        add_virtqueue(dev, VIRTQUEUE_NUM, handle_net_output);
 
         /* We need a socket to perform the magic network ioctls to bring up the
          * tap interface, connect to the bridge etc.  Any socket will do! */
@@ -1271,44 +1288,251 @@ static void setup_tun_net(const char *arg, struct device_list *devices)
         } else /* It is an IP address to set up the device with */
                 ip = str2ip(arg);
 
-        /* We are peer 0, ie. first slot, so we hand dev->mem to this routine
-         * to write the MAC address at the start of the device memory.  */
-        configure_device(ipfd, ifr.ifr_name, ip, dev->mem);
+        /* Set up the tun device, and get the mac address for the interface. */
+        configure_device(ipfd, ifr.ifr_name, ip, hwaddr);
 
-        /* Set "promisc" bit: we want every single packet if we're going to
-         * bridge to other machines (and otherwise it doesn't matter). */
-        *((u8 *)dev->mem) |= 0x1;
+        /* Tell Guest what MAC address to use. */
+        add_desc_field(dev, VIRTIO_CONFIG_NET_MAC_F, sizeof(hwaddr), hwaddr);
 
+        /* We don't seed the socket any more; setup is done. */
         close(ipfd);
 
-        verbose("device %p: tun net %u.%u.%u.%u\n",
-                (void *)(dev->desc->pfn * getpagesize()),
-                (u8)(ip>>24), (u8)(ip>>16), (u8)(ip>>8), (u8)ip);
+        verbose("device %u: tun net %u.%u.%u.%u\n",
+                devices.device_num++,
+                (u8)(ip>>24),(u8)(ip>>16),(u8)(ip>>8),(u8)ip);
         if (br_name)
                 verbose("attached to bridge: %s\n", br_name);
 }
+
+
+/*
+ * Block device.
+ *
+ * Serving a block device is really easy: the Guest asks for a block number and
+ * we read or write that position in the file.
+ *
+ * Unfortunately, this is amazingly slow: the Guest waits until the read is
+ * finished before running anything else, even if it could be doing useful
+ * work.  We could use async I/O, except it's reputed to suck so hard that
+ * characters actually go missing from your code when you try to use it.
+ *
+ * So we farm the I/O out to thread, and communicate with it via a pipe. */
+
+/* This hangs off device->priv, with the data. */
+struct vblk_info
+{
+        /* The size of the file. */
+        off64_t len;
+
+        /* The file descriptor for the file. */
+        int fd;
+
+        /* IO thread listens on this file descriptor [0]. */
+        int workpipe[2];
+
+        /* IO thread writes to this file descriptor to mark it done, then
+         * Launcher triggers interrupt to Guest. */
+        int done_fd;
+};
+
+/* This is the core of the I/O thread.  It returns true if it did something. */
+static bool service_io(struct device *dev)
+{
+        struct vblk_info *vblk = dev->priv;
+        unsigned int head, out_num, in_num, wlen;
+        int ret;
+        struct virtio_blk_inhdr *in;
+        struct virtio_blk_outhdr *out;
+        struct iovec iov[dev->vq->vring.num];
+        off64_t off;
+
+        head = get_vq_desc(dev->vq, iov, &out_num, &in_num);
+        if (head == dev->vq->vring.num)
+                return false;
+
+        if (out_num == 0 || in_num == 0)
+                errx(1, "Bad virtblk cmd %u out=%u in=%u",
+                     head, out_num, in_num);
+
+        out = convert(&iov[0], struct virtio_blk_outhdr);
+        in = convert(&iov[out_num+in_num-1], struct virtio_blk_inhdr);
+        off = out->sector * 512;
+
+        /* This is how we implement barriers.  Pretty poor, no? */
+        if (out->type & VIRTIO_BLK_T_BARRIER)
+                fdatasync(vblk->fd);
+
+        if (out->type & VIRTIO_BLK_T_SCSI_CMD) {
+                fprintf(stderr, "Scsi commands unsupported\n");
+                in->status = VIRTIO_BLK_S_UNSUPP;
+                wlen = sizeof(in);
+        } else if (out->type & VIRTIO_BLK_T_OUT) {
+                /* Write */
+
+                /* Move to the right location in the block file.  This can fail
+                 * if they try to write past end. */
+                if (lseek64(vblk->fd, off, SEEK_SET) != off)
+                        err(1, "Bad seek to sector %llu", out->sector);
+
+                ret = writev(vblk->fd, iov+1, out_num-1);
+                verbose("WRITE to sector %llu: %i\n", out->sector, ret);
+
+                /* Grr... Now we know how long the descriptor they sent was, we
+                 * make sure they didn't try to write over the end of the block
+                 * file (possibly extending it). */
+                if (ret > 0 && off + ret > vblk->len) {
+                        /* Trim it back to the correct length */
+                        ftruncate64(vblk->fd, vblk->len);
+                        /* Die, bad Guest, die. */
+                        errx(1, "Write past end %llu+%u", off, ret);
+                }
+                wlen = sizeof(in);
+                in->status = (ret >= 0 ? VIRTIO_BLK_S_OK : VIRTIO_BLK_S_IOERR);
+        } else {
+                /* Read */
+
+                /* Move to the right location in the block file.  This can fail
+                 * if they try to read past end. */
+                if (lseek64(vblk->fd, off, SEEK_SET) != off)
+                        err(1, "Bad seek to sector %llu", out->sector);
+
+                ret = readv(vblk->fd, iov+1, in_num-1);
+                verbose("READ from sector %llu: %i\n", out->sector, ret);
+                if (ret >= 0) {
+                        wlen = sizeof(in) + ret;
+                        in->status = VIRTIO_BLK_S_OK;
+                } else {
+                        wlen = sizeof(in);
+                        in->status = VIRTIO_BLK_S_IOERR;
+                }
+        }
+
+        /* We can't trigger an IRQ, because we're not the Launcher.  It does
+         * that when we tell it we're done. */
+        add_used(dev->vq, head, wlen);
+        return true;
+}
+
+/* This is the thread which actually services the I/O. */
+static int io_thread(void *_dev)
+{
+        struct device *dev = _dev;
+        struct vblk_info *vblk = dev->priv;
+        char c;
+
+        /* Close other side of workpipe so we get 0 read when main dies. */
+        close(vblk->workpipe[1]);
+        /* Close the other side of the done_fd pipe. */
+        close(dev->fd);
+
+        /* When this read fails, it means Launcher died, so we follow. */
+        while (read(vblk->workpipe[0], &c, 1) == 1) {
+                /* We acknowledge each request immediately, to reduce latency,
+                 * rather than waiting until we've done them all.  I haven't
+                 * measured to see if it makes any difference. */
+                while (service_io(dev))
+                        write(vblk->done_fd, &c, 1);
+        }
+        return 0;
+}
+
+/* When the thread says some I/O is done, we interrupt the Guest. */
+static bool handle_io_finish(int fd, struct device *dev)
+{
+        char c;
+
+        /* If child died, presumably it printed message. */
+        if (read(dev->fd, &c, 1) != 1)
+                exit(1);
+
+        /* It did some work, so trigger the irq. */
+        trigger_irq(fd, dev->vq);
+        return true;
+}
+
+/* When the Guest submits some I/O, we wake the I/O thread. */
+static void handle_virtblk_output(int fd, struct virtqueue *vq)
+{
+        struct vblk_info *vblk = vq->dev->priv;
+        char c = 0;
+
+        /* Wake up I/O thread and tell it to go to work! */
+        if (write(vblk->workpipe[1], &c, 1) != 1)
+                /* Presumably it indicated why it died. */
+                exit(1);
+}
+
+/* This creates a virtual block device. */
+static void setup_block_file(const char *filename)
+{
+        int p[2];
+        struct device *dev;
+        struct vblk_info *vblk;
+        void *stack;
+        u64 cap;
+        unsigned int val;
+
+        /* This is the pipe the I/O thread will use to tell us I/O is done. */
+        pipe(p);
+
+        /* The device responds to return from I/O thread. */
+        dev = new_device("block", VIRTIO_ID_BLOCK, p[0], handle_io_finish);
+
+        /* The device has a virtqueue. */
+        add_virtqueue(dev, VIRTQUEUE_NUM, handle_virtblk_output);
+
+        /* Allocate the room for our own bookkeeping */
+        vblk = dev->priv = malloc(sizeof(*vblk));
+
+        /* First we open the file and store the length. */
+        vblk->fd = open_or_die(filename, O_RDWR|O_LARGEFILE);
+        vblk->len = lseek64(vblk->fd, 0, SEEK_END);
+
+        /* Tell Guest how many sectors this device has. */
+        cap = cpu_to_le64(vblk->len / 512);
+        add_desc_field(dev, VIRTIO_CONFIG_BLK_F_CAPACITY, sizeof(cap), &cap);
+
+        /* Tell Guest not to put in too many descriptors at once: two are used
+         * for the in and out elements. */
+        val = cpu_to_le32(VIRTQUEUE_NUM - 2);
+        add_desc_field(dev, VIRTIO_CONFIG_BLK_F_SEG_MAX, sizeof(val), &val);
+
+        /* The I/O thread writes to this end of the pipe when done. */
+        vblk->done_fd = p[1];
+
+        /* This is how we tell the I/O thread about more work. */
+        pipe(vblk->workpipe);
+
+        /* Create stack for thread and run it */
+        stack = malloc(32768);
+        if (clone(io_thread, stack + 32768, CLONE_VM, dev) == -1)
+                err(1, "Creating clone");
+
+        /* We don't need to keep the I/O thread's end of the pipes open. */
+        close(vblk->done_fd);
+        close(vblk->workpipe[0]);
+
+        verbose("device %u: virtblock %llu sectors\n",
+                devices.device_num, cap);
+}
 /* That's the end of device setup. */
 
 /*L:220 Finally we reach the core of the Launcher, which runs the Guest, serves
  * its input and output, and finally, lays it to rest. */
-static void __attribute__((noreturn))
-run_guest(int lguest_fd, struct device_list *device_list)
+static void __attribute__((noreturn)) run_guest(int lguest_fd)
 {
         for (;;) {
                 unsigned long args[] = { LHREQ_BREAK, 0 };
-                unsigned long arr[2];
+                unsigned long notify_addr;
                 int readval;
 
                 /* We read from the /dev/lguest device to run the Guest. */
-                readval = read(lguest_fd, arr, sizeof(arr));
+                readval = read(lguest_fd, &notify_addr, sizeof(notify_addr));
 
-                /* The read can only really return sizeof(arr) (the Guest did a
-                 * SEND_DMA to us), or an error. */
-
-                /* For a successful read, arr[0] is the address of the "struct
-                 * lguest_dma", and arr[1] is the key the Guest sent to. */
-                if (readval == sizeof(arr)) {
-                        handle_output(lguest_fd, arr[0], arr[1], device_list);
+                /* One unsigned long means the Guest did HCALL_NOTIFY */
+                if (readval == sizeof(notify_addr)) {
+                        verbose("Notify on address %#lx\n", notify_addr);
+                        handle_output(lguest_fd, notify_addr);
                         continue;
                 /* ENOENT means the Guest died.  Reading tells us why. */
                 } else if (errno == ENOENT) {
@@ -1322,7 +1546,7 @@ run_guest(int lguest_fd, struct device_list *device_list)
 
                 /* Service input, then unset the BREAK which releases
                  * the Waker. */
-                handle_input(lguest_fd, device_list);
+                handle_input(lguest_fd);
                 if (write(lguest_fd, args, sizeof(args)) < 0)
                         err(1, "Resetting break");
         }
@@ -1336,7 +1560,6 @@ run_guest(int lguest_fd, struct device_list *device_list)
 
 static struct option opts[] = {
         { "verbose", 0, NULL, 'v' },
-        { "sharenet", 1, NULL, 's' },
         { "tunnet", 1, NULL, 't' },
         { "block", 1, NULL, 'b' },
         { "initrd", 1, NULL, 'i' },
@@ -1345,7 +1568,7 @@ static struct option opts[] = {
 static void usage(void)
 {
         errx(1, "Usage: lguest [--verbose] "
-             "[--sharenet=<filename>|--tunnet=(<ipaddr>|bridge:<bridgename>)\n"
+             "[--tunnet=(<ipaddr>|bridge:<bridgename>)\n"
              "|--block=<filename>|--initrd=<filename>]...\n"
              "<mem-in-mb> vmlinux [args...]");
 }
@@ -1358,8 +1581,6 @@ int main(int argc, char *argv[])
         unsigned long mem = 0, pgdir, start, initrd_size = 0;
         /* A temporary and the /dev/lguest file descriptor. */
         int i, c, lguest_fd;
-        /* The list of Guest devices, based on command line arguments. */
-        struct device_list device_list;
         /* The boot information for the Guest. */
         void *boot;
         /* If they specify an initrd file to load. */
@@ -1369,11 +1590,12 @@ int main(int argc, char *argv[])
          * device receive input from a file descriptor, we keep an fdset
          * (infds) and the maximum fd number (max_infd) with the head of the
          * list.  We also keep a pointer to the last device, for easy appending
-         * to the list. */
-        device_list.max_infd = -1;
-        device_list.dev = NULL;
-        device_list.lastdev = &device_list.dev;
-        FD_ZERO(&device_list.infds);
+         * to the list.  Finally, we keep the next interrupt number to hand out
+         * (1: remember that 0 is used by the timer). */
+        FD_ZERO(&devices.infds);
+        devices.max_infd = -1;
+        devices.lastdev = &devices.dev;
+        devices.next_irq = 1;
 
         /* We need to know how much memory so we can set up the device
          * descriptor and memory pages for the devices as we parse the command
@@ -1390,7 +1612,7 @@ int main(int argc, char *argv[])
                                                       + DEVICE_PAGES);
                         guest_limit = mem;
                         guest_max = mem + DEVICE_PAGES*getpagesize();
-                        device_list.descs = get_pages(1);
+                        devices.descpage = get_pages(1);
                         break;
                 }
         }
@@ -1401,14 +1623,11 @@ int main(int argc, char *argv[])
                 case 'v':
                         verbose = true;
                         break;
-                case 's':
-                        setup_net_file(optarg, &device_list);
-                        break;
                 case 't':
-                        setup_tun_net(optarg, &device_list);
+                        setup_tun_net(optarg);
                         break;
                 case 'b':
-                        setup_block_file(optarg, &device_list);
+                        setup_block_file(optarg);
                         break;
                 case 'i':
                         initrd_name = optarg;
@@ -1426,7 +1645,7 @@ int main(int argc, char *argv[])
         verbose("Guest base is at %p\n", guest_base);
 
         /* We always have a console device */
-        setup_console(&device_list);
+        setup_console();
 
         /* Now we load the kernel */
         start = load_kernel(open_or_die(argv[optind+1], O_RDONLY));
@@ -1468,10 +1687,10 @@ int main(int argc, char *argv[])
         /* We fork off a child process, which wakes the Launcher whenever one
          * of the input file descriptors needs attention.  Otherwise we would
          * run the Guest until it tries to output something. */
-        waker_fd = setup_waker(lguest_fd, &device_list);
+        waker_fd = setup_waker(lguest_fd);
 
         /* Finally, run the Guest.  This doesn't return. */
-        run_guest(lguest_fd, &device_list);
+        run_guest(lguest_fd);
 }
 /*:*/