Virtio core support

This patch adds core support for VirtIO.  VirtIO is a paravirtualization
framework that has been in Linux since 2.6.21.  A PCI transport has been
available since 2.6.25.  Network drivers are also available for Windows.

Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>



git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@5869 c046a42c-6fe2-441c-8c8c-71466251a162

2 files changed, 968 insertions, 0 deletions

diff --git a/hw/virtio.c b/hw/virtio.c
new file mode 100644
index 0000000000..93965800df
--- /dev/null
+++ b/hw/virtio.c
@@ -0,0 +1,847 @@
+/*
+ * Virtio Support
+ *
+ * Copyright IBM, Corp. 2007
+ *
+ * Authors:
+ *  Anthony Liguori   <aliguori@us.ibm.com>
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2.  See
+ * the COPYING file in the top-level directory.
+ *
+ */
+
+#include <inttypes.h>
+#include <err.h>
+
+#include "virtio.h"
+#include "sysemu.h"
+
+//#define VIRTIO_ZERO_COPY
+
+/* from Linux's linux/virtio_pci.h */
+
+/* A 32-bit r/o bitmask of the features supported by the host */
+#define VIRTIO_PCI_HOST_FEATURES        0
+
+/* A 32-bit r/w bitmask of features activated by the guest */
+#define VIRTIO_PCI_GUEST_FEATURES       4
+
+/* A 32-bit r/w PFN for the currently selected queue */
+#define VIRTIO_PCI_QUEUE_PFN            8
+
+/* A 16-bit r/o queue size for the currently selected queue */
+#define VIRTIO_PCI_QUEUE_NUM            12
+
+/* A 16-bit r/w queue selector */
+#define VIRTIO_PCI_QUEUE_SEL            14
+
+/* A 16-bit r/w queue notifier */
+#define VIRTIO_PCI_QUEUE_NOTIFY         16
+
+/* An 8-bit device status register.  */
+#define VIRTIO_PCI_STATUS               18
+
+/* An 8-bit r/o interrupt status register.  Reading the value will return the
+ * current contents of the ISR and will also clear it.  This is effectively
+ * a read-and-acknowledge. */
+#define VIRTIO_PCI_ISR                  19
+
+#define VIRTIO_PCI_CONFIG               20
+
+/* Virtio ABI version, if we increment this, we break the guest driver. */
+#define VIRTIO_PCI_ABI_VERSION          0
+
+/* QEMU doesn't strictly need write barriers since everything runs in
+ * lock-step.  We'll leave the calls to wmb() in though to make it obvious for
+ * KVM or if kqemu gets SMP support.
+ */
+#define wmb() do { } while (0)
+
+typedef struct VRingDesc
+{
+    uint64_t addr;
+    uint32_t len;
+    uint16_t flags;
+    uint16_t next;
+} VRingDesc;
+
+typedef struct VRingAvail
+{
+    uint16_t flags;
+    uint16_t idx;
+    uint16_t ring[0];
+} VRingAvail;
+
+typedef struct VRingUsedElem
+{
+    uint32_t id;
+    uint32_t len;
+} VRingUsedElem;
+
+typedef struct VRingUsed
+{
+    uint16_t flags;
+    uint16_t idx;
+    VRingUsedElem ring[0];
+} VRingUsed;
+
+typedef struct VRing
+{
+    unsigned int num;
+    target_phys_addr_t desc;
+    target_phys_addr_t avail;
+    target_phys_addr_t used;
+} VRing;
+
+struct VirtQueue
+{
+    VRing vring;
+    uint32_t pfn;
+    uint16_t last_avail_idx;
+    int inuse;
+    void (*handle_output)(VirtIODevice *vdev, VirtQueue *vq);
+};
+
+#define VIRTIO_PCI_QUEUE_MAX        16
+
+/* virt queue functions */
+#ifdef VIRTIO_ZERO_COPY
+static void *virtio_map_gpa(target_phys_addr_t addr, size_t size)
+{
+    ram_addr_t off;
+    target_phys_addr_t addr1;
+
+    off = cpu_get_physical_page_desc(addr);
+    if ((off & ~TARGET_PAGE_MASK) != IO_MEM_RAM) {
+        fprintf(stderr, "virtio DMA to IO ram\n");
+        exit(1);
+    }
+
+    off = (off & TARGET_PAGE_MASK) | (addr & ~TARGET_PAGE_MASK);
+
+    for (addr1 = addr + TARGET_PAGE_SIZE;
+         addr1 < TARGET_PAGE_ALIGN(addr + size);
+         addr1 += TARGET_PAGE_SIZE) {
+        ram_addr_t off1;
+
+        off1 = cpu_get_physical_page_desc(addr1);
+        if ((off1 & ~TARGET_PAGE_MASK) != IO_MEM_RAM) {
+            fprintf(stderr, "virtio DMA to IO ram\n");
+            exit(1);
+        }
+
+        off1 = (off1 & TARGET_PAGE_MASK) | (addr1 & ~TARGET_PAGE_MASK);
+
+        if (off1 != (off + (addr1 - addr))) {
+            fprintf(stderr, "discontigous virtio memory\n");
+            exit(1);
+        }
+    }
+
+    return phys_ram_base + off;
+}
+#endif
+
+static void virtqueue_init(VirtQueue *vq, target_phys_addr_t pa)
+{
+    vq->vring.desc = pa;
+    vq->vring.avail = pa + vq->vring.num * sizeof(VRingDesc);
+    vq->vring.used = TARGET_PAGE_ALIGN(vq->vring.avail + offsetof(VRingAvail, ring[vq->vring.num]));
+}
+
+static inline uint64_t vring_desc_addr(VirtQueue *vq, int i)
+{
+    target_phys_addr_t pa;
+    pa = vq->vring.desc + sizeof(VRingDesc) * i + offsetof(VRingDesc, addr);
+    return ldq_phys(pa);
+}
+
+static inline uint32_t vring_desc_len(VirtQueue *vq, int i)
+{
+    target_phys_addr_t pa;
+    pa = vq->vring.desc + sizeof(VRingDesc) * i + offsetof(VRingDesc, len);
+    return ldl_phys(pa);
+}
+
+static inline uint16_t vring_desc_flags(VirtQueue *vq, int i)
+{
+    target_phys_addr_t pa;
+    pa = vq->vring.desc + sizeof(VRingDesc) * i + offsetof(VRingDesc, flags);
+    return lduw_phys(pa);
+}
+
+static inline uint16_t vring_desc_next(VirtQueue *vq, int i)
+{
+    target_phys_addr_t pa;
+    pa = vq->vring.desc + sizeof(VRingDesc) * i + offsetof(VRingDesc, next);
+    return lduw_phys(pa);
+}
+
+static inline uint16_t vring_avail_flags(VirtQueue *vq)
+{
+    target_phys_addr_t pa;
+    pa = vq->vring.avail + offsetof(VRingAvail, flags);
+    return lduw_phys(pa);
+}
+
+static inline uint16_t vring_avail_idx(VirtQueue *vq)
+{
+    target_phys_addr_t pa;
+    pa = vq->vring.avail + offsetof(VRingAvail, idx);
+    return lduw_phys(pa);
+}
+
+static inline uint16_t vring_avail_ring(VirtQueue *vq, int i)
+{
+    target_phys_addr_t pa;
+    pa = vq->vring.avail + offsetof(VRingAvail, ring[i]);
+    return lduw_phys(pa);
+}
+
+static inline void vring_used_ring_id(VirtQueue *vq, int i, uint32_t val)
+{
+    target_phys_addr_t pa;
+    pa = vq->vring.used + offsetof(VRingUsed, ring[i].id);
+    stl_phys(pa, val);
+}
+
+static inline void vring_used_ring_len(VirtQueue *vq, int i, uint32_t val)
+{
+    target_phys_addr_t pa;
+    pa = vq->vring.used + offsetof(VRingUsed, ring[i].len);
+    stl_phys(pa, val);
+}
+
+static uint16_t vring_used_idx(VirtQueue *vq)
+{
+    target_phys_addr_t pa;
+    pa = vq->vring.used + offsetof(VRingUsed, idx);
+    return lduw_phys(pa);
+}
+
+static inline void vring_used_idx_increment(VirtQueue *vq, uint16_t val)
+{
+    target_phys_addr_t pa;
+    pa = vq->vring.used + offsetof(VRingUsed, idx);
+    stw_phys(pa, vring_used_idx(vq) + val);
+}
+
+static inline void vring_used_flags_set_bit(VirtQueue *vq, int mask)
+{
+    target_phys_addr_t pa;
+    pa = vq->vring.used + offsetof(VRingUsed, flags);
+    stw_phys(pa, lduw_phys(pa) | mask);
+}
+
+static inline void vring_used_flags_unset_bit(VirtQueue *vq, int mask)
+{
+    target_phys_addr_t pa;
+    pa = vq->vring.used + offsetof(VRingUsed, flags);
+    stw_phys(pa, lduw_phys(pa) & ~mask);
+}
+
+void virtio_queue_set_notification(VirtQueue *vq, int enable)
+{
+    if (enable)
+        vring_used_flags_unset_bit(vq, VRING_USED_F_NO_NOTIFY);
+    else
+        vring_used_flags_set_bit(vq, VRING_USED_F_NO_NOTIFY);
+}
+
+int virtio_queue_ready(VirtQueue *vq)
+{
+    return vq->vring.avail != 0;
+}
+
+int virtio_queue_empty(VirtQueue *vq)
+{
+    return vring_avail_idx(vq) == vq->last_avail_idx;
+}
+
+void virtqueue_fill(VirtQueue *vq, const VirtQueueElement *elem,
+                    unsigned int len, unsigned int idx)
+{
+    unsigned int offset;
+    int i;
+
+#ifndef VIRTIO_ZERO_COPY
+    for (i = 0; i < elem->out_num; i++)
+        qemu_free(elem->out_sg[i].iov_base);
+#endif
+
+    offset = 0;
+    for (i = 0; i < elem->in_num; i++) {
+        size_t size = MIN(len - offset, elem->in_sg[i].iov_len);
+
+#ifdef VIRTIO_ZERO_COPY
+        if (size) {
+            ram_addr_t addr = (uint8_t *)elem->in_sg[i].iov_base - phys_ram_base;
+            ram_addr_t off;
+
+            for (off = 0; off < size; off += TARGET_PAGE_SIZE)
+                cpu_physical_memory_set_dirty(addr + off);
+        }
+#else
+        if (size)
+            cpu_physical_memory_write(elem->in_addr[i],
+                                      elem->in_sg[i].iov_base,
+                                      size);
+
+        qemu_free(elem->in_sg[i].iov_base);
+#endif
+        
+        offset += size;
+    }
+
+    idx = (idx + vring_used_idx(vq)) % vq->vring.num;
+
+    /* Get a pointer to the next entry in the used ring. */
+    vring_used_ring_id(vq, idx, elem->index);
+    vring_used_ring_len(vq, idx, len);
+}
+
+void virtqueue_flush(VirtQueue *vq, unsigned int count)
+{
+    /* Make sure buffer is written before we update index. */
+    wmb();
+    vring_used_idx_increment(vq, count);
+    vq->inuse -= count;
+}
+
+void virtqueue_push(VirtQueue *vq, const VirtQueueElement *elem,
+                    unsigned int len)
+{
+    virtqueue_fill(vq, elem, len, 0);
+    virtqueue_flush(vq, 1);
+}
+
+static int virtqueue_num_heads(VirtQueue *vq, unsigned int idx)
+{
+    uint16_t num_heads = vring_avail_idx(vq) - idx;
+
+    /* Check it isn't doing very strange things with descriptor numbers. */
+    if (num_heads > vq->vring.num)
+        errx(1, "Guest moved used index from %u to %u",
+             idx, vring_avail_idx(vq));
+
+    return num_heads;
+}
+
+static unsigned int virtqueue_get_head(VirtQueue *vq, unsigned int idx)
+{
+    unsigned int head;
+
+    /* Grab the next descriptor number they're advertising, and increment
+     * the index we've seen. */
+    head = vring_avail_ring(vq, 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);
+
+    return head;
+}
+
+static unsigned virtqueue_next_desc(VirtQueue *vq, unsigned int i)
+{
+    unsigned int next;
+
+    /* If this descriptor says it doesn't chain, we're done. */
+    if (!(vring_desc_flags(vq, i) & VRING_DESC_F_NEXT))
+        return vq->vring.num;
+
+    /* Check they're not leading us off end of descriptors. */
+    next = vring_desc_next(vq, i);
+    /* 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;
+}
+
+int virtqueue_avail_bytes(VirtQueue *vq, int in_bytes, int out_bytes)
+{
+    unsigned int idx;
+    int num_bufs, in_total, out_total;
+
+    idx = vq->last_avail_idx;
+
+    num_bufs = in_total = out_total = 0;
+    while (virtqueue_num_heads(vq, idx)) {
+        int i;
+
+        i = virtqueue_get_head(vq, idx++);
+        do {
+            /* If we've got too many, that implies a descriptor loop. */
+            if (++num_bufs > vq->vring.num)
+                errx(1, "Looped descriptor");
+
+            if (vring_desc_flags(vq, i) & VRING_DESC_F_WRITE) {
+                if (in_bytes > 0 &&
+                    (in_total += vring_desc_len(vq, i)) >= in_bytes)
+                    return 1;
+            } else {
+                if (out_bytes > 0 &&
+                    (out_total += vring_desc_len(vq, i)) >= out_bytes)
+                    return 1;
+            }
+        } while ((i = virtqueue_next_desc(vq, i)) != vq->vring.num);
+    }
+
+    return 0;
+}
+
+int virtqueue_pop(VirtQueue *vq, VirtQueueElement *elem)
+{
+    unsigned int i, head;
+
+    if (!virtqueue_num_heads(vq, vq->last_avail_idx))
+        return 0;
+
+    /* When we start there are none of either input nor output. */
+    elem->out_num = elem->in_num = 0;
+
+    i = head = virtqueue_get_head(vq, vq->last_avail_idx++);
+    do {
+        struct iovec *sg;
+
+        if (vring_desc_flags(vq, i) & VRING_DESC_F_WRITE) {
+            elem->in_addr[elem->in_num] = vring_desc_addr(vq, i);
+            sg = &elem->in_sg[elem->in_num++];
+        } else
+            sg = &elem->out_sg[elem->out_num++];
+
+        /* Grab the first descriptor, and check it's OK. */
+        sg->iov_len = vring_desc_len(vq, i);
+
+#ifdef VIRTIO_ZERO_COPY
+        sg->iov_base = virtio_map_gpa(vring_desc_addr(vq, i), sg->iov_len);
+#else
+        /* cap individual scatter element size to prevent unbounded allocations
+           of memory from the guest.  Practically speaking, no virtio driver
+           will ever pass more than a page in each element.  We set the cap to
+           be 2MB in case for some reason a large page makes it way into the
+           sg list.  When we implement a zero copy API, this limitation will
+           disappear */
+        if (sg->iov_len > (2 << 20))
+            sg->iov_len = 2 << 20;
+
+        sg->iov_base = qemu_malloc(sg->iov_len);
+        if (sg->iov_base && 
+            !(vring_desc_flags(vq, i) & VRING_DESC_F_WRITE)) {
+            cpu_physical_memory_read(vring_desc_addr(vq, i),
+                                     sg->iov_base,
+                                     sg->iov_len);
+        }
+#endif
+        if (sg->iov_base == NULL)
+            errx(1, "Invalid mapping\n");
+
+        /* If we've got too many, that implies a descriptor loop. */
+        if ((elem->in_num + elem->out_num) > vq->vring.num)
+            errx(1, "Looped descriptor");
+    } while ((i = virtqueue_next_desc(vq, i)) != vq->vring.num);
+
+    elem->index = head;
+
+    vq->inuse++;
+
+    return elem->in_num + elem->out_num;
+}
+
+/* virtio device */
+
+static VirtIODevice *to_virtio_device(PCIDevice *pci_dev)
+{
+    return (VirtIODevice *)pci_dev;
+}
+
+static void virtio_update_irq(VirtIODevice *vdev)
+{
+    qemu_set_irq(vdev->pci_dev.irq[0], vdev->isr & 1);
+}
+
+void virtio_reset(void *opaque)
+{
+    VirtIODevice *vdev = opaque;
+    int i;
+
+    if (vdev->reset)
+        vdev->reset(vdev);
+
+    vdev->features = 0;
+    vdev->queue_sel = 0;
+    vdev->status = 0;
+    vdev->isr = 0;
+    virtio_update_irq(vdev);
+
+    for(i = 0; i < VIRTIO_PCI_QUEUE_MAX; i++) {
+        vdev->vq[i].vring.desc = 0;
+        vdev->vq[i].vring.avail = 0;
+        vdev->vq[i].vring.used = 0;
+        vdev->vq[i].last_avail_idx = 0;
+        vdev->vq[i].pfn = 0;
+    }
+}
+
+static void virtio_ioport_write(void *opaque, uint32_t addr, uint32_t val)
+{
+    VirtIODevice *vdev = to_virtio_device(opaque);
+    ram_addr_t pa;
+
+    addr -= vdev->addr;
+
+    switch (addr) {
+    case VIRTIO_PCI_GUEST_FEATURES:
+        if (vdev->set_features)
+            vdev->set_features(vdev, val);
+        vdev->features = val;
+        break;
+    case VIRTIO_PCI_QUEUE_PFN:
+        pa = (ram_addr_t)val << TARGET_PAGE_BITS;
+        vdev->vq[vdev->queue_sel].pfn = val;
+        if (pa == 0) {
+            virtio_reset(vdev);
+        } else {
+            virtqueue_init(&vdev->vq[vdev->queue_sel], pa);
+        }
+        break;
+    case VIRTIO_PCI_QUEUE_SEL:
+        if (val < VIRTIO_PCI_QUEUE_MAX)
+            vdev->queue_sel = val;
+        break;
+    case VIRTIO_PCI_QUEUE_NOTIFY:
+        if (val < VIRTIO_PCI_QUEUE_MAX && vdev->vq[val].vring.desc)
+            vdev->vq[val].handle_output(vdev, &vdev->vq[val]);
+        break;
+    case VIRTIO_PCI_STATUS:
+        vdev->status = val & 0xFF;
+        if (vdev->status == 0)
+            virtio_reset(vdev);
+        break;
+    }
+}
+
+static uint32_t virtio_ioport_read(void *opaque, uint32_t addr)
+{
+    VirtIODevice *vdev = to_virtio_device(opaque);
+    uint32_t ret = 0xFFFFFFFF;
+
+    addr -= vdev->addr;
+
+    switch (addr) {
+    case VIRTIO_PCI_HOST_FEATURES:
+        ret = vdev->get_features(vdev);
+        ret |= (1 << VIRTIO_F_NOTIFY_ON_EMPTY);
+        break;
+    case VIRTIO_PCI_GUEST_FEATURES:
+        ret = vdev->features;
+        break;
+    case VIRTIO_PCI_QUEUE_PFN:
+        ret = vdev->vq[vdev->queue_sel].pfn;
+        break;
+    case VIRTIO_PCI_QUEUE_NUM:
+        ret = vdev->vq[vdev->queue_sel].vring.num;
+        break;
+    case VIRTIO_PCI_QUEUE_SEL:
+        ret = vdev->queue_sel;
+        break;
+    case VIRTIO_PCI_STATUS:
+        ret = vdev->status;
+        break;
+    case VIRTIO_PCI_ISR:
+        /* reading from the ISR also clears it. */
+        ret = vdev->isr;
+        vdev->isr = 0;
+        virtio_update_irq(vdev);
+        break;
+    default:
+        break;
+    }
+
+    return ret;
+}
+
+static uint32_t virtio_config_readb(void *opaque, uint32_t addr)
+{
+    VirtIODevice *vdev = opaque;
+    uint8_t val;
+
+    vdev->get_config(vdev, vdev->config);
+
+    addr -= vdev->addr + VIRTIO_PCI_CONFIG;
+    if (addr > (vdev->config_len - sizeof(val)))
+        return (uint32_t)-1;
+
+    memcpy(&val, vdev->config + addr, sizeof(val));
+    return val;
+}
+
+static uint32_t virtio_config_readw(void *opaque, uint32_t addr)
+{
+    VirtIODevice *vdev = opaque;
+    uint16_t val;
+
+    vdev->get_config(vdev, vdev->config);
+
+    addr -= vdev->addr + VIRTIO_PCI_CONFIG;
+    if (addr > (vdev->config_len - sizeof(val)))
+        return (uint32_t)-1;
+
+    memcpy(&val, vdev->config + addr, sizeof(val));
+    return val;
+}
+
+static uint32_t virtio_config_readl(void *opaque, uint32_t addr)
+{
+    VirtIODevice *vdev = opaque;
+    uint32_t val;
+
+    vdev->get_config(vdev, vdev->config);
+
+    addr -= vdev->addr + VIRTIO_PCI_CONFIG;
+    if (addr > (vdev->config_len - sizeof(val)))
+        return (uint32_t)-1;
+
+    memcpy(&val, vdev->config + addr, sizeof(val));
+    return val;
+}
+
+static void virtio_config_writeb(void *opaque, uint32_t addr, uint32_t data)
+{
+    VirtIODevice *vdev = opaque;
+    uint8_t val = data;
+
+    addr -= vdev->addr + VIRTIO_PCI_CONFIG;
+    if (addr > (vdev->config_len - sizeof(val)))
+        return;
+
+    memcpy(vdev->config + addr, &val, sizeof(val));
+
+    if (vdev->set_config)
+        vdev->set_config(vdev, vdev->config);
+}
+
+static void virtio_config_writew(void *opaque, uint32_t addr, uint32_t data)
+{
+    VirtIODevice *vdev = opaque;
+    uint16_t val = data;
+
+    addr -= vdev->addr + VIRTIO_PCI_CONFIG;
+    if (addr > (vdev->config_len - sizeof(val)))
+        return;
+
+    memcpy(vdev->config + addr, &val, sizeof(val));
+
+    if (vdev->set_config)
+        vdev->set_config(vdev, vdev->config);
+}
+
+static void virtio_config_writel(void *opaque, uint32_t addr, uint32_t data)
+{
+    VirtIODevice *vdev = opaque;
+    uint32_t val = data;
+
+    addr -= vdev->addr + VIRTIO_PCI_CONFIG;
+    if (addr > (vdev->config_len - sizeof(val)))
+        return;
+
+    memcpy(vdev->config + addr, &val, sizeof(val));
+
+    if (vdev->set_config)
+        vdev->set_config(vdev, vdev->config);
+}
+
+static void virtio_map(PCIDevice *pci_dev, int region_num,
+                       uint32_t addr, uint32_t size, int type)
+{
+    VirtIODevice *vdev = to_virtio_device(pci_dev);
+    int i;
+
+    vdev->addr = addr;
+    for (i = 0; i < 3; i++) {
+        register_ioport_write(addr, 20, 1 << i, virtio_ioport_write, vdev);
+        register_ioport_read(addr, 20, 1 << i, virtio_ioport_read, vdev);
+    }
+
+    if (vdev->config_len) {
+        register_ioport_write(addr + 20, vdev->config_len, 1,
+                              virtio_config_writeb, vdev);
+        register_ioport_write(addr + 20, vdev->config_len, 2,
+                              virtio_config_writew, vdev);
+        register_ioport_write(addr + 20, vdev->config_len, 4,
+                              virtio_config_writel, vdev);
+        register_ioport_read(addr + 20, vdev->config_len, 1,
+                             virtio_config_readb, vdev);
+        register_ioport_read(addr + 20, vdev->config_len, 2,
+                             virtio_config_readw, vdev);
+        register_ioport_read(addr + 20, vdev->config_len, 4,
+                             virtio_config_readl, vdev);
+
+        vdev->get_config(vdev, vdev->config);
+    }
+}
+
+VirtQueue *virtio_add_queue(VirtIODevice *vdev, int queue_size,
+                            void (*handle_output)(VirtIODevice *, VirtQueue *))
+{
+    int i;
+
+    for (i = 0; i < VIRTIO_PCI_QUEUE_MAX; i++) {
+        if (vdev->vq[i].vring.num == 0)
+            break;
+    }
+
+    if (i == VIRTIO_PCI_QUEUE_MAX || queue_size > VIRTQUEUE_MAX_SIZE)
+        abort();
+
+    vdev->vq[i].vring.num = queue_size;
+    vdev->vq[i].handle_output = handle_output;
+
+    return &vdev->vq[i];
+}
+
+void virtio_notify(VirtIODevice *vdev, VirtQueue *vq)
+{
+    /* Always notify when queue is empty */
+    if ((vq->inuse || vring_avail_idx(vq) != vq->last_avail_idx) &&
+        (vring_avail_flags(vq) & VRING_AVAIL_F_NO_INTERRUPT))
+        return;
+
+    vdev->isr |= 0x01;
+    virtio_update_irq(vdev);
+}
+
+void virtio_notify_config(VirtIODevice *vdev)
+{
+    vdev->isr |= 0x03;
+    virtio_update_irq(vdev);
+}
+
+void virtio_save(VirtIODevice *vdev, QEMUFile *f)
+{
+    int i;
+
+    pci_device_save(&vdev->pci_dev, f);
+
+    qemu_put_be32s(f, &vdev->addr);
+    qemu_put_8s(f, &vdev->status);
+    qemu_put_8s(f, &vdev->isr);
+    qemu_put_be16s(f, &vdev->queue_sel);
+    qemu_put_be32s(f, &vdev->features);
+    qemu_put_be32(f, vdev->config_len);
+    qemu_put_buffer(f, vdev->config, vdev->config_len);
+
+    for (i = 0; i < VIRTIO_PCI_QUEUE_MAX; i++) {
+        if (vdev->vq[i].vring.num == 0)
+            break;
+    }
+
+    qemu_put_be32(f, i);
+
+    for (i = 0; i < VIRTIO_PCI_QUEUE_MAX; i++) {
+        if (vdev->vq[i].vring.num == 0)
+            break;
+
+        qemu_put_be32(f, vdev->vq[i].vring.num);
+        qemu_put_be32s(f, &vdev->vq[i].pfn);
+        qemu_put_be16s(f, &vdev->vq[i].last_avail_idx);
+    }
+}
+
+void virtio_load(VirtIODevice *vdev, QEMUFile *f)
+{
+    int num, i;
+
+    pci_device_load(&vdev->pci_dev, f);
+
+    qemu_get_be32s(f, &vdev->addr);
+    qemu_get_8s(f, &vdev->status);
+    qemu_get_8s(f, &vdev->isr);
+    qemu_get_be16s(f, &vdev->queue_sel);
+    qemu_get_be32s(f, &vdev->features);
+    vdev->config_len = qemu_get_be32(f);
+    qemu_get_buffer(f, vdev->config, vdev->config_len);
+
+    num = qemu_get_be32(f);
+
+    for (i = 0; i < num; i++) {
+        vdev->vq[i].vring.num = qemu_get_be32(f);
+        qemu_get_be32s(f, &vdev->vq[i].pfn);
+        qemu_get_be16s(f, &vdev->vq[i].last_avail_idx);
+
+        if (vdev->vq[i].pfn) {
+            target_phys_addr_t pa;
+
+            pa = (ram_addr_t)vdev->vq[i].pfn << TARGET_PAGE_BITS;
+            virtqueue_init(&vdev->vq[i], pa);
+        }
+    }
+
+    virtio_update_irq(vdev);
+}
+
+VirtIODevice *virtio_init_pci(PCIBus *bus, const char *name,
+                              uint16_t vendor, uint16_t device,
+                              uint16_t subvendor, uint16_t subdevice,
+                              uint8_t class_code, uint8_t subclass_code,
+                              uint8_t pif, size_t config_size,
+                              size_t struct_size)
+{
+    VirtIODevice *vdev;
+    PCIDevice *pci_dev;
+    uint8_t *config;
+    uint32_t size;
+
+    pci_dev = pci_register_device(bus, name, struct_size,
+                                  -1, NULL, NULL);
+    if (!pci_dev)
+        return NULL;
+
+    vdev = to_virtio_device(pci_dev);
+
+    vdev->status = 0;
+    vdev->isr = 0;
+    vdev->queue_sel = 0;
+    vdev->vq = qemu_mallocz(sizeof(VirtQueue) * VIRTIO_PCI_QUEUE_MAX);
+
+    config = pci_dev->config;
+    config[0x00] = vendor & 0xFF;
+    config[0x01] = (vendor >> 8) & 0xFF;
+    config[0x02] = device & 0xFF;
+    config[0x03] = (device >> 8) & 0xFF;
+
+    config[0x08] = VIRTIO_PCI_ABI_VERSION;
+
+    config[0x09] = pif;
+    config[0x0a] = subclass_code;
+    config[0x0b] = class_code;
+    config[0x0e] = 0x00;
+
+    config[0x2c] = subvendor & 0xFF;
+    config[0x2d] = (subvendor >> 8) & 0xFF;
+    config[0x2e] = subdevice & 0xFF;
+    config[0x2f] = (subdevice >> 8) & 0xFF;
+
+    config[0x3d] = 1;
+
+    vdev->name = name;
+    vdev->config_len = config_size;
+    if (vdev->config_len)
+        vdev->config = qemu_mallocz(config_size);
+    else
+        vdev->config = NULL;
+
+    size = 20 + config_size;
+    if (size & (size-1))
+        size = 1 << fls(size);
+
+    pci_register_io_region(pci_dev, 0, size, PCI_ADDRESS_SPACE_IO,
+                           virtio_map);
+    qemu_register_reset(virtio_reset, vdev);
+
+    return vdev;
+}
diff --git a/hw/virtio.h b/hw/virtio.h
new file mode 100644
index 0000000000..f04e75f887
--- /dev/null
+++ b/hw/virtio.h
@@ -0,0 +1,121 @@
+/*
+ * Virtio Support
+ *
+ * Copyright IBM, Corp. 2007
+ *
+ * Authors:
+ *  Anthony Liguori   <aliguori@us.ibm.com>
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2.  See
+ * the COPYING file in the top-level directory.
+ *
+ */
+
+#ifndef _QEMU_VIRTIO_H
+#define _QEMU_VIRTIO_H
+
+#include <sys/uio.h>
+#include "hw.h"
+#include "pci.h"
+
+/* from Linux's linux/virtio_config.h */
+
+/* Status byte for guest to report progress, and synchronize features. */
+/* We have seen device and processed generic fields (VIRTIO_CONFIG_F_VIRTIO) */
+#define VIRTIO_CONFIG_S_ACKNOWLEDGE     1
+/* We have found a driver for the device. */
+#define VIRTIO_CONFIG_S_DRIVER          2
+/* Driver has used its parts of the config, and is happy */
+#define VIRTIO_CONFIG_S_DRIVER_OK       4
+/* We've given up on this device. */
+#define VIRTIO_CONFIG_S_FAILED          0x80
+
+/* We notify when the ring is completely used, even if the guest is supressing
+ * callbacks */
+#define VIRTIO_F_NOTIFY_ON_EMPTY        24
+
+/* from Linux's linux/virtio_ring.h */
+
+/* This marks a buffer as continuing via the next field. */
+#define VRING_DESC_F_NEXT       1
+/* This marks a buffer as write-only (otherwise read-only). */
+#define VRING_DESC_F_WRITE      2
+
+/* This means don't notify other side when buffer added. */
+#define VRING_USED_F_NO_NOTIFY  1
+/* This means don't interrupt guest when buffer consumed. */
+#define VRING_AVAIL_F_NO_INTERRUPT      1
+
+struct VirtQueue;
+
+typedef struct VirtQueue VirtQueue;
+typedef struct VirtIODevice VirtIODevice;
+
+#define VIRTQUEUE_MAX_SIZE 1024
+
+typedef struct VirtQueueElement
+{
+    unsigned int index;
+    unsigned int out_num;
+    unsigned int in_num;
+    target_phys_addr_t in_addr[VIRTQUEUE_MAX_SIZE];
+    struct iovec in_sg[VIRTQUEUE_MAX_SIZE];
+    struct iovec out_sg[VIRTQUEUE_MAX_SIZE];
+} VirtQueueElement;
+
+#define VIRTIO_PCI_QUEUE_MAX 16
+
+struct VirtIODevice
+{
+    PCIDevice pci_dev;
+    const char *name;
+    uint32_t addr;
+    uint8_t status;
+    uint8_t isr;
+    uint16_t queue_sel;
+    uint32_t features;
+    size_t config_len;
+    void *config;
+    uint32_t (*get_features)(VirtIODevice *vdev);
+    void (*set_features)(VirtIODevice *vdev, uint32_t val);
+    void (*get_config)(VirtIODevice *vdev, uint8_t *config);
+    void (*set_config)(VirtIODevice *vdev, const uint8_t *config);
+    void (*reset)(VirtIODevice *vdev);
+    VirtQueue *vq;
+};
+
+VirtIODevice *virtio_init_pci(PCIBus *bus, const char *name,
+                              uint16_t vendor, uint16_t device,
+                              uint16_t subvendor, uint16_t subdevice,
+                              uint8_t class_code, uint8_t subclass_code,
+                              uint8_t pif, size_t config_size,
+                              size_t struct_size);
+
+VirtQueue *virtio_add_queue(VirtIODevice *vdev, int queue_size,
+                            void (*handle_output)(VirtIODevice *,
+                                                  VirtQueue *));
+
+void virtqueue_push(VirtQueue *vq, const VirtQueueElement *elem,
+                    unsigned int len);
+void virtqueue_flush(VirtQueue *vq, unsigned int count);
+void virtqueue_fill(VirtQueue *vq, const VirtQueueElement *elem,
+                    unsigned int len, unsigned int idx);
+
+int virtqueue_pop(VirtQueue *vq, VirtQueueElement *elem);
+int virtqueue_avail_bytes(VirtQueue *vq, int in_bytes, int out_bytes);
+
+void virtio_notify(VirtIODevice *vdev, VirtQueue *vq);
+
+void virtio_save(VirtIODevice *vdev, QEMUFile *f);
+
+void virtio_load(VirtIODevice *vdev, QEMUFile *f);
+
+void virtio_notify_config(VirtIODevice *vdev);
+
+void virtio_queue_set_notification(VirtQueue *vq, int enable);
+
+int virtio_queue_ready(VirtQueue *vq);
+
+int virtio_queue_empty(VirtQueue *vq);
+
+#endif