[01/11] virtio-bus: remove vdev field

diff --git a/hw/virtio/virtio-bus.c b/hw/virtio/virtio-bus.c
index 6849a01..669ce38 100644
--- a/hw/virtio/virtio-bus.c
+++ b/hw/virtio/virtio-bus.c
@@ -46,8 +46,6 @@  int virtio_bus_plug_device(VirtIODevice *vdev)
     VirtioBusClass *klass = VIRTIO_BUS_GET_CLASS(bus);
     DPRINTF("%s: plug device.\n", qbus->name);
 
-    bus->vdev = vdev;
-
     if (klass->device_plugged != NULL) {
         klass->device_plugged(qbus->parent);
     }
@@ -58,75 +56,84 @@  int virtio_bus_plug_device(VirtIODevice *vdev)
 /* Reset the virtio_bus */
 void virtio_bus_reset(VirtioBusState *bus)
 {
+    VirtIODevice *vdev = virtio_bus_get_device(bus);
+
     DPRINTF("%s: reset device.\n", qbus->name);
-    if (bus->vdev != NULL) {
-        virtio_reset(bus->vdev);
+    if (vdev != NULL) {
+        virtio_reset(vdev);
     }
 }
 
 /* Destroy the VirtIODevice */
 void virtio_bus_destroy_device(VirtioBusState *bus)
 {
-    DeviceState *qdev;
     BusState *qbus = BUS(bus);
     VirtioBusClass *klass = VIRTIO_BUS_GET_CLASS(bus);
+    VirtIODevice *vdev = virtio_bus_get_device(bus);
+
     DPRINTF("%s: remove device.\n", qbus->name);
 
-    if (bus->vdev != NULL) {
+    if (vdev != NULL) {
         if (klass->device_unplug != NULL) {
             klass->device_unplug(qbus->parent);
         }
-        qdev = DEVICE(bus->vdev);
-        qdev_free(qdev);
-        bus->vdev = NULL;
+        qdev_free(DEVICE(vdev));
     }
 }
 
 /* Get the device id of the plugged device. */
 uint16_t virtio_bus_get_vdev_id(VirtioBusState *bus)
 {
-    assert(bus->vdev != NULL);
-    return bus->vdev->device_id;
+    VirtIODevice *vdev = virtio_bus_get_device(bus);
+    assert(vdev != NULL);
+    return vdev->device_id;
 }
 
 /* Get the config_len field of the plugged device. */
 size_t virtio_bus_get_vdev_config_len(VirtioBusState *bus)
 {
-    assert(bus->vdev != NULL);
-    return bus->vdev->config_len;
+    VirtIODevice *vdev = virtio_bus_get_device(bus);
+    assert(vdev != NULL);
+    return vdev->config_len;
 }
 
 /* Get the features of the plugged device. */
 uint32_t virtio_bus_get_vdev_features(VirtioBusState *bus,
                                     uint32_t requested_features)
 {
+    VirtIODevice *vdev = virtio_bus_get_device(bus);
     VirtioDeviceClass *k;
-    assert(bus->vdev != NULL);
-    k = VIRTIO_DEVICE_GET_CLASS(bus->vdev);
+
+    assert(vdev != NULL);
+    k = VIRTIO_DEVICE_GET_CLASS(vdev);
     assert(k->get_features != NULL);
-    return k->get_features(bus->vdev, requested_features);
+    return k->get_features(vdev, requested_features);
 }
 
 /* Set the features of the plugged device. */
 void virtio_bus_set_vdev_features(VirtioBusState *bus,
                                       uint32_t requested_features)
 {
+    VirtIODevice *vdev = virtio_bus_get_device(bus);
     VirtioDeviceClass *k;
-    assert(bus->vdev != NULL);
-    k = VIRTIO_DEVICE_GET_CLASS(bus->vdev);
+
+    assert(vdev != NULL);
+    k = VIRTIO_DEVICE_GET_CLASS(vdev);
     if (k->set_features != NULL) {
-        k->set_features(bus->vdev, requested_features);
+        k->set_features(vdev, requested_features);
     }
 }
 
 /* Get bad features of the plugged device. */
 uint32_t virtio_bus_get_vdev_bad_features(VirtioBusState *bus)
 {
+    VirtIODevice *vdev = virtio_bus_get_device(bus);
     VirtioDeviceClass *k;
-    assert(bus->vdev != NULL);
-    k = VIRTIO_DEVICE_GET_CLASS(bus->vdev);
+
+    assert(vdev != NULL);
+    k = VIRTIO_DEVICE_GET_CLASS(vdev);
     if (k->bad_features != NULL) {
-        return k->bad_features(bus->vdev);
+        return k->bad_features(vdev);
     } else {
         return 0;
     }
@@ -135,22 +142,26 @@  uint32_t virtio_bus_get_vdev_bad_features(VirtioBusState *bus)
 /* Get config of the plugged device. */
 void virtio_bus_get_vdev_config(VirtioBusState *bus, uint8_t *config)
 {
+    VirtIODevice *vdev = virtio_bus_get_device(bus);
     VirtioDeviceClass *k;
-    assert(bus->vdev != NULL);
-    k = VIRTIO_DEVICE_GET_CLASS(bus->vdev);
+
+    assert(vdev != NULL);
+    k = VIRTIO_DEVICE_GET_CLASS(vdev);
     if (k->get_config != NULL) {
-        k->get_config(bus->vdev, config);
+        k->get_config(vdev, config);
     }
 }
 
 /* Set config of the plugged device. */
 void virtio_bus_set_vdev_config(VirtioBusState *bus, uint8_t *config)
 {
+    VirtIODevice *vdev = virtio_bus_get_device(bus);
     VirtioDeviceClass *k;
-    assert(bus->vdev != NULL);
-    k = VIRTIO_DEVICE_GET_CLASS(bus->vdev);
+
+    assert(vdev != NULL);
+    k = VIRTIO_DEVICE_GET_CLASS(vdev);
     if (k->set_config != NULL) {
-        k->set_config(bus->vdev, config);
+        k->set_config(vdev, config);
     }
 }
 
diff --git a/hw/virtio/virtio-mmio.c b/hw/virtio/virtio-mmio.c
index 29cf284..8829eb0 100644
--- a/hw/virtio/virtio-mmio.c
+++ b/hw/virtio/virtio-mmio.c
@@ -95,7 +95,7 @@  static void virtio_mmio_bus_new(VirtioBusState *bus, size_t bus_size,
 static uint64_t virtio_mmio_read(void *opaque, hwaddr offset, unsigned size)
 {
     VirtIOMMIOProxy *proxy = (VirtIOMMIOProxy *)opaque;
-    VirtIODevice *vdev = proxy->bus.vdev;
+    VirtIODevice *vdev = virtio_bus_get_device(&proxy->bus);
 
     DPRINTF("virtio_mmio_read offset 0x%x\n", (int)offset);
 
@@ -185,7 +185,7 @@  static void virtio_mmio_write(void *opaque, hwaddr offset, uint64_t value,
                               unsigned size)
 {
     VirtIOMMIOProxy *proxy = (VirtIOMMIOProxy *)opaque;
-    VirtIODevice *vdev = proxy->bus.vdev;
+    VirtIODevice *vdev = virtio_bus_get_device(&proxy->bus);
 
     DPRINTF("virtio_mmio_write offset 0x%x value 0x%" PRIx64 "\n",
             (int)offset, value);
@@ -298,12 +298,13 @@  static const MemoryRegionOps virtio_mem_ops = {
 static void virtio_mmio_update_irq(DeviceState *opaque, uint16_t vector)
 {
     VirtIOMMIOProxy *proxy = VIRTIO_MMIO(opaque);
+    VirtIODevice *vdev = virtio_bus_get_device(&proxy->bus);
     int level;
 
-    if (!proxy->bus.vdev) {
+    if (!vdev) {
         return;
     }
-    level = (proxy->bus.vdev->isr != 0);
+    level = (vdev->isr != 0);
     DPRINTF("virtio_mmio setting IRQ %d\n", level);
     qemu_set_irq(proxy->irq, level);
 }
diff --git a/hw/virtio/virtio-pci.c b/hw/virtio/virtio-pci.c
index 4825802..07708a3 100644
--- a/hw/virtio/virtio-pci.c
+++ b/hw/virtio/virtio-pci.c
@@ -943,7 +943,7 @@  static void virtio_pci_device_plugged(DeviceState *d)
     uint8_t *config;
     uint32_t size;
 
-    proxy->vdev = bus->vdev;
+    proxy->vdev = virtio_bus_get_device(bus);
 
     config = proxy->pci_dev.config;
     if (proxy->class_code) {
diff --git a/include/hw/virtio/virtio-bus.h b/include/hw/virtio/virtio-bus.h
index 9217f85..48afb7c 100644
--- a/include/hw/virtio/virtio-bus.h
+++ b/include/hw/virtio/virtio-bus.h
@@ -72,10 +72,6 @@  typedef struct VirtioBusClass {
 
 struct VirtioBusState {
     BusState parent_obj;
-    /*
-     * Only one VirtIODevice can be plugged on the bus.
-     */
-    VirtIODevice *vdev;
 };
 
 int virtio_bus_plug_device(VirtIODevice *vdev);
@@ -98,4 +94,16 @@  void virtio_bus_get_vdev_config(VirtioBusState *bus, uint8_t *config);
 /* Set config of the plugged device. */
 void virtio_bus_set_vdev_config(VirtioBusState *bus, uint8_t *config);
 
+static inline VirtIODevice *virtio_bus_get_device(VirtioBusState *bus)
+{
+    BusState *qbus = &bus->parent_obj;
+    BusChild *kid = QTAILQ_FIRST(&qbus->children);
+    DeviceState *qdev = kid ? kid->child : NULL;
+
+    /* This is used on the data path, the cast is guaranteed
+     * to succeed by the qdev machinery.
+     */
+    return (VirtIODevice *)qdev;
+}
+
 #endif /* VIRTIO_BUS_H */