virtio: device/driver area size calculation refactor for split ring

There is slight size difference between split/packed rings.

This is the refactor of split ring as well as a helper to expanding
device and driver area size calculation for packed ring.

Signed-off-by: Wei Xu <wexu@redhat.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
Reviewed-by: Jens Freimann <jfreimann@redhat.com>
Message-Id: <20191025083527.30803-3-eperezma@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

hw/virtio/virtio.c

@@ -159,10 +159,8 @@ static void virtio_init_region_cache(VirtIODevice *vdev, int n)
     VRingMemoryRegionCaches *old = vq->vring.caches;
     VRingMemoryRegionCaches *new = NULL;
     hwaddr addr, size;
-    int event_size;
     int64_t len;
 
-    event_size = virtio_vdev_has_feature(vq->vdev, VIRTIO_RING_F_EVENT_IDX) ? 2 : 0;
 
     addr = vq->vring.desc;
     if (!addr) {
@@ -177,7 +175,7 @@ static void virtio_init_region_cache(VirtIODevice *vdev, int n)
         goto err_desc;
     }
 
-    size = virtio_queue_get_used_size(vdev, n) + event_size;
+    size = virtio_queue_get_used_size(vdev, n);
     len = address_space_cache_init(&new->used, vdev->dma_as,
                                    vq->vring.used, size, true);
     if (len < size) {
@@ -185,7 +183,7 @@ static void virtio_init_region_cache(VirtIODevice *vdev, int n)
         goto err_used;
     }
 
-    size = virtio_queue_get_avail_size(vdev, n) + event_size;
+    size = virtio_queue_get_avail_size(vdev, n);
     len = address_space_cache_init(&new->avail, vdev->dma_as,
                                    vq->vring.avail, size, false);
     if (len < size) {
@@ -2414,14 +2412,20 @@ hwaddr virtio_queue_get_desc_size(VirtIODevice *vdev, int n)
 
 hwaddr virtio_queue_get_avail_size(VirtIODevice *vdev, int n)
 {
+    int s;
+
+    s = virtio_vdev_has_feature(vdev, VIRTIO_RING_F_EVENT_IDX) ? 2 : 0;
     return offsetof(VRingAvail, ring) +
-        sizeof(uint16_t) * vdev->vq[n].vring.num;
+        sizeof(uint16_t) * vdev->vq[n].vring.num + s;
 }
 
 hwaddr virtio_queue_get_used_size(VirtIODevice *vdev, int n)
 {
+    int s;
+
+    s = virtio_vdev_has_feature(vdev, VIRTIO_RING_F_EVENT_IDX) ? 2 : 0;
     return offsetof(VRingUsed, ring) +
-        sizeof(VRingUsedElem) * vdev->vq[n].vring.num;
+        sizeof(VRingUsedElem) * vdev->vq[n].vring.num + s;
 }
 
 uint16_t virtio_queue_get_last_avail_idx(VirtIODevice *vdev, int n)