virtio-ccw: fix ring sizing

Current code seems to assume ring size is
always decreased but this is not required by spec:
what spec says is just that size can not exceed
the maximum. Fix it up.
Signed-off-by: NMichael S. Tsirkin <mst@redhat.com>
Message-Id: <1484256243-1982-1-git-send-email-mst@redhat.com>
Signed-off-by: NCornelia Huck <cornelia.huck@de.ibm.com>

hw/s390x/virtio-ccw.c

@@ -149,7 +149,7 @@ static int virtio_ccw_set_vqs(SubchDev *sch, VqInfoBlock *info,
     } else {
         if (info) {
             /* virtio-1 allows changing the ring size. */
-            if (virtio_queue_get_num(vdev, index) < num) {
+            if (virtio_queue_get_max_num(vdev, index) < num) {
                 /* Fail if we exceed the maximum number. */
                 return -EINVAL;
             }

hw/virtio/virtio.c

@@ -1262,6 +1262,11 @@ int virtio_queue_get_num(VirtIODevice *vdev, int n)
     return vdev->vq[n].vring.num;
 }
 
+int virtio_queue_get_max_num(VirtIODevice *vdev, int n)
+{
+    return vdev->vq[n].vring.num_default;
+}
+
 int virtio_get_num_queues(VirtIODevice *vdev)
 {
     int i;

include/hw/virtio/virtio.h

@@ -228,6 +228,7 @@ void virtio_queue_set_addr(VirtIODevice *vdev, int n, hwaddr addr);
 hwaddr virtio_queue_get_addr(VirtIODevice *vdev, int n);
 void virtio_queue_set_num(VirtIODevice *vdev, int n, int num);
 int virtio_queue_get_num(VirtIODevice *vdev, int n);
+int virtio_queue_get_max_num(VirtIODevice *vdev, int n);
 int virtio_get_num_queues(VirtIODevice *vdev);
 void virtio_queue_set_rings(VirtIODevice *vdev, int n, hwaddr desc,
                             hwaddr avail, hwaddr used);