virtio: Add support for guest setting of queue size

The MMIO virtio transport spec allows the guest to tell the host how
large the queue size is. Add virtio_queue_set_num() function which
implements this in the QEMU common virtio support code.
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>
Message-id: 1373977512-28932-4-git-send-email-peter.maydell@linaro.org

hw/virtio/virtio.c

@@ -667,6 +667,14 @@ hwaddr virtio_queue_get_addr(VirtIODevice *vdev, int n)
     return vdev->vq[n].pa;
 }
 
+void virtio_queue_set_num(VirtIODevice *vdev, int n, int num)
+{
+    if (num <= VIRTQUEUE_MAX_SIZE) {
+        vdev->vq[n].vring.num = num;
+        virtqueue_init(&vdev->vq[n]);
+    }
+}
+
 int virtio_queue_get_num(VirtIODevice *vdev, int n)
 {
     return vdev->vq[n].vring.num;

include/hw/virtio/virtio.h

@@ -200,6 +200,7 @@ void virtio_config_writew(VirtIODevice *vdev, uint32_t addr, uint32_t data);
 void virtio_config_writel(VirtIODevice *vdev, uint32_t addr, uint32_t data);
 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);
 void virtio_queue_notify(VirtIODevice *vdev, int n);
 uint16_t virtio_queue_vector(VirtIODevice *vdev, int n);