virtio ring packed supports resize.

Only after the new vring is successfully allocated based on the new num,
we will release the old vring. In any case, an error is returned,
indicating that the vring still points to the old vring.

In the case of an error, re-initialize(by virtqueue_reinit_packed()) the
virtqueue to ensure that the vring can be used.

Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
---
  drivers/virtio/virtio_ring.c | 29 +++++++++++++++++++++++++++++
  1 file changed, 29 insertions(+)

diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index 650f701a5480..4860787286db 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c

@@ -2042,6 +2042,35 @@ static struct virtqueue *vring_create_virtqueue_packed(
  	return NULL;
  }
  
+static int virtqueue_resize_packed(struct virtqueue *_vq, u32 num)
+{
+	struct vring_virtqueue_packed vring = {};
+	struct vring_virtqueue *vq = to_vvq(_vq);
+	struct virtio_device *vdev = _vq->vdev;
+	int err;
+
+	if (vring_alloc_queue_packed(&vring, vdev, num))
+		goto err_ring;
+
+	err = vring_alloc_state_extra_packed(&vring);
+	if (err)
+		goto err_state_extra;
+
+	vring_free(&vq->vq);
+
+	virtqueue_init(vq, vring.vring.num);
+	virtqueue_vring_attach_packed(vq, &vring);
+	virtqueue_vring_init_packed(vq);
+
+	return 0;
+
+err_state_extra:
+	vring_free_packed(&vring, vdev);
+err_ring:
+	virtqueue_reinit_packed(vq);