virtio_ring: split: introduce virtqueue_resize_split()

virtio ring split 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(virtqueue_reinit_split()) the
virtqueue to ensure that the vring can be used.
Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Message-Id: <20220801063902.129329-17-xuanzhuo@linux.alibaba.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

drivers/virtio/virtio_ring.c

@@ -220,6 +220,7 @@ static struct virtqueue *__vring_new_virtqueue(unsigned int index,
 					       void (*callback)(struct virtqueue *),
 					       const char *name);
 static struct vring_desc_extra *vring_alloc_desc_extra(unsigned int num);
+static void vring_free(struct virtqueue *_vq);
 
 /*
  * Helpers.
@@ -1114,6 +1115,39 @@ static struct virtqueue *vring_create_virtqueue_split(
 	return vq;
 }
 
+static int virtqueue_resize_split(struct virtqueue *_vq, u32 num)
+{
+	struct vring_virtqueue_split vring_split = {};
+	struct vring_virtqueue *vq = to_vvq(_vq);
+	struct virtio_device *vdev = _vq->vdev;
+	int err;
+
+	err = vring_alloc_queue_split(&vring_split, vdev, num,
+				      vq->split.vring_align,
+				      vq->split.may_reduce_num);
+	if (err)
+		goto err;
+
+	err = vring_alloc_state_extra_split(&vring_split);
+	if (err)
+		goto err_state_extra;
+
+	vring_free(&vq->vq);
+
+	virtqueue_vring_init_split(&vring_split, vq);
+
+	virtqueue_init(vq, vring_split.vring.num);
+	virtqueue_vring_attach_split(vq, &vring_split);
+
+	return 0;
+
+err_state_extra:
+	vring_free_split(&vring_split, vdev);
+err:
+	virtqueue_reinit_split(vq);
+	return -ENOMEM;
+}
+
 
 /*
  * Packed ring specific functions - *_packed().