virtio_ring: split: introduce virtqueue_reinit_split()

Introduce a function to initialize vq without allocating new ring,
desc_state, desc_extra.

Subsequent patches will call this function after reset vq to
reinitialize vq.
Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Message-Id: <20220801063902.129329-15-xuanzhuo@linux.alibaba.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

drivers/virtio/virtio_ring.c

@@ -957,6 +957,29 @@ static void virtqueue_vring_init_split(struct vring_virtqueue_split *vring_split
 	}
 }
 
+static void virtqueue_reinit_split(struct vring_virtqueue *vq)
+{
+	int num;
+
+	num = vq->split.vring.num;
+
+	vq->split.vring.avail->flags = 0;
+	vq->split.vring.avail->idx = 0;
+
+	/* reset avail event */
+	vq->split.vring.avail->ring[num] = 0;
+
+	vq->split.vring.used->flags = 0;
+	vq->split.vring.used->idx = 0;
+
+	/* reset used event */
+	*(__virtio16 *)&(vq->split.vring.used->ring[num]) = 0;
+
+	virtqueue_init(vq, num);
+
+	virtqueue_vring_init_split(&vq->split, vq);
+}
+
 static void virtqueue_vring_attach_split(struct vring_virtqueue *vq,
 					 struct vring_virtqueue_split *vring_split)
 {