vhost_net: Also populate XDP frame size

In vhost_net_build_xdp() the 'buf' that gets queued via an xdp_buff
have embedded a struct tun_xdp_hdr (located at xdp->data_hard_start)
which contains the buffer length 'buflen' (with tailroom for
skb_shared_info). Also storing this buflen in xdp->frame_sz, does not
obsolete struct tun_xdp_hdr, as it also contains a struct
virtio_net_hdr with other information.
Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Link: https://lore.kernel.org/bpf/158945343928.97035.4620233649151726289.stgit@firesoul

drivers/vhost/net.c

@@ -747,6 +747,7 @@ static int vhost_net_build_xdp(struct vhost_net_virtqueue *nvq,
 	xdp->data = buf + pad;
 	xdp->data_end = xdp->data + len;
 	hdr->buflen = buflen;
+	xdp->frame_sz = buflen;
 
 	--net->refcnt_bias;
 	alloc_frag->offset += buflen;