tun: Implement ethtool's get_channels() callback

Implement the tun .get_channels functionality. This feature is necessary
for some tools, such as libxdp, which need to retrieve the queue count.
Signed-off-by: Yunjian Wang <wangyunjian@huawei.com>
Reviewed-by: Jiri Pirko <jiri@nvidia.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/tun.c

@@ -3643,12 +3643,22 @@ static int tun_set_coalesce(struct net_device *dev,
 	return 0;
 }
 
+static void tun_get_channels(struct net_device *dev,
+			     struct ethtool_channels *channels)
+{
+	struct tun_struct *tun = netdev_priv(dev);
+
+	channels->combined_count = tun->numqueues;
+	channels->max_combined = tun->flags & IFF_MULTI_QUEUE ? MAX_TAP_QUEUES : 1;
+}
+
 static const struct ethtool_ops tun_ethtool_ops = {
 	.supported_coalesce_params = ETHTOOL_COALESCE_RX_MAX_FRAMES,
 	.get_drvinfo	= tun_get_drvinfo,
 	.get_msglevel	= tun_get_msglevel,
 	.set_msglevel	= tun_set_msglevel,
 	.get_link	= ethtool_op_get_link,
+	.get_channels   = tun_get_channels,
 	.get_ts_info	= ethtool_op_get_ts_info,
 	.get_coalesce   = tun_get_coalesce,
 	.set_coalesce   = tun_set_coalesce,