virtio_net: reject unsupported coalescing params

Set ethtool_ops->supported_coalesce_params to let
the core reject unsupported coalescing parameters.

This driver correctly rejects all unsupported parameters.
As a side effect of these changes the error code for
unsupported params changes from EINVAL to EOPNOTSUPP.

v2: correctly handle rx-frames (and adjust the commit msg)
v3: adjust commit message for new error code and member name

Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/virtio_net.c

@@ -2202,23 +2202,14 @@ static int virtnet_get_link_ksettings(struct net_device *dev,
 static int virtnet_set_coalesce(struct net_device *dev,
 				struct ethtool_coalesce *ec)
 {
-	struct ethtool_coalesce ec_default = {
-		.cmd = ETHTOOL_SCOALESCE,
-		.rx_max_coalesced_frames = 1,
-	};
 	struct virtnet_info *vi = netdev_priv(dev);
 	int i, napi_weight;
 
-	if (ec->tx_max_coalesced_frames > 1)
+	if (ec->tx_max_coalesced_frames > 1 ||
+	    ec->rx_max_coalesced_frames != 1)
 		return -EINVAL;
 
-	ec_default.tx_max_coalesced_frames = ec->tx_max_coalesced_frames;
 	napi_weight = ec->tx_max_coalesced_frames ? NAPI_POLL_WEIGHT : 0;
-
-	/* disallow changes to fields not explicitly tested above */
-	if (memcmp(ec, &ec_default, sizeof(ec_default)))
-		return -EINVAL;
-
 	if (napi_weight ^ vi->sq[0].napi.weight) {
 		if (dev->flags & IFF_UP)
 			return -EBUSY;
@@ -2273,6 +2264,7 @@ static void virtnet_update_settings(struct virtnet_info *vi)
 }
 
 static const struct ethtool_ops virtnet_ethtool_ops = {
+	.supported_coalesce_params = ETHTOOL_COALESCE_MAX_FRAMES,
 	.get_drvinfo = virtnet_get_drvinfo,
 	.get_link = ethtool_op_get_link,
 	.get_ringparam = virtnet_get_ringparam,