Re: [PATCH net-next] geneve: add rtnl changelink support

On 5/16/17 12:31 PM, David Miller wrote:

From: Girish Moodalbail <redacted>
Date: Mon, 15 May 2017 10:47:04 -0700

quoted

 	if (data[IFLA_GENEVE_REMOTE]) {
-		info.key.u.ipv4.dst =
+		info->key.u.ipv4.dst =
 			nla_get_in_addr(data[IFLA_GENEVE_REMOTE]);

-		if (IN_MULTICAST(ntohl(info.key.u.ipv4.dst))) {
+		if (IN_MULTICAST(ntohl(info->key.u.ipv4.dst))) {
 			netdev_dbg(dev, "multicast remote is unsupported\n");
 			return -EINVAL;
 		}
+		if (changelink &&
+		    ip_tunnel_info_af(&geneve->info) == AF_INET6) {
+			info->mode &= ~IP_TUNNEL_INFO_IPV6;
+			info->key.tun_flags &= ~TUNNEL_CSUM;
+			*use_udp6_rx_checksums = false;
+		}
 	}

I don't understand this "changelink" guarded code, why do you need to
clear all of this state out if the existing tunnel type if AF_INET6
and only when doing a changelink?

In any event, I think you need to add a comment explaining it.

If geneve link was overlayed over IPv6 network and now the user modifies the 
link to be over IPv4 network by doing

# ip link set gen0 type geneve id 100 remote 192.168.13.2

Then we will need to

  - reset info->mode to be not IPv6 type
  - the default for UDP checksum over IPv4 is 'no', so reset that and
  - set use_udp6_rx_checksums to its default value which is false.

I will capture the above information concisely in a comment around that 
'changelink' guard.

thanks,
~Girish