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

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Date:   Tue, 16 May 2017 13:09:10 -0700
From:   Girish Moodalbail <girish.moodalbail@...cle.com>
To:     David Miller <davem@...emloft.net>
Cc:     netdev@...r.kernel.org, pshelar@....org, joe@....org,
        jbenc@...hat.com
Subject: Re: [PATCH net-next] geneve: add rtnl changelink support

On 5/16/17 12:31 PM, David Miller wrote:
> From: Girish Moodalbail <girish.moodalbail@...cle.com>
> Date: Mon, 15 May 2017 10:47:04 -0700
>
>>  	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