On Tue, Oct 10, 2017 at 8:59 PM, William Tu <u9012...@gmail.com> wrote:
>>> @@ -1242,14 +1241,14 @@ static int erspan_tunnel_init(struct net_device
>>> *dev)
>>> struct ip_tunnel *tunnel = netdev_priv(dev);
>>> int t_hlen;
>>>
>>> - tunnel->tun_hlen = 8;
>>> + tunnel->tun_hlen = ERSPAN_GREHDR_LEN;
>>> tunnel->parms.iph.protocol = IPPROTO_GRE;
>>> tunnel->hlen = tunnel->tun_hlen + tunnel->encap_hlen +
>>> sizeof(struct erspanhdr);
>>> t_hlen = tunnel->hlen + sizeof(struct iphdr);
>>>
>>> - dev->needed_headroom = LL_MAX_HEADER + t_hlen + 4;
>>> - dev->mtu = ETH_DATA_LEN - t_hlen - 4;
>>> + dev->needed_headroom = LL_MAX_HEADER + t_hlen;
>>> + dev->mtu = ETH_DATA_LEN - t_hlen;
>> 1. I guess '+4-4' stuff was copied from __gre_tunnel_init(), I'm thinking
>> it may be there for some reason.
>>
> I traced back to
> 4565e9919cda ("gre: Setup and TX path for gre/UDP foo-over-udp encapsulation")
> and I think '+4-4' is there for GRE base header length.
>
> Since now we do
> dev->mtu = ETH_DATA_LEN - t_hlen;
> and t_hlen already counts the the gre base header + optional header
> len, I think it's not needed.
okay. thanks.
>
>> 2. 'dev->needed_headroom =' and 'dev->mtu =' are really needed ?
>> As I've seen both will be updated in .newlink:
>> ipgre_newlink() -> ip_tunnel_newlink() -> ip_tunnel_bind_dev()
>>
> right, I also find both values gets overwritten by
> ip_tunnel_bind_dev() using my test cases. Maybe we can remove them?
It's there just in case that there is no lower dev found, but
ip_tunnel_newlink/create always updates dev->mtu even if
there is no lower dev found.
let's leave as it is for now, ipgre may just not be sure ip_tunnel_xxx would
do it when no lower dev found.
