On Sun, Oct 06, 2013 at 08:18:15PM +0100, Oussama Ghorbel wrote: > Yes, to summarize, the idea of this patch was to fix the incoherence > in the condition of ip6gre_tunnel_change_mtu function > > if (new_mtu < 68 || > new_mtu > 0xFFF8 - dev->hard_header_len - tunnel->hlen) > > From the ip6gre_tnl_link_config function we can see that: > The variable addend is equal the ipv6 header + gre header (including > the gre options) > On the other hand hard_header_len equal to the header of the lower > layer + addend. > So the quantity - (dev->hard_header_len + tunnel->hlen) equals - (eth > header + ipv6 header + gre header + ipv6 header + gre header) which by > no means this would represent anything! (I've just taken ipv6 over > ethernet as example) > > As we have seen there is another approach to fix this issue is to > re-factor the hlen to hold only the length of gre as it's done for > ipv4 gre, however the solution provided in the patch seems to be > regression risk-less.
I agree, it actually does not worsen the situation: Acked-by: Hannes Frederic Sowa <han...@stressinduktion.org> > Although the value hold by hlen is not coherent with the variable name > nor with ipv4, I think there is an advantage of the current approach > of ipv6 hlen over ipv4 hlen, because we save the calculation of ipv6 > header each time. Ex: > In ipv4 gre and in the function ipgre_header: > iph = (struct iphdr *)skb_push(skb, t->hlen + sizeof(*iph)); > In ipv6 and in the function ip6gre_header > ipv6h = (struct ipv6hdr *)skb_push(skb, t->hlen); I see your point. But we should take care that t->hlen is always initialized, regardless if we got a route and outgoing device or not. Greetings, Hannes -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
