On Mon, Oct 7, 2013 at 3:02 AM, Hannes Frederic Sowa <han...@stressinduktion.org> wrote: > 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. >
OK, I'll investigate on this and I'll open a dedicated thread mail/send patch... > Greetings, > > Hannes > Thanks, Oussama -- 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/
