Hi Jiri, On Tue, May 10, 2016 at 02:06:18PM +0200, Jiri Benc wrote: > On Mon, 9 May 2016 17:18:20 +0900, Simon Horman wrote: > > On Fri, May 06, 2016 at 11:35:04AM +0200, Jiri Benc wrote: > > > In addition, we should check whether mac_len > 0 and in such case, > > > change skb->protocol to ETH_P_TEB first (and store that value in the > > > pushed eth header). > > > > > > Similarly on pop_eth, we need to check skb->protocol and if it is > > > ETH_P_TEB, call eth_type_trans on the modified frame to set the new > > > skb->protocol correctly. It's probably not that simple, as we'd need a > > > version of eth_type_trans that doesn't need a net device. > > > > I'm not sure I understand the interaction with ETH_P_TEB here. > > > > In my mind skb->protocol == ETH_P_TEB may be used early on in OvS's receive > > processing to find the inner protocol from the packet and at that point > > skb->protocol is set to that value. And that for further packet processing > > the fact the packet was received as TEB is transparent. > > Yes but think about the case when you have two Ethernet headers pushed. > > We can either disallow it, or do what I described. > > Specifically, let's assume we have an IP packet with an Ethernet > header present. skb->protocol is ETH_P_IP. Now, when there's skb_push, > the correct operation would be setting skb->protocol to ETH_P_TEB, > pushing a new Ethernet header and filing ETH_P_TEB to the ethertype > field in the new header. The packet is not ETH_P_IP anymore, as the L2 > header is followed by another Ethernet header now.
Thanks for the clarification, I had not considered the case of two ethernet headers when I wrote my previous email. I think that at this stage I would prefer to prohibit push_eth() acting on a packet which already has an ethernet header. Indeed that is what my patch-set already does in its modifications of __ovs_nla_copy_actions(). The reason that I lean towards prohibiting this is that I do not have an easy way to exercise this case within the current patch-set. And thus this extra complexity seems well suited to being handled handled incrementally as further work.
