From: Tom Herbert <t...@herbertland.com>
Date: Mon, 17 Oct 2016 12:41:55 -0700
> Now that we have a means to perform a UDP socket lookup without taking
> a reference, it is feasible to have flow dissector crack open UDP
> encapsulated packets. Generally, we would expect that the UDP source
> port or the flow label in IPv6 would contain enough entropy about
> the encapsulated flow. However, there will be cases, such as a static
> UDP tunnel with fixed ports, where dissecting the encapsulated packet
> is valuable.
> The model is here is similar to that implemented for UDP GRO. A
> tunnel implementation (e.g. GUE) may set a flow_dissect function
> in the udp_sk. In __skb_flow_dissect a case has been added for
> UDP to check if there is a socket with flow_dissect set. If there
> is the function is called. The (per tunnel implementation)
> function can parse the encapsulation headers and return the
> next protocol for __skb_flow_dissect to process and it's position
> in nhoff.
> Since performing a UDP lookup on every packet might be expensive
> I added a static key check to bypass the lookup if there are no
> sockets with flow_dissect set. I should mention that doing the
> lookup wasn't particularly a big hit anyway.
> Fou/gue was modified to perform tunnel dissection. This is enabled
> on each listener socket via a netlink configuration option.
Series applied, thanks Tom.