Re: [PATCH net-next 11/14] net: Add a facility to support application defined GSO

From: Tom Herbert <redacted>
Date: Mon, 18 Sep 2017 17:39:01 -0700

Allow applications or encapsulation protocols to register a GSO segment
function to their specific protocol. To faciliate this I reserved the
upper four bits in the gso_type to indicate the application specific GSO
type. Zero in these bits indicates no application GSO, so there are
fifteen instance that can be defined.

An application registers a a gso_segment using the skb_gso_app_register
this takes a struct skb_gso_app that indicates a callback function as
well as a set of GSO types for which at least one must be matched before
calling he segment function. GSO returns one of the application GSO
types described above (not a fixed value for the applications).
Subsequently, when the application sends a GSO packet the application
gso_type is set in the skb gso_type along with any other types.

skb_gso_app_segment is the function called from another GSO segment
function to handle segmentation of the application or encapsulation
protocol. This function includes check flags that provides context for
the appropriate GSO instance to match. For instance, in order to handle
a protocol encapsulated in UDP (GTP for instance) skb_gso_app_segment is
call from udp_tunnel_segment and check flags would be
SKB_GSO_UDP_TUNNEL_CSUM | SKB_GSO_UDP_TUNNEL.

Signed-off-by: Tom Herbert <redacted>

What happens on cards that can offload existing arbitrary UDP tunnel
encapsulations?

Will something about the state of the GSO type bits you are adding
prevent that?  Or do we need to add some new checks somewhere?