On Tue, Mar 26, 2019 at 11:17:19AM -0700, Stanislav Fomichev wrote: > On 03/26, Alexei Starovoitov wrote: > > On Tue, Mar 26, 2019 at 10:52 AM Willem de Bruijn > > <willemdebruijn.kernel@xxxxxxxxx> wrote: > > > The BPF flow dissector should work the same. It is fine to pass the > > > data including ethernet header, but parsing can start at nhoff with > > > proto explicitly passed. > > > > > > We should not assume Ethernet link layer. > > > > then skb-less dissector has to be different program type > > because semantics are different. > The semantics are the same as for c-based __skb_flow_dissect. > We just need to pass nhoff and proto that has been passed to > __skb_flow_dissect to the bpf program. In case of with-skb, > take this initial data from skb, like __skb_flow_dissect does (and don't > ask BPF program to do it essentially): > > https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf.git/tree/net/core/flow_dissector.c#n763 > > I was thinking of passing proto as flow_keys->n_proto and we already > pass flow_keys->nhoff, so no need to do anything for it. With that, > BPF program doesn't need to look into skb and can parse optional vlan > and L3+ headers. The same way __skb_flow_dissect does that. makes sense. then I'd also prefer for proto to be in flow_keys to high light this difference. may be add vlan_proto/present/tci there as well? At least on the kernel side ctx rewriter will be the same for w/ & w/o skb cases.
