David Ahern <[email protected]> writes: > On 7/1/26 5:02 AM, Toke Høiland-Jørgensen wrote: >> David Ahern <[email protected]> writes: >>> Seems to me the fib_lookup for xdp needs to return the bottom device, >>> not the vlan device, for forwarding to work. That's why I added the >>> fields to the struct. That allows the program to push the vlan header if >>> required. My preference (dream?) was that Tx path had support to tell >>> the redirect the vlan and h/w added it on send. >> >> Sure, returning the bottom device index with the VLAN tag makes sense, >> and that's basically what this series does (but bails out on stacked >> VLANs). However, that's not what the helper does today, which is why the >> flag is there, to opt-in to the new behaviour. I don't think we can just >> change the ifindex without breaking existing applications (as noted >> up-thread). > > I do not see it as breaking existing programs which is why I chimed in > on the thread. > >> >>> But really, once stacked devices come into play, I just wanted to make >>> sure thought is given to different use cases. As you know the lookup >>> struct if hard bound to 64B and it is trying to cover a lot of use cases. >> >> Agreed, I don't think we can handle stacked devices in this helper. But >> we could split it out into a new one. Something like: >> >> struct lower_device_info { >> enum device_type type; >> struct { >> __be16 h_vlan_proto; >> __be16 h_vlan_TCI; >> } vlan; >> /* add other types here */ >> }; >> >> int xdp_get_lower_device(int ifindex, struct lower_device_info *info); >> >> called like: >> >> int xdp_program(struct xdp_md *ctx) >> { >> struct lower_device_info dev_info = {}; >> int ifindex, ret; >> >> ifindex = find_destination(ctx); /* does fib lookup, or something >> else */ >> >> while ((ret = xdp_get_lower_device_info(ifindex, &dev_info)) > 0) { >> if (dev_info.type == VLAN) { >> push_vlan_tag(ctx, &dev_info.vlan); >> ifindex = ret; >> } else { >> return XDP_PASS; /* we only handle VLAN devices */ >> } >> } >> >> return bpf_redirect(ifindex, 0); >> } >> >> >> With a helper like this, we obviously don't strictly speaking need to >> change the fib lookup helper at all. However, for the single-tagged VLAN >> case, I think supporting it directly in the fib lookup could still have >> value, as an optimisation: it saves an extra call for resolving the >> ifindex, and the fields are already there. So I think my preference >> would be to merge this series as-is, and then follow up with a new kfunc >> to handle the stacked case. But we could also just drop this series and >> go straight to the new kfunc. >> >> WDYT? > > no preference. I only chimed in because of the added flag to the uapi > which I do not see as needed. If the consensus is that it is in fact > needed, all good then.
Alright, cool - care to provide an ACK, then? :) -Toke
