On 4/16/21 9:12 AM, Konrad Zemek wrote: > (Sorry for the double mail David, I missed the "reply all" button). > > On Friday, April 16, 2021 5:35 PM, David Ahern <dsahern@xxxxxxxxx> wrote: >> On 4/16/21 5:03 AM, Konrad Zemek wrote: >> >>> So both vlan fields in the output struct bpf_fib_lookup are always zero. I >>> haven't seen this commented on anywhere, including the discussion around >>> introducing bpf_fib_lookup, so I assume it's an accidental oversight. >> >> The uapi was setup to cover the use case, but VLANs are not supported at >> the moment. > > I'm surprised it's not marked as such in the bpf.h, the comments (or rather > lack of) made me convinced that it works just as well as the MAC address > fields. > >> On 4/16/21 5:03 AM, Konrad Zemek wrote: >>> Do you have any proposals for a workaround? Right now I'm thinking of >>> creating a BPF map that would map ifindex->vlan, populated in the userspace >>> >>> - but that assumes the output (struct bpf_fib_lookup*)->ifindex will be an >>> index of the vlan device and not the physical device the vlan is attached >>> on, which I'm not sure is the case yet. >>> >> >> vlan netdevices do not support XDP redirect. >> >> It's not a trivial problem to handle VLANs or stacked devices in >> general. I have working code here: >> >> https://github.com/dsahern/linux/commits/bpf/mpls-vlan-fwd >> >> but it is not ready for submitting upstream yet. The use case and >> related ones need more work. > > They don't, but it's not that important for my use case. I have just > one interface and all the VLANs are on that, so if I learn that a > VLAN is needed it's just another thing I push in front of the tunnel > frames that I already push. If I had multiple interfaces, I'd just > need one more piece of info which is "what's the physical interface > number this VLAN is attached on". Your use case is fairly trivial to support, but generically the vlan can be on a bridge, bond, or port. To properly support VLAN redirects, the fib lookup needs to resolve the stack to the egress port. > > XDP programs are already pretty specific to the infrastructure one's > running, and already very manual with packet manipulation (which is > actually a boon to a lot of things I'm doing), so I don't mind this > not being a generic solution. > As I recall (it has been a few years), the fib lookup device index is the vlan device. You could have a map that converts that return to the real port and vlan. It should work, just more maintenance.
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