Attaching XDP program into wireguard interface

[Toke Høiland-Jørgensen]

"Jason A. Donenfeld" <Jason at zx2c4.com> writes:

> On Fri, Apr 24, 2020 at 3:59 PM Toke Høiland-Jørgensen <toke at toke.dk> wrote:
>>
>> "Jason A. Donenfeld" <Jason at zx2c4.com> writes:
>>
>> > Oh. Set XDP_FLAGS_SKB_MODE.
>>
>> Yeah, you'd definitely need to run this in skb/generic XDP mode.
>>
>> -Toke
>
> It looks like the code in question is likely:
>
>         bpf_op = bpf_chk = ops->ndo_bpf;
>        if (!bpf_op && (flags & (XDP_FLAGS_DRV_MODE | XDP_FLAGS_HW_MODE))) {
>                NL_SET_ERR_MSG(extack, "underlying driver does not
> support XDP in native mode");
>                return -EOPNOTSUPP;
>        }
>        if (!bpf_op || (flags & XDP_FLAGS_SKB_MODE))
>                bpf_op = generic_xdp_install;
>        if (bpf_op == bpf_chk)
>                bpf_chk = generic_xdp_install;
>
> It looks like bpf_op == generic_xdp_install is the case when neither
> XDP_FLAGS_DRV_MODE or XDP_FLAGS_HW_MODE is set. Setting
> XDP_FLAGS_SKB_MODE explicitly will force it on all drivers, but not
> specifying it will fallback to it if the driver doesn't have hardware
> support, which is WireGuard's case, unless either XDP_FLAGS_DRV_MODE
> or XDP_FLAGS_HW_MODE are set.

Yup, that sounds right :)

-Toke