Re: Different packet handling after bpf_redirect_map with BPF_F_BROADCAST

["Toke Høiland-Jørgensen" <toke@redhat.com>]

Florian Kauer <florian.kauer@linutronix.de> writes:

>>>>> 3. Extend the kernel with a way to let the xdp/devmap prog know from
>>>>> which DEVMAP entry its execution originates (like an additional entry
>>>>> in the bpf_devmap_val that is then set in the xdp_md).
>>>>
>>>> This could be useful in any case, so I would personally be fine with
>>>> adding something like this (for both devmap and cpumap) :)
>>>
>>> Would you prefer a simple u32 (or similar) that could then be used as
>>> index for an array or a more complex data structure/void* to fill
>>> with arbitrary data?
>> 
>> Well, the API for map indexing specifies a u64 map index, so just
>> reusing that would be the simplest :)
>
> u64? Now I am confused:
> "The key type is an unsigned 32-bit integer (4 bytes)"
> https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/tree/Documentation/bpf/map_array.rst?h=next-20240703

That's the documentation for array maps. Devmap is documented here:

https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/tree/Documentation/bpf/map_devmap.rst?h=next-20240703

The text doesn't say anything explicitly about the key type, but the
function signature for the redirect function has not been updated, it
seems. The key type was changed to u64 in commit:

32637e33003f ("bpf: Expand map key argument of bpf_redirect_map to u64")

-Toke