Re: Pass a map to a global BPF function

Re: Pass a map to a global BPF function

[Alexei Starovoitov]

On Mon, Sep 13, 2021 at 10:44 AM Zvi Effron <zeffron@riotgames.com> wrote:
>
> Hi all,
>
> We have some map-of-arrays that we use for tracking labeled metrics in
> our XDP code. The inner map tracks the metrics for a given label,
> which is the key in the outer map.
>
> Our XDP code calls several global BPF functions (freplaced, so can't
> be inlined). Currently, each global function has to make a lookup to
> get the inner map to record its metrics. Now that non-context pointers
> can be passed to global BPF functions, is it possible to pass maps to
> these global functions?

The program can pass a pointer to struct bpf_map and the verifier
will recognize it as PTR_TO_BTF_ID.
It won't be a CONST_PTR_TO_MAP, so secondary lookup won't be
allowed, but if that's the desired use case then the verifier can be extended
to recognize it.