Re: [PATCH bpf-next] libbpf: Export bpf_object__load_vmlinux_btf

From: Andrii Nakryiko
Date: Wed May 27 2020 - 01:09:26 EST

On Tue, May 26, 2020 at 7:09 PM Daniel Xu <dxu@xxxxxxxxx> wrote:
> Right now the libbpf model encourages loading the entire object at once.
> In this model, libbpf handles loading BTF from vmlinux for us. However,
> it can be useful to selectively load certain maps and programs inside an
> object without loading everything else.

There is no way to selectively load or not load a map. All maps are
created, unless they are reusing map FD or pinned instances. See
below, I'd like to understand the use case better.

> In the latter model, there was perviously no way to load BTF on-demand.
> This commit exports the bpf_object__load_vmlinux_btf such that we are
> able to load BTF on demand.

Let's start with the real problem, not a solution. Do you have
specific use case where you need bpf_object__load_vmlinux_btf()? It
might not do anything if none of BPF programs in the object requires
BTF, because it's very much tightly coupled with loading bpf_object as
a whole model. I'd like to understand what you are after with this,
before exposing internal implementation details as an API.

> Signed-off-by: Daniel Xu <dxu@xxxxxxxxx>
> ---
> tools/lib/bpf/libbpf.c | 2 +-
> tools/lib/bpf/libbpf.h | 1 +
> tools/lib/bpf/ | 1 +
> 3 files changed, 3 insertions(+), 1 deletion(-)