Re: [PATCH bpf-next 1/2] bpftool: improve skeleton backwards compat with old buggy libbpfs

[Quentin Monnet <qmo@kernel.org>]

On 04/07/2024 01:15, Andrii Nakryiko wrote:
> Old versions of libbpf don't handle varying sizes of bpf_map_skeleton
> struct correctly. As such, BPF skeleton generated by newest bpftool
> might not be compatible with older libbpf (though only when libbpf is
> used as a shared library), even though it, by design, should.
> 
> Going forward libbpf will be fixed, plus we'll release bug fixed
> versions of relevant old libbpfs, but meanwhile try to mitigate from
> bpftool side by conservatively assuming older and smaller definition of
> bpf_map_skeleton, if possible. Meaning, if there are no struct_ops maps.
> 
> If there are struct_ops, then presumably user would like to have
> auto-attaching logic and struct_ops map link placeholders, so use the
> full bpf_map_skeleton definition in that case.
> 
> Co-developed-by: Mykyta Yatsenko <yatsenko@meta.com>
> Signed-off-by: Andrii Nakryiko <andrii@kernel.org>

Note: I don't know to what extent we enforce this, but kernel docs state
that "Since Co-developed-by: denotes authorship, every Co-developed-by:
must be immediately followed by a Signed-off-by: of the associated
co-author". Mykyta's sign-off is missing from both patches.

Other than that, the patch looks good, thanks for fixing bpftool!

Acked-by: Quentin Monnet <qmo@kernel.org>