Re: [RFC PATCH v2 1/5] btf: search local BTF before base BTF

[Eduard Zingerman <eddyz87@gmail.com>]

On Mon, 2025-10-20 at 17:39 +0800, Donglin Peng wrote:
> Change btf_find_by_name_kind() to search the local BTF first,
> then fall back to the base BTF. This can skip traversing the large
> vmlinux BTF when the target type resides in a kernel module's BTF,
> thereby significantly improving lookup performance.
> 
> In a test searching for the btf_type of function ext2_new_inode
> located in the ext2 kernel module:
> 
> Before: 408631 ns
> After:     499 ns
> 
> Performance improvement: ~819x faster

[...]

> ---

The flip makes sense, but are we sure that there are no implicit
expectations to return base type in case of a name conflict?

E.g. kernel/bpf/btf.c:btf_parse_struct_metas() takes a pointer to
`btf` instance and looks for types in alloc_obj_fields array by name
(e.g. "bpf_spin_lock"). This will get confused if module declares a
type with the same name. Probably not a problem in this particular
case, but did you inspect other uses?