Re: [PATCH bpf-next v2 14/18] libbpf: add btf type hash lookup support

[Menglong Dong]

On 7/15/25 06:07, Andrii Nakryiko wrote:
> On Thu, Jul 3, 2025 at 5:22 AM Menglong Dong <menglong8.dong@xxxxxxxxx> wrote:
> > For now, the libbpf find the btf type id by loop all the btf types and
> > compare its name, which is inefficient if we have many functions to
> > lookup.
> >
> > We add the "use_hash" to the function args of find_kernel_btf_id() to
> > indicate if we should lookup the btf type id by hash. The hash table will
> > be initialized if it has not yet.
> Or we could build hashtable-based index outside of struct btf for a
> specific use case, because there is no one perfect hashtable-based
> indexing that can be done generically (e.g., just by name, or
> name+kind, or kind+name, or some more complicated lookup key) and
> cover all potential use cases. I'd prefer not to get into a problem of
> defining and building indexes and leave it to callers (even if the
> caller is other part of libbpf itself).


I think that works. We can define a global hash table in libbpf.c,
and add all the btf type to it. I'll redesign this part, and make it
separate with the btf.

Thanks!
Menglong Dong

> > Signed-off-by: Menglong Dong <dongml2@xxxxxxxxxxxxxxx>
> > ---
> >   tools/lib/bpf/btf.c      | 102 +++++++++++++++++++++++++++++++++++++++
> >   tools/lib/bpf/btf.h      |   6 +++
> >   tools/lib/bpf/libbpf.c   |  37 +++++++++++---
> >   tools/lib/bpf/libbpf.map |   3 ++
> >   4 files changed, 140 insertions(+), 8 deletions(-)
> [...]