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

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Message-ID: <CAEf4BzaoKNNf5pr4z8vEokj3AyLNZYyjYQUOoEMMZHN6ETUg4g@mail.gmail.com>
Date: Mon, 14 Jul 2025 15:07:33 -0700
From: Andrii Nakryiko <andrii.nakryiko@...il.com>
To: Menglong Dong <menglong8.dong@...il.com>
Cc: alexei.starovoitov@...il.com, rostedt@...dmis.org, jolsa@...nel.org, 
	bpf@...r.kernel.org, Menglong Dong <dongml2@...natelecom.cn>, 
	Martin KaFai Lau <martin.lau@...ux.dev>, Eduard Zingerman <eddyz87@...il.com>, Song Liu <song@...nel.org>, 
	Yonghong Song <yonghong.song@...ux.dev>, John Fastabend <john.fastabend@...il.com>, 
	KP Singh <kpsingh@...nel.org>, Stanislav Fomichev <sdf@...ichev.me>, Hao Luo <haoluo@...gle.com>, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH bpf-next v2 14/18] libbpf: add btf type hash lookup support

On Thu, Jul 3, 2025 at 5:22 AM Menglong Dong <menglong8.dong@...il.com> 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).

>
> Signed-off-by: Menglong Dong <dongml2@...natelecom.cn>
> ---
>  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(-)
>

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