netdev - Re: [PATCH bpf-next v6 03/11] bpf: Populate kfunc BTF ID sets in struct btf

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Date:   Fri, 7 Jan 2022 11:56:45 +0530
From:   Kumar Kartikeya Dwivedi <memxor@...il.com>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:     bpf <bpf@...r.kernel.org>, Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Network Development <netdev@...r.kernel.org>,
        netfilter-devel <netfilter-devel@...r.kernel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        Maxim Mikityanskiy <maximmi@...dia.com>,
        Pablo Neira Ayuso <pablo@...filter.org>,
        Florian Westphal <fw@...len.de>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Toke Høiland-Jørgensen <toke@...hat.com>
Subject: Re: [PATCH bpf-next v6 03/11] bpf: Populate kfunc BTF ID sets in
 struct btf

On Fri, Jan 07, 2022 at 05:10:56AM IST, Alexei Starovoitov wrote:
> On Thu, Jan 6, 2022 at 12:59 AM Kumar Kartikeya Dwivedi
> <memxor@...il.com> wrote:
> >
> > I'm not insisting, but for vmlinux we will have multiple
> > register_btf_kfunc_id_set calls for same hook, so we have to concat multiple
> > sets into one, which may result in an unsorted set. It's ok to not sort for
> > modules where only one register call per hook is allowed.
> >
> > Unless we switch to linear search for now (which is ok by me), we have to
> > re-sort for vmlinux BTF, to make btf_id_set_contains (in
> > btf_kfunc_id_set_contains) work.
>
> Could you give an example when it happens in vmlinux?
> Is it when modules are built-in (like tcp_bbr.c, tcp_cubic.c) ?
> But then they should go into struct btf of the module?
> Or THIS_MODULE becomes vmlinux and everything goes there?
> If that's the case then yeah, sorting is needed.

Yep, THIS_MODULE would be NULL, and it would pick vmlinux BTF for storing the
set.

Your suggestion to do direct assignment for module case is also good, since we
always ensure module refcount is held when looking into set, access to it should
be safe.

> Please make it clear in the comment and the commit log.
> It should be clear to reviewers without having to grill the author
> with questions.
> Would certainly save time for both author and reviewer. Agree?

Agreed, I'll add the comments and respin.

Thanks for your review.

--
Kartikeya