Re: [PATCH bpf-next 2/3] bpf: Show precise rejected function when attaching to __btf_id functions

[KaFai Wan <mannkafai@gmail.com>]

On Fri, 2025-07-11 at 17:57 +0800, Yafang Shao wrote:
> On Fri, Jul 11, 2025 at 1:19 AM Alexei Starovoitov
> <alexei.starovoitov@gmail.com> wrote:
> > 
> > On Thu, Jul 10, 2025 at 9:27 AM KaFai Wan <mannkafai@gmail.com>
> > wrote:
> > > 
> > > Show the precise rejected function name when attaching tracing to
> > > __btf_id functions.
> > > 
> > > $ ./fentry
> > > libbpf: prog 'migrate_disable': BPF program load failed: -EINVAL
> > > libbpf: prog 'migrate_disable': -- BEGIN PROG LOAD LOG --
> > > Attaching tracing to __btf_id function 'migrate_disable' is
> > > rejected.
> > > 
> > > Signed-off-by: KaFai Wan <mannkafai@gmail.com>
> > > ---
> > >  kernel/bpf/verifier.c | 2 ++
> > >  1 file changed, 2 insertions(+)
> > > 
> > > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> > > index 275d82fb1a1a..2779d63e1f8b 100644
> > > --- a/kernel/bpf/verifier.c
> > > +++ b/kernel/bpf/verifier.c
> > > @@ -23938,6 +23938,8 @@ static int check_attach_btf_id(struct
> > > bpf_verifier_env *env)
> > >                         return ret;
> > >         } else if (prog->type == BPF_PROG_TYPE_TRACING &&
> > >                    btf_id_set_contains(&btf_id_deny, btf_id)) {
> > > +               verbose(env, "Attaching tracing to __btf_id
> > > function '%s' is rejected.\n",
> > > +                       tgt_info.tgt_name);
> > 
> > "Attaching tracing to __btf_id" ?! What does it mean?
> 
> The term "tracing" refers to BPF_PROG_TYPE_TRACING. I believe it is
> useful because it helps identify which functions cannot be attached
> by
> a given BPF program type.

Thanks, this is what I want to express.

> Perhaps we should replace "tracing" with "a tracing prog" for
> clarity?

Looks good, may be 'tracing programs' could be fine.

> 
> > Drop "__btf_id" and "tracing" bits.
> 

-- 
Thanks,
KaFai