Re: [PATCH] selftests/bpf: Fix return value check in attach_bpf()

[yukuai (C)]

On 2021/05/29 4:46, Daniel Borkmann wrote:
> On 5/28/21 11:07 AM, Yu Kuai wrote:
> > use libbpf_get_error() to check the return value of
> > bpf_program__attach().
> >
> > Reported-by: Hulk Robot <hulkci@xxxxxxxxxx>
> > Signed-off-by: Yu Kuai <yukuai3@xxxxxxxxxx>
> > ---
> >   tools/testing/selftests/bpf/benchs/bench_rename.c | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/tools/testing/selftests/bpf/benchs/bench_rename.c 
> > b/tools/testing/selftests/bpf/benchs/bench_rename.c
> > index c7ec114eca56..b7d4a1d74fca 100644
> > --- a/tools/testing/selftests/bpf/benchs/bench_rename.c
> > +++ b/tools/testing/selftests/bpf/benchs/bench_rename.c
> > @@ -65,7 +65,7 @@ static void attach_bpf(struct bpf_program *prog)
> >       struct bpf_link *link;
> >       link = bpf_program__attach(prog);
> > -    if (!link) {
> > +    if (libbpf_get_error(link)) {
> >           fprintf(stderr, "failed to attach program!\n");
> >           exit(1);
> >       }
>
> Could you explain the rationale of this patch? bad2e478af3b 
> ("selftests/bpf: Turn
> on libbpf 1.0 mode and fix all IS_ERR checks") explains: 'Fix all the 
> explicit
> IS_ERR checks that now will be broken because libbpf returns NULL on 
> error (and
> sets errno).' So the !link check looks totally reasonable to me. 
> Converting to
> libbpf_get_error() is not wrong in itself, but given you don't make any 
> use of
> the err code, there is also no point in this diff here.
Hi,

I was thinking that bpf_program__attach() can return error code
theoretically(for example -ESRCH), and such case need to be handled.

Thanks,
Yu Kuai
> Thanks,
> Daniel
> .