linux-kernel - Re: [PATCH bpf-next v3 2/3] selftests: bpf: add a test for mmapable vmlinux BTF

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Message-ID: <CAEf4BzZ85DyEj2ey7y46tRHd=kP4xvqn5z8H3NO3bRTXZ2Mbaw@mail.gmail.com>
Date: Wed, 7 May 2025 11:18:20 -0700
From: Andrii Nakryiko <andrii.nakryiko@...il.com>
To: Lorenz Bauer <lmb@...valent.com>
Cc: Arnd Bergmann <arnd@...db.de>, Alexei Starovoitov <ast@...nel.org>, 
	Daniel Borkmann <daniel@...earbox.net>, Andrii Nakryiko <andrii@...nel.org>, 
	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>, 
	Jiri Olsa <jolsa@...nel.org>, Mykola Lysenko <mykolal@...com>, Shuah Khan <shuah@...nel.org>, 
	linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org, bpf@...r.kernel.org, 
	linux-kselftest@...r.kernel.org
Subject: Re: [PATCH bpf-next v3 2/3] selftests: bpf: add a test for mmapable
 vmlinux BTF

On Wed, May 7, 2025 at 2:14 AM Lorenz Bauer <lmb@...valent.com> wrote:
>
> On Tue, May 6, 2025 at 10:39 PM Andrii Nakryiko
> <andrii.nakryiko@...il.com> wrote:
>
> > > +       raw_data = mmap(NULL, end, PROT_READ, MAP_PRIVATE, fd, 0);
> > > +       if (!ASSERT_NEQ(raw_data, MAP_FAILED, "mmap_btf"))
> >
> > ASSERT_OK_PTR()?
>
> Don't think that mmap follows libbpf_get_error conventions? I'd keep
> it as it is.

ASSERT_OK_PTR() isn't libbpf specific (and libbpf is actually
returning a NULL or valid pointer for all public APIs, since libbpf
1.0). But if you look at the implementation, "an OK" pointer is a
non-NULL pointer that is also not a small negative value. NULL is a
bad pointer, -1 (MAP_FAILED) is a bad pointer, and so on. So it's a
pretty universal check for anything pointer-related. Please do use
OK_PTR, it's semantically better in tests

>
> > > +       btf = btf__new_split(raw_data, btf_size, base);
> > > +       if (!ASSERT_NEQ(btf, NULL, "parse_btf"))
> >
> > ASSERT_OK_PTR()
>
> Ack.
>
> > Do you intend to add more subtests? if not, why even using a subtest structure
>
> The original intention was to add kmod support, but that didn't pan
> out, see my discussion with Alexei. I can drop the subtest if you
> want, but I'd probably keep the helper as it is.

yeah, let's drop the subtest, it's a bit easier to work with
non-subtest tests, IMO