linux-kernel - Re: [PATCH bpf-next v10 01/23] selftests/bpf: regroup and declare similar kfuncs selftests in an array

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Date:   Tue, 6 Sep 2022 15:50:00 +0200
From:   Benjamin Tissoires <benjamin.tissoires@...hat.com>
To:     Kumar Kartikeya Dwivedi <memxor@...il.com>
Cc:     Greg KH <gregkh@...uxfoundation.org>,
        Jiri Kosina <jikos@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>, Shuah Khan <shuah@...nel.org>,
        Dave Marchevsky <davemarchevsky@...com>,
        Joe Stringer <joe@...ium.io>, Jonathan Corbet <corbet@....net>,
        Tero Kristo <tero.kristo@...ux.intel.com>,
        lkml <linux-kernel@...r.kernel.org>,
        "open list:HID CORE LAYER" <linux-input@...r.kernel.org>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>,
        Linux Doc Mailing List <linux-doc@...r.kernel.org>
Subject: Re: [PATCH bpf-next v10 01/23] selftests/bpf: regroup and declare
 similar kfuncs selftests in an array

On Tue, Sep 6, 2022 at 5:27 AM Kumar Kartikeya Dwivedi <memxor@...il.com> wrote:
>
> On Tue, 6 Sept 2022 at 05:25, Kumar Kartikeya Dwivedi <memxor@...il.com> wrote:
> >
> > On Fri, 2 Sept 2022 at 15:29, Benjamin Tissoires
> > <benjamin.tissoires@...hat.com> wrote:
> > >
> > > Similar to tools/testing/selftests/bpf/prog_tests/dynptr.c:
> > > we declare an array of tests that we run one by one in a for loop.
> > >
> > > Followup patches will add more similar-ish tests, so avoid a lot of copy
> > > paste by grouping the declaration in an array.
> > >
> > > To be able to call bpf_object__find_program_by_name(), we need to use
> > > plain libbpf calls, and not light skeletons. So also change the Makefile
> > > to not generate light skeletons.
> > >
> > > Signed-off-by: Benjamin Tissoires <benjamin.tissoires@...hat.com>
> > >
> > > ---
> >
> > I see your point, but this is also a test so that we keep verifying
> > kfunc call in light skeleton.
> > Code for relocating both is different in libbpf (we generate BPF ASM
> > for light skeleton so it is done inside a loader BPF program instead
> > of userspace).
>
> Err, hit send too early.
> We can probably use a macro to hide how program is called, then do
> X(prog1)
> X(prog2)
> in a series, won't look too bad and avoids duplication at the same time.
>
> > You might then be able to make it work for both light and normal skeleton.
> >
> WDYT?
>

On this patch alone, I concede the benefit is minimum. But if you look
at 6/23, I must confess I definitely prefer having just an array of
tests at the beginning instead of crippling the tests functions with
calls or macros.

The actual reason for me to ditch light skeletons was because I was
using bpf_object__find_program_by_name().

But I can work around that by relying on the offsetof() macro, and
make the whole thing working for *both* light skeleton and libbpf:
+struct kfunc_test_params {
+       const char *prog_name;
+       unsigned long int lskel_prog_desc_offset;
+       int retval;
+};
+
+#define TC_TEST(name,__retval) \
+       { \
+         .prog_name = #name, \
+         .lskel_prog_desc_offset = offsetof(struct
kfunc_call_test_lskel, progs.name), \
+         .retval = __retval, \
+       }
+
+static struct kfunc_test_params kfunc_tests[] = {
+       TC_TEST(kfunc_call_test1, 12),
+       TC_TEST(kfunc_call_test2, 3),
+       TC_TEST(kfunc_call_test_ref_btf_id, 0),
+};
+
+static void verify_success(struct kfunc_test_params *param)
 {
[...]
+       struct bpf_prog_desc *lskel_prog = (struct bpf_prog_desc
*)((char *)lskel + param->lskel_prog_desc_offset);

However, for failing tests, I can not really rely on light skeletons
because we can not dynamically set the autoload property.
So either I split every failed test in its own file, or I only test
the ones that are supposed to load, which don't add a lot IMO.

I'll repost the bpf-core changes only so you can have a better idea of
what I am saying.

Cheers,
Benjamin