Re: [PATCH bpf 2/2] selftests/bpf: Cover partial copy of non-linear skb test_run output

[sun jian]

On Mon, Jun 15, 2026 at 10:13 PM Paul Chaignon <paul.chaignon@xxxxxxxxx> wrote:
>
> On Mon, Jun 15, 2026 at 03:38:56PM +0800, Sun Jian wrote:
> > Add a test case for BPF_PROG_TEST_RUN with a non-linear skb and a short
> > data_out buffer.
> >
> > The test verifies that test_run returns -ENOSPC, reports the full packet
> > length through data_size_out, and copies the packet prefix into data_out.
> > The test uses a 100-byte data_out buffer with a 64-byte linear head, so the
> > expected output spans both the skb head and the first fragment.
> >
> > Signed-off-by: Sun Jian <sun.jian.kdev@xxxxxxxxx>
> > ---
> >  .../selftests/bpf/prog_tests/skb_load_bytes.c | 35 +++++++++++++++++++
> >  1 file changed, 35 insertions(+)
> >
> > diff --git a/tools/testing/selftests/bpf/prog_tests/skb_load_bytes.c b/tools/testing/selftests/bpf/prog_tests/skb_load_bytes.c
> > index d7f83c0a40a5..134be0ea8ed7 100644
> > --- a/tools/testing/selftests/bpf/prog_tests/skb_load_bytes.c
> > +++ b/tools/testing/selftests/bpf/prog_tests/skb_load_bytes.c
> > @@ -3,6 +3,39 @@
> >  #include <network_helpers.h>
> >  #include "skb_load_bytes.skel.h"
> >
> > +#define NONLINEAR_PKT_LEN 9000
> > +#define NONLINEAR_HEAD_LEN 64
> > +#define SHORT_OUT_LEN 100
> > +
> > +static void test_nonlinear_data_out_partial(int prog_fd)
> > +{
> > +     LIBBPF_OPTS(bpf_test_run_opts, tattr);
> > +     __u8 pkt[NONLINEAR_PKT_LEN];
> > +     __u8 out[SHORT_OUT_LEN];
> > +     struct __sk_buff skb = {};
> > +     int err, i;
> > +
> > +     for (i = 0; i < sizeof(pkt); i++)
> > +             pkt[i] = i & 0xff;
> > +
> > +     memset(out, 0xa5, sizeof(out));
> > +
> > +     skb.data_end = NONLINEAR_HEAD_LEN;
> > +
> > +     tattr.data_in = pkt;
> > +     tattr.data_size_in = sizeof(pkt);
> > +     tattr.data_out = out;
> > +     tattr.data_size_out = sizeof(out);
> > +     tattr.ctx_in = &skb;
> > +     tattr.ctx_size_in = sizeof(skb);
> > +
> > +     err = bpf_prog_test_run_opts(prog_fd, &tattr);
> > +
> > +     ASSERT_EQ(err, -ENOSPC, "nonlinear_partial_err");
> > +     ASSERT_EQ(tattr.data_size_out, sizeof(pkt), "nonlinear_partial_data_size_out");
> > +     ASSERT_OK(memcmp(out, pkt, sizeof(out)), "nonlinear_partial_data_out");
> > +}
> > +
> >  void test_skb_load_bytes(void)
> >  {
> >       struct skb_load_bytes *skel;
> > @@ -40,6 +73,8 @@ void test_skb_load_bytes(void)
> >       if (!ASSERT_EQ(test_result, 0, "offset 10"))
> >               goto out;
> >
> > +     test_nonlinear_data_out_partial(prog_fd);
> > +
>
> Maybe prog_tests/prog_run_opts.c would be a better place to cover this?
> test_skb_load_bytes() is meant to cover the bpf_skb_load_bytes helper.
>
> >  out:
> >       skb_load_bytes__destroy(skel);
> >  }
> > --
> > 2.43.0
> >

Hi Paul,

Thanks, agreed. The test is really about BPF_PROG_TEST_RUN copy-out
semantics, not the bpf_skb_load_bytes() helper.

I'll move it to prog_run_opts.c in v2.

Thanks,
Sun Jian