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

[Paul Chaignon <paul.chaignon@gmail.com>]

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@gmail.com>
> ---
>  .../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
>