Re: [PATCH net v4 2/2] selftests/bpf: cover AF_XDP multi-buffer TX software checksum

[Stanislav Fomichev <sdf.kernel@gmail.com>]

On 10/30, Rongzheng Wang wrote:
> Extend test_xdp_metadata to send the same UDP packet using every descriptor
> count from 1 through MAX_TX_DESCS (MAX_SKB_FRAGS + 1), and to run the
> existing metadata and checksum verification for each case.
> 
> Build the packet once and write it into the TX descriptors in a loop
> instead of using a flat two-descriptor layout. Keep the first descriptor
> large enough to cover the checksum offset; the remaining payload is split
> across the continuation descriptors, with the last descriptor taking the
> remaining length.
> 
> Reuse the existing AF_XDP setup, packet generation, completion, and receive
> helpers in xdp_metadata.c instead of adding a separate test harness.
> 
> Signed-off-by: Rongzheng Wang <testwrzwrz@gmail.com>
> ---
>  .../selftests/bpf/prog_tests/xdp_metadata.c   | 147 +++++++++++-------
>  1 file changed, 92 insertions(+), 55 deletions(-)
> 
> diff --git a/tools/testing/selftests/bpf/prog_tests/xdp_metadata.c b/tools/testing/selftests/bpf/prog_tests/xdp_metadata.c
> index 5c31054ad4a4..17da0a145666 100644
> --- a/tools/testing/selftests/bpf/prog_tests/xdp_metadata.c
> +++ b/tools/testing/selftests/bpf/prog_tests/xdp_metadata.c
> @@ -18,12 +18,15 @@
>  #define TX_NAME "veTX"
>  #define RX_NAME "veRX"
>  
> -#define UDP_PAYLOAD_BYTES 4
> +#define UDP_PAYLOAD_BYTES 32
> +

[..]

> +#define MAX_SKB_FRAGS 17 /* minimum CONFIG_MAX_SKB_FRAGS */

Any reason you're not reading the real value from
/proc/sys/net/core/max_skb_frags ?