[xdp-hints] Re: [PATCH bpf-next V2 3/6] selftests/bpf: xdp_hw_metadata RX hash return code info

[Stanislav Fomichev <sdf@google.com>]

On Tue, Mar 21, 2023 at 6:47 AM Jesper Dangaard Brouer
<brouer@redhat.com> wrote:
>
> When driver developers add XDP-hints kfuncs for RX hash it is
> practical to print the return code in bpf_printk trace pipe log.
>
> Print hash value as a hex value, both AF_XDP userspace and bpf_prog,
> as this makes it easier to spot poor quality hashes.
>
> Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
> ---
>  .../testing/selftests/bpf/progs/xdp_hw_metadata.c  |    9 ++++++---
>  tools/testing/selftests/bpf/xdp_hw_metadata.c      |    5 ++++-
>  2 files changed, 10 insertions(+), 4 deletions(-)
>
> diff --git a/tools/testing/selftests/bpf/progs/xdp_hw_metadata.c b/tools/testing/selftests/bpf/progs/xdp_hw_metadata.c
> index 40c17adbf483..ce07010e4d48 100644
> --- a/tools/testing/selftests/bpf/progs/xdp_hw_metadata.c
> +++ b/tools/testing/selftests/bpf/progs/xdp_hw_metadata.c
> @@ -77,10 +77,13 @@ int rx(struct xdp_md *ctx)
>                 meta->rx_timestamp = 0; /* Used by AF_XDP as not avail signal */
>         }
>
> -       if (!bpf_xdp_metadata_rx_hash(ctx, &meta->rx_hash))
> -               bpf_printk("populated rx_hash with %u", meta->rx_hash);
> -       else
> +       ret = bpf_xdp_metadata_rx_hash(ctx, &meta->rx_hash);
> +       if (ret >= 0) {
> +               bpf_printk("populated rx_hash with 0x%08X", meta->rx_hash);
> +       } else {
> +               bpf_printk("rx_hash not-avail errno:%d", ret);
>                 meta->rx_hash = 0; /* Used by AF_XDP as not avail signal */
> +       }
>
>         return bpf_redirect_map(&xsk, ctx->rx_queue_index, XDP_PASS);
>  }
> diff --git a/tools/testing/selftests/bpf/xdp_hw_metadata.c b/tools/testing/selftests/bpf/xdp_hw_metadata.c
> index 400bfe19abfe..f3ec07ccdc95 100644
> --- a/tools/testing/selftests/bpf/xdp_hw_metadata.c
> +++ b/tools/testing/selftests/bpf/xdp_hw_metadata.c
> @@ -3,6 +3,9 @@
>  /* Reference program for verifying XDP metadata on real HW. Functional test
>   * only, doesn't test the performance.
>   *
> + * BPF-prog bpf_printk info outout can be access via
> + * /sys/kernel/debug/tracing/trace_pipe

s/outout/output/

But let's maybe drop it? If you want to make it more usable, let's
have a separate patch to enable tracing and periodically dump it to
the console instead (as previously discussed).

With this addressed:
Acked-by: Stanislav Fomichev <sdf@google.com>

> + *
>   * RX:
>   * - UDP 9091 packets are diverted into AF_XDP
>   * - Metadata verified:
> @@ -156,7 +159,7 @@ static void verify_xdp_metadata(void *data, clockid_t clock_id)
>
>         meta = data - sizeof(*meta);
>
> -       printf("rx_hash: %u\n", meta->rx_hash);
> +       printf("rx_hash: 0x%08X\n", meta->rx_hash);
>         printf("rx_timestamp:  %llu (sec:%0.4f)\n", meta->rx_timestamp,
>                (double)meta->rx_timestamp / NANOSEC_PER_SEC);
>         if (meta->rx_timestamp) {
>
>