Re: [PATCH bpf-next] selftests/bpf: Use ping_command() for IPv6 pings in lwt_ip_encap

> commit 0717c3442da506b8360051a6f87406ecc25dde4c
> Author: Andrii Nakryiko <[email protected]>
> Date:   Thu Aug 13 14:35:58 2026 -0700
>
>     selftests/bpf: Use ping_command() for IPv6 pings in lwt_ip_encap
>
>     lwt_ip_encap hardcodes the ping6 binary for its IPv6 pings. iputils
>     merged ping6 into ping long ago and distros have started dropping the
>     compat symlink -- Arch's iputils 20250605 ships only arping, clockdiff,
>     ping and tracepath. There, every lwt_ip_encap subtest fails:
>
>       check_ping_ok:FAIL:ip netns exec ns-lwt-ip-encap-1-0101330 ping6 -c 1 \
>         -W1 -I veth1 fb04::1 > /dev/null unexpected error: 256 (errno 2)
>       #217/1   lwt_ip_encap_ipv4/egress:FAIL

The sentence "every lwt_ip_encap subtest fails" isn't quite accurate.
Looking at test_lwt_ip_encap_vxlan_ipv4() in the patched code, it calls
lwt_ip_encap_vxlan(IPV4_ENCAP), which only ever runs the IPv4 arm:

    if (ipv4_encap)
            SYS(out, "ip netns exec %s ping -c 1 -W1 %s", ns1, IP4_ADDR_DST);
    else
            SYS(out, "ip netns exec %s %s -c 1 -W1 %s", ns1,
                ping_command(AF_INET6), IP6_ADDR_DST);

This path never touches ping6 or ping_command(), so the
test_lwt_ip_encap_vxlan_ipv4 subtest passes on a ping6-less host both
before and after this patch.

The other 9 subtests do fail: lwt_ip_encap_ipv4/{egress,ingress},
lwt_ip_encap_ipv6/{egress,ingress}, lwt_ip_encap_vrf_ipv4/{egress,ingress},
lwt_ip_encap_vrf_ipv6/{egress,ingress}, and lwt_ip_encap_vxlan_ipv6.

Would it be more accurate to say "every subtest that pings over IPv6 fails"
so the reproducer description matches the code behavior?


---
AI reviewed your patch. Please fix the bug or email reply why it's not a bug.
See: https://github.com/kernel-patches/vmtest/blob/master/ci/claude/README.md

CI run summary: https://github.com/kernel-patches/bpf/actions/runs/31747915907