[PATCH bpf-next] 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 IPv4 subtests fail too, because check_ping_ok() pings both families.
SYS() runs the command through system(), so a missing binary is
indistinguishable from an unreachable peer.

network_helpers.c has had ping_command() for exactly this since commit
372642ea83ff ("selftests/bpf: Move netcnt test under test_progs"): it
falls back to "ping -6" when ping6 is not present. lwt_ip_encap.c is the
last hardcoded ping6 user. Fix that.

Fixes: f5e288943e2c ("selftests/bpf: Move test_lwt_ip_encap to test_progs")
Signed-off-by: Andrii Nakryiko <[email protected]>
---
 tools/testing/selftests/bpf/prog_tests/lwt_ip_encap.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/tools/testing/selftests/bpf/prog_tests/lwt_ip_encap.c b/tools/testing/selftests/bpf/prog_tests/lwt_ip_encap.c
index 6606f0ed9a9a..39e8a3b8b6af 100644
--- a/tools/testing/selftests/bpf/prog_tests/lwt_ip_encap.c
+++ b/tools/testing/selftests/bpf/prog_tests/lwt_ip_encap.c
@@ -410,7 +410,8 @@ static int test_gso_fix(const char *ns1, const char *ns3, int family)
 static int check_ping_ok(const char *ns1)
 {
 	SYS(fail, "ip netns exec %s ping -c 1 -W1 -I veth1 %s > /dev/null", ns1, IP4_ADDR_DST);
-	SYS(fail, "ip netns exec %s ping6 -c 1 -W1 -I veth1 %s > /dev/null", ns1, IP6_ADDR_DST);
+	SYS(fail, "ip netns exec %s %s -c 1 -W1 -I veth1 %s > /dev/null", ns1,
+	    ping_command(AF_INET6), IP6_ADDR_DST);
 	return 0;
 fail:
 	return -1;
@@ -424,7 +425,8 @@ static int check_ping_fails(const char *ns1)
 	if (!ret)
 		return -1;
 
-	ret = SYS_NOFAIL("ip netns exec %s ping6 -c 1 -W1 -I veth1 %s", ns1, IP6_ADDR_DST);
+	ret = SYS_NOFAIL("ip netns exec %s %s -c 1 -W1 -I veth1 %s", ns1,
+			 ping_command(AF_INET6), IP6_ADDR_DST);
 	if (!ret)
 		return -1;
 
@@ -657,9 +659,10 @@ static void lwt_ip_encap_vxlan(bool ipv4_encap)
 	skel->bss->fexit_triggered = false;
 
 	if (ipv4_encap)
-		SYS(out, "ip netns exec %s ping  -c 1 -W1 %s", ns1, IP4_ADDR_DST);
+		SYS(out, "ip netns exec %s ping -c 1 -W1 %s", ns1, IP4_ADDR_DST);
 	else
-		SYS(out, "ip netns exec %s ping6 -c 1 -W1 %s", ns1, IP6_ADDR_DST);
+		SYS(out, "ip netns exec %s %s -c 1 -W1 %s", ns1,
+		    ping_command(AF_INET6), IP6_ADDR_DST);
 
 	if (!ASSERT_TRUE(skel->bss->fexit_triggered, "fexit_triggered"))
 		goto out;
-- 
2.53.0-Meta