landlock08: Skip IPv6 variant if not supported

Check for IPv6 support before forking the server process to avoid
checkpoint timeout issues. If IPv6 is not available (EAFNOSUPPORT),
report TCONF and skip the variant gracefully.

This allows the landlock08 test to be executed on systems without
IPv6 support.

Signed-off-by: Brian Grech <bgrech@redhat.com>

Author: Brian Grech via ltp

testcases/kernel/syscalls/landlock/landlock08.c

@@ -102,12 +102,28 @@ static void test_connect(const int addr_family, const in_port_t port,
 	SAFE_CLOSE(socket.fd);
 }
 
+static int check_ipv6_support(void)
+{
+	int fd;
+
+	fd = socket(AF_INET6, SOCK_STREAM, 0);
+	if (fd == -1 && errno == EAFNOSUPPORT) {
+		tst_res(TCONF, "IPv6 not supported in kernel");
+		return 0;
+	}
+	if (fd != -1)
+		close(fd);
+	return 1;
+}
+
 static void run(void)
 {
 	int addr_family = variants[tst_variant];
 
 	tst_res(TINFO, "Using %s protocol",
 		addr_family == AF_INET ? "IPV4" : "IPV6");
+	if (addr_family == AF_INET6 && !check_ipv6_support())
+		return;
 
 	if (!SAFE_FORK()) {
 		create_server(addr_family);