selftests/bpf: Add socket_kind_to_str() to socket_helpers

Add function that returns string representation of socket's domain/type.

Suggested-by: Jakub Sitnicki <jakub@cloudflare.com>
Signed-off-by: Michal Luczaj <mhal@rbox.co>
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>
Reviewed-by: Jakub Sitnicki <jakub@cloudflare.com>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Link: https://lore.kernel.org/r/20250515-selftests-sockmap-redir-v3-2-a1ea723f7e7e@rbox.co

Author: mmhal

tools/testing/selftests/bpf/prog_tests/socket_helpers.h

@@ -410,4 +410,59 @@ static inline int create_socket_pairs(int family, int sotype, int *c0, int *c1,
 	return err;
 }
 
+static inline const char *socket_kind_to_str(int sock_fd)
+{
+	socklen_t opt_len;
+	int domain, type;
+
+	opt_len = sizeof(domain);
+	if (getsockopt(sock_fd, SOL_SOCKET, SO_DOMAIN, &domain, &opt_len))
+		FAIL_ERRNO("getsockopt(SO_DOMAIN)");
+
+	opt_len = sizeof(type);
+	if (getsockopt(sock_fd, SOL_SOCKET, SO_TYPE, &type, &opt_len))
+		FAIL_ERRNO("getsockopt(SO_TYPE)");
+
+	switch (domain) {
+	case AF_INET:
+		switch (type) {
+		case SOCK_STREAM:
+			return "tcp4";
+		case SOCK_DGRAM:
+			return "udp4";
+		}
+		break;
+	case AF_INET6:
+		switch (type) {
+		case SOCK_STREAM:
+			return "tcp6";
+		case SOCK_DGRAM:
+			return "udp6";
+		}
+		break;
+	case AF_UNIX:
+		switch (type) {
+		case SOCK_STREAM:
+			return "u_str";
+		case SOCK_DGRAM:
+			return "u_dgr";
+		case SOCK_SEQPACKET:
+			return "u_seq";
+		}
+		break;
+	case AF_VSOCK:
+		switch (type) {
+		case SOCK_STREAM:
+			return "v_str";
+		case SOCK_DGRAM:
+			return "v_dgr";
+		case SOCK_SEQPACKET:
+			return "v_seq";
+		}
+		break;
+	}
+
+	return "???";
+}
+
 #endif // __SOCKET_HELPERS__