+/*
+ * Try a getsockname() on a connected datagram socket.
+ *
+ * Returns 1 and fills in @buf if successful; otherwise, zero.
+ *
+ * A connected datagram socket prevents leaving a socket in TIME_WAIT.
+ * This conserves the ephemeral port number space, helping reduce failed
+ * socket binds during mount storms.
+ */
+static int nfs_ca_sockname(const struct sockaddr *sap, const socklen_t salen,
+ struct sockaddr *buf, socklen_t *buflen)
+{
+ struct sockaddr_in sin = {
+ .sin_family = AF_INET,
+ .sin_addr.s_addr = htonl(INADDR_ANY),
+ };
+ struct sockaddr_in6 sin6 = {
+ .sin6_family = AF_INET6,
+ .sin6_addr = IN6ADDR_ANY_INIT,
+ };
+ int sock;
+
+ sock = socket(sap->sa_family, SOCK_DGRAM, IPPROTO_UDP);
+ if (sock < 0)
+ return 0;
+
+ switch (sap->sa_family) {
+ case AF_INET:
+ if (bind(sock, (struct sockaddr *)&sin, sizeof(sin)) < 0) {
+ close(sock);
+ return 0;
+ }
+ break;
+ case AF_INET6:
+ if (bind(sock, (struct sockaddr *)&sin6, sizeof(sin6)) < 0) {
+ close(sock);
+ return 0;
+ }
+ break;
+ default:
+ errno = EAFNOSUPPORT;
+ return 0;
+ }
+
+ if (connect(sock, sap, salen) < 0) {
+ close(sock);
+ return 0;
+ }
+
+ return !getsockname(sock, buf, buflen);
+}
+
+/*
+ * Try to generate an address that prevents the server from calling us.
+ *
+ * Returns 1 and fills in @buf if successful; otherwise, zero.
+ */
+static int nfs_ca_gai(const struct sockaddr *sap, const socklen_t salen,
+ struct sockaddr *buf, socklen_t *buflen)
+{
+ struct addrinfo *gai_results;
+ struct addrinfo gai_hint = {
+ .ai_family = sap->sa_family,
+ .ai_flags = AI_PASSIVE, /* ANYADDR */
+ };
+
+ if (getaddrinfo(NULL, "", &gai_hint, &gai_results))
+ return 0;
+
+ *buflen = gai_results->ai_addrlen;
+ memcpy(buf, gai_results->ai_addr, *buflen);
+
+ freeaddrinfo(gai_results);
+
+ return 1;
+}
+