Add/improve comment, shorten some usage texts. No code changes.

ipsvd/tcpudp.c

@@ -331,12 +331,31 @@ int tcpudpsvd_main(int argc, char **argv)
 		 * to ones coming from this remote IP. */
 		xconnect(0, &remote.sa, sa_len);
 	/* hole? at this point we have no wildcard udp socket...
-	 * can this cause clients to get "port unreachable" icmp? */
+	 * can this cause clients to get "port unreachable" icmp?
+	 * Yup, time window is very small, but it exists (is it?) */
 		/* Open new non-connected UDP socket for further clients */
 		sock = xsocket(lsa->sa.sa_family, tcp ? SOCK_STREAM : SOCK_DGRAM, 0);
 		setsockopt_reuseaddr(sock);
 		xbind(sock, &lsa->sa, sa_len);
 		socket_want_pktinfo(sock);
+
+		/* Doesn't work:
+		 * we cannot replace fd #0 - we will lose pending packet
+		 * which is already buffered for us! And we cannot use fd #1
+		 * instead - it will "intercept" all following packets, but child
+		 * do not expect data coming *from fd #1*! */
+#if 0
+		/* Make it so that local addr is fixed to localp->sa
+		 * and we don't accidentally accept packets to other local IPs. */
+		/* NB: we possibly bind to the _very_ same_ address & port as the one
+		 * already bound in parent! This seems to work in Linux.
+		 * (otherwise we can move socket to fd #0 only if bind succeeds) */
+		close(0);
+		set_nport(localp, htons(local_port));
+		xmove_fd(xsocket(localp->sa.sa_family, SOCK_DGRAM, 0), 0);
+		setsockopt_reuseaddr(0); /* crucial */
+		xbind(0, &localp->sa, localp->len);
+#endif
 	}
 
 	pid = fork();