Disable IPv6 socket auto-binding to IPv4 socket

Sometimes getaddrinfo returns IPv4 addresses before IPv6 addresses.
IPv6 sockets default to attempting to bind to IPv4 addresses too.
So if the IPv4 address is activated first, then binding to IPv6
will unneccessarily fail.

* daemon/libvirtd.c: Bind to IPv6 and IPv4 addresses separately

daemon/libvirtd.c

@@ -615,6 +615,21 @@ remoteMakeSockets (int *fds, int max_fds, int *nfds_r, const char *node, const c
         int opt = 1;
         setsockopt (fds[*nfds_r], SOL_SOCKET, SO_REUSEADDR, &opt, sizeof opt);
 
+#ifdef IPV6_V6ONLY
+        if (runp->ai_family == PF_INET6) {
+            int on = 1;
+            /*
+             * Normally on Linux an INET6 socket will bind to the INET4
+             * address too. If getaddrinfo returns results with INET4
+             * first though, this will result in INET6 binding failing.
+             * We can trivially cope with multiple server sockets, so
+             * we force it to only listen on IPv6
+             */
+            setsockopt(fds[*nfds_r], IPPROTO_IPV6,IPV6_V6ONLY,
+                       (void*)&on, sizeof on);
+        }
+#endif
+
         if (bind (fds[*nfds_r], runp->ai_addr, runp->ai_addrlen) == -1) {
             if (errno != EADDRINUSE) {
                 VIR_ERROR(_("bind: %s"), virStrerror (errno, ebuf, sizeof ebuf));