+/*
+ * have_route_to - determine if the system has any route to
+ * a given IP address. `addr' is in network byte order.
+ * For demand mode to work properly, we have to ignore routes
+ * through our own interface.
+ */
+int have_route_to(u_int32_t addr)
+{
+ char buf[sizeof(struct rt_msghdr) + (sizeof(struct sockaddr_in))];
+ int status;
+ int s, n;
+ struct rt_msghdr *rtm;
+ struct sockaddr_in *sin;
+ int msglen = sizeof(*rtm) + (sizeof(*sin));
+ char *cp;
+ char msg[2048];
+
+ rtm = (struct rt_msghdr *)buf;
+ memset(rtm, 0, msglen);
+ rtm->rtm_msglen = msglen;
+ rtm->rtm_version = RTM_VERSION;
+ rtm->rtm_type = RTM_GET;
+ rtm->rtm_addrs = RTA_DST;
+ /* rtm->rtm_addrs, rtm_flags should be set on output */
+
+ sin = (struct sockaddr_in *)((u_char *)rtm + sizeof(*rtm));
+ sin->sin_len = sizeof(*sin);
+ sin->sin_family = AF_INET;
+ sin->sin_addr.s_addr = addr;
+
+ status = 0;
+
+ if ((s = socket(PF_ROUTE, SOCK_RAW, 0)) < 0)
+ return -1;
+ if (write(s, (char *)rtm, msglen) != msglen) {
+ close(s);
+ return status == ESRCH? 0: -1;
+ }
+
+ n = read(s, msg, 2048);
+ close(s);
+ if (n <= 0)
+ return -1;
+
+ rtm = (struct rt_msghdr *) msg;
+ if (rtm->rtm_version != RTM_VERSION)
+ return -1;
+
+ /* here we try to work out if the route is through our own interface */
+ cp = (char *)(rtm + 1);
+ if (rtm->rtm_addrs & RTA_DST) {
+ struct sockaddr *sa = (struct sockaddr *) cp;
+ cp = (char *)(((unsigned long)cp + sa->sa_len
+ + sizeof(long) - 1) & ~(sizeof(long) - 1));
+ }
+ if (rtm->rtm_addrs & RTA_GATEWAY) {
+ sin = (struct sockaddr_in *) cp;
+ if (sin->sin_addr.s_addr == ifaddrs[0]
+ || sin->sin_addr.s_addr == ifaddrs[1])
+ return 0; /* route is through our interface */
+ }