New -F option not to enable forwarding at startup

To be pushed upstream.

babeld.c

@@ -100,7 +100,7 @@ int
 main(int argc, char **argv)
 {
     struct sockaddr_in6 sin6;
-    int rc, fd, i, opt;
+    int rc, fd, i, opt, setup = 2;
     time_t expiry_time, source_expiry_time, kernel_dump_time;
     const char **config_files = NULL;
     int num_config_files = 0;
@@ -124,7 +124,7 @@ main(int argc, char **argv)
     change_smoothing_half_life(4);
 
     while(1) {
-        opt = getopt(argc, argv, "m:p:h:H:i:k:A:sruS:d:g:lwz:M:t:T:c:C:DL:I:");
+        opt = getopt(argc, argv, "m:p:h:H:i:k:A:sruS:d:g:lwz:M:t:T:c:C:DL:I:F");
         if(opt < 0)
             break;
 
@@ -259,6 +259,9 @@ main(int argc, char **argv)
         case 'I':
             pidfile = optarg;
             break;
+        case 'F':
+            setup = 1;
+            break;
         default:
             goto usage;
         }
@@ -363,7 +366,7 @@ main(int argc, char **argv)
         close(pfd);
     }
 
-    rc = kernel_setup(1);
+    rc = kernel_setup(setup);
     if(rc < 0) {
         fprintf(stderr, "kernel_setup failed.\n");
         goto fail_pid;
@@ -817,7 +820,7 @@ main(int argc, char **argv)
             "                "
             "[-k metric] [-A metric] [-s] [-l] [-w] [-r] [-u] [-g port]\n"
             "                "
-            "[-t table] [-T table] [-c file] [-C statement]\n"
+            "[-F] [-t table] [-T table] [-c file] [-C statement]\n"
             "                "
             "[-d level] [-D] [-L logfile] [-I pidfile]\n"
             "                "

babeld.man

@@ -99,6 +99,11 @@ Do not flush unfeasible (useless) routes.  This is useful in order to
 announce more information to a front-end (see
 .BR \-g ).
 .TP
+.B \-F
+Assume forwarding is already set, or not wanted. By not touching
+net.*.conf.all.forwarding at startup, it is also useful to prevent the
+kernel from removing a default IPv6 route provided by autoconfiguration.
+.TP
 .BI \-d " level"
 Debug level.  A value of 1 requests a routing table dump at every
 iteration through the daemon's main loop.  A value of 2 additionally

kernel_netlink.c

@@ -502,6 +502,7 @@ kernel_setup(int setup)
         }
         nl_setup = 1;
 
+        if(setup > 1) {
             old_forwarding = read_proc("/proc/sys/net/ipv6/conf/all/forwarding");
             if(old_forwarding < 0) {
                 perror("Couldn't read forwarding knob.");
@@ -526,7 +527,7 @@ kernel_setup(int setup)
                 perror("Couldn't write IPv4 forwarding knob.");
                 return -1;
             }
-
+        }
 
         old_accept_redirects =
             read_proc("/proc/sys/net/ipv6/conf/all/accept_redirects");