Implement setting of IPv4 forwarding flag.

babel.c

@@ -286,7 +286,7 @@ main(int argc, char **argv)
         fprintf(stderr, "Respecting %ld second silent time.\n",
                 (long int)(reboot_time + silent_time - now.tv_sec));
 
-    rc = kernel_setup(1);
+    rc = kernel_setup(1, do_ipv4);
     if(rc < 0) {
         fprintf(stderr, "kernel_setup failed.\n");
         exit(1);
@@ -571,7 +571,7 @@ main(int argc, char **argv)
         kernel_setup_interface(0, nets[i].ifname, nets[i].ifindex);
     }
     kernel_setup_socket(0);
-    kernel_setup(0);
+    kernel_setup(0, do_ipv4);
 
     fd = open(state_file, O_WRONLY | O_TRUNC | O_CREAT, 0644);
     if(fd < 0) {
@@ -614,7 +614,7 @@ main(int argc, char **argv)
     for(i = 0; i < numnets; i++)
         kernel_setup_interface(0, nets[i].ifname, nets[i].ifindex);
     kernel_setup_socket(0);
-    kernel_setup(0);
+    kernel_setup(0, do_ipv4);
     exit(1);
 }
 

kernel.h

@@ -34,7 +34,7 @@ struct kernel_route {
 #define ROUTE_ADD 1
 #define ROUTE_MODIFY 2
 
-int kernel_setup(int setup);
+int kernel_setup(int setup, int ipv4);
 int kernel_setup_socket(int setup);
 int kernel_setup_interface(int setup, const char *ifname, int ifindex);
 int kernel_interface_ipv4(const char *ifname, int ifindex, char *addr_r);

kernel_netlink.c

@@ -45,6 +45,7 @@ THE SOFTWARE.
 #include "util.h"
 
 static int old_forwarding = -1;
+static int old_ipv4_forwarding = -1;
 static int old_accept_redirects = -1;
 static int old_rp_filter = -1;
 
@@ -379,7 +380,7 @@ netlink_send_dump(int type, void *data, int len) {
 }
 
 int
-kernel_setup(int setup)
+kernel_setup(int setup, int ipv4)
 {
     int rc;
 
@@ -403,6 +404,22 @@ kernel_setup(int setup)
             return -1;
         }
 
+        if(ipv4) {
+            old_ipv4_forwarding =
+                read_proc("/proc/sys/net/ipv4/conf/all/forwarding");
+            if(old_ipv4_forwarding < 0) {
+                perror("Couldn't read IPv4 forwarding knob.");
+                return -1;
+            }
+
+            rc = write_proc("/proc/sys/net/ipv4/conf/all/forwarding", 1);
+            if(rc < 0) {
+                perror("Couldn't write IPv4 forwarding knob.");
+                return -1;
+            }
+        }
+
+
         old_accept_redirects =
             read_proc("/proc/sys/net/ipv6/conf/all/accept_redirects");
         if(old_accept_redirects < 0) {
@@ -435,10 +452,20 @@ kernel_setup(int setup)
             rc = write_proc("/proc/sys/net/ipv6/conf/all/forwarding",
                             old_forwarding);
             if(rc < 0) {
-                perror("Couldn't write accept_redirects knob.\n");
+                perror("Couldn't write forwarding knob.\n");
+                return -1;
+            }
+        }
+
+        if(old_ipv4_forwarding >= 0) {
+            rc = write_proc("/proc/sys/net/ipv4/conf/all/forwarding",
+                            old_ipv4_forwarding);
+            if(rc < 0) {
+                perror("Couldn't write IPv4 forwarding knob.\n");
                 return -1;
             }
         }
+
         if(old_accept_redirects >= 0) {
             rc = write_proc("/proc/sys/net/ipv6/conf/all/accept_redirects",
                             old_accept_redirects);

kernel_socket.c

@@ -136,7 +136,7 @@ plen2mask(int n, struct in6_addr *dest)
 }
 
 int
-kernel_setup(int setup)
+kernel_setup(int setup, int ipv4)
 {
     int rc;
     if(setup) {