Add a 'named' option to run only for ipv4.

I remember the 'named' log was giving annoying messages on systems not ipv6
capable (I can't recall if lacking the kernel ipv6 code or unconfigured ipv6
addresses).


svn path=/nixos/trunk/; revision=34419

modules/services/networking/bind.nix

@@ -78,6 +78,13 @@ in
         ";
       };
 
+      ipv4Only = mkOption {
+        default = false;
+        description = "
+          Only use ipv4, even if the host supports ipv6
+        ";
+      };
+
       zones = mkOption {
         default = [];
         description = "
@@ -121,7 +128,7 @@ in
             ${pkgs.coreutils}/bin/mkdir -p /var/run/named
           '';
 
-        exec = "${pkgs.bind}/sbin/named -c ${cfg.configFile} -f";
+        exec = "${pkgs.bind}/sbin/named ${optionalString cfg.ipv4Only "-4"} -c ${cfg.configFile} -f";
       };
 
   };