nixos/nsd: symlink conf file to /etc/nsd

We remove the configFile build flag override in the NixOS module.

Instead of embedding the conf file link to the binaries, we symlink it
to /etc/nsd/nsd.nix, the hardcoded config file location for the
various CLI nsd utilities.

This config file build option override is triggerring a nsd rebuild
for each configuration change. This prevent us to use the nixos cache
in many cases.

Co-authored-by: Erjo <erjo@cocoba.work>

nixos/modules/services/networking/nsd.nix

@@ -11,8 +11,6 @@ let
 
   # build nsd with the options needed for the given config
   nsdPkg = pkgs.nsd.override {
-    configFile = "${configFile}/nsd.conf";
-
     bind8Stats = cfg.bind8Stats;
     ipv6 = cfg.ipv6;
     ratelimit = cfg.ratelimit.enable;
@@ -897,7 +895,10 @@ in
               + "want, please enable 'services.nsd.rootServer'.";
     };
 
-    environment.systemPackages = [ nsdPkg ];
+    environment = {
+      systemPackages = [ nsdPkg ];
+      etc."nsd/nsd.conf".source = "${configFile}/nsd.conf";
+    };
 
     users.groups.${username}.gid = config.ids.gids.nsd;
 

pkgs/servers/dns/nsd/default.nix

@@ -11,7 +11,7 @@
 , rrtypes          ? false
 , zoneStats        ? false
 
-, configFile ? "etc/nsd/nsd.conf"
+, configFile ? "/etc/nsd/nsd.conf"
 }:
 
 stdenv.mkDerivation rec {