add secrets-subscriber service, make hostapd use it

examples/router-with-l2tp.nix

@@ -177,16 +177,6 @@ in rec {
     };
   };
 
-  services.restart-on-change = longrun {
-    name = "wlan0-restart-on-change";
-    run = ''
-      ${pkgs.watch-outputs}/bin/watch-outputs -r wlan0.link.hostapd ${config.services.secrets} wpa_passphrase
-    '';
-    dependencies = [
-      config.services.hostap-liminix
-      config.services.hostap-liminix5
-    ];
-  };
 
   services.bootstrap-dhcpc = svc.network.dhcp.client.build {
     interface = config.services.wwan;

modules/hostapd/default.nix

@@ -16,6 +16,7 @@ let
   inherit (lib) mkOption types;
   inherit (pkgs) liminix;
 in {
+  imports = [ ../secrets ];
   options = {
     system.service.hostapd = mkOption {
       type = liminix.lib.types.serviceDefn;

modules/hostapd/service.nix

@@ -1,5 +1,6 @@
 {
   liminix
+, svc
 , hostapd
 , output-template
 , writeText
@@ -39,7 +40,7 @@ let
         (mapAttrsToList
           format_value
           attrs)) + "\n"));
-in longrun {
+  service = longrun {
     inherit name;
     dependencies = [ interface ];
     run = ''
@@ -48,4 +49,12 @@ in longrun {
       ${output-template}/bin/output-template '{{' '}}'  < ${conf}  > /run/${name}/hostapd.conf
       exec ${hostapd}/bin/hostapd -i $(output ${interface} ifname)  -P /run/${name}/hostapd.pid -S /run/${name}/hostapd.conf
     '';
+  };
+in svc.secrets.subscriber.build {
+  watch = {
+    service = attrs.wpa_passphrase.service;
+    paths = ["wpa_passphrase"];
+  };
+  inherit service;
+  action = "restart-all";
 }

modules/secrets/default.nix

@@ -14,6 +14,10 @@ in {
       description = "fetch secrets from external vault with https";
       type = liminix.lib.types.serviceDefn;
     };
+    subscriber = mkOption {
+      description = "wrapper around a service that needs notifying (e.g. restarting) when secrets change";
+      type = liminix.lib.types.serviceDefn;
+    };
 
   };
   config.system.service.secrets = {
@@ -32,5 +36,31 @@ in {
         description = "how often to check the source, in minutes";
       };
     };
+    subscriber = config.system.callService ./subscriber.nix {
+      watch = {
+        service = mkOption {
+          description = "secrets service to subscribe to";
+          type = liminix.lib.types.service;
+        };
+        paths = mkOption {
+          description = "list of output paths we are interested in";
+          example = ["wan/l2tp" "wifi/wlan5"];
+          type = types.listOf types.str;
+        };
+      };
+      service = mkOption {
+        description = "subscribing service that will receive notification";
+        type = liminix.lib.types.service;
+      };
+      action = mkOption {
+        description = "how do we notify the service to regenerate its config";
+        default = "restart-all";
+        type = types.enum [
+          "restart" "restart-all"
+          "hup" "int" "quit" "kill" "term"
+          "winch" "usr1" "usr2"
+        ];
+      };
+    };
   };
 }

modules/secrets/subscriber.nix

@@ -0,0 +1,23 @@
+{
+  liminix, lib, lim, s6, s6-rc, watch-outputs
+}:
+{ watch, service, action } :
+let
+  inherit (liminix.services) oneshot longrun;
+  inherit (builtins) toString;
+  inherit (service) name;
+  watcher = let name' = "check-${name}"; in longrun {
+    name = name';
+    run = ''
+      dir=/run/service/${name}
+      echo waiting for $dir
+      if test -e $dir/notification-fd; then flag="-U"; else flag="-u"; fi
+      ${s6}/bin/s6-svwait $flag /run/service/${name} || exit
+      PATH=${s6-rc}/bin:${s6}/bin:$PATH
+      ${watch-outputs}/bin/watch-outputs -r ${name} ${watch.service} ${lib.concatStringsSep " " watch.paths}
+    '';
+  };
+in service.overrideAttrs(o: {
+  buildInputs =  (lim.orEmpty o.buildInputs) ++ [ watcher ];
+  dependencies = (lim.orEmpty o.dependencies) ++ [ watcher ];
+})

pkgs/watch-outputs/watch-outputs.fnl

@@ -33,12 +33,13 @@
                _ path (ipairs paths)]
     (or changed? (not (table= (dig old-tree path) (dig new-tree path))))))
 
+(fn %% [fmt ...] (string.format fmt ...))
 
 (fn do-action [action service]
   (case action
-    :restart (system "s6-svc -r /run/service/%s" service)
-    :restart-all (system "s6-rc -b -d %q; s6-rc-up-tree %q" service service)
-    [:signal n] (system "s6-svc -s %d /run/service/%s" n service)))
+    :restart (system (%% "s6-svc -r /run/service/%s" service))
+    :restart-all (system (%% "s6-rc -b -d %q; s6-rc-up-tree %q" service service))
+    [:signal n] (system (%% "s6-svc -s %d /run/service/%s" n service))))
 
 (fn run []
   (let [{