modules/external-storage: add strictMounts to systemd service options

modules/external-storage/default.nix

@@ -13,6 +13,10 @@ let
 in
 
 {
+  imports = [
+    ./strict-mounts.nix
+  ];
+
   options = {
     services.external-storage = {
       fileSystems = lib.mkOption {

modules/external-storage/filesystem-type.nix

@@ -26,5 +26,9 @@ with lib;
       type = types.str;
       default = "default";
     };
+    dependentServices = mkOption {
+      type = with types; listOf str;
+      default = [];
+    };
   };
 }

modules/external-storage/strict-mounts.nix

@@ -0,0 +1,27 @@
+{ config, lib, ... }:
+
+let
+  cfg = config.services.external-storage;
+in
+
+with lib;
+{
+  options.systemd.services = mkOption {
+    type = with types; attrsOf (submodule ({ config, ... }: {
+      options.strictMounts = mkOption {
+        type = with types; listOf path;
+        default = [];
+      };
+      config = mkIf (config.strictMounts != []) (let
+        findFilesystemsFor = mount: pipe cfg.fileSystems [
+          (filterAttrs (_: fs: hasPrefix "${fs.mountpoint}/" "${mount}/"))
+          (mapAttrsToList (_: fs: "${fs.unitName}.service"))
+        ];
+        services = flatten (map findFilesystemsFor config.strictMounts);
+      in {
+        after = services;
+        bindsTo = services;
+      });
+    }));
+  };
+}