nixos/lib, nixos/filesystems: Make fsBefore more stable, and add `depends` option

1 files changed, 18 insertions, 2 deletions

diff --git a/nixos/modules/tasks/filesystems.nix b/nixos/modules/tasks/filesystems.nix
index 065d6cc95d18..2949c82df8fe 100644
--- a/nixos/modules/tasks/filesystems.nix
+++ b/nixos/modules/tasks/filesystems.nix
@@ -24,13 +24,15 @@ let
 
   specialFSTypes = [ "proc" "sysfs" "tmpfs" "ramfs" "devtmpfs" "devpts" ];
 
+  nonEmptyWithoutTrailingSlash = addCheckDesc "non-empty without trailing slash" types.str
+    (s: isNonEmpty s && (builtins.match ".+/" s) == null);
+
   coreFileSystemOpts = { name, config, ... }: {
 
     options = {
       mountPoint = mkOption {
         example = "/mnt/usb";
-        type = addCheckDesc "non-empty without trailing slash" types.str
-          (s: isNonEmpty s && (builtins.match ".+/" s) == null);
+        type = nonEmptyWithoutTrailingSlash;
         description = "Location of the mounted the file system.";
       };
 
@@ -55,6 +57,20 @@ let
         type = types.listOf nonEmptyStr;
       };
 
+      depends = mkOption {
+        default = [ ];
+        example = [ "/persist" ];
+        type = types.listOf nonEmptyWithoutTrailingSlash;
+        description = ''
+          List of paths that should be mounted before this one. This filesystem's
+          <option>device</option> and <option>mountPoint</option> are always
+          checked and do not need to be included explicitly. If a path is added
+          to this list, any other filesystem whose mount point is a parent of
+          the path will be mounted before this filesystem. The paths do not need
+          to actually be the <option>mountPoint</option> of some other filesystem.
+        '';
+      };
+
     };
 
     config = {