Add a separate option for mounts

lib/modules/fileSystems.nix

@@ -2,14 +2,53 @@
 let
   inherit (lib) types mkOption;
   cfg = config.valhalla.fileSystems;
-in {
+
+  mountType = types.submodule (
+    { config, name, ... }: {
+      options = {
+        device = mkOption {
+          type = types.nullOr types.str;
+          description = "The device to mount.";
+          default = null;
+        };
+
+        mountPoint = mkOption {
+          type = types.str;
+          description = "The path to mount the device to.";
+          default = name;
+        };
+
+        fsType = mkOption {
+          type = types.nullOr types.str;
+          description = "The file system type of the mount.";
+          default = null;
+        };
+
+        options = mkOption {
+          type = types.listOf types.str;
+          description = "The options of the mount.";
+          default = [ ];
+        };
+      };
+    }
+  );
+in
+{
   imports = [
+    ./fileSystems/btrfs.nix
     ./fileSystems/disks.nix
   ];
 
   options = {
     valhalla = {
+
       fileSystems = {
+        mounts = mkOption {
+          type = types.attrsOf mountType;
+          description = "The devices to mount.";
+          default = { };
+        };
+
         script = mkOption {
           type = types.str;
           description = "The script for preparing the system's mounts.";
@@ -21,9 +60,11 @@ in {
   config = {
     valhalla = {
       fileSystems = {
-        script = let
+        script =
+          let
             devices = (builtins.attrValues cfg.diskSetup.devices);
-        in ''
+          in
+          ''
             #!/bin/bash
             set -o errexit
             ${cfg.diskSetup.scripts.init}

lib/modules/fileSystems/disks.nix

@@ -4,6 +4,7 @@ let
 
   fs = import ./fs.nix;
 
+  cfg = config.valhalla.fileSystems;
   deviceListVarName = "myDevices";
   isSwap = partition: builtins.elem partition.type [ fs.swap 19 ];
 
@@ -333,10 +334,28 @@ in
 
   config = {
     valhalla = {
-      fileSystems.diskSetup = {
+      fileSystems = {
+        mounts = (lib.attrsets.concatMapAttrs
+          (
+            name: device:
+              lib.attrsets.concatMapAttrs
+                (
+                  name: partition:
+                    if partition.mountPoint != null then {
+                      ${partition.mountPoint} = {
+                        device = "/dev/disk/by-label/${partition.label}";
+                        fsType = partition.format;
+                        options = partition.mountOptions;
+                      };
+                    } else { }
+                )
+                device.partitions
+          )
+          cfg.diskSetup.devices);
+
+        diskSetup = {
           scripts =
             let
-            cfg = config.valhalla.fileSystems;
               inherit (cfg) rootDir;
               inherit (lib.strings) normalizePath;
               partPath = part: "/dev/disk/by-label/${part.label}";
@@ -378,4 +397,5 @@ in
         };
       };
     };
+  };
 }