Allow specifying mountpaths and swap usage

lib/modules/partition.nix

@@ -209,6 +209,18 @@
             description = "A script for printing the size to the console.";
             internal = true;
           };
+
+          useSwap = mkOption {
+            type = types.bool;
+            description = "A value indicating whether this partition should be used as swap.";
+            default = isSwap config;
+          };
+
+          mountPoint = mkOption {
+            type = types.nullOr types.str;
+            description = "The mountpoint of the partition.";
+            default = null;
+          };
         };
 
         config = {
@@ -225,6 +237,12 @@
   in {
     options = {
       partition = {
+        rootDir = mkOption {
+          type = types.str;
+          description = "The root of the installation directory to mount disks into.";
+          default = "/mnt";
+        };
+
         os = mkOption {
           type = mkDiskType true;
           description = "The partition layout of the OS disk.";
@@ -270,11 +288,32 @@
 
         script =
           let
-            inherit (config.partition)
+            inherit (config.partition) os rootDir;
-              os
+            inherit (lib.strings) normalizePath;
-              disks
+
-            ;
+            partPath = part: "/dev/disk/by-label/${part.label}";
-          in lib.strings.concatLines (builtins.map (_: _.script) ([os] ++ (builtins.attrValues disks)));
+            disks = ([os] ++ (builtins.attrValues config.partition.disks));
+            partitions = (builtins.concatMap (_: (builtins.attrValues _.partitions)) disks);
+
+            mountScript = lib.strings.concatLines (
+              builtins.map
+                (_: builtins.concatStringsSep " " [
+                  "mount"
+                  (partPath _)
+                  (normalizePath "/${rootDir}/${_.mountPoint}")
+                ])
+                (builtins.filter (_: _.mountPoint != null) partitions));
+
+            swapScript = lib.strings.concatLines (
+              builtins.map
+                (_: "swapon ${partPath _}")
+                (builtins.filter (_: _.useSwap) partitions));
+          in lib.strings.concatLines (
+            (builtins.map (_: _.script) disks) ++ [
+              mountScript
+              swapScript
+            ]
+          );
       };
     };
   }