diff --git a/src/fs-filo-ext2.ads b/src/fs-filo-ext2.ads
index d8cc7e9..32e31fe 100644
--- a/src/fs-filo-ext2.ads
+++ b/src/fs-filo-ext2.ads
@@ -42,8 +42,22 @@
 private
    type State is (Unmounted, Mounted, File_Opened);
 
+   -- maximum block size is 64KiB (2^16):
+   subtype Log_Block_Size is Positive range 10 .. 16;
+
+   subtype Inode_Size is Positive range 128 .. Positive (Unsigned_16'Last);
+   subtype Desc_Size  is Positive range  32 .. Positive (Unsigned_16'Last);
+
    type T is record
       S : State;
+      Part_Len          : Partition_Length := 0;
+      First_Data_Block  : Block_Offset := 0;
+      Block_Size_Bits   : Log_Block_Size := 10;
+      Inodes_Per_Group  : Positive := 1;
+      Inode_Size        : Ext2.Inode_Size := Ext2.Inode_Size'First;
+      Desc_Size         : Ext2.Desc_Size := Ext2.Desc_Size'First;
+      Feature_Extents   : Boolean := False;
+      Feature_64Bit     : Boolean := False;
    end record;
 
 end FS.FILO.Ext2;