diff --git a/src/fs-filo-vfs.adb b/src/fs-filo-vfs.adb
index 30f1bca..660a1cf 100644
--- a/src/fs-filo-vfs.adb
+++ b/src/fs-filo-vfs.adb
@@ -9,21 +9,39 @@
    Convention => C
 is
 
+   State : T := Initial;
+
    function C_Mount return int
    is
       Success : Boolean;
    begin
-      Mount (Success);
+      if not Is_Mounted (State) then
+         State := Initial; -- Work around not having an unmount in FILO.
+      end if;
+      Mount (State, Part_Len, Success);
       return (if Success then 1 else 0);
    end C_Mount;
 
    function C_Open (File_Path : Strings.chars_ptr) return int
    is
+      File_Len : File_Length;
       Success : Boolean;
    begin
-      Open (Strings.Value (File_Path), Success);
+      if Is_Mounted (State) and not Is_Open (State) then
+         Open (State, File_Len, Strings.Value (File_Path), Success);
+         Set_File_Max (File_Len);
+      else
+         Success := False;
+      end if;
       return (if Success then 1 else 0);
    end C_Open;
+
+   procedure C_Close is
+   begin
+      if Is_Open (State) then
+         Close (State);
+      end if;
+   end C_Close;
    
    function C_Read (Buf : System.Address; Len : int) return int
    is
@@ -33,9 +51,15 @@
          Convention => C,
          Address => Buf;
 
+      File_Pos : File_Offset := FILO.File_Pos;
       Read_Len : Natural;
    begin
-      Read (Buffer, Read_Len);
+      if Is_Open (State) then
+         Read (State, File_Max, File_Pos, Buffer, Read_Len);
+         Set_File_Pos (File_Pos);
+      else
+         Read_Len := 0;
+      end if;
       return int (Read_Len);
    end C_Read;
 
diff --git a/src/fs-filo-vfs.ads b/src/fs-filo-vfs.ads
index 6115554..2b6dd52 100644
--- a/src/fs-filo-vfs.ads
+++ b/src/fs-filo-vfs.ads
@@ -6,19 +6,53 @@
 
 generic
 
-   with procedure Mount (Success : out Boolean);
+   type T (<>) is private;
 
-   with procedure Open (File_Path : String; Success : out Boolean);
-   with procedure Close with Convention => C;
+   with function Is_Mounted (State : T) return Boolean;
+   with function Is_Open (State : T) return Boolean
+   with
+      Post => (if Is_Open'Result then Is_Mounted (State));
 
-   with procedure Read (Buf : out Buffer_Type; Len : out Natural);
+   Initial : T;
+
+   with procedure Mount
+     (State    : in out T;
+      Part_Len : in     Partition_Length;
+      Success  :    out Boolean)
+   with
+      Pre => not Is_Mounted (State),
+      Post => Success = Is_Mounted (State);
+
+   with procedure Open
+     (State       : in out T;
+      File_Len    :    out File_Length;
+      File_Path   : in     String;
+      Success     : out    Boolean)
+   with
+      Pre => Is_Mounted (State) and not Is_Open (State),
+      Post => Success = Is_Open (State);
+
+   with procedure Close (State : in out T)
+   with
+      Pre => Is_Open (State),
+      Post => Is_Mounted (State);
+
+   with procedure Read
+     (State    : in out T;
+      File_Len : in     File_Length;
+      File_Pos : in out File_Offset;
+      Buf      :    out Buffer_Type;
+      Len      :    out Natural)
+   with
+      Pre => Is_Open (State),
+      Post => Is_Open (State);
 
 package FS.FILO.VFS is
 
    function C_Mount return int;
 
    function C_Open (File_Path : Strings.chars_ptr) return int;
-   procedure C_Close renames Close;
+   procedure C_Close;
    
    function C_Read (Buf : System.Address; Len : int) return int;
 
diff --git a/src/fs-filo.adb b/src/fs-filo.adb
index f92455e..20162fc 100644
--- a/src/fs-filo.adb
+++ b/src/fs-filo.adb
@@ -22,7 +22,7 @@
       Convention     => C,
       External_Name  => "filepos";
 
-   function Part_Length return Partition_Length is (Partition_Length (C_Part_Length));
+   function Part_Len return Partition_Length is (Partition_Length (C_Part_Length));
 
    function File_Max return File_Length is
    begin
diff --git a/src/fs-filo.ads b/src/fs-filo.ads
index b9e5742..fb836fc 100644
--- a/src/fs-filo.ads
+++ b/src/fs-filo.ads
@@ -5,14 +5,14 @@
 
 package FS.FILO is
 
-private
    type Partition_Length is range 0 .. Interfaces.Unsigned_64'Last;
 
-   function Part_Length return Partition_Length;
-
    type File_Length is range 0 .. int'Last; -- Should be higher, fix FILO first
    subtype File_Offset is File_Length range 0 .. File_Length'Last - 1;
 
+private
+   function Part_Len return Partition_Length;
+
    function File_Max return File_Length;
    procedure Set_File_Max (Len : File_Length);