diff --git a/src/filo-fs-iso9660.adb b/src/filo-fs-iso9660.adb
new file mode 100644
index 0000000..8c1b441
--- /dev/null
+++ b/src/filo-fs-iso9660.adb
@@ -0,0 +1,381 @@
+-- Copyright (C) 2024 secunet Security Networks AG
+--
+-- This program is free software; you can redistribute it and/or modify
+-- it under the terms of the GNU General Public License as published by
+-- the Free Software Foundation; either version 2 of the License, or
+-- (at your option) any later version.
+
+with System;
+with Interfaces;
+with Interfaces.C;
+
+with FILO.Blockdev;
+with FILO.FS.VFS;
+
+use Interfaces.C;
+
+package body FILO.FS.ISO9660 is
+
+   function Is_Mounted (State : T) return Boolean is (State.S >= Mounted);
+   function Is_Open (State : T) return Boolean is (State.S = File_Opened);
+
+   --------------------------------------------------------------------------
+
+   procedure Read
+     (Buf      : in out Buffer_Type;
+      Block    : in     FSBlock;
+      Offset   : in     FSBlock_Index;
+      FS_Len   : in     Partition_Length;
+      Success  :    out Boolean)
+   with
+      Pre => Buf'Length <= FSBlock_Size - Offset
+   is
+      Block_64 : constant Integer_64 := Integer_64 (Block);
+      Offset_64 : constant Integer_64 := Integer_64 (Offset);
+      Max_Block_Offset : constant Integer_64 := Integer_64 (FS_Len) / FSBlock_Size - 1;
+   begin
+      if Block_64 > Max_Block_Offset then
+         Success := False;
+         return;
+      end if;
+      Blockdev.Read (Buf, Blockdev_Length (Block_64 * FSBlock_Size + Offset_64), Success);
+   end Read;
+
+   procedure Mount
+     (State    : in out T;
+      Part_Len : in     Partition_Length;
+      Success  :    out Boolean)
+   is
+      D_Type   : constant Index_Type := 0;
+      D_Id     : constant Index_Type := 1;
+      D_Ver    : constant Index_Type := 6;
+
+      D_Type_Primary    : constant := 1;
+      D_Type_Terminator : constant := 255;
+
+      CD001 : constant Buffer_Type :=
+        (Character'Pos ('C'), Character'Pos ('D'),
+         Character'Pos ('0'), Character'Pos ('0'), Character'Pos ('1'));
+
+      Static : Mount_State renames State.Static;
+
+      Volume_Descriptor : Buffer_Type (0 .. 190 - 1);
+      Block : FSBlock := 32;
+   begin
+      loop
+         pragma Loop_Invariant (Block < 1024);
+
+         if Part_Len < Partition_Length (Block + 1) * FSBlock_Size then
+            Success := False;
+            return;
+         end if;
+
+         Read (Volume_Descriptor (0 .. D_Ver), Block, 0, Part_Len, Success);
+         if not Success then
+            return;
+         end if;
+
+         if Volume_Descriptor (D_Ver) /= 1 or
+            Volume_Descriptor (D_Id .. D_Ver - 1) /= CD001 or
+            Volume_Descriptor (D_Type) = D_Type_Terminator
+         then
+            return;
+         end if;
+
+         exit when Volume_Descriptor (D_Type) = D_Type_Primary;
+
+         Block := Block + 1;
+         if Block >= 1024 then
+            return;
+         end if;
+      end loop;
+
+      Static.Part_Len := Part_Len;
+      Static.Root_Inode := (Block, 156);
+
+      State.S := Mounted;
+   end Mount;
+
+   procedure Open
+     (State    : in out T;
+      I        : in     Inode_Index;
+      Success  : out Boolean)
+   with
+      Pre => Is_Mounted (State),
+      Post => Is_Mounted (State) and (Success = Is_Open (State))
+   is
+      Static : Mount_State renames State.Static;
+      Inode : Inode_Info renames State.Inode;
+
+      Dir_Rec : Directory_Record;
+   begin
+      Inode := (I, others => <>);
+
+      Read (Dir_Rec, I.Block, I.Offset, Static.Part_Len, Success);
+      if not Success then
+         return;
+      end if;
+
+      declare
+         D_Flag_Dir  : constant := 16#02#;
+         D_Flag_Cont : constant := 16#80#;
+         D_Flags : constant Unsigned_8 := Dir_Rec (25);
+      begin
+         if (D_Flags and D_Flag_Cont) /= 0 then
+            Success := False;
+            return;
+         end if;
+         if (D_Flags and D_Flag_Dir) /= 0 then
+            Inode.Mode := Dir;
+         else
+            Inode.Mode := Regular;
+         end if;
+         Inode.Size := Inode_Length (Read_LE32 (Dir_Rec, 10));
+         Inode.Extents (0) :=
+           (Start => FSBlock (Read_LE32 (Dir_Rec, 2)),
+            Count => FSBlock_Count (Inode.Size / Inode_Length (FSBlock_Size)));
+         State.S := File_Opened;
+      end;
+   end Open;
+
+   procedure Open
+     (State       : in out T;
+      File_Len    :    out File_Length;
+      File_Type   :    out FS.File_Type;
+      File_Name   : in     String;
+      In_Root     : in     Boolean;
+      Success     : out    Boolean)
+   is
+      File_Name_Max : constant := 255;
+
+      function Str_Buf_Equal (Str : String; Buf : Buffer_Type) return Boolean
+      with
+         Pre => Str'Length <= Buf'Length
+      is
+      begin
+         for I in Str'Range loop
+            if Character'Pos (Str (I)) /= Buf (Buf'First + (I - Str'First)) then
+               return False;
+            end if;
+         end loop;
+         return True;
+      end Str_Buf_Equal;
+
+      Found_Inode : Inode_Index;
+      Dir_Pos : File_Length;
+   begin
+      File_Len := 0;
+      File_Type := FS.File_Type'First;
+
+      if File_Name'Length > File_Name_Max then
+         Success := False;
+         return;
+      end if;
+
+      -- Ensure dir is opened:
+      --
+      if State.S = File_Opened then
+         if State.Cur_Dir /= State.Inode.I then
+            Success := False;
+            return;
+         end if;
+      else
+         if In_Root then
+            State.Cur_Dir := State.Static.Root_Inode;
+         end if;
+         declare
+            Cur_Dir : constant Inode_Index := State.Cur_Dir;
+         begin
+            Open (State, Cur_Dir, Success);
+            if not Success then
+               return;
+            end if;
+         end;
+      end if;
+
+      -- Lookup file in opened dir:
+      --
+      Dir_Pos := 0;
+      Success := False;
+      loop
+         pragma Loop_Invariant (Is_Open (State) and not Success);
+         declare
+            Dir_Rec : Directory_Record;
+            Dir_Rec_Name : Buffer_Type (0 .. File_Name_Max - 1);
+            Record_Dir_Pos : File_Offset := Dir_Pos;
+            Dir_Rec_Length : File_Length;
+            Inode : Inode_Index;
+            Len : Natural;
+         begin
+            Read
+              (State    => State,
+               File_Pos => Record_Dir_Pos,
+               Buf      => Dir_Rec,
+               Len      => Len);
+            if Len < Dir_Rec'Length then
+               return;
+            end if;
+
+            -- FIXME: need to strip trailing . and file version
+            if File_Name'Length = Natural (Dir_Rec (32)) then
+               pragma Warnings
+                 (GNATprove, Off, """Record_Dir_Pos"" is set*but not used",
+                  Reason => "We only care about intermedidate values.");
+               Read
+                 (State    => State,
+                  File_Pos => Record_Dir_Pos,
+                  Buf      => Dir_Rec_Name,
+                  Len      => Len);
+               pragma Warnings (GNATprove, On, """Record_Dir_Pos"" is set*but not used");
+               if Len < File_Name'Length then
+                  return;
+               end if;
+
+               Success := Str_Buf_Equal (File_Name, Dir_Rec_Name);
+               if Success then
+                  Found_Inode :=
+                    (Block => FSBlock (Dir_Pos / FSBlock_Size),
+                     Offset => FSBlock_Index (Dir_Pos mod FSBlock_Size));
+                  exit;
+               end if;
+            end if;
+
+            Dir_Rec_Length := File_Length (Dir_Rec (0));
+            if Dir_Rec_Length = 0 or
+               Dir_Pos > File_Length'Last - Dir_Rec_Length or
+               Unsigned_64 (Dir_Pos) >= Unsigned_64 (State.Inode.Size) - Unsigned_64 (Dir_Rec_Length)
+            then
+               return;
+            end if;
+            Dir_Pos := Dir_Pos + Dir_Rec_Length;
+         end;
+      end loop;
+      pragma Assert_And_Cut (Success and Is_Mounted (State));
+
+      Open (State, Found_Inode, Success);
+      if not Success then
+         return;
+      end if;
+
+      if State.Inode.Mode = Dir then
+         State.Cur_Dir := Found_Inode;
+      end if;
+
+      --Success := State.Inode.Size <= Inode_Length (File_Length'Last);
+      if Success then
+         File_Len := File_Length (State.Inode.Size);
+         File_Type := State.Inode.Mode;
+      else
+         Close (State);
+      end if;
+   end Open;
+
+   procedure Close (State : in out T) is
+   begin
+      State.S := Mounted;
+   end Close;
+
+   procedure Read
+     (State    : in out T;
+      File_Pos : in out File_Offset;
+      Buf      :    out Buffer_Type;
+      Len      :    out Natural)
+   is
+      Static : Mount_State renames State.Static;
+
+      Pos : Natural range Buf'First .. Buf'Last + 1;
+   begin
+      Len := 0;
+      Pos := Buf'First;
+      while Pos <= Buf'Last and
+            File_Pos < File_Offset'Last and
+            Inode_Length (File_Pos) < State.Inode.Size
+      loop
+         pragma Loop_Invariant (Is_Open (State));
+         declare
+            In_Block : constant FSBlock_Index := Natural (File_Pos mod FSBlock_Size);
+            Logical : constant FSBlock_Logical := FSBlock_Logical (File_Pos / FSBlock_Size);
+            In_Block_Space : constant Positive := Index_Type (FSBlock_Size) - In_Block;
+            In_File_Space : constant Inode_Length := State.Inode.Size - Inode_Length (File_Pos);
+            In_Buf_Space : constant Positive := Buf'Last - Pos + 1;
+            Len_Here : Positive;
+         begin
+            exit when FSBlock (Logical) > FSBlock'Last - State.Inode.Extents (0).Start;
+
+            Len_Here := In_Block_Space;
+            if In_File_Space < Inode_Length (Len_Here) then
+               Len_Here := Positive (In_File_Space);
+            end if;
+            if In_Buf_Space < Len_Here then
+               Len_Here := In_Buf_Space;
+            end if;
+            if File_Offset'Last - File_Pos < File_Length (Len_Here) then
+               Len_Here := Positive (File_Offset'Last - File_Pos);
+            end if;
+
+            declare
+               Last : constant Index_Type := Pos + Len_Here - 1;
+               Physical : constant FSBlock := State.Inode.Extents (0).Start + FSBlock (Logical);
+               Success : Boolean;
+            begin
+               Read
+                 (Buf      => Buf (Pos .. Last),
+                  Block    => Physical,
+                  Offset   => In_Block,
+                  FS_Len   => Static.Part_Len,
+                  Success  => Success);
+               exit when not Success;
+
+               File_Pos := File_Pos + File_Length (Len_Here);
+               Pos := Pos + Len_Here;
+               Len := Pos - Buf'First;
+            end;
+         end;
+      end loop;
+      Buf (Pos .. Buf'Last) := (others => 16#00#);
+   end Read;
+
+   --------------------------------------------------------------------------
+
+   package C is new VFS (T => T, Initial => (S => Unmounted, others => <>));
+
+   function C_Mount return int
+   with
+      Export,
+      Convention => C,
+      External_Name => "iso9660_mount";
+   function C_Mount return int
+   with
+      SPARK_Mode => Off
+   is
+   begin
+      return C.C_Mount;
+   end C_Mount;
+
+   function C_Open (File_Path : System.Address) return int
+   with
+      Export,
+      Convention => C,
+      External_Name => "iso9660_dir";
+   function C_Open (File_Path : System.Address) return int
+   with
+      SPARK_Mode => Off
+   is
+   begin
+      return C.C_Open (File_Path);
+   end C_Open;
+
+   function C_Read (Buf : System.Address; Len : int) return int
+   with
+      Export,
+      Convention => C,
+      External_Name => "iso9660_read";
+   function C_Read (Buf : System.Address; Len : int) return int
+   with
+      SPARK_Mode => Off
+   is
+   begin
+      return C.C_Read (Buf, Len);
+   end C_Read;
+
+end FILO.FS.ISO9660;
diff --git a/src/filo-fs-iso9660.ads b/src/filo-fs-iso9660.ads
new file mode 100644
index 0000000..dd82d74
--- /dev/null
+++ b/src/filo-fs-iso9660.ads
@@ -0,0 +1,90 @@
+package FILO.FS.ISO9660 is
+
+   type T is private;
+
+   function Is_Mounted (State : T) return Boolean;
+   function Is_Open (State : T) return Boolean
+   with
+      Post => (if Is_Open'Result then Is_Mounted (State));
+
+   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);
+
+   procedure Open
+     (State       : in out T;
+      File_Len    :    out File_Length;
+      File_Type   :    out FS.File_Type;
+      File_Name   : in     String;
+      In_Root     : in     Boolean;
+      Success     : out    Boolean)
+   with
+      Pre => Is_Mounted (State),
+      Post => (if Success then Is_Open (State) else Is_Mounted (State));
+
+   procedure Close (State : in out T)
+   with
+      Pre => Is_Open (State),
+      Post => Is_Mounted (State);
+
+   procedure Read
+     (State    : in out T;
+      File_Pos : in out File_Offset;
+      Buf      :    out Buffer_Type;
+      Len      :    out Natural)
+   with
+      Pre => Is_Open (State) and Buf'Length > 0,
+      Post => Is_Open (State);
+
+private
+   type State is (Unmounted, Mounted, File_Opened);
+
+   FSBlock_Size : constant := 2048;
+   subtype FSBlock_Index is Index_Type range 0 .. FSBlock_Size - 1;
+
+   type FSBlock_Count is range 0 .. 2 ** 32 - 1;
+   subtype FSBlock is FSBlock_Count range 0 .. FSBlock_Count'Last - 1;
+   type FSBlock_Logical is new FSBlock;
+
+   subtype Directory_Record_Range is Index_Type range 0 .. 32;
+   subtype Directory_Record is Buffer_Type (Directory_Record_Range);
+
+   -- We'll use the absolute position of the dir record
+   type Inode_Index is record
+      Block : FSBlock := 0;
+      Offset : FSBlock_Index := 0;
+   end record;
+   type Inode_Length is range 0 .. FSBlock_Count'Last * FSBlock_Size;
+
+   type Mount_State is record
+      Part_Len    : Partition_Length := 0;
+      Root_Inode  : Inode_Index := (others => <>);
+   end record;
+
+   type Extent is record
+      Start : FSBlock := 0;
+      Count : FSBlock_Count := 0;
+   end record;
+
+   type Extent_Range is range 0 .. 0; -- Linux allows 100 "file sections"
+   type Extents is array (Extent_Range) of Extent;
+
+   type Inode_Info is record
+      I        : Inode_Index := (others => <>);
+      Mode     : File_Type := File_Type'First;
+      Size     : Inode_Length := 0;
+      Extents  : ISO9660.Extents := (Extent_Range => (others => <>));
+   end record;
+
+   type T is record
+      Static   : Mount_State  := (others => <>);
+      S        : State;
+      Inode    : Inode_Info := (others => <>);
+      Cur_Dir  : Inode_Index := (others => <>);
+   end record;
+
+end FILO.FS.ISO9660;
diff --git a/src/vfs.c b/src/vfs.c
index 943fea4..03e9374 100644
--- a/src/vfs.c
+++ b/src/vfs.c
@@ -12,6 +12,7 @@
 	int (*close_func) (void);
 } static const fsys_table[] = {
 	{ "ext2", ext2fs_mount, ext2fs_read, ext2fs_dir, NULL },
+	{ "iso9660", iso9660_mount, iso9660_read, iso9660_dir, NULL },
 };
 
 static const size_t fsys_table_length = sizeof(fsys_table) / sizeof(fsys_table[0]);
diff --git a/src/vfs.h b/src/vfs.h
index d811def..cff04cd 100644
--- a/src/vfs.h
+++ b/src/vfs.h
@@ -31,5 +31,8 @@
 int ext2fs_mount(void);
 int ext2fs_read(char *buf, int len);
 int ext2fs_dir(char *path);
+int iso9660_mount(void);
+int iso9660_read(char *buf, int len);
+int iso9660_dir(char *path);
 
 #endif /* VFS_H */
diff --git a/ext2-test.sh b/test.sh
similarity index 90%
rename from ext2-test.sh
rename to test.sh
index 504d8d3..8a594a8 100755
--- a/ext2-test.sh
+++ b/test.sh
@@ -7,7 +7,7 @@
 
 build=${PWD}/build
 
-test() {
+test_ext2() {
 	type=$1
 	img=${tmp}/${type}.img
 
@@ -70,6 +70,27 @@
 
 	sudo umount ${mnt}
 
+	test_img ${img}
+}
+
+test_isofs() {
+	img=${tmp}/test.iso
+	template=${tmp}/ext2.img
+
+	printf "\n===> Prepping \`${img}'\n"
+
+	sudo mount -o loop ${template} ${mnt} -o ro
+
+	mkisofs -o ${img} ${mnt}
+
+	sudo umount ${mnt}
+
+	test_img ${img}
+}
+
+test_img() {
+	img=$1
+
 	sudo mount -o loop ${img} ${mnt} -o ro
 	cd ${mnt}
 
@@ -97,5 +118,6 @@
 	sudo umount ${mnt}
 }
 
-test ext2
-test ext4
+test_ext2 ext2
+test_ext2 ext4
+test_isofs