diff --git a/tests/qemu-iotests/qcow2.py b/tests/qemu-iotests/qcow2.py
index 40241b1..773c947 100755
--- a/tests/qemu-iotests/qcow2.py
+++ b/tests/qemu-iotests/qcow2.py
@@ -15,7 +15,20 @@ class QcowHeaderExtension:
     def create(cls, magic, data):
         return QcowHeaderExtension(magic, len(data), data)
 
-class Qcow:
+class ImageFile:
+    def __init__(self, fd, fields):
+        self.__dict__ = fields
+        self.fd = fd
+
+    def raw_pread(self, offset, size):
+        self.fd.seek(offset)
+        return self.fd.read(size)
+
+    def raw_pwrite(self, offset, data):
+        self.fd.seek(offset)
+        return self.fd.write(data)
+
+class Qcow(ImageFile):
 
     uint32_t = 'I'
     uint64_t = 'Q'
@@ -54,18 +67,19 @@ class Qcow:
         buf = fd.read(buf_size)
 
         header = struct.unpack(Qcow.HEADER_FMT, buf)
-        self.__dict__ = dict((field[2], header[i])
+        fields = dict((field[2], header[i])
             for i, field in enumerate(Qcow.fields))
 
+        ImageFile.__init__(self, fd, fields)
         self.set_defaults()
         self.cluster_size = 1 << self.cluster_bits
 
         fd.seek(self.header_length)
-        self.load_extensions(fd)
+        self.load_extensions()
 
         if self.backing_file_offset:
-            fd.seek(self.backing_file_offset)
-            self.backing_file = fd.read(self.backing_file_size)
+            self.backing_file = self.raw_pread(self.backing_file_offset,
+                                               self.backing_file_size)
         else:
             self.backing_file = None
 
@@ -77,7 +91,7 @@ class Qcow:
             self.refcount_order = 4
             self.header_length = 72
 
-    def load_extensions(self, fd):
+    def load_extensions(self):
         self.extensions = []
 
         if self.backing_file_offset != 0:
@@ -85,43 +99,41 @@ class Qcow:
         else:
             end = self.cluster_size
 
-        while fd.tell() < end:
-            (magic, length) = struct.unpack('>II', fd.read(8))
+        while self.fd.tell() < end:
+            (magic, length) = struct.unpack('>II', self.fd.read(8))
             if magic == 0:
                 break
             else:
                 padded = (length + 7) & ~7
-                data = fd.read(padded)
+                data = self.fd.read(padded)
                 self.extensions.append(QcowHeaderExtension(magic, length, data))
 
-    def update_extensions(self, fd):
+    def update_extensions(self):
 
-        fd.seek(self.header_length)
+        self.fd.seek(self.header_length)
         extensions = self.extensions
         extensions.append(QcowHeaderExtension(0, 0, ""))
         for ex in extensions:
             buf = struct.pack('>II', ex.magic, ex.length)
-            fd.write(buf)
-            fd.write(ex.data)
+            self.fd.write(buf)
+            self.fd.write(ex.data)
 
         if self.backing_file != None:
-            self.backing_file_offset = fd.tell()
-            fd.write(self.backing_file)
+            self.backing_file_offset = self.fd.tell()
+            self.fd.write(self.backing_file)
 
-        if fd.tell() > self.cluster_size:
+        if self.fd.tell() > self.cluster_size:
             raise Exception("I think I just broke the image...")
 
-
-    def update(self, fd):
+    def update(self):
         header_bytes = self.header_length
 
-        self.update_extensions(fd)
+        self.update_extensions()
 
-        fd.seek(0)
         header = tuple(self.__dict__[f] for t, p, f in Qcow.fields)
         buf = struct.pack(Qcow.HEADER_FMT, *header)
         buf = buf[0:header_bytes-1]
-        fd.write(buf)
+        self.raw_pwrite(0, buf)
 
     def dump(self):
         for f in Qcow.fields:
@@ -158,7 +170,7 @@ def cmd_add_header_ext(fd, magic, data):
 
     h = Qcow(fd)
     h.extensions.append(QcowHeaderExtension.create(magic, data))
-    h.update(fd)
+    h.update()
 
 def cmd_del_header_ext(fd, magic):
     try:
@@ -179,7 +191,7 @@ def cmd_del_header_ext(fd, magic):
         print "No such header extension"
         return
 
-    h.update(fd)
+    h.update()
 
 def cmd_set_feature_bit(fd, group, bit):
     try:
@@ -201,7 +213,7 @@ def cmd_set_feature_bit(fd, group, bit):
         print "'%s' is not a valid group, try 'incompatible', 'compatible', or 'autoclear'" % group
         sys.exit(1)
 
-    h.update(fd)
+    h.update()
 
 cmds = [
     [ 'dump-header',    cmd_dump_header,    0, 'Dump image header and header extensions' ],
