[Qemu-devel] [RFC PATCH 4/5] qcow2.py: add method to load backing image

[Paolo Bonzini <pbonzini@redhat.com>]

This also adds support for raw ImageFiles.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 tests/qemu-iotests/qcow2.py | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/tests/qemu-iotests/qcow2.py b/tests/qemu-iotests/qcow2.py
index 77e03cb..77a9d52 100755
--- a/tests/qemu-iotests/qcow2.py
+++ b/tests/qemu-iotests/qcow2.py
@@ -19,12 +19,22 @@ class QcowHeaderExtension:
 class ImageFile:
     def __init__(self, fd, fields):
         self.__dict__ = fields
+        if 'backing_file' not in fields:
+            self.backing_file = None
+        self.backing_image = None
         self.fd = fd
 
     def close(self):
         self.fd.close()
         self.fd = None
 
+    def open_backing_image(self, mode='rb'):
+        if not self.backing_image:
+            if self.backing_file:
+                self.backing_image = load_image(self.backing_file, mode,
+                                                self.backing_format)
+        return None
+
     def raw_pread(self, offset, size):
         self.fd.seek(offset)
         return self.fd.read(size)
@@ -33,6 +43,10 @@ class ImageFile:
         self.fd.seek(offset)
         return self.fd.write(data)
 
+class Raw(ImageFile):
+    def __init__(self, fd):
+        size = os.fstat(fd.fileno()).st_size
+        ImageFile.__init__(self, fd, dict(size=size))
 
 class Qcow(ImageFile):
 
@@ -65,6 +79,8 @@ class Qcow(ImageFile):
 
     HEADER_FMT = '>' + ''.join(field[0] for field in fields)
     QCOW_MAGIC = 0x514649fb
+    EXT_BACKING_FORMAT = 0xE2792ACA
+    EXT_FEATURE_NAMES = 0x6803f857
 
     def __init__(self, fd):
 
@@ -93,6 +109,8 @@ class Qcow(ImageFile):
         else:
             self.backing_file = None
 
+        self.backing_format = self.get_extension(Qcow.EXT_BACKING_FORMAT)
+
     def set_defaults(self):
         if self.version == 2:
             self.incompatible_features = 0
@@ -135,6 +153,12 @@ class Qcow(ImageFile):
         if self.fd.tell() > self.cluster_size:
             raise Exception("I think I just broke the image...")
 
+    def get_extension(self, magic):
+        for ex in self.extensions:
+            if ex.magic == magic:
+                return ex.data
+        return None
+
     def update(self):
         header_bytes = self.header_length
 
@@ -178,6 +202,8 @@ def load_image(filename, mode='rb', format=None):
 
     if format == 'qcow2':
         return Qcow(fd)
+    elif format == 'raw':
+        return Raw(fd)
 
     raise Error('unknown format %s' % format)
 
-- 
1.8.2