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[PATCH v10 03/10] qcow2_format.py: change Qcow2BitmapExt initialization


From: Andrey Shinkevich
Subject: [PATCH v10 03/10] qcow2_format.py: change Qcow2BitmapExt initialization method
Date: Tue, 14 Jul 2020 00:36:36 +0300

There are two ways to initialize a class derived from Qcow2Struct:
1. Pass a block of binary data to the constructor.
2. Pass the file descriptor to allow reading the file from constructor.
Let's change the Qcow2BitmapExt initialization method from 1 to 2 to
support a scattered reading in the initialization chain.
The implementation comes with the patch that follows.

Suggested-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Signed-off-by: Andrey Shinkevich <andrey.shinkevich@virtuozzo.com>
---
 tests/qemu-iotests/qcow2_format.py | 33 +++++++++++++++++++--------------
 1 file changed, 19 insertions(+), 14 deletions(-)

diff --git a/tests/qemu-iotests/qcow2_format.py 
b/tests/qemu-iotests/qcow2_format.py
index 2f3681b..cbaffc4 100644
--- a/tests/qemu-iotests/qcow2_format.py
+++ b/tests/qemu-iotests/qcow2_format.py
@@ -113,6 +113,11 @@ class Qcow2BitmapExt(Qcow2Struct):
         ('u64', '{:#x}', 'bitmap_directory_offset')
     )
 
+    def __init__(self, fd):
+        super().__init__(fd=fd)
+        pad = (struct.calcsize(self.fmt) + 7) & ~7
+        if pad:
+            fd.seek(pad, 1)
 
 QCOW2_EXT_MAGIC_BITMAPS = 0x23852875
 
@@ -161,21 +166,21 @@ class QcowHeaderExtension(Qcow2Struct):
         else:
             assert all(v is None for v in (magic, length, data))
             super().__init__(fd=fd)
-            padded = (self.length + 7) & ~7
-            self.data = fd.read(padded)
-            assert self.data is not None
-
-        data_str = self.data[:self.length]
-        if all(c in string.printable.encode('ascii') for c in data_str):
-            data_str = f"'{ data_str.decode('ascii') }'"
-        else:
-            data_str = '<binary>'
-        self.data_str = data_str
+            if self.magic == QCOW2_EXT_MAGIC_BITMAPS:
+                self.obj = Qcow2BitmapExt(fd=fd)
+            else:
+                padded = (self.length + 7) & ~7
+                self.data = fd.read(padded)
+                assert self.data is not None
+                self.obj = None
+                data_str = self.data[:self.length]
+                if all(c in string.printable.encode(
+                    'ascii') for c in data_str):
+                    data_str = f"'{ data_str.decode('ascii') }'"
+                else:
+                    data_str = '<binary>'
+                self.data_str = data_str
 
-        if self.magic == QCOW2_EXT_MAGIC_BITMAPS:
-            self.obj = Qcow2BitmapExt(data=self.data)
-        else:
-            self.obj = None
 
     def dump(self):
         super().dump()
-- 
1.8.3.1




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