qcow2_format.py: change Qcow2BitmapExt initialization method
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> Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> Message-Id: <1596742557-320265-4-git-send-email-andrey.shinkevich@virtuozzo.com> Signed-off-by: Eric Blake <eblake@redhat.com>
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@ -113,6 +113,11 @@ class Qcow2BitmapExt(Qcow2Struct):
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('u64', '{:#x}', 'bitmap_directory_offset')
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)
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def __init__(self, fd):
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super().__init__(fd=fd)
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tail = struct.calcsize(self.fmt) % 8
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if tail:
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fd.seek(8 - tail, 1)
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QCOW2_EXT_MAGIC_BITMAPS = 0x23852875
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@ -161,21 +166,24 @@ class QcowHeaderExtension(Qcow2Struct):
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else:
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assert all(v is None for v in (magic, length, data))
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super().__init__(fd=fd)
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padded = (self.length + 7) & ~7
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self.data = fd.read(padded)
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assert self.data is not None
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if self.magic == QCOW2_EXT_MAGIC_BITMAPS:
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self.obj = Qcow2BitmapExt(fd=fd)
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self.data = None
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else:
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padded = (self.length + 7) & ~7
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self.data = fd.read(padded)
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assert self.data is not None
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self.obj = None
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data_str = self.data[:self.length]
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if all(c in string.printable.encode('ascii') for c in data_str):
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data_str = f"'{ data_str.decode('ascii') }'"
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else:
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data_str = '<binary>'
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self.data_str = data_str
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if self.data is not None:
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data_str = self.data[:self.length]
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if all(c in string.printable.encode(
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'ascii') for c in data_str):
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data_str = f"'{ data_str.decode('ascii') }'"
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else:
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data_str = '<binary>'
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self.data_str = data_str
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if self.magic == QCOW2_EXT_MAGIC_BITMAPS:
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self.obj = Qcow2BitmapExt(data=self.data)
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else:
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self.obj = None
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def dump(self):
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super().dump()
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