mirror of https://gitee.com/openkylin/qemu.git
288 lines
8.6 KiB
Python
288 lines
8.6 KiB
Python
# Library for manipulations with qcow2 image
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#
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# Copyright (c) 2020 Virtuozzo International GmbH.
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# Copyright (C) 2012 Red Hat, Inc.
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#
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# This program is free software; you can redistribute it and/or modify
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# it under the terms of the GNU General Public License as published by
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# the Free Software Foundation; either version 2 of the License, or
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# (at your option) any later version.
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#
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# This program is distributed in the hope that it will be useful,
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# but WITHOUT ANY WARRANTY; without even the implied warranty of
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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# GNU General Public License for more details.
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#
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# You should have received a copy of the GNU General Public License
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# along with this program. If not, see <http://www.gnu.org/licenses/>.
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#
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import struct
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import string
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class Qcow2Field:
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def __init__(self, value):
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self.value = value
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def __str__(self):
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return str(self.value)
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class Flags64(Qcow2Field):
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def __str__(self):
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bits = []
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for bit in range(64):
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if self.value & (1 << bit):
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bits.append(bit)
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return str(bits)
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class Enum(Qcow2Field):
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def __str__(self):
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return f'{self.value:#x} ({self.mapping.get(self.value, "<unknown>")})'
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class Qcow2StructMeta(type):
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# Mapping from c types to python struct format
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ctypes = {
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'u8': 'B',
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'u16': 'H',
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'u32': 'I',
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'u64': 'Q'
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}
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def __init__(self, name, bases, attrs):
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if 'fields' in attrs:
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self.fmt = '>' + ''.join(self.ctypes[f[0]] for f in self.fields)
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class Qcow2Struct(metaclass=Qcow2StructMeta):
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"""Qcow2Struct: base class for qcow2 data structures
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Successors should define fields class variable, which is: list of tuples,
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each of three elements:
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- c-type (one of 'u8', 'u16', 'u32', 'u64')
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- format (format_spec to use with .format() when dump or 'mask' to dump
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bitmasks)
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- field name
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"""
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def __init__(self, fd=None, offset=None, data=None):
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"""
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Two variants:
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1. Specify data. fd and offset must be None.
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2. Specify fd and offset, data must be None. offset may be omitted
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in this case, than current position of fd is used.
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"""
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if data is None:
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assert fd is not None
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buf_size = struct.calcsize(self.fmt)
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if offset is not None:
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fd.seek(offset)
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data = fd.read(buf_size)
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else:
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assert fd is None and offset is None
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values = struct.unpack(self.fmt, data)
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self.__dict__ = dict((field[2], values[i])
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for i, field in enumerate(self.fields))
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def dump(self):
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for f in self.fields:
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value = self.__dict__[f[2]]
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if isinstance(f[1], str):
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value_str = f[1].format(value)
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else:
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value_str = str(f[1](value))
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print('{:<25} {}'.format(f[2], value_str))
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class Qcow2BitmapExt(Qcow2Struct):
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fields = (
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('u32', '{}', 'nb_bitmaps'),
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('u32', '{}', 'reserved32'),
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('u64', '{:#x}', 'bitmap_directory_size'),
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('u64', '{:#x}', 'bitmap_directory_offset')
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)
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QCOW2_EXT_MAGIC_BITMAPS = 0x23852875
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class QcowHeaderExtension(Qcow2Struct):
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class Magic(Enum):
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mapping = {
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0xe2792aca: 'Backing format',
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0x6803f857: 'Feature table',
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0x0537be77: 'Crypto header',
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QCOW2_EXT_MAGIC_BITMAPS: 'Bitmaps',
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0x44415441: 'Data file'
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}
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fields = (
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('u32', Magic, 'magic'),
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('u32', '{}', 'length')
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# length bytes of data follows
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# then padding to next multiply of 8
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)
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def __init__(self, magic=None, length=None, data=None, fd=None):
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"""
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Support both loading from fd and creation from user data.
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For fd-based creation current position in a file will be used to read
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the data.
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This should be somehow refactored and functionality should be moved to
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superclass (to allow creation of any qcow2 struct), but then, fields
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of variable length (data here) should be supported in base class
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somehow. Note also, that we probably want to parse different
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extensions. Should they be subclasses of this class, or how to do it
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better? Should it be something like QAPI union with discriminator field
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(magic here). So, it's a TODO. We'll see how to properly refactor this
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when we have more qcow2 structures.
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"""
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if fd is None:
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assert all(v is not None for v in (magic, length, data))
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self.magic = magic
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self.length = length
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if length % 8 != 0:
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padding = 8 - (length % 8)
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data += b'\0' * padding
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self.data = data
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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(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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if self.obj is None:
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data = self.data[:self.length]
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if all(c in string.printable.encode('ascii') for c in data):
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data = f"'{ data.decode('ascii') }'"
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else:
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data = '<binary>'
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print(f'{"data":<25} {data}')
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else:
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self.obj.dump()
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@classmethod
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def create(cls, magic, data):
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return QcowHeaderExtension(magic, len(data), data)
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class QcowHeader(Qcow2Struct):
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fields = (
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# Version 2 header fields
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('u32', '{:#x}', 'magic'),
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('u32', '{}', 'version'),
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('u64', '{:#x}', 'backing_file_offset'),
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('u32', '{:#x}', 'backing_file_size'),
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('u32', '{}', 'cluster_bits'),
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('u64', '{}', 'size'),
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('u32', '{}', 'crypt_method'),
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('u32', '{}', 'l1_size'),
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('u64', '{:#x}', 'l1_table_offset'),
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('u64', '{:#x}', 'refcount_table_offset'),
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('u32', '{}', 'refcount_table_clusters'),
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('u32', '{}', 'nb_snapshots'),
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('u64', '{:#x}', 'snapshot_offset'),
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# Version 3 header fields
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('u64', Flags64, 'incompatible_features'),
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('u64', Flags64, 'compatible_features'),
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('u64', Flags64, 'autoclear_features'),
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('u32', '{}', 'refcount_order'),
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('u32', '{}', 'header_length'),
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)
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def __init__(self, fd):
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super().__init__(fd=fd, offset=0)
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self.set_defaults()
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self.cluster_size = 1 << self.cluster_bits
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fd.seek(self.header_length)
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self.load_extensions(fd)
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if self.backing_file_offset:
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fd.seek(self.backing_file_offset)
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self.backing_file = fd.read(self.backing_file_size)
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else:
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self.backing_file = None
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def set_defaults(self):
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if self.version == 2:
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self.incompatible_features = 0
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self.compatible_features = 0
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self.autoclear_features = 0
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self.refcount_order = 4
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self.header_length = 72
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def load_extensions(self, fd):
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self.extensions = []
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if self.backing_file_offset != 0:
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end = min(self.cluster_size, self.backing_file_offset)
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else:
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end = self.cluster_size
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while fd.tell() < end:
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ext = QcowHeaderExtension(fd=fd)
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if ext.magic == 0:
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break
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else:
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self.extensions.append(ext)
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def update_extensions(self, fd):
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fd.seek(self.header_length)
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extensions = self.extensions
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extensions.append(QcowHeaderExtension(0, 0, b''))
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for ex in extensions:
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buf = struct.pack('>II', ex.magic, ex.length)
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fd.write(buf)
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fd.write(ex.data)
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if self.backing_file is not None:
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self.backing_file_offset = fd.tell()
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fd.write(self.backing_file)
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if fd.tell() > self.cluster_size:
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raise Exception('I think I just broke the image...')
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def update(self, fd):
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header_bytes = self.header_length
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self.update_extensions(fd)
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fd.seek(0)
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header = tuple(self.__dict__[f] for t, p, f in QcowHeader.fields)
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buf = struct.pack(QcowHeader.fmt, *header)
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buf = buf[0:header_bytes-1]
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fd.write(buf)
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def dump_extensions(self):
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for ex in self.extensions:
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print('Header extension:')
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ex.dump()
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print()
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