We are going to move field-parsing to super-class, this will be simpler with simple string specifiers instead of variables. For some reason, python doesn't allow the definition of ctypes variable in the class alongside fields: it would not be available then for use by the 'for' operator. Don't worry: ctypes will be moved to metaclass soon. Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> Reviewed-by: Andrey Shinkevich <andrey.shinkevich@virtuozzo.com> Message-Id: <20200606081806.23897-8-vsementsov@virtuozzo.com> Signed-off-by: Eric Blake <eblake@redhat.com>
179 lines
5.3 KiB
Python
179 lines
5.3 KiB
Python
# Library for manipulations with qcow2 image
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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 QcowHeaderExtension:
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def __init__(self, magic, length, data):
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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.magic = magic
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self.length = length
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self.data = data
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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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# 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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class QcowHeader:
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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', 'mask', 'incompatible_features'),
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('u64', 'mask', 'compatible_features'),
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('u64', 'mask', 'autoclear_features'),
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('u32', '{}', 'refcount_order'),
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('u32', '{}', 'header_length'),
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)
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fmt = '>' + ''.join(ctypes[f[0]] for f in fields)
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def __init__(self, fd):
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buf_size = struct.calcsize(QcowHeader.fmt)
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fd.seek(0)
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buf = fd.read(buf_size)
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header = struct.unpack(QcowHeader.fmt, buf)
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self.__dict__ = dict((field[2], header[i])
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for i, field in enumerate(QcowHeader.fields))
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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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(magic, length) = struct.unpack('>II', fd.read(8))
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if magic == 0:
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break
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else:
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padded = (length + 7) & ~7
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data = fd.read(padded)
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self.extensions.append(QcowHeaderExtension(magic, length,
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data))
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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(self):
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for f in QcowHeader.fields:
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value = self.__dict__[f[2]]
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if f[1] == 'mask':
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bits = []
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for bit in range(64):
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if value & (1 << bit):
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bits.append(bit)
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value_str = str(bits)
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else:
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value_str = f[1].format(value)
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print(f'{f[2]:<25} {value_str}')
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def dump_extensions(self):
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for ex in self.extensions:
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data = ex.data[:ex.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('Header extension:')
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print(f'{"magic":<25} {ex.magic:#x}')
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print(f'{"length":<25} {ex.length}')
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print(f'{"data":<25} {data}')
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print()
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