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# Library for manipulations with qcow2 image
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 2 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program. If not, see <http://www.gnu.org/licenses/>.
#
import struct
import string
class QcowHeaderExtension:
def __init__(self, magic, length, data):
if length % 8 != 0:
padding = 8 - (length % 8)
data += b"\0" * padding
self.magic = magic
self.length = length
self.data = data
@classmethod
def create(cls, magic, data):
return QcowHeaderExtension(magic, len(data), data)
class QcowHeader:
uint32_t = 'I'
uint64_t = 'Q'
fields = [
# Version 2 header fields
[uint32_t, '%#x', 'magic'],
[uint32_t, '%d', 'version'],
[uint64_t, '%#x', 'backing_file_offset'],
[uint32_t, '%#x', 'backing_file_size'],
[uint32_t, '%d', 'cluster_bits'],
[uint64_t, '%d', 'size'],
[uint32_t, '%d', 'crypt_method'],
[uint32_t, '%d', 'l1_size'],
[uint64_t, '%#x', 'l1_table_offset'],
[uint64_t, '%#x', 'refcount_table_offset'],
[uint32_t, '%d', 'refcount_table_clusters'],
[uint32_t, '%d', 'nb_snapshots'],
[uint64_t, '%#x', 'snapshot_offset'],
# Version 3 header fields
[uint64_t, 'mask', 'incompatible_features'],
[uint64_t, 'mask', 'compatible_features'],
[uint64_t, 'mask', 'autoclear_features'],
[uint32_t, '%d', 'refcount_order'],
[uint32_t, '%d', 'header_length'],
]
fmt = '>' + ''.join(field[0] for field in fields)
def __init__(self, fd):
buf_size = struct.calcsize(QcowHeader.fmt)
fd.seek(0)
buf = fd.read(buf_size)
header = struct.unpack(QcowHeader.fmt, buf)
self.__dict__ = dict((field[2], header[i])
for i, field in enumerate(QcowHeader.fields))
self.set_defaults()
self.cluster_size = 1 << self.cluster_bits
fd.seek(self.header_length)
self.load_extensions(fd)
if self.backing_file_offset:
fd.seek(self.backing_file_offset)
self.backing_file = fd.read(self.backing_file_size)
else:
self.backing_file = None
def set_defaults(self):
if self.version == 2:
self.incompatible_features = 0
self.compatible_features = 0
self.autoclear_features = 0
self.refcount_order = 4
self.header_length = 72
def load_extensions(self, fd):
self.extensions = []
if self.backing_file_offset != 0:
end = min(self.cluster_size, self.backing_file_offset)
else:
end = self.cluster_size
while fd.tell() < end:
(magic, length) = struct.unpack('>II', fd.read(8))
if magic == 0:
break
else:
padded = (length + 7) & ~7
data = fd.read(padded)
self.extensions.append(QcowHeaderExtension(magic, length,
data))
def update_extensions(self, fd):
fd.seek(self.header_length)
extensions = self.extensions
extensions.append(QcowHeaderExtension(0, 0, b""))
for ex in extensions:
buf = struct.pack('>II', ex.magic, ex.length)
fd.write(buf)
fd.write(ex.data)
if self.backing_file is not None:
self.backing_file_offset = fd.tell()
fd.write(self.backing_file)
if fd.tell() > self.cluster_size:
raise Exception("I think I just broke the image...")
def update(self, fd):
header_bytes = self.header_length
self.update_extensions(fd)
fd.seek(0)
header = tuple(self.__dict__[f] for t, p, f in QcowHeader.fields)
buf = struct.pack(QcowHeader.fmt, *header)
buf = buf[0:header_bytes-1]
fd.write(buf)
def dump(self):
for f in QcowHeader.fields:
value = self.__dict__[f[2]]
if f[1] == 'mask':
bits = []
for bit in range(64):
if value & (1 << bit):
bits.append(bit)
value_str = str(bits)
else:
value_str = f[1] % value
print("%-25s" % f[2], value_str)
def dump_extensions(self):
for ex in self.extensions:
data = ex.data[:ex.length]
if all(c in string.printable.encode('ascii') for c in data):
data = "'%s'" % data.decode('ascii')
else:
data = "<binary>"
print("Header extension:")
print("%-25s %#x" % ("magic", ex.magic))
print("%-25s %d" % ("length", ex.length))
print("%-25s %s" % ("data", data))
print("")
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