# 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 . # 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) print("") 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 = "" print("Header extension:") print("%-25s %#x" % ("magic", ex.magic)) print("%-25s %d" % ("length", ex.length)) print("%-25s %s" % ("data", data)) print("")