@@ -1,5 +1,7 @@
# Library for manipulations with qcow2 image
#
+# Copyright (c) 2020 Virtuozzo International GmbH.
+#
# 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
@@ -18,6 +20,68 @@ import struct
import string
+class Qcow2StructMeta(type):
+
+ # Mapping from c types to python struct format
+ ctypes = {
+ 'u8': 'B',
+ 'u16': 'H',
+ 'u32': 'I',
+ 'u64': 'Q'
+ }
+
+ def __init__(self, name, bases, attrs):
+ if 'fields' in attrs:
+ self.fmt = '>' + ''.join(self.ctypes[f[0]] for f in self.fields)
+
+
+class Qcow2Struct(metaclass=Qcow2StructMeta):
+
+ """Qcow2Struct: base class for qcow2 data structures
+
+ Successors should define fields class variable, which is: list of tuples,
+ each of three elements:
+ - c-type (one of 'u8', 'u16', 'u32', 'u64')
+ - format (format_spec to use with .format() when dump or 'mask' to dump
+ bitmasks)
+ - field name
+ """
+
+ def __init__(self, fd=None, offset=None, data=None):
+ """
+ Two variants:
+ 1. Specify data. fd and offset must be None.
+ 2. Specify fd and offset, data must be None. offset may be omitted
+ in this case, than current position of fd is used.
+ """
+ if data is None:
+ assert fd is not None
+ buf_size = struct.calcsize(self.fmt)
+ if offset is not None:
+ fd.seek(offset)
+ data = fd.read(buf_size)
+ else:
+ assert fd is None and offset is None
+
+ values = struct.unpack(self.fmt, data)
+ self.__dict__ = dict((field[2], values[i])
+ for i, field in enumerate(self.fields))
+
+ def dump(self):
+ for f in self.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].format(value)
+
+ print('{:<25} {}'.format(f[2], value_str))
+
+
class QcowHeaderExtension:
def __init__(self, magic, length, data):
@@ -34,16 +98,7 @@ class QcowHeaderExtension:
return QcowHeaderExtension(magic, len(data), data)
-# Mapping from c types to python struct format
-ctypes = {
- 'u8': 'B',
- 'u16': 'H',
- 'u32': 'I',
- 'u64': 'Q'
-}
-
-
-class QcowHeader:
+class QcowHeader(Qcow2Struct):
fields = (
# Version 2 header fields
@@ -69,18 +124,8 @@ class QcowHeader:
('u32', '{}', 'header_length'),
)
- fmt = '>' + ''.join(ctypes[f[0]] for f 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))
+ super().__init__(fd=fd, offset=0)
self.set_defaults()
self.cluster_size = 1 << self.cluster_bits
@@ -148,20 +193,6 @@ class QcowHeader:
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].format(value)
-
- print(f'{f[2]:<25} {value_str}')
-
def dump_extensions(self):
for ex in self.extensions: