qemu-e2k/tests/qemu-iotests/qcow2_format.py

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# Library for manipulations with qcow2 image
#
# Copyright (c) 2020 Virtuozzo International GmbH.
# Copyright (C) 2012 Red Hat, Inc.
#
# 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 Qcow2Field:
def __init__(self, value):
self.value = value
def __str__(self):
return str(self.value)
class Flags64(Qcow2Field):
def __str__(self):
bits = []
for bit in range(64):
if self.value & (1 << bit):
bits.append(bit)
return str(bits)
class BitmapFlags(Qcow2Field):
flags = {
0x1: 'in-use',
0x2: 'auto'
}
def __str__(self):
bits = []
for bit in range(64):
flag = self.value & (1 << bit)
if flag:
bits.append(self.flags.get(flag, f'bit-{bit}'))
return f'{self.value:#x} ({bits})'
class Enum(Qcow2Field):
def __str__(self):
return f'{self.value:#x} ({self.mapping.get(self.value, "<unknown>")})'
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 isinstance(f[1], str):
value_str = f[1].format(value)
else:
value_str = str(f[1](value))
print('{:<25} {}'.format(f[2], value_str))
class Qcow2BitmapExt(Qcow2Struct):
fields = (
('u32', '{}', 'nb_bitmaps'),
('u32', '{}', 'reserved32'),
('u64', '{:#x}', 'bitmap_directory_size'),
('u64', '{:#x}', 'bitmap_directory_offset')
)
def __init__(self, fd, cluster_size):
super().__init__(fd=fd)
tail = struct.calcsize(self.fmt) % 8
if tail:
fd.seek(8 - tail, 1)
position = fd.tell()
self.cluster_size = cluster_size
self.read_bitmap_directory(fd)
fd.seek(position)
def read_bitmap_directory(self, fd):
fd.seek(self.bitmap_directory_offset)
self.bitmap_directory = \
[Qcow2BitmapDirEntry(fd, cluster_size=self.cluster_size)
for _ in range(self.nb_bitmaps)]
def dump(self):
super().dump()
for entry in self.bitmap_directory:
print()
entry.dump()
class Qcow2BitmapDirEntry(Qcow2Struct):
fields = (
('u64', '{:#x}', 'bitmap_table_offset'),
('u32', '{}', 'bitmap_table_size'),
('u32', BitmapFlags, 'flags'),
('u8', '{}', 'type'),
('u8', '{}', 'granularity_bits'),
('u16', '{}', 'name_size'),
('u32', '{}', 'extra_data_size')
)
def __init__(self, fd, cluster_size):
super().__init__(fd=fd)
self.cluster_size = cluster_size
# Seek relative to the current position in the file
fd.seek(self.extra_data_size, 1)
bitmap_name = fd.read(self.name_size)
self.name = bitmap_name.decode('ascii')
# Move position to the end of the entry in the directory
entry_raw_size = self.bitmap_dir_entry_raw_size()
padding = ((entry_raw_size + 7) & ~7) - entry_raw_size
fd.seek(padding, 1)
self.bitmap_table = Qcow2BitmapTable(fd=fd,
offset=self.bitmap_table_offset,
nb_entries=self.bitmap_table_size,
cluster_size=self.cluster_size)
def bitmap_dir_entry_raw_size(self):
return struct.calcsize(self.fmt) + self.name_size + \
self.extra_data_size
def dump(self):
print(f'{"Bitmap name":<25} {self.name}')
super(Qcow2BitmapDirEntry, self).dump()
self.bitmap_table.dump()
class Qcow2BitmapTableEntry(Qcow2Struct):
fields = (
('u64', '{}', 'entry'),
)
BME_TABLE_ENTRY_RESERVED_MASK = 0xff000000000001fe
BME_TABLE_ENTRY_OFFSET_MASK = 0x00fffffffffffe00
BME_TABLE_ENTRY_FLAG_ALL_ONES = 1
def __init__(self, fd):
super().__init__(fd=fd)
self.reserved = self.entry & self.BME_TABLE_ENTRY_RESERVED_MASK
self.offset = self.entry & self.BME_TABLE_ENTRY_OFFSET_MASK
if self.offset:
if self.entry & self.BME_TABLE_ENTRY_FLAG_ALL_ONES:
self.type = 'invalid'
else:
self.type = 'serialized'
elif self.entry & self.BME_TABLE_ENTRY_FLAG_ALL_ONES:
self.type = 'all-ones'
else:
self.type = 'all-zeroes'
class Qcow2BitmapTable:
def __init__(self, fd, offset, nb_entries, cluster_size):
self.cluster_size = cluster_size
position = fd.tell()
fd.seek(offset)
self.entries = [Qcow2BitmapTableEntry(fd) for _ in range(nb_entries)]
fd.seek(position)
def dump(self):
bitmap_table = enumerate(self.entries)
print(f'{"Bitmap table":<14} {"type":<15} {"size":<12} {"offset"}')
for i, entry in bitmap_table:
if entry.type == 'serialized':
size = self.cluster_size
else:
size = 0
print(f'{i:<14} {entry.type:<15} {size:<12} {entry.offset}')
QCOW2_EXT_MAGIC_BITMAPS = 0x23852875
class QcowHeaderExtension(Qcow2Struct):
class Magic(Enum):
mapping = {
0xe2792aca: 'Backing format',
0x6803f857: 'Feature table',
0x0537be77: 'Crypto header',
QCOW2_EXT_MAGIC_BITMAPS: 'Bitmaps',
0x44415441: 'Data file'
}
fields = (
('u32', Magic, 'magic'),
('u32', '{}', 'length')
# length bytes of data follows
# then padding to next multiply of 8
)
def __init__(self, magic=None, length=None, data=None, fd=None,
cluster_size=None):
"""
Support both loading from fd and creation from user data.
For fd-based creation current position in a file will be used to read
the data.
The cluster_size value may be obtained by dependent structures.
This should be somehow refactored and functionality should be moved to
superclass (to allow creation of any qcow2 struct), but then, fields
of variable length (data here) should be supported in base class
somehow. Note also, that we probably want to parse different
extensions. Should they be subclasses of this class, or how to do it
better? Should it be something like QAPI union with discriminator field
(magic here). So, it's a TODO. We'll see how to properly refactor this
when we have more qcow2 structures.
"""
if fd is None:
assert all(v is not None for v in (magic, length, data))
self.magic = magic
self.length = length
if length % 8 != 0:
padding = 8 - (length % 8)
data += b'\0' * padding
self.data = data
else:
assert all(v is None for v in (magic, length, data))
super().__init__(fd=fd)
if self.magic == QCOW2_EXT_MAGIC_BITMAPS:
self.obj = Qcow2BitmapExt(fd=fd, cluster_size=cluster_size)
self.data = None
else:
padded = (self.length + 7) & ~7
self.data = fd.read(padded)
assert self.data is not None
self.obj = None
if self.data is not None:
data_str = self.data[:self.length]
if all(c in string.printable.encode(
'ascii') for c in data_str):
data_str = f"'{ data_str.decode('ascii') }'"
else:
data_str = '<binary>'
self.data_str = data_str
def dump(self):
super().dump()
if self.obj is None:
print(f'{"data":<25} {self.data_str}')
else:
self.obj.dump()
@classmethod
def create(cls, magic, data):
return QcowHeaderExtension(magic, len(data), data)
class QcowHeader(Qcow2Struct):
fields = (
# Version 2 header fields
('u32', '{:#x}', 'magic'),
('u32', '{}', 'version'),
('u64', '{:#x}', 'backing_file_offset'),
('u32', '{:#x}', 'backing_file_size'),
('u32', '{}', 'cluster_bits'),
('u64', '{}', 'size'),
('u32', '{}', 'crypt_method'),
('u32', '{}', 'l1_size'),
('u64', '{:#x}', 'l1_table_offset'),
('u64', '{:#x}', 'refcount_table_offset'),
('u32', '{}', 'refcount_table_clusters'),
('u32', '{}', 'nb_snapshots'),
('u64', '{:#x}', 'snapshot_offset'),
# Version 3 header fields
('u64', Flags64, 'incompatible_features'),
('u64', Flags64, 'compatible_features'),
('u64', Flags64, 'autoclear_features'),
('u32', '{}', 'refcount_order'),
('u32', '{}', 'header_length'),
)
def __init__(self, fd):
super().__init__(fd=fd, offset=0)
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:
ext = QcowHeaderExtension(fd=fd, cluster_size=self.cluster_size)
if ext.magic == 0:
break
else:
self.extensions.append(ext)
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_extensions(self):
for ex in self.extensions:
print('Header extension:')
ex.dump()
print()