1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
|
#!/usr/bin/env python
import sys
import struct
import string
class QcowHeaderExtension:
def __init__(self, magic, length, data):
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, '%#x', 'incompatible_features' ],
[ uint64_t, '%#x', 'compatible_features' ],
[ uint64_t, '%#x', '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, ""))
for ex in extensions:
buf = struct.pack('>II', ex.magic, ex.length)
fd.write(buf)
fd.write(ex.data)
if self.backing_file != 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:
print "%-25s" % f[2], f[1] % self.__dict__[f[2]]
print ""
def dump_extensions(self):
for ex in self.extensions:
data = ex.data[:ex.length]
if all(c in string.printable for c in data):
data = "'%s'" % data
else:
data = "<binary>"
print "Header extension:"
print "%-25s %#x" % ("magic", ex.magic)
print "%-25s %d" % ("length", ex.length)
print "%-25s %s" % ("data", data)
print ""
def cmd_dump_header(fd):
h = QcowHeader(fd)
h.dump()
h.dump_extensions()
def cmd_add_header_ext(fd, magic, data):
try:
magic = int(magic, 0)
except:
print "'%s' is not a valid magic number" % magic
sys.exit(1)
h = QcowHeader(fd)
h.extensions.append(QcowHeaderExtension.create(magic, data))
h.update(fd)
def cmd_del_header_ext(fd, magic):
try:
magic = int(magic, 0)
except:
print "'%s' is not a valid magic number" % magic
sys.exit(1)
h = QcowHeader(fd)
found = False
for ex in h.extensions:
if ex.magic == magic:
found = True
h.extensions.remove(ex)
if not found:
print "No such header extension"
return
h.update(fd)
cmds = [
[ 'dump-header', cmd_dump_header, 0, 'Dump image header and header extensions' ],
[ 'add-header-ext', cmd_add_header_ext, 2, 'Add a header extension' ],
[ 'del-header-ext', cmd_del_header_ext, 1, 'Delete a header extension' ],
]
def main(filename, cmd, args):
fd = open(filename, "r+b")
try:
for name, handler, num_args, desc in cmds:
if name != cmd:
continue
elif len(args) != num_args:
usage()
return
else:
handler(fd, *args)
return
print "Unknown command '%s'" % cmd
finally:
fd.close()
def usage():
print "Usage: %s <file> <cmd> [<arg>, ...]" % sys.argv[0]
print ""
print "Supported commands:"
for name, handler, num_args, desc in cmds:
print " %-20s - %s" % (name, desc)
if len(sys.argv) < 3:
usage()
sys.exit(1)
main(sys.argv[1], sys.argv[2], sys.argv[3:])
|
