#!/usr/bin/env python
import sys
import struct
import string
class QcowHeaderExtension:
def __init__(self, magic, length, data):
if length % 8 != 0:
padding = 8 - (length % 8)
data += "\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, '%#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_set_header(fd, name, value):
try:
value = int(value, 0)
except:
print "'%s' is not a valid number" % value
sys.exit(1)
fields = (field[2] for field in QcowHeader.fields)
if not name in fields:
print "'%s' is not a known header field" % name
sys.exit(1)
h = QcowHeader(fd)
h.__dict__[name] = value
h.update(fd)
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_add_header_ext_stdio(fd, magic):
data = sys.stdin.read()
cmd_add_header_ext(fd, magic, data)
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)
def cmd_set_feature_bit(fd, group, bit):
try:
bit = int(bit, 0)
if bit < 0 or bit >= 64:
raise ValueError
except:
print "'%s' is not a valid bit number in range [0, 64)" % bit
sys.exit(1)
h = QcowHeader(fd)
if group == 'incompatible':
h.incompatible_features |= 1 << bit
elif group == 'compatible':
h.compatible_features |= 1 << bit
elif group == 'autoclear':
h.autoclear_features |= 1 << bit
else:
print "'%s' is not a valid group, try 'incompatible', 'compatible', or 'autoclear'" % group
sys.exit(1)
h.update(fd)
cmds = [
[ 'dump-header', cmd_dump_header, 0, 'Dump image header and header extensions' ],
[ 'set-header', cmd_set_header, 2, 'Set a field in the header'],
[ 'add-header-ext', cmd_add_header_ext, 2, 'Add a header extension' ],
[ 'add-header-ext-stdio', cmd_add_header_ext_stdio, 1, 'Add a header extension, data from stdin' ],
[ 'del-header-ext', cmd_del_header_ext, 1, 'Delete a header extension' ],
[ 'set-feature-bit', cmd_set_feature_bit, 2, 'Set a feature bit'],
]
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 __name__ == '__main__':
if len(sys.argv) < 3:
usage()
sys.exit(1)
main(sys.argv[1], sys.argv[2], sys.argv[3:])
