1#!/usr/bin/env python 2 3import sys 4import struct 5import string 6 7class QcowHeaderExtension: 8 9 def __init__(self, magic, length, data): 10 if length % 8 != 0: 11 padding = 8 - (length % 8) 12 data += "\0" * padding 13 14 self.magic = magic 15 self.length = length 16 self.data = data 17 18 @classmethod 19 def create(cls, magic, data): 20 return QcowHeaderExtension(magic, len(data), data) 21 22class QcowHeader: 23 24 uint32_t = 'I' 25 uint64_t = 'Q' 26 27 fields = [ 28 # Version 2 header fields 29 [ uint32_t, '%#x', 'magic' ], 30 [ uint32_t, '%d', 'version' ], 31 [ uint64_t, '%#x', 'backing_file_offset' ], 32 [ uint32_t, '%#x', 'backing_file_size' ], 33 [ uint32_t, '%d', 'cluster_bits' ], 34 [ uint64_t, '%d', 'size' ], 35 [ uint32_t, '%d', 'crypt_method' ], 36 [ uint32_t, '%d', 'l1_size' ], 37 [ uint64_t, '%#x', 'l1_table_offset' ], 38 [ uint64_t, '%#x', 'refcount_table_offset' ], 39 [ uint32_t, '%d', 'refcount_table_clusters' ], 40 [ uint32_t, '%d', 'nb_snapshots' ], 41 [ uint64_t, '%#x', 'snapshot_offset' ], 42 43 # Version 3 header fields 44 [ uint64_t, '%#x', 'incompatible_features' ], 45 [ uint64_t, '%#x', 'compatible_features' ], 46 [ uint64_t, '%#x', 'autoclear_features' ], 47 [ uint32_t, '%d', 'refcount_order' ], 48 [ uint32_t, '%d', 'header_length' ], 49 ]; 50 51 fmt = '>' + ''.join(field[0] for field in fields) 52 53 def __init__(self, fd): 54 55 buf_size = struct.calcsize(QcowHeader.fmt) 56 57 fd.seek(0) 58 buf = fd.read(buf_size) 59 60 header = struct.unpack(QcowHeader.fmt, buf) 61 self.__dict__ = dict((field[2], header[i]) 62 for i, field in enumerate(QcowHeader.fields)) 63 64 self.set_defaults() 65 self.cluster_size = 1 << self.cluster_bits 66 67 fd.seek(self.header_length) 68 self.load_extensions(fd) 69 70 if self.backing_file_offset: 71 fd.seek(self.backing_file_offset) 72 self.backing_file = fd.read(self.backing_file_size) 73 else: 74 self.backing_file = None 75 76 def set_defaults(self): 77 if self.version == 2: 78 self.incompatible_features = 0 79 self.compatible_features = 0 80 self.autoclear_features = 0 81 self.refcount_order = 4 82 self.header_length = 72 83 84 def load_extensions(self, fd): 85 self.extensions = [] 86 87 if self.backing_file_offset != 0: 88 end = min(self.cluster_size, self.backing_file_offset) 89 else: 90 end = self.cluster_size 91 92 while fd.tell() < end: 93 (magic, length) = struct.unpack('>II', fd.read(8)) 94 if magic == 0: 95 break 96 else: 97 padded = (length + 7) & ~7 98 data = fd.read(padded) 99 self.extensions.append(QcowHeaderExtension(magic, length, data)) 100 101 def update_extensions(self, fd): 102 103 fd.seek(self.header_length) 104 extensions = self.extensions 105 extensions.append(QcowHeaderExtension(0, 0, "")) 106 for ex in extensions: 107 buf = struct.pack('>II', ex.magic, ex.length) 108 fd.write(buf) 109 fd.write(ex.data) 110 111 if self.backing_file != None: 112 self.backing_file_offset = fd.tell() 113 fd.write(self.backing_file) 114 115 if fd.tell() > self.cluster_size: 116 raise Exception("I think I just broke the image...") 117 118 119 def update(self, fd): 120 header_bytes = self.header_length 121 122 self.update_extensions(fd) 123 124 fd.seek(0) 125 header = tuple(self.__dict__[f] for t, p, f in QcowHeader.fields) 126 buf = struct.pack(QcowHeader.fmt, *header) 127 buf = buf[0:header_bytes-1] 128 fd.write(buf) 129 130 def dump(self): 131 for f in QcowHeader.fields: 132 print "%-25s" % f[2], f[1] % self.__dict__[f[2]] 133 print "" 134 135 def dump_extensions(self): 136 for ex in self.extensions: 137 138 data = ex.data[:ex.length] 139 if all(c in string.printable for c in data): 140 data = "'%s'" % data 141 else: 142 data = "<binary>" 143 144 print "Header extension:" 145 print "%-25s %#x" % ("magic", ex.magic) 146 print "%-25s %d" % ("length", ex.length) 147 print "%-25s %s" % ("data", data) 148 print "" 149 150 151def cmd_dump_header(fd): 152 h = QcowHeader(fd) 153 h.dump() 154 h.dump_extensions() 155 156def cmd_set_header(fd, name, value): 157 try: 158 value = int(value, 0) 159 except: 160 print "'%s' is not a valid number" % value 161 sys.exit(1) 162 163 fields = (field[2] for field in QcowHeader.fields) 164 if not name in fields: 165 print "'%s' is not a known header field" % name 166 sys.exit(1) 167 168 h = QcowHeader(fd) 169 h.__dict__[name] = value 170 h.update(fd) 171 172def cmd_add_header_ext(fd, magic, data): 173 try: 174 magic = int(magic, 0) 175 except: 176 print "'%s' is not a valid magic number" % magic 177 sys.exit(1) 178 179 h = QcowHeader(fd) 180 h.extensions.append(QcowHeaderExtension.create(magic, data)) 181 h.update(fd) 182 183def cmd_add_header_ext_stdio(fd, magic): 184 data = sys.stdin.read() 185 cmd_add_header_ext(fd, magic, data) 186 187def cmd_del_header_ext(fd, magic): 188 try: 189 magic = int(magic, 0) 190 except: 191 print "'%s' is not a valid magic number" % magic 192 sys.exit(1) 193 194 h = QcowHeader(fd) 195 found = False 196 197 for ex in h.extensions: 198 if ex.magic == magic: 199 found = True 200 h.extensions.remove(ex) 201 202 if not found: 203 print "No such header extension" 204 return 205 206 h.update(fd) 207 208def cmd_set_feature_bit(fd, group, bit): 209 try: 210 bit = int(bit, 0) 211 if bit < 0 or bit >= 64: 212 raise ValueError 213 except: 214 print "'%s' is not a valid bit number in range [0, 64)" % bit 215 sys.exit(1) 216 217 h = QcowHeader(fd) 218 if group == 'incompatible': 219 h.incompatible_features |= 1 << bit 220 elif group == 'compatible': 221 h.compatible_features |= 1 << bit 222 elif group == 'autoclear': 223 h.autoclear_features |= 1 << bit 224 else: 225 print "'%s' is not a valid group, try 'incompatible', 'compatible', or 'autoclear'" % group 226 sys.exit(1) 227 228 h.update(fd) 229 230cmds = [ 231 [ 'dump-header', cmd_dump_header, 0, 'Dump image header and header extensions' ], 232 [ 'set-header', cmd_set_header, 2, 'Set a field in the header'], 233 [ 'add-header-ext', cmd_add_header_ext, 2, 'Add a header extension' ], 234 [ 'add-header-ext-stdio', cmd_add_header_ext_stdio, 1, 'Add a header extension, data from stdin' ], 235 [ 'del-header-ext', cmd_del_header_ext, 1, 'Delete a header extension' ], 236 [ 'set-feature-bit', cmd_set_feature_bit, 2, 'Set a feature bit'], 237] 238 239def main(filename, cmd, args): 240 fd = open(filename, "r+b") 241 try: 242 for name, handler, num_args, desc in cmds: 243 if name != cmd: 244 continue 245 elif len(args) != num_args: 246 usage() 247 return 248 else: 249 handler(fd, *args) 250 return 251 print "Unknown command '%s'" % cmd 252 finally: 253 fd.close() 254 255def usage(): 256 print "Usage: %s <file> <cmd> [<arg>, ...]" % sys.argv[0] 257 print "" 258 print "Supported commands:" 259 for name, handler, num_args, desc in cmds: 260 print " %-20s - %s" % (name, desc) 261 262if __name__ == '__main__': 263 if len(sys.argv) < 3: 264 usage() 265 sys.exit(1) 266 267 main(sys.argv[1], sys.argv[2], sys.argv[3:]) 268