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