block/dmg.c

   1 /*
   2  * QEMU Block driver for DMG images
   3  *
   4  * Copyright (c) 2004 Johannes E. Schindelin
   5  *
   6  * Permission is hereby granted, free of charge, to any person obtaining a copy
   7  * of this software and associated documentation files (the "Software"), to deal
   8  * in the Software without restriction, including without limitation the rights
   9  * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  10  * copies of the Software, and to permit persons to whom the Software is
  11  * furnished to do so, subject to the following conditions:
  12  *
  13  * The above copyright notice and this permission notice shall be included in
  14  * all copies or substantial portions of the Software.
  15  *
  16  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  17  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  18  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
  19  * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  20  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  21  * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
  22  * THE SOFTWARE.
  23  */
  24 #include "qemu-common.h"
  25 #include "block/block_int.h"
  26 #include "qemu/bswap.h"
  27 #include "qemu/module.h"
  28 #include <zlib.h>
  29 #include <glib.h>
  30
  31 enum {
  32     /* Limit chunk sizes to prevent unreasonable amounts of memory being used
  33      * or truncating when converting to 32-bit types
  34      */
  35     DMG_LENGTHS_MAX = 64 * 1024 * 1024, /* 64 MB */
  36     DMG_SECTORCOUNTS_MAX = DMG_LENGTHS_MAX / 512,
  37 };
  38
  39 typedef struct BDRVDMGState {
  40     CoMutex lock;
  41     /* each chunk contains a certain number of sectors,
  42      * offsets[i] is the offset in the .dmg file,
  43      * lengths[i] is the length of the compressed chunk,
  44      * sectors[i] is the sector beginning at offsets[i],
  45      * sectorcounts[i] is the number of sectors in that chunk,
  46      * the sectors array is ordered
  47      * 0<=i<n_chunks */
  48
  49     uint32_t n_chunks;
  50     uint32_t* types;
  51     uint64_t* offsets;
  52     uint64_t* lengths;
  53     uint64_t* sectors;
  54     uint64_t* sectorcounts;
  55     uint32_t current_chunk;
  56     uint8_t *compressed_chunk;
  57     uint8_t *uncompressed_chunk;
  58     z_stream zstream;
  59 } BDRVDMGState;
  60
  61 static int dmg_probe(const uint8_t *buf, int buf_size, const char *filename)
  62 {
  63     int len;
  64
  65     if (!filename) {
  66         return 0;
  67     }
  68
  69     len = strlen(filename);
  70     if (len > 4 && !strcmp(filename + len - 4, ".dmg")) {
  71         return 2;
  72     }
  73     return 0;
  74 }
  75
  76 static int read_uint64(BlockDriverState *bs, int64_t offset, uint64_t *result)
  77 {
  78     uint64_t buffer;
  79     int ret;
  80
  81     ret = bdrv_pread(bs->file, offset, &buffer, 8);
  82     if (ret < 0) {
  83         return ret;
  84     }
  85
  86     *result = be64_to_cpu(buffer);
  87     return 0;
  88 }
  89
  90 static int read_uint32(BlockDriverState *bs, int64_t offset, uint32_t *result)
  91 {
  92     uint32_t buffer;
  93     int ret;
  94
  95     ret = bdrv_pread(bs->file, offset, &buffer, 4);
  96     if (ret < 0) {
  97         return ret;
  98     }
  99
 100     *result = be32_to_cpu(buffer);
 101     return 0;
 102 }
 103
 104 static inline uint64_t buff_read_uint64(const uint8_t *buffer, int64_t offset)
 105 {
 106     return be64_to_cpu(*(uint64_t *)&buffer[offset]);
 107 }
 108
 109 static inline uint32_t buff_read_uint32(const uint8_t *buffer, int64_t offset)
 110 {
 111     return be32_to_cpu(*(uint32_t *)&buffer[offset]);
 112 }
 113
 114 /* Increase max chunk sizes, if necessary.  This function is used to calculate
 115  * the buffer sizes needed for compressed/uncompressed chunk I/O.
 116  */
 117 static void update_max_chunk_size(BDRVDMGState *s, uint32_t chunk,
 118                                   uint32_t *max_compressed_size,
 119                                   uint32_t *max_sectors_per_chunk)
 120 {
 121     uint32_t compressed_size = 0;
 122     uint32_t uncompressed_sectors = 0;
 123
 124     switch (s->types[chunk]) {
 125     case 0x80000005: /* zlib compressed */
 126         compressed_size = s->lengths[chunk];
 127         uncompressed_sectors = s->sectorcounts[chunk];
 128         break;
 129     case 1: /* copy */
 130         uncompressed_sectors = (s->lengths[chunk] + 511) / 512;
 131         break;
 132     case 2: /* zero */
 133         uncompressed_sectors = s->sectorcounts[chunk];
 134         break;
 135     }
 136
 137     if (compressed_size > *max_compressed_size) {
 138         *max_compressed_size = compressed_size;
 139     }
 140     if (uncompressed_sectors > *max_sectors_per_chunk) {
 141         *max_sectors_per_chunk = uncompressed_sectors;
 142     }
 143 }
 144
 145 static int64_t dmg_find_koly_offset(BlockDriverState *file_bs, Error **errp)
 146 {
 147     int64_t length;
 148     int64_t offset = 0;
 149     uint8_t buffer[515];
 150     int i, ret;
 151
 152     /* bdrv_getlength returns a multiple of block size (512), rounded up. Since
 153      * dmg images can have odd sizes, try to look for the "koly" magic which
 154      * marks the begin of the UDIF trailer (512 bytes). This magic can be found
 155      * in the last 511 bytes of the second-last sector or the first 4 bytes of
 156      * the last sector (search space: 515 bytes) */
 157     length = bdrv_getlength(file_bs);
 158     if (length < 0) {
 159         error_setg_errno(errp, -length,
 160             "Failed to get file size while reading UDIF trailer");
 161         return length;
 162     } else if (length < 512) {
 163         error_setg(errp, "dmg file must be at least 512 bytes long");
 164         return -EINVAL;
 165     }
 166     if (length > 511 + 512) {
 167         offset = length - 511 - 512;
 168     }
 169     length = length < 515 ? length : 515;
 170     ret = bdrv_pread(file_bs, offset, buffer, length);
 171     if (ret < 0) {
 172         error_setg_errno(errp, -ret, "Failed while reading UDIF trailer");
 173         return ret;
 174     }
 175     for (i = 0; i < length - 3; i++) {
 176         if (buffer[i] == 'k' && buffer[i+1] == 'o' &&
 177             buffer[i+2] == 'l' && buffer[i+3] == 'y') {
 178             return offset + i;
 179         }
 180     }
 181     error_setg(errp, "Could not locate UDIF trailer in dmg file");
 182     return -EINVAL;
 183 }
 184
 185 /* used when building the sector table */
 186 typedef struct DmgHeaderState {
 187     /* used internally by dmg_read_mish_block to remember offsets of blocks
 188      * across calls */
 189     uint64_t data_fork_offset;
 190     /* exported for dmg_open */
 191     uint32_t max_compressed_size;
 192     uint32_t max_sectors_per_chunk;
 193 } DmgHeaderState;
 194
 195 static int dmg_read_mish_block(BDRVDMGState *s, DmgHeaderState *ds,
 196                                uint8_t *buffer, uint32_t count)
 197 {
 198     uint32_t type, i;
 199     int ret;
 200     size_t new_size;
 201     uint32_t chunk_count;
 202     int64_t offset = 0;
 203     uint64_t data_offset;
 204     uint64_t in_offset = ds->data_fork_offset;
 205     uint64_t out_offset;
 206
 207     type = buff_read_uint32(buffer, offset);
 208     /* skip data that is not a valid MISH block (invalid magic or too small) */
 209     if (type != 0x6d697368 || count < 244) {
 210         /* assume success for now */
 211         return 0;
 212     }
 213
 214     /* chunk offsets are relative to this sector number */
 215     out_offset = buff_read_uint64(buffer, offset + 8);
 216
 217     /* location in data fork for (compressed) blob (in bytes) */
 218     data_offset = buff_read_uint64(buffer, offset + 0x18);
 219     in_offset += data_offset;
 220
 221     /* move to begin of chunk entries */
 222     offset += 204;
 223
 224     chunk_count = (count - 204) / 40;
 225     new_size = sizeof(uint64_t) * (s->n_chunks + chunk_count);
 226     s->types = g_realloc(s->types, new_size / 2);
 227     s->offsets = g_realloc(s->offsets, new_size);
 228     s->lengths = g_realloc(s->lengths, new_size);
 229     s->sectors = g_realloc(s->sectors, new_size);
 230     s->sectorcounts = g_realloc(s->sectorcounts, new_size);
 231
 232     for (i = s->n_chunks; i < s->n_chunks + chunk_count; i++) {
 233         s->types[i] = buff_read_uint32(buffer, offset);
 234         offset += 4;
 235         if (s->types[i] != 0x80000005 && s->types[i] != 1 &&
 236             s->types[i] != 2) {
 237             chunk_count--;
 238             i--;
 239             offset += 36;
 240             continue;
 241         }
 242         offset += 4;
 243
 244         s->sectors[i] = buff_read_uint64(buffer, offset);
 245         s->sectors[i] += out_offset;
 246         offset += 8;
 247
 248         s->sectorcounts[i] = buff_read_uint64(buffer, offset);
 249         offset += 8;
 250
 251         if (s->sectorcounts[i] > DMG_SECTORCOUNTS_MAX) {
 252             error_report("sector count %" PRIu64 " for chunk %" PRIu32
 253                          " is larger than max (%u)",
 254                          s->sectorcounts[i], i, DMG_SECTORCOUNTS_MAX);
 255             ret = -EINVAL;
 256             goto fail;
 257         }
 258
 259         s->offsets[i] = buff_read_uint64(buffer, offset);
 260         s->offsets[i] += in_offset;
 261         offset += 8;
 262
 263         s->lengths[i] = buff_read_uint64(buffer, offset);
 264         offset += 8;
 265
 266         if (s->lengths[i] > DMG_LENGTHS_MAX) {
 267             error_report("length %" PRIu64 " for chunk %" PRIu32
 268                          " is larger than max (%u)",
 269                          s->lengths[i], i, DMG_LENGTHS_MAX);
 270             ret = -EINVAL;
 271             goto fail;
 272         }
 273
 274         update_max_chunk_size(s, i, &ds->max_compressed_size,
 275                               &ds->max_sectors_per_chunk);
 276     }
 277     s->n_chunks += chunk_count;
 278     return 0;
 279
 280 fail:
 281     return ret;
 282 }
 283
 284 static int dmg_read_resource_fork(BlockDriverState *bs, DmgHeaderState *ds,
 285                                   uint64_t info_begin, uint64_t info_length)
 286 {
 287     BDRVDMGState *s = bs->opaque;
 288     int ret;
 289     uint32_t count, rsrc_data_offset;
 290     uint8_t *buffer = NULL;
 291     uint64_t info_end;
 292     uint64_t offset;
 293
 294     /* read offset from begin of resource fork (info_begin) to resource data */
 295     ret = read_uint32(bs, info_begin, &rsrc_data_offset);
 296     if (ret < 0) {
 297         goto fail;
 298     } else if (rsrc_data_offset > info_length) {
 299         ret = -EINVAL;
 300         goto fail;
 301     }
 302
 303     /* read length of resource data */
 304     ret = read_uint32(bs, info_begin + 8, &count);
 305     if (ret < 0) {
 306         goto fail;
 307     } else if (count == 0 || rsrc_data_offset + count > info_length) {
 308         ret = -EINVAL;
 309         goto fail;
 310     }
 311
 312     /* begin of resource data (consisting of one or more resources) */
 313     offset = info_begin + rsrc_data_offset;
 314
 315     /* end of resource data (there is possibly a following resource map
 316      * which will be ignored). */
 317     info_end = offset + count;
 318
 319     /* read offsets (mish blocks) from one or more resources in resource data */
 320     while (offset < info_end) {
 321         /* size of following resource */
 322         ret = read_uint32(bs, offset, &count);
 323         if (ret < 0) {
 324             goto fail;
 325         } else if (count == 0 || count > info_end - offset) {
 326             ret = -EINVAL;
 327             goto fail;
 328         }
 329         offset += 4;
 330
 331         buffer = g_realloc(buffer, count);
 332         ret = bdrv_pread(bs->file, offset, buffer, count);
 333         if (ret < 0) {
 334             goto fail;
 335         }
 336
 337         ret = dmg_read_mish_block(s, ds, buffer, count);
 338         if (ret < 0) {
 339             goto fail;
 340         }
 341         /* advance offset by size of resource */
 342         offset += count;
 343     }
 344     ret = 0;
 345
 346 fail:
 347     g_free(buffer);
 348     return ret;
 349 }
 350
 351 static int dmg_read_plist_xml(BlockDriverState *bs, DmgHeaderState *ds,
 352                               uint64_t info_begin, uint64_t info_length)
 353 {
 354     BDRVDMGState *s = bs->opaque;
 355     int ret;
 356     uint8_t *buffer = NULL;
 357     char *data_begin, *data_end;
 358
 359     /* Have at least some length to avoid NULL for g_malloc. Attempt to set a
 360      * safe upper cap on the data length. A test sample had a XML length of
 361      * about 1 MiB. */
 362     if (info_length == 0 || info_length > 16 * 1024 * 1024) {
 363         ret = -EINVAL;
 364         goto fail;
 365     }
 366
 367     buffer = g_malloc(info_length + 1);
 368     buffer[info_length] = '\0';
 369     ret = bdrv_pread(bs->file, info_begin, buffer, info_length);
 370     if (ret != info_length) {
 371         ret = -EINVAL;
 372         goto fail;
 373     }
 374
 375     /* look for <data>...</data>. The data is 284 (0x11c) bytes after base64
 376      * decode. The actual data element has 431 (0x1af) bytes which includes tabs
 377      * and line feeds. */
 378     data_end = (char *)buffer;
 379     while ((data_begin = strstr(data_end, "<data>")) != NULL) {
 380         guchar *mish;
 381         gsize out_len = 0;
 382
 383         data_begin += 6;
 384         data_end = strstr(data_begin, "</data>");
 385         /* malformed XML? */
 386         if (data_end == NULL) {
 387             ret = -EINVAL;
 388             goto fail;
 389         }
 390         *data_end++ = '\0';
 391         mish = g_base64_decode(data_begin, &out_len);
 392         ret = dmg_read_mish_block(s, ds, mish, (uint32_t)out_len);
 393         g_free(mish);
 394         if (ret < 0) {
 395             goto fail;
 396         }
 397     }
 398     ret = 0;
 399
 400 fail:
 401     g_free(buffer);
 402     return ret;
 403 }
 404
 405 static int dmg_open(BlockDriverState *bs, QDict *options, int flags,
 406                     Error **errp)
 407 {
 408     BDRVDMGState *s = bs->opaque;
 409     DmgHeaderState ds;
 410     uint64_t rsrc_fork_offset, rsrc_fork_length;
 411     uint64_t plist_xml_offset, plist_xml_length;
 412     int64_t offset;
 413     int ret;
 414
 415     bs->read_only = 1;
 416     s->n_chunks = 0;
 417     s->offsets = s->lengths = s->sectors = s->sectorcounts = NULL;
 418     /* used by dmg_read_mish_block to keep track of the current I/O position */
 419     ds.data_fork_offset = 0;
 420     ds.max_compressed_size = 1;
 421     ds.max_sectors_per_chunk = 1;
 422
 423     /* locate the UDIF trailer */
 424     offset = dmg_find_koly_offset(bs->file, errp);
 425     if (offset < 0) {
 426         ret = offset;
 427         goto fail;
 428     }
 429
 430     /* offset of data fork (DataForkOffset) */
 431     ret = read_uint64(bs, offset + 0x18, &ds.data_fork_offset);
 432     if (ret < 0) {
 433         goto fail;
 434     } else if (ds.data_fork_offset > offset) {
 435         ret = -EINVAL;
 436         goto fail;
 437     }
 438
 439     /* offset of resource fork (RsrcForkOffset) */
 440     ret = read_uint64(bs, offset + 0x28, &rsrc_fork_offset);
 441     if (ret < 0) {
 442         goto fail;
 443     }
 444     ret = read_uint64(bs, offset + 0x30, &rsrc_fork_length);
 445     if (ret < 0) {
 446         goto fail;
 447     }
 448     if (rsrc_fork_offset >= offset ||
 449         rsrc_fork_length > offset - rsrc_fork_offset) {
 450         ret = -EINVAL;
 451         goto fail;
 452     }
 453     /* offset of property list (XMLOffset) */
 454     ret = read_uint64(bs, offset + 0xd8, &plist_xml_offset);
 455     if (ret < 0) {
 456         goto fail;
 457     }
 458     ret = read_uint64(bs, offset + 0xe0, &plist_xml_length);
 459     if (ret < 0) {
 460         goto fail;
 461     }
 462     if (plist_xml_offset >= offset ||
 463         plist_xml_length > offset - plist_xml_offset) {
 464         ret = -EINVAL;
 465         goto fail;
 466     }
 467     ret = read_uint64(bs, offset + 0x1ec, (uint64_t *)&bs->total_sectors);
 468     if (ret < 0) {
 469         goto fail;
 470     }
 471     if (bs->total_sectors < 0) {
 472         ret = -EINVAL;
 473         goto fail;
 474     }
 475     if (rsrc_fork_length != 0) {
 476         ret = dmg_read_resource_fork(bs, &ds,
 477                                      rsrc_fork_offset, rsrc_fork_length);
 478         if (ret < 0) {
 479             goto fail;
 480         }
 481     } else if (plist_xml_length != 0) {
 482         ret = dmg_read_plist_xml(bs, &ds, plist_xml_offset, plist_xml_length);
 483         if (ret < 0) {
 484             goto fail;
 485         }
 486     } else {
 487         ret = -EINVAL;
 488         goto fail;
 489     }
 490
 491     /* initialize zlib engine */
 492     s->compressed_chunk = qemu_try_blockalign(bs->file,
 493                                               ds.max_compressed_size + 1);
 494     s->uncompressed_chunk = qemu_try_blockalign(bs->file,
 495                                                 512 * ds.max_sectors_per_chunk);
 496     if (s->compressed_chunk == NULL || s->uncompressed_chunk == NULL) {
 497         ret = -ENOMEM;
 498         goto fail;
 499     }
 500
 501     if (inflateInit(&s->zstream) != Z_OK) {
 502         ret = -EINVAL;
 503         goto fail;
 504     }
 505
 506     s->current_chunk = s->n_chunks;
 507
 508     qemu_co_mutex_init(&s->lock);
 509     return 0;
 510
 511 fail:
 512     g_free(s->types);
 513     g_free(s->offsets);
 514     g_free(s->lengths);
 515     g_free(s->sectors);
 516     g_free(s->sectorcounts);
 517     qemu_vfree(s->compressed_chunk);
 518     qemu_vfree(s->uncompressed_chunk);
 519     return ret;
 520 }
 521
 522 static inline int is_sector_in_chunk(BDRVDMGState* s,
 523                 uint32_t chunk_num, uint64_t sector_num)
 524 {
 525     if (chunk_num >= s->n_chunks || s->sectors[chunk_num] > sector_num ||
 526             s->sectors[chunk_num] + s->sectorcounts[chunk_num] <= sector_num) {
 527         return 0;
 528     } else {
 529         return -1;
 530     }
 531 }
 532
 533 static inline uint32_t search_chunk(BDRVDMGState *s, uint64_t sector_num)
 534 {
 535     /* binary search */
 536     uint32_t chunk1 = 0, chunk2 = s->n_chunks, chunk3;
 537     while (chunk1 != chunk2) {
 538         chunk3 = (chunk1 + chunk2) / 2;
 539         if (s->sectors[chunk3] > sector_num) {
 540             chunk2 = chunk3;
 541         } else if (s->sectors[chunk3] + s->sectorcounts[chunk3] > sector_num) {
 542             return chunk3;
 543         } else {
 544             chunk1 = chunk3;
 545         }
 546     }
 547     return s->n_chunks; /* error */
 548 }
 549
 550 static inline int dmg_read_chunk(BlockDriverState *bs, uint64_t sector_num)
 551 {
 552     BDRVDMGState *s = bs->opaque;
 553
 554     if (!is_sector_in_chunk(s, s->current_chunk, sector_num)) {
 555         int ret;
 556         uint32_t chunk = search_chunk(s, sector_num);
 557
 558         if (chunk >= s->n_chunks) {
 559             return -1;
 560         }
 561
 562         s->current_chunk = s->n_chunks;
 563         switch (s->types[chunk]) {
 564         case 0x80000005: { /* zlib compressed */
 565             /* we need to buffer, because only the chunk as whole can be
 566              * inflated. */
 567             ret = bdrv_pread(bs->file, s->offsets[chunk],
 568                              s->compressed_chunk, s->lengths[chunk]);
 569             if (ret != s->lengths[chunk]) {
 570                 return -1;
 571             }
 572
 573             s->zstream.next_in = s->compressed_chunk;
 574             s->zstream.avail_in = s->lengths[chunk];
 575             s->zstream.next_out = s->uncompressed_chunk;
 576             s->zstream.avail_out = 512 * s->sectorcounts[chunk];
 577             ret = inflateReset(&s->zstream);
 578             if (ret != Z_OK) {
 579                 return -1;
 580             }
 581             ret = inflate(&s->zstream, Z_FINISH);
 582             if (ret != Z_STREAM_END ||
 583                 s->zstream.total_out != 512 * s->sectorcounts[chunk]) {
 584                 return -1;
 585             }
 586             break; }
 587         case 1: /* copy */
 588             ret = bdrv_pread(bs->file, s->offsets[chunk],
 589                              s->uncompressed_chunk, s->lengths[chunk]);
 590             if (ret != s->lengths[chunk]) {
 591                 return -1;
 592             }
 593             break;
 594         case 2: /* zero */
 595             memset(s->uncompressed_chunk, 0, 512 * s->sectorcounts[chunk]);
 596             break;
 597         }
 598         s->current_chunk = chunk;
 599     }
 600     return 0;
 601 }
 602
 603 static int dmg_read(BlockDriverState *bs, int64_t sector_num,
 604                     uint8_t *buf, int nb_sectors)
 605 {
 606     BDRVDMGState *s = bs->opaque;
 607     int i;
 608
 609     for (i = 0; i < nb_sectors; i++) {
 610         uint32_t sector_offset_in_chunk;
 611         if (dmg_read_chunk(bs, sector_num + i) != 0) {
 612             return -1;
 613         }
 614         sector_offset_in_chunk = sector_num + i - s->sectors[s->current_chunk];
 615         memcpy(buf + i * 512,
 616                s->uncompressed_chunk + sector_offset_in_chunk * 512, 512);
 617     }
 618     return 0;
 619 }
 620
 621 static coroutine_fn int dmg_co_read(BlockDriverState *bs, int64_t sector_num,
 622                                     uint8_t *buf, int nb_sectors)
 623 {
 624     int ret;
 625     BDRVDMGState *s = bs->opaque;
 626     qemu_co_mutex_lock(&s->lock);
 627     ret = dmg_read(bs, sector_num, buf, nb_sectors);
 628     qemu_co_mutex_unlock(&s->lock);
 629     return ret;
 630 }
 631
 632 static void dmg_close(BlockDriverState *bs)
 633 {
 634     BDRVDMGState *s = bs->opaque;
 635
 636     g_free(s->types);
 637     g_free(s->offsets);
 638     g_free(s->lengths);
 639     g_free(s->sectors);
 640     g_free(s->sectorcounts);
 641     qemu_vfree(s->compressed_chunk);
 642     qemu_vfree(s->uncompressed_chunk);
 643
 644     inflateEnd(&s->zstream);
 645 }
 646
 647 static BlockDriver bdrv_dmg = {
 648     .format_name    = "dmg",
 649     .instance_size  = sizeof(BDRVDMGState),
 650     .bdrv_probe     = dmg_probe,
 651     .bdrv_open      = dmg_open,
 652     .bdrv_read      = dmg_co_read,
 653     .bdrv_close     = dmg_close,
 654 };
 655
 656 static void bdrv_dmg_init(void)
 657 {
 658     bdrv_register(&bdrv_dmg);
 659 }
 660
 661 block_init(bdrv_dmg_init);