block/qcow2-refcount.c

   1 /*
   2  * Block driver for the QCOW version 2 format
   3  *
   4  * Copyright (c) 2004-2006 Fabrice Bellard
   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
  25 #include "qemu-common.h"
  26 #include "block_int.h"
  27 #include "block/qcow2.h"
  28
  29 static int64_t alloc_clusters_noref(BlockDriverState *bs, int64_t size);
  30 static int update_refcount(BlockDriverState *bs,
  31                             int64_t offset, int64_t length,
  32                             int addend);
  33
  34
  35 static int cache_refcount_updates = 0;
  36
  37 static int write_refcount_block(BDRVQcowState *s)
  38 {
  39     size_t size = s->cluster_size;
  40
  41     if (s->refcount_block_cache_offset == 0) {
  42         return 0;
  43     }
  44
  45     if (bdrv_pwrite(s->hd, s->refcount_block_cache_offset,
  46             s->refcount_block_cache, size) != size)
  47     {
  48         return -EIO;
  49     }
  50
  51     return 0;
  52 }
  53
  54 /*********************************************************/
  55 /* refcount handling */
  56
  57 int qcow2_refcount_init(BlockDriverState *bs)
  58 {
  59     BDRVQcowState *s = bs->opaque;
  60     int ret, refcount_table_size2, i;
  61
  62     s->refcount_block_cache = qemu_malloc(s->cluster_size);
  63     refcount_table_size2 = s->refcount_table_size * sizeof(uint64_t);
  64     s->refcount_table = qemu_malloc(refcount_table_size2);
  65     if (s->refcount_table_size > 0) {
  66         ret = bdrv_pread(s->hd, s->refcount_table_offset,
  67                          s->refcount_table, refcount_table_size2);
  68         if (ret != refcount_table_size2)
  69             goto fail;
  70         for(i = 0; i < s->refcount_table_size; i++)
  71             be64_to_cpus(&s->refcount_table[i]);
  72     }
  73     return 0;
  74  fail:
  75     return -ENOMEM;
  76 }
  77
  78 void qcow2_refcount_close(BlockDriverState *bs)
  79 {
  80     BDRVQcowState *s = bs->opaque;
  81     qemu_free(s->refcount_block_cache);
  82     qemu_free(s->refcount_table);
  83 }
  84
  85
  86 static int load_refcount_block(BlockDriverState *bs,
  87                                int64_t refcount_block_offset)
  88 {
  89     BDRVQcowState *s = bs->opaque;
  90     int ret;
  91
  92     if (cache_refcount_updates) {
  93         write_refcount_block(s);
  94     }
  95
  96     ret = bdrv_pread(s->hd, refcount_block_offset, s->refcount_block_cache,
  97                      s->cluster_size);
  98     if (ret != s->cluster_size)
  99         return -EIO;
 100     s->refcount_block_cache_offset = refcount_block_offset;
 101     return 0;
 102 }
 103
 104 static int get_refcount(BlockDriverState *bs, int64_t cluster_index)
 105 {
 106     BDRVQcowState *s = bs->opaque;
 107     int refcount_table_index, block_index;
 108     int64_t refcount_block_offset;
 109
 110     refcount_table_index = cluster_index >> (s->cluster_bits - REFCOUNT_SHIFT);
 111     if (refcount_table_index >= s->refcount_table_size)
 112         return 0;
 113     refcount_block_offset = s->refcount_table[refcount_table_index];
 114     if (!refcount_block_offset)
 115         return 0;
 116     if (refcount_block_offset != s->refcount_block_cache_offset) {
 117         /* better than nothing: return allocated if read error */
 118         if (load_refcount_block(bs, refcount_block_offset) < 0)
 119             return 1;
 120     }
 121     block_index = cluster_index &
 122         ((1 << (s->cluster_bits - REFCOUNT_SHIFT)) - 1);
 123     return be16_to_cpu(s->refcount_block_cache[block_index]);
 124 }
 125
 126 static int grow_refcount_table(BlockDriverState *bs, int min_size)
 127 {
 128     BDRVQcowState *s = bs->opaque;
 129     int new_table_size, new_table_size2, refcount_table_clusters, i, ret;
 130     uint64_t *new_table;
 131     int64_t table_offset;
 132     uint8_t data[12];
 133     int old_table_size;
 134     int64_t old_table_offset;
 135
 136     if (min_size <= s->refcount_table_size)
 137         return 0;
 138     /* compute new table size */
 139     refcount_table_clusters = s->refcount_table_size >> (s->cluster_bits - 3);
 140     for(;;) {
 141         if (refcount_table_clusters == 0) {
 142             refcount_table_clusters = 1;
 143         } else {
 144             refcount_table_clusters = (refcount_table_clusters * 3 + 1) / 2;
 145         }
 146         new_table_size = refcount_table_clusters << (s->cluster_bits - 3);
 147         if (min_size <= new_table_size)
 148             break;
 149     }
 150 #ifdef DEBUG_ALLOC2
 151     printf("grow_refcount_table from %d to %d\n",
 152            s->refcount_table_size,
 153            new_table_size);
 154 #endif
 155     new_table_size2 = new_table_size * sizeof(uint64_t);
 156     new_table = qemu_mallocz(new_table_size2);
 157     memcpy(new_table, s->refcount_table,
 158            s->refcount_table_size * sizeof(uint64_t));
 159     for(i = 0; i < s->refcount_table_size; i++)
 160         cpu_to_be64s(&new_table[i]);
 161     /* Note: we cannot update the refcount now to avoid recursion */
 162     table_offset = alloc_clusters_noref(bs, new_table_size2);
 163     ret = bdrv_pwrite(s->hd, table_offset, new_table, new_table_size2);
 164     if (ret != new_table_size2)
 165         goto fail;
 166     for(i = 0; i < s->refcount_table_size; i++)
 167         be64_to_cpus(&new_table[i]);
 168
 169     cpu_to_be64w((uint64_t*)data, table_offset);
 170     cpu_to_be32w((uint32_t*)(data + 8), refcount_table_clusters);
 171     if (bdrv_pwrite(s->hd, offsetof(QCowHeader, refcount_table_offset),
 172                     data, sizeof(data)) != sizeof(data))
 173         goto fail;
 174     qemu_free(s->refcount_table);
 175     old_table_offset = s->refcount_table_offset;
 176     old_table_size = s->refcount_table_size;
 177     s->refcount_table = new_table;
 178     s->refcount_table_size = new_table_size;
 179     s->refcount_table_offset = table_offset;
 180
 181     update_refcount(bs, table_offset, new_table_size2, 1);
 182     qcow2_free_clusters(bs, old_table_offset, old_table_size * sizeof(uint64_t));
 183     return 0;
 184  fail:
 185     qcow2_free_clusters(bs, table_offset, new_table_size2);
 186     qemu_free(new_table);
 187     return -EIO;
 188 }
 189
 190
 191 static int64_t alloc_refcount_block(BlockDriverState *bs, int64_t cluster_index)
 192 {
 193     BDRVQcowState *s = bs->opaque;
 194     int64_t offset, refcount_block_offset;
 195     int ret, refcount_table_index;
 196     uint64_t data64;
 197     int cache = cache_refcount_updates;
 198
 199     /* Find L1 index and grow refcount table if needed */
 200     refcount_table_index = cluster_index >> (s->cluster_bits - REFCOUNT_SHIFT);
 201     if (refcount_table_index >= s->refcount_table_size) {
 202         ret = grow_refcount_table(bs, refcount_table_index + 1);
 203         if (ret < 0)
 204             return ret;
 205     }
 206
 207     /* Load or allocate the refcount block */
 208     refcount_block_offset = s->refcount_table[refcount_table_index];
 209     if (!refcount_block_offset) {
 210         if (cache_refcount_updates) {
 211             write_refcount_block(s);
 212             cache_refcount_updates = 0;
 213         }
 214         /* create a new refcount block */
 215         /* Note: we cannot update the refcount now to avoid recursion */
 216         offset = alloc_clusters_noref(bs, s->cluster_size);
 217         memset(s->refcount_block_cache, 0, s->cluster_size);
 218         ret = bdrv_pwrite(s->hd, offset, s->refcount_block_cache, s->cluster_size);
 219         if (ret != s->cluster_size)
 220             return -EINVAL;
 221         s->refcount_table[refcount_table_index] = offset;
 222         data64 = cpu_to_be64(offset);
 223         ret = bdrv_pwrite(s->hd, s->refcount_table_offset +
 224                           refcount_table_index * sizeof(uint64_t),
 225                           &data64, sizeof(data64));
 226         if (ret != sizeof(data64))
 227             return -EINVAL;
 228
 229         refcount_block_offset = offset;
 230         s->refcount_block_cache_offset = offset;
 231         update_refcount(bs, offset, s->cluster_size, 1);
 232         cache_refcount_updates = cache;
 233     } else {
 234         if (refcount_block_offset != s->refcount_block_cache_offset) {
 235             if (load_refcount_block(bs, refcount_block_offset) < 0)
 236                 return -EIO;
 237         }
 238     }
 239
 240     return refcount_block_offset;
 241 }
 242
 243 #define REFCOUNTS_PER_SECTOR (512 >> REFCOUNT_SHIFT)
 244 static int write_refcount_block_entries(BDRVQcowState *s,
 245     int64_t refcount_block_offset, int first_index, int last_index)
 246 {
 247     size_t size;
 248
 249     if (cache_refcount_updates) {
 250         return 0;
 251     }
 252
 253     first_index &= ~(REFCOUNTS_PER_SECTOR - 1);
 254     last_index = (last_index + REFCOUNTS_PER_SECTOR)
 255         & ~(REFCOUNTS_PER_SECTOR - 1);
 256
 257     size = (last_index - first_index) << REFCOUNT_SHIFT;
 258     if (bdrv_pwrite(s->hd,
 259         refcount_block_offset + (first_index << REFCOUNT_SHIFT),
 260         &s->refcount_block_cache[first_index], size) != size)
 261     {
 262         return -EIO;
 263     }
 264
 265     return 0;
 266 }
 267
 268 /* XXX: cache several refcount block clusters ? */
 269 static int update_refcount(BlockDriverState *bs,
 270                             int64_t offset, int64_t length,
 271                             int addend)
 272 {
 273     BDRVQcowState *s = bs->opaque;
 274     int64_t start, last, cluster_offset;
 275     int64_t refcount_block_offset = 0;
 276     int64_t table_index = -1, old_table_index;
 277     int first_index = -1, last_index = -1;
 278
 279 #ifdef DEBUG_ALLOC2
 280     printf("update_refcount: offset=%" PRId64 " size=%" PRId64 " addend=%d\n",
 281            offset, length, addend);
 282 #endif
 283     if (length <= 0)
 284         return -EINVAL;
 285     start = offset & ~(s->cluster_size - 1);
 286     last = (offset + length - 1) & ~(s->cluster_size - 1);
 287     for(cluster_offset = start; cluster_offset <= last;
 288         cluster_offset += s->cluster_size)
 289     {
 290         int block_index, refcount;
 291         int64_t cluster_index = cluster_offset >> s->cluster_bits;
 292
 293         /* Only write refcount block to disk when we are done with it */
 294         old_table_index = table_index;
 295         table_index = cluster_index >> (s->cluster_bits - REFCOUNT_SHIFT);
 296         if ((old_table_index >= 0) && (table_index != old_table_index)) {
 297
 298             if (write_refcount_block_entries(s, refcount_block_offset,
 299                 first_index, last_index) < 0)
 300             {
 301                 return -EIO;
 302             }
 303
 304             first_index = -1;
 305             last_index = -1;
 306         }
 307
 308         /* Load the refcount block and allocate it if needed */
 309         refcount_block_offset = alloc_refcount_block(bs, cluster_index);
 310         if (refcount_block_offset < 0) {
 311             return refcount_block_offset;
 312         }
 313
 314         /* we can update the count and save it */
 315         block_index = cluster_index &
 316             ((1 << (s->cluster_bits - REFCOUNT_SHIFT)) - 1);
 317         if (first_index == -1 || block_index < first_index) {
 318             first_index = block_index;
 319         }
 320         if (block_index > last_index) {
 321             last_index = block_index;
 322         }
 323
 324         refcount = be16_to_cpu(s->refcount_block_cache[block_index]);
 325         refcount += addend;
 326         if (refcount < 0 || refcount > 0xffff)
 327             return -EINVAL;
 328         if (refcount == 0 && cluster_index < s->free_cluster_index) {
 329             s->free_cluster_index = cluster_index;
 330         }
 331         s->refcount_block_cache[block_index] = cpu_to_be16(refcount);
 332     }
 333
 334     /* Write last changed block to disk */
 335     if (refcount_block_offset != 0) {
 336         if (write_refcount_block_entries(s, refcount_block_offset,
 337             first_index, last_index) < 0)
 338         {
 339             return -EIO;
 340         }
 341     }
 342
 343     return 0;
 344 }
 345
 346 /* addend must be 1 or -1 */
 347 static int update_cluster_refcount(BlockDriverState *bs,
 348                                    int64_t cluster_index,
 349                                    int addend)
 350 {
 351     BDRVQcowState *s = bs->opaque;
 352     int ret;
 353
 354     ret = update_refcount(bs, cluster_index << s->cluster_bits, 1, addend);
 355     if (ret < 0) {
 356         return ret;
 357     }
 358
 359     return get_refcount(bs, cluster_index);
 360 }
 361
 362
 363
 364 /*********************************************************/
 365 /* cluster allocation functions */
 366
 367
 368
 369 /* return < 0 if error */
 370 static int64_t alloc_clusters_noref(BlockDriverState *bs, int64_t size)
 371 {
 372     BDRVQcowState *s = bs->opaque;
 373     int i, nb_clusters;
 374
 375     nb_clusters = size_to_clusters(s, size);
 376 retry:
 377     for(i = 0; i < nb_clusters; i++) {
 378         int64_t i = s->free_cluster_index++;
 379         if (get_refcount(bs, i) != 0)
 380             goto retry;
 381     }
 382 #ifdef DEBUG_ALLOC2
 383     printf("alloc_clusters: size=%" PRId64 " -> %" PRId64 "\n",
 384             size,
 385             (s->free_cluster_index - nb_clusters) << s->cluster_bits);
 386 #endif
 387     return (s->free_cluster_index - nb_clusters) << s->cluster_bits;
 388 }
 389
 390 int64_t qcow2_alloc_clusters(BlockDriverState *bs, int64_t size)
 391 {
 392     int64_t offset;
 393
 394     offset = alloc_clusters_noref(bs, size);
 395     update_refcount(bs, offset, size, 1);
 396     return offset;
 397 }
 398
 399 /* only used to allocate compressed sectors. We try to allocate
 400    contiguous sectors. size must be <= cluster_size */
 401 int64_t qcow2_alloc_bytes(BlockDriverState *bs, int size)
 402 {
 403     BDRVQcowState *s = bs->opaque;
 404     int64_t offset, cluster_offset;
 405     int free_in_cluster;
 406
 407     assert(size > 0 && size <= s->cluster_size);
 408     if (s->free_byte_offset == 0) {
 409         s->free_byte_offset = qcow2_alloc_clusters(bs, s->cluster_size);
 410     }
 411  redo:
 412     free_in_cluster = s->cluster_size -
 413         (s->free_byte_offset & (s->cluster_size - 1));
 414     if (size <= free_in_cluster) {
 415         /* enough space in current cluster */
 416         offset = s->free_byte_offset;
 417         s->free_byte_offset += size;
 418         free_in_cluster -= size;
 419         if (free_in_cluster == 0)
 420             s->free_byte_offset = 0;
 421         if ((offset & (s->cluster_size - 1)) != 0)
 422             update_cluster_refcount(bs, offset >> s->cluster_bits, 1);
 423     } else {
 424         offset = qcow2_alloc_clusters(bs, s->cluster_size);
 425         cluster_offset = s->free_byte_offset & ~(s->cluster_size - 1);
 426         if ((cluster_offset + s->cluster_size) == offset) {
 427             /* we are lucky: contiguous data */
 428             offset = s->free_byte_offset;
 429             update_cluster_refcount(bs, offset >> s->cluster_bits, 1);
 430             s->free_byte_offset += size;
 431         } else {
 432             s->free_byte_offset = offset;
 433             goto redo;
 434         }
 435     }
 436     return offset;
 437 }
 438
 439 void qcow2_free_clusters(BlockDriverState *bs,
 440                           int64_t offset, int64_t size)
 441 {
 442     update_refcount(bs, offset, size, -1);
 443 }
 444
 445 /*
 446  * free_any_clusters
 447  *
 448  * free clusters according to its type: compressed or not
 449  *
 450  */
 451
 452 void qcow2_free_any_clusters(BlockDriverState *bs,
 453     uint64_t cluster_offset, int nb_clusters)
 454 {
 455     BDRVQcowState *s = bs->opaque;
 456
 457     /* free the cluster */
 458
 459     if (cluster_offset & QCOW_OFLAG_COMPRESSED) {
 460         int nb_csectors;
 461         nb_csectors = ((cluster_offset >> s->csize_shift) &
 462                        s->csize_mask) + 1;
 463         qcow2_free_clusters(bs,
 464             (cluster_offset & s->cluster_offset_mask) & ~511,
 465             nb_csectors * 512);
 466         return;
 467     }
 468
 469     qcow2_free_clusters(bs, cluster_offset, nb_clusters << s->cluster_bits);
 470
 471     return;
 472 }
 473
 474
 475
 476 /*********************************************************/
 477 /* snapshots and image creation */
 478
 479
 480
 481 void qcow2_create_refcount_update(QCowCreateState *s, int64_t offset,
 482     int64_t size)
 483 {
 484     int refcount;
 485     int64_t start, last, cluster_offset;
 486     uint16_t *p;
 487
 488     start = offset & ~(s->cluster_size - 1);
 489     last = (offset + size - 1)  & ~(s->cluster_size - 1);
 490     for(cluster_offset = start; cluster_offset <= last;
 491         cluster_offset += s->cluster_size) {
 492         p = &s->refcount_block[cluster_offset >> s->cluster_bits];
 493         refcount = be16_to_cpu(*p);
 494         refcount++;
 495         *p = cpu_to_be16(refcount);
 496     }
 497 }
 498
 499 /* update the refcounts of snapshots and the copied flag */
 500 int qcow2_update_snapshot_refcount(BlockDriverState *bs,
 501     int64_t l1_table_offset, int l1_size, int addend)
 502 {
 503     BDRVQcowState *s = bs->opaque;
 504     uint64_t *l1_table, *l2_table, l2_offset, offset, l1_size2, l1_allocated;
 505     int64_t old_offset, old_l2_offset;
 506     int l2_size, i, j, l1_modified, l2_modified, nb_csectors, refcount;
 507
 508     qcow2_l2_cache_reset(bs);
 509     cache_refcount_updates = 1;
 510
 511     l2_table = NULL;
 512     l1_table = NULL;
 513     l1_size2 = l1_size * sizeof(uint64_t);
 514     l1_allocated = 0;
 515     if (l1_table_offset != s->l1_table_offset) {
 516         l1_table = qemu_mallocz(align_offset(l1_size2, 512));
 517         l1_allocated = 1;
 518         if (bdrv_pread(s->hd, l1_table_offset,
 519                        l1_table, l1_size2) != l1_size2)
 520             goto fail;
 521         for(i = 0;i < l1_size; i++)
 522             be64_to_cpus(&l1_table[i]);
 523     } else {
 524         assert(l1_size == s->l1_size);
 525         l1_table = s->l1_table;
 526         l1_allocated = 0;
 527     }
 528
 529     l2_size = s->l2_size * sizeof(uint64_t);
 530     l2_table = qemu_malloc(l2_size);
 531     l1_modified = 0;
 532     for(i = 0; i < l1_size; i++) {
 533         l2_offset = l1_table[i];
 534         if (l2_offset) {
 535             old_l2_offset = l2_offset;
 536             l2_offset &= ~QCOW_OFLAG_COPIED;
 537             l2_modified = 0;
 538             if (bdrv_pread(s->hd, l2_offset, l2_table, l2_size) != l2_size)
 539                 goto fail;
 540             for(j = 0; j < s->l2_size; j++) {
 541                 offset = be64_to_cpu(l2_table[j]);
 542                 if (offset != 0) {
 543                     old_offset = offset;
 544                     offset &= ~QCOW_OFLAG_COPIED;
 545                     if (offset & QCOW_OFLAG_COMPRESSED) {
 546                         nb_csectors = ((offset >> s->csize_shift) &
 547                                        s->csize_mask) + 1;
 548                         if (addend != 0)
 549                             update_refcount(bs, (offset & s->cluster_offset_mask) & ~511,
 550                                             nb_csectors * 512, addend);
 551                         /* compressed clusters are never modified */
 552                         refcount = 2;
 553                     } else {
 554                         if (addend != 0) {
 555                             refcount = update_cluster_refcount(bs, offset >> s->cluster_bits, addend);
 556                         } else {
 557                             refcount = get_refcount(bs, offset >> s->cluster_bits);
 558                         }
 559                     }
 560
 561                     if (refcount == 1) {
 562                         offset |= QCOW_OFLAG_COPIED;
 563                     }
 564                     if (offset != old_offset) {
 565                         l2_table[j] = cpu_to_be64(offset);
 566                         l2_modified = 1;
 567                     }
 568                 }
 569             }
 570             if (l2_modified) {
 571                 if (bdrv_pwrite(s->hd,
 572                                 l2_offset, l2_table, l2_size) != l2_size)
 573                     goto fail;
 574             }
 575
 576             if (addend != 0) {
 577                 refcount = update_cluster_refcount(bs, l2_offset >> s->cluster_bits, addend);
 578             } else {
 579                 refcount = get_refcount(bs, l2_offset >> s->cluster_bits);
 580             }
 581             if (refcount == 1) {
 582                 l2_offset |= QCOW_OFLAG_COPIED;
 583             }
 584             if (l2_offset != old_l2_offset) {
 585                 l1_table[i] = l2_offset;
 586                 l1_modified = 1;
 587             }
 588         }
 589     }
 590     if (l1_modified) {
 591         for(i = 0; i < l1_size; i++)
 592             cpu_to_be64s(&l1_table[i]);
 593         if (bdrv_pwrite(s->hd, l1_table_offset, l1_table,
 594                         l1_size2) != l1_size2)
 595             goto fail;
 596         for(i = 0; i < l1_size; i++)
 597             be64_to_cpus(&l1_table[i]);
 598     }
 599     if (l1_allocated)
 600         qemu_free(l1_table);
 601     qemu_free(l2_table);
 602     cache_refcount_updates = 0;
 603     write_refcount_block(s);
 604     return 0;
 605  fail:
 606     if (l1_allocated)
 607         qemu_free(l1_table);
 608     qemu_free(l2_table);
 609     cache_refcount_updates = 0;
 610     write_refcount_block(s);
 611     return -EIO;
 612 }
 613
 614
 615
 616
 617 /*********************************************************/
 618 /* refcount checking functions */
 619
 620
 621
 622 /*
 623  * Increases the refcount for a range of clusters in a given refcount table.
 624  * This is used to construct a temporary refcount table out of L1 and L2 tables
 625  * which can be compared the the refcount table saved in the image.
 626  *
 627  * Returns the number of errors in the image that were found
 628  */
 629 static int inc_refcounts(BlockDriverState *bs,
 630                           uint16_t *refcount_table,
 631                           int refcount_table_size,
 632                           int64_t offset, int64_t size)
 633 {
 634     BDRVQcowState *s = bs->opaque;
 635     int64_t start, last, cluster_offset;
 636     int k;
 637     int errors = 0;
 638
 639     if (size <= 0)
 640         return 0;
 641
 642     start = offset & ~(s->cluster_size - 1);
 643     last = (offset + size - 1) & ~(s->cluster_size - 1);
 644     for(cluster_offset = start; cluster_offset <= last;
 645         cluster_offset += s->cluster_size) {
 646         k = cluster_offset >> s->cluster_bits;
 647         if (k < 0 || k >= refcount_table_size) {
 648             fprintf(stderr, "ERROR: invalid cluster offset=0x%" PRIx64 "\n",
 649                 cluster_offset);
 650             errors++;
 651         } else {
 652             if (++refcount_table[k] == 0) {
 653                 fprintf(stderr, "ERROR: overflow cluster offset=0x%" PRIx64
 654                     "\n", cluster_offset);
 655                 errors++;
 656             }
 657         }
 658     }
 659
 660     return errors;
 661 }
 662
 663 /*
 664  * Increases the refcount in the given refcount table for the all clusters
 665  * referenced in the L2 table. While doing so, performs some checks on L2
 666  * entries.
 667  *
 668  * Returns the number of errors found by the checks or -errno if an internal
 669  * error occurred.
 670  */
 671 static int check_refcounts_l2(BlockDriverState *bs,
 672     uint16_t *refcount_table, int refcount_table_size, int64_t l2_offset,
 673     int check_copied)
 674 {
 675     BDRVQcowState *s = bs->opaque;
 676     uint64_t *l2_table, offset;
 677     int i, l2_size, nb_csectors, refcount;
 678     int errors = 0;
 679
 680     /* Read L2 table from disk */
 681     l2_size = s->l2_size * sizeof(uint64_t);
 682     l2_table = qemu_malloc(l2_size);
 683
 684     if (bdrv_pread(s->hd, l2_offset, l2_table, l2_size) != l2_size)
 685         goto fail;
 686
 687     /* Do the actual checks */
 688     for(i = 0; i < s->l2_size; i++) {
 689         offset = be64_to_cpu(l2_table[i]);
 690         if (offset != 0) {
 691             if (offset & QCOW_OFLAG_COMPRESSED) {
 692                 /* Compressed clusters don't have QCOW_OFLAG_COPIED */
 693                 if (offset & QCOW_OFLAG_COPIED) {
 694                     fprintf(stderr, "ERROR: cluster %" PRId64 ": "
 695                         "copied flag must never be set for compressed "
 696                         "clusters\n", offset >> s->cluster_bits);
 697                     offset &= ~QCOW_OFLAG_COPIED;
 698                     errors++;
 699                 }
 700
 701                 /* Mark cluster as used */
 702                 nb_csectors = ((offset >> s->csize_shift) &
 703                                s->csize_mask) + 1;
 704                 offset &= s->cluster_offset_mask;
 705                 errors += inc_refcounts(bs, refcount_table,
 706                               refcount_table_size,
 707                               offset & ~511, nb_csectors * 512);
 708             } else {
 709                 /* QCOW_OFLAG_COPIED must be set iff refcount == 1 */
 710                 if (check_copied) {
 711                     uint64_t entry = offset;
 712                     offset &= ~QCOW_OFLAG_COPIED;
 713                     refcount = get_refcount(bs, offset >> s->cluster_bits);
 714                     if ((refcount == 1) != ((entry & QCOW_OFLAG_COPIED) != 0)) {
 715                         fprintf(stderr, "ERROR OFLAG_COPIED: offset=%"
 716                             PRIx64 " refcount=%d\n", entry, refcount);
 717                         errors++;
 718                     }
 719                 }
 720
 721                 /* Mark cluster as used */
 722                 offset &= ~QCOW_OFLAG_COPIED;
 723                 errors += inc_refcounts(bs, refcount_table,
 724                               refcount_table_size,
 725                               offset, s->cluster_size);
 726
 727                 /* Correct offsets are cluster aligned */
 728                 if (offset & (s->cluster_size - 1)) {
 729                     fprintf(stderr, "ERROR offset=%" PRIx64 ": Cluster is not "
 730                         "properly aligned; L2 entry corrupted.\n", offset);
 731                     errors++;
 732                 }
 733             }
 734         }
 735     }
 736
 737     qemu_free(l2_table);
 738     return errors;
 739
 740 fail:
 741     fprintf(stderr, "ERROR: I/O error in check_refcounts_l1\n");
 742     qemu_free(l2_table);
 743     return -EIO;
 744 }
 745
 746 /*
 747  * Increases the refcount for the L1 table, its L2 tables and all referenced
 748  * clusters in the given refcount table. While doing so, performs some checks
 749  * on L1 and L2 entries.
 750  *
 751  * Returns the number of errors found by the checks or -errno if an internal
 752  * error occurred.
 753  */
 754 static int check_refcounts_l1(BlockDriverState *bs,
 755                               uint16_t *refcount_table,
 756                               int refcount_table_size,
 757                               int64_t l1_table_offset, int l1_size,
 758                               int check_copied)
 759 {
 760     BDRVQcowState *s = bs->opaque;
 761     uint64_t *l1_table, l2_offset, l1_size2;
 762     int i, refcount, ret;
 763     int errors = 0;
 764
 765     l1_size2 = l1_size * sizeof(uint64_t);
 766
 767     /* Mark L1 table as used */
 768     errors += inc_refcounts(bs, refcount_table, refcount_table_size,
 769                   l1_table_offset, l1_size2);
 770
 771     /* Read L1 table entries from disk */
 772     l1_table = qemu_malloc(l1_size2);
 773     if (bdrv_pread(s->hd, l1_table_offset,
 774                    l1_table, l1_size2) != l1_size2)
 775         goto fail;
 776     for(i = 0;i < l1_size; i++)
 777         be64_to_cpus(&l1_table[i]);
 778
 779     /* Do the actual checks */
 780     for(i = 0; i < l1_size; i++) {
 781         l2_offset = l1_table[i];
 782         if (l2_offset) {
 783             /* QCOW_OFLAG_COPIED must be set iff refcount == 1 */
 784             if (check_copied) {
 785                 refcount = get_refcount(bs, (l2_offset & ~QCOW_OFLAG_COPIED)
 786                     >> s->cluster_bits);
 787                 if ((refcount == 1) != ((l2_offset & QCOW_OFLAG_COPIED) != 0)) {
 788                     fprintf(stderr, "ERROR OFLAG_COPIED: l2_offset=%" PRIx64
 789                         " refcount=%d\n", l2_offset, refcount);
 790                     errors++;
 791                 }
 792             }
 793
 794             /* Mark L2 table as used */
 795             l2_offset &= ~QCOW_OFLAG_COPIED;
 796             errors += inc_refcounts(bs, refcount_table,
 797                           refcount_table_size,
 798                           l2_offset,
 799                           s->cluster_size);
 800
 801             /* L2 tables are cluster aligned */
 802             if (l2_offset & (s->cluster_size - 1)) {
 803                 fprintf(stderr, "ERROR l2_offset=%" PRIx64 ": Table is not "
 804                     "cluster aligned; L1 entry corrupted\n", l2_offset);
 805                 errors++;
 806             }
 807
 808             /* Process and check L2 entries */
 809             ret = check_refcounts_l2(bs, refcount_table, refcount_table_size,
 810                 l2_offset, check_copied);
 811             if (ret < 0) {
 812                 goto fail;
 813             }
 814             errors += ret;
 815         }
 816     }
 817     qemu_free(l1_table);
 818     return errors;
 819
 820 fail:
 821     fprintf(stderr, "ERROR: I/O error in check_refcounts_l1\n");
 822     qemu_free(l1_table);
 823     return -EIO;
 824 }
 825
 826 /*
 827  * Checks an image for refcount consistency.
 828  *
 829  * Returns 0 if no errors are found, the number of errors in case the image is
 830  * detected as corrupted, and -errno when an internal error occured.
 831  */
 832 int qcow2_check_refcounts(BlockDriverState *bs)
 833 {
 834     BDRVQcowState *s = bs->opaque;
 835     int64_t size;
 836     int nb_clusters, refcount1, refcount2, i;
 837     QCowSnapshot *sn;
 838     uint16_t *refcount_table;
 839     int ret, errors = 0;
 840
 841     size = bdrv_getlength(s->hd);
 842     nb_clusters = size_to_clusters(s, size);
 843     refcount_table = qemu_mallocz(nb_clusters * sizeof(uint16_t));
 844
 845     /* header */
 846     errors += inc_refcounts(bs, refcount_table, nb_clusters,
 847                   0, s->cluster_size);
 848
 849     /* current L1 table */
 850     ret = check_refcounts_l1(bs, refcount_table, nb_clusters,
 851                        s->l1_table_offset, s->l1_size, 1);
 852     if (ret < 0) {
 853         return ret;
 854     }
 855     errors += ret;
 856
 857     /* snapshots */
 858     for(i = 0; i < s->nb_snapshots; i++) {
 859         sn = s->snapshots + i;
 860         check_refcounts_l1(bs, refcount_table, nb_clusters,
 861                            sn->l1_table_offset, sn->l1_size, 0);
 862     }
 863     errors += inc_refcounts(bs, refcount_table, nb_clusters,
 864                   s->snapshots_offset, s->snapshots_size);
 865
 866     /* refcount data */
 867     errors += inc_refcounts(bs, refcount_table, nb_clusters,
 868                   s->refcount_table_offset,
 869                   s->refcount_table_size * sizeof(uint64_t));
 870     for(i = 0; i < s->refcount_table_size; i++) {
 871         int64_t offset;
 872         offset = s->refcount_table[i];
 873         if (offset != 0) {
 874             errors += inc_refcounts(bs, refcount_table, nb_clusters,
 875                           offset, s->cluster_size);
 876         }
 877     }
 878
 879     /* compare ref counts */
 880     for(i = 0; i < nb_clusters; i++) {
 881         refcount1 = get_refcount(bs, i);
 882         refcount2 = refcount_table[i];
 883         if (refcount1 != refcount2) {
 884             fprintf(stderr, "ERROR cluster %d refcount=%d reference=%d\n",
 885                    i, refcount1, refcount2);
 886             errors++;
 887         }
 888     }
 889
 890     qemu_free(refcount_table);
 891
 892     return errors;
 893 }
 894