block/qcow2-snapshot.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/osdep.h"
  26 #include "qapi/error.h"
  27 #include "qemu-common.h"
  28 #include "block/block_int.h"
  29 #include "block/qcow2.h"
  30 #include "qemu/error-report.h"
  31
  32 void qcow2_free_snapshots(BlockDriverState *bs)
  33 {
  34     BDRVQcow2State *s = bs->opaque;
  35     int i;
  36
  37     for(i = 0; i < s->nb_snapshots; i++) {
  38         g_free(s->snapshots[i].name);
  39         g_free(s->snapshots[i].id_str);
  40     }
  41     g_free(s->snapshots);
  42     s->snapshots = NULL;
  43     s->nb_snapshots = 0;
  44 }
  45
  46 int qcow2_read_snapshots(BlockDriverState *bs)
  47 {
  48     BDRVQcow2State *s = bs->opaque;
  49     QCowSnapshotHeader h;
  50     QCowSnapshotExtraData extra;
  51     QCowSnapshot *sn;
  52     int i, id_str_size, name_size;
  53     int64_t offset;
  54     uint32_t extra_data_size;
  55     int ret;
  56
  57     if (!s->nb_snapshots) {
  58         s->snapshots = NULL;
  59         s->snapshots_size = 0;
  60         return 0;
  61     }
  62
  63     offset = s->snapshots_offset;
  64     s->snapshots = g_new0(QCowSnapshot, s->nb_snapshots);
  65
  66     for(i = 0; i < s->nb_snapshots; i++) {
  67         /* Read statically sized part of the snapshot header */
  68         offset = align_offset(offset, 8);
  69         ret = bdrv_pread(bs->file->bs, offset, &h, sizeof(h));
  70         if (ret < 0) {
  71             goto fail;
  72         }
  73
  74         offset += sizeof(h);
  75         sn = s->snapshots + i;
  76         sn->l1_table_offset = be64_to_cpu(h.l1_table_offset);
  77         sn->l1_size = be32_to_cpu(h.l1_size);
  78         sn->vm_state_size = be32_to_cpu(h.vm_state_size);
  79         sn->date_sec = be32_to_cpu(h.date_sec);
  80         sn->date_nsec = be32_to_cpu(h.date_nsec);
  81         sn->vm_clock_nsec = be64_to_cpu(h.vm_clock_nsec);
  82         extra_data_size = be32_to_cpu(h.extra_data_size);
  83
  84         id_str_size = be16_to_cpu(h.id_str_size);
  85         name_size = be16_to_cpu(h.name_size);
  86
  87         /* Read extra data */
  88         ret = bdrv_pread(bs->file->bs, offset, &extra,
  89                          MIN(sizeof(extra), extra_data_size));
  90         if (ret < 0) {
  91             goto fail;
  92         }
  93         offset += extra_data_size;
  94
  95         if (extra_data_size >= 8) {
  96             sn->vm_state_size = be64_to_cpu(extra.vm_state_size_large);
  97         }
  98
  99         if (extra_data_size >= 16) {
 100             sn->disk_size = be64_to_cpu(extra.disk_size);
 101         } else {
 102             sn->disk_size = bs->total_sectors * BDRV_SECTOR_SIZE;
 103         }
 104
 105         /* Read snapshot ID */
 106         sn->id_str = g_malloc(id_str_size + 1);
 107         ret = bdrv_pread(bs->file->bs, offset, sn->id_str, id_str_size);
 108         if (ret < 0) {
 109             goto fail;
 110         }
 111         offset += id_str_size;
 112         sn->id_str[id_str_size] = '\0';
 113
 114         /* Read snapshot name */
 115         sn->name = g_malloc(name_size + 1);
 116         ret = bdrv_pread(bs->file->bs, offset, sn->name, name_size);
 117         if (ret < 0) {
 118             goto fail;
 119         }
 120         offset += name_size;
 121         sn->name[name_size] = '\0';
 122
 123         if (offset - s->snapshots_offset > QCOW_MAX_SNAPSHOTS_SIZE) {
 124             ret = -EFBIG;
 125             goto fail;
 126         }
 127     }
 128
 129     assert(offset - s->snapshots_offset <= INT_MAX);
 130     s->snapshots_size = offset - s->snapshots_offset;
 131     return 0;
 132
 133 fail:
 134     qcow2_free_snapshots(bs);
 135     return ret;
 136 }
 137
 138 /* add at the end of the file a new list of snapshots */
 139 static int qcow2_write_snapshots(BlockDriverState *bs)
 140 {
 141     BDRVQcow2State *s = bs->opaque;
 142     QCowSnapshot *sn;
 143     QCowSnapshotHeader h;
 144     QCowSnapshotExtraData extra;
 145     int i, name_size, id_str_size, snapshots_size;
 146     struct {
 147         uint32_t nb_snapshots;
 148         uint64_t snapshots_offset;
 149     } QEMU_PACKED header_data;
 150     int64_t offset, snapshots_offset = 0;
 151     int ret;
 152
 153     /* compute the size of the snapshots */
 154     offset = 0;
 155     for(i = 0; i < s->nb_snapshots; i++) {
 156         sn = s->snapshots + i;
 157         offset = align_offset(offset, 8);
 158         offset += sizeof(h);
 159         offset += sizeof(extra);
 160         offset += strlen(sn->id_str);
 161         offset += strlen(sn->name);
 162
 163         if (offset > QCOW_MAX_SNAPSHOTS_SIZE) {
 164             ret = -EFBIG;
 165             goto fail;
 166         }
 167     }
 168
 169     assert(offset <= INT_MAX);
 170     snapshots_size = offset;
 171
 172     /* Allocate space for the new snapshot list */
 173     snapshots_offset = qcow2_alloc_clusters(bs, snapshots_size);
 174     offset = snapshots_offset;
 175     if (offset < 0) {
 176         ret = offset;
 177         goto fail;
 178     }
 179     ret = bdrv_flush(bs);
 180     if (ret < 0) {
 181         goto fail;
 182     }
 183
 184     /* The snapshot list position has not yet been updated, so these clusters
 185      * must indeed be completely free */
 186     ret = qcow2_pre_write_overlap_check(bs, 0, offset, snapshots_size);
 187     if (ret < 0) {
 188         goto fail;
 189     }
 190
 191
 192     /* Write all snapshots to the new list */
 193     for(i = 0; i < s->nb_snapshots; i++) {
 194         sn = s->snapshots + i;
 195         memset(&h, 0, sizeof(h));
 196         h.l1_table_offset = cpu_to_be64(sn->l1_table_offset);
 197         h.l1_size = cpu_to_be32(sn->l1_size);
 198         /* If it doesn't fit in 32 bit, older implementations should treat it
 199          * as a disk-only snapshot rather than truncate the VM state */
 200         if (sn->vm_state_size <= 0xffffffff) {
 201             h.vm_state_size = cpu_to_be32(sn->vm_state_size);
 202         }
 203         h.date_sec = cpu_to_be32(sn->date_sec);
 204         h.date_nsec = cpu_to_be32(sn->date_nsec);
 205         h.vm_clock_nsec = cpu_to_be64(sn->vm_clock_nsec);
 206         h.extra_data_size = cpu_to_be32(sizeof(extra));
 207
 208         memset(&extra, 0, sizeof(extra));
 209         extra.vm_state_size_large = cpu_to_be64(sn->vm_state_size);
 210         extra.disk_size = cpu_to_be64(sn->disk_size);
 211
 212         id_str_size = strlen(sn->id_str);
 213         name_size = strlen(sn->name);
 214         assert(id_str_size <= UINT16_MAX && name_size <= UINT16_MAX);
 215         h.id_str_size = cpu_to_be16(id_str_size);
 216         h.name_size = cpu_to_be16(name_size);
 217         offset = align_offset(offset, 8);
 218
 219         ret = bdrv_pwrite(bs->file->bs, offset, &h, sizeof(h));
 220         if (ret < 0) {
 221             goto fail;
 222         }
 223         offset += sizeof(h);
 224
 225         ret = bdrv_pwrite(bs->file->bs, offset, &extra, sizeof(extra));
 226         if (ret < 0) {
 227             goto fail;
 228         }
 229         offset += sizeof(extra);
 230
 231         ret = bdrv_pwrite(bs->file->bs, offset, sn->id_str, id_str_size);
 232         if (ret < 0) {
 233             goto fail;
 234         }
 235         offset += id_str_size;
 236
 237         ret = bdrv_pwrite(bs->file->bs, offset, sn->name, name_size);
 238         if (ret < 0) {
 239             goto fail;
 240         }
 241         offset += name_size;
 242     }
 243
 244     /*
 245      * Update the header to point to the new snapshot table. This requires the
 246      * new table and its refcounts to be stable on disk.
 247      */
 248     ret = bdrv_flush(bs);
 249     if (ret < 0) {
 250         goto fail;
 251     }
 252
 253     QEMU_BUILD_BUG_ON(offsetof(QCowHeader, snapshots_offset) !=
 254         offsetof(QCowHeader, nb_snapshots) + sizeof(header_data.nb_snapshots));
 255
 256     header_data.nb_snapshots        = cpu_to_be32(s->nb_snapshots);
 257     header_data.snapshots_offset    = cpu_to_be64(snapshots_offset);
 258
 259     ret = bdrv_pwrite_sync(bs->file->bs, offsetof(QCowHeader, nb_snapshots),
 260                            &header_data, sizeof(header_data));
 261     if (ret < 0) {
 262         goto fail;
 263     }
 264
 265     /* free the old snapshot table */
 266     qcow2_free_clusters(bs, s->snapshots_offset, s->snapshots_size,
 267                         QCOW2_DISCARD_SNAPSHOT);
 268     s->snapshots_offset = snapshots_offset;
 269     s->snapshots_size = snapshots_size;
 270     return 0;
 271
 272 fail:
 273     if (snapshots_offset > 0) {
 274         qcow2_free_clusters(bs, snapshots_offset, snapshots_size,
 275                             QCOW2_DISCARD_ALWAYS);
 276     }
 277     return ret;
 278 }
 279
 280 static void find_new_snapshot_id(BlockDriverState *bs,
 281                                  char *id_str, int id_str_size)
 282 {
 283     BDRVQcow2State *s = bs->opaque;
 284     QCowSnapshot *sn;
 285     int i;
 286     unsigned long id, id_max = 0;
 287
 288     for(i = 0; i < s->nb_snapshots; i++) {
 289         sn = s->snapshots + i;
 290         id = strtoul(sn->id_str, NULL, 10);
 291         if (id > id_max)
 292             id_max = id;
 293     }
 294     snprintf(id_str, id_str_size, "%lu", id_max + 1);
 295 }
 296
 297 static int find_snapshot_by_id_and_name(BlockDriverState *bs,
 298                                         const char *id,
 299                                         const char *name)
 300 {
 301     BDRVQcow2State *s = bs->opaque;
 302     int i;
 303
 304     if (id && name) {
 305         for (i = 0; i < s->nb_snapshots; i++) {
 306             if (!strcmp(s->snapshots[i].id_str, id) &&
 307                 !strcmp(s->snapshots[i].name, name)) {
 308                 return i;
 309             }
 310         }
 311     } else if (id) {
 312         for (i = 0; i < s->nb_snapshots; i++) {
 313             if (!strcmp(s->snapshots[i].id_str, id)) {
 314                 return i;
 315             }
 316         }
 317     } else if (name) {
 318         for (i = 0; i < s->nb_snapshots; i++) {
 319             if (!strcmp(s->snapshots[i].name, name)) {
 320                 return i;
 321             }
 322         }
 323     }
 324
 325     return -1;
 326 }
 327
 328 static int find_snapshot_by_id_or_name(BlockDriverState *bs,
 329                                        const char *id_or_name)
 330 {
 331     int ret;
 332
 333     ret = find_snapshot_by_id_and_name(bs, id_or_name, NULL);
 334     if (ret >= 0) {
 335         return ret;
 336     }
 337     return find_snapshot_by_id_and_name(bs, NULL, id_or_name);
 338 }
 339
 340 /* if no id is provided, a new one is constructed */
 341 int qcow2_snapshot_create(BlockDriverState *bs, QEMUSnapshotInfo *sn_info)
 342 {
 343     BDRVQcow2State *s = bs->opaque;
 344     QCowSnapshot *new_snapshot_list = NULL;
 345     QCowSnapshot *old_snapshot_list = NULL;
 346     QCowSnapshot sn1, *sn = &sn1;
 347     int i, ret;
 348     uint64_t *l1_table = NULL;
 349     int64_t l1_table_offset;
 350
 351     if (s->nb_snapshots >= QCOW_MAX_SNAPSHOTS) {
 352         return -EFBIG;
 353     }
 354
 355     memset(sn, 0, sizeof(*sn));
 356
 357     /* Generate an ID */
 358     find_new_snapshot_id(bs, sn_info->id_str, sizeof(sn_info->id_str));
 359
 360     /* Check that the ID is unique */
 361     if (find_snapshot_by_id_and_name(bs, sn_info->id_str, NULL) >= 0) {
 362         return -EEXIST;
 363     }
 364
 365     /* Populate sn with passed data */
 366     sn->id_str = g_strdup(sn_info->id_str);
 367     sn->name = g_strdup(sn_info->name);
 368
 369     sn->disk_size = bs->total_sectors * BDRV_SECTOR_SIZE;
 370     sn->vm_state_size = sn_info->vm_state_size;
 371     sn->date_sec = sn_info->date_sec;
 372     sn->date_nsec = sn_info->date_nsec;
 373     sn->vm_clock_nsec = sn_info->vm_clock_nsec;
 374
 375     /* Allocate the L1 table of the snapshot and copy the current one there. */
 376     l1_table_offset = qcow2_alloc_clusters(bs, s->l1_size * sizeof(uint64_t));
 377     if (l1_table_offset < 0) {
 378         ret = l1_table_offset;
 379         goto fail;
 380     }
 381
 382     sn->l1_table_offset = l1_table_offset;
 383     sn->l1_size = s->l1_size;
 384
 385     l1_table = g_try_new(uint64_t, s->l1_size);
 386     if (s->l1_size && l1_table == NULL) {
 387         ret = -ENOMEM;
 388         goto fail;
 389     }
 390
 391     for(i = 0; i < s->l1_size; i++) {
 392         l1_table[i] = cpu_to_be64(s->l1_table[i]);
 393     }
 394
 395     ret = qcow2_pre_write_overlap_check(bs, 0, sn->l1_table_offset,
 396                                         s->l1_size * sizeof(uint64_t));
 397     if (ret < 0) {
 398         goto fail;
 399     }
 400
 401     ret = bdrv_pwrite(bs->file->bs, sn->l1_table_offset, l1_table,
 402                       s->l1_size * sizeof(uint64_t));
 403     if (ret < 0) {
 404         goto fail;
 405     }
 406
 407     g_free(l1_table);
 408     l1_table = NULL;
 409
 410     /*
 411      * Increase the refcounts of all clusters and make sure everything is
 412      * stable on disk before updating the snapshot table to contain a pointer
 413      * to the new L1 table.
 414      */
 415     ret = qcow2_update_snapshot_refcount(bs, s->l1_table_offset, s->l1_size, 1);
 416     if (ret < 0) {
 417         goto fail;
 418     }
 419
 420     /* Append the new snapshot to the snapshot list */
 421     new_snapshot_list = g_new(QCowSnapshot, s->nb_snapshots + 1);
 422     if (s->snapshots) {
 423         memcpy(new_snapshot_list, s->snapshots,
 424                s->nb_snapshots * sizeof(QCowSnapshot));
 425         old_snapshot_list = s->snapshots;
 426     }
 427     s->snapshots = new_snapshot_list;
 428     s->snapshots[s->nb_snapshots++] = *sn;
 429
 430     ret = qcow2_write_snapshots(bs);
 431     if (ret < 0) {
 432         g_free(s->snapshots);
 433         s->snapshots = old_snapshot_list;
 434         s->nb_snapshots--;
 435         goto fail;
 436     }
 437
 438     g_free(old_snapshot_list);
 439
 440     /* The VM state isn't needed any more in the active L1 table; in fact, it
 441      * hurts by causing expensive COW for the next snapshot. */
 442     qcow2_discard_clusters(bs, qcow2_vm_state_offset(s),
 443                            align_offset(sn->vm_state_size, s->cluster_size)
 444                                 >> BDRV_SECTOR_BITS,
 445                            QCOW2_DISCARD_NEVER, false);
 446
 447 #ifdef DEBUG_ALLOC
 448     {
 449       BdrvCheckResult result = {0};
 450       qcow2_check_refcounts(bs, &result, 0);
 451     }
 452 #endif
 453     return 0;
 454
 455 fail:
 456     g_free(sn->id_str);
 457     g_free(sn->name);
 458     g_free(l1_table);
 459
 460     return ret;
 461 }
 462
 463 /* copy the snapshot 'snapshot_name' into the current disk image */
 464 int qcow2_snapshot_goto(BlockDriverState *bs, const char *snapshot_id)
 465 {
 466     BDRVQcow2State *s = bs->opaque;
 467     QCowSnapshot *sn;
 468     int i, snapshot_index;
 469     int cur_l1_bytes, sn_l1_bytes;
 470     int ret;
 471     uint64_t *sn_l1_table = NULL;
 472
 473     /* Search the snapshot */
 474     snapshot_index = find_snapshot_by_id_or_name(bs, snapshot_id);
 475     if (snapshot_index < 0) {
 476         return -ENOENT;
 477     }
 478     sn = &s->snapshots[snapshot_index];
 479
 480     if (sn->disk_size != bs->total_sectors * BDRV_SECTOR_SIZE) {
 481         error_report("qcow2: Loading snapshots with different disk "
 482             "size is not implemented");
 483         ret = -ENOTSUP;
 484         goto fail;
 485     }
 486
 487     /*
 488      * Make sure that the current L1 table is big enough to contain the whole
 489      * L1 table of the snapshot. If the snapshot L1 table is smaller, the
 490      * current one must be padded with zeros.
 491      */
 492     ret = qcow2_grow_l1_table(bs, sn->l1_size, true);
 493     if (ret < 0) {
 494         goto fail;
 495     }
 496
 497     cur_l1_bytes = s->l1_size * sizeof(uint64_t);
 498     sn_l1_bytes = sn->l1_size * sizeof(uint64_t);
 499
 500     /*
 501      * Copy the snapshot L1 table to the current L1 table.
 502      *
 503      * Before overwriting the old current L1 table on disk, make sure to
 504      * increase all refcounts for the clusters referenced by the new one.
 505      * Decrease the refcount referenced by the old one only when the L1
 506      * table is overwritten.
 507      */
 508     sn_l1_table = g_try_malloc0(cur_l1_bytes);
 509     if (cur_l1_bytes && sn_l1_table == NULL) {
 510         ret = -ENOMEM;
 511         goto fail;
 512     }
 513
 514     ret = bdrv_pread(bs->file->bs, sn->l1_table_offset,
 515                      sn_l1_table, sn_l1_bytes);
 516     if (ret < 0) {
 517         goto fail;
 518     }
 519
 520     ret = qcow2_update_snapshot_refcount(bs, sn->l1_table_offset,
 521                                          sn->l1_size, 1);
 522     if (ret < 0) {
 523         goto fail;
 524     }
 525
 526     ret = qcow2_pre_write_overlap_check(bs, QCOW2_OL_ACTIVE_L1,
 527                                         s->l1_table_offset, cur_l1_bytes);
 528     if (ret < 0) {
 529         goto fail;
 530     }
 531
 532     ret = bdrv_pwrite_sync(bs->file->bs, s->l1_table_offset, sn_l1_table,
 533                            cur_l1_bytes);
 534     if (ret < 0) {
 535         goto fail;
 536     }
 537
 538     /*
 539      * Decrease refcount of clusters of current L1 table.
 540      *
 541      * At this point, the in-memory s->l1_table points to the old L1 table,
 542      * whereas on disk we already have the new one.
 543      *
 544      * qcow2_update_snapshot_refcount special cases the current L1 table to use
 545      * the in-memory data instead of really using the offset to load a new one,
 546      * which is why this works.
 547      */
 548     ret = qcow2_update_snapshot_refcount(bs, s->l1_table_offset,
 549                                          s->l1_size, -1);
 550
 551     /*
 552      * Now update the in-memory L1 table to be in sync with the on-disk one. We
 553      * need to do this even if updating refcounts failed.
 554      */
 555     for(i = 0;i < s->l1_size; i++) {
 556         s->l1_table[i] = be64_to_cpu(sn_l1_table[i]);
 557     }
 558
 559     if (ret < 0) {
 560         goto fail;
 561     }
 562
 563     g_free(sn_l1_table);
 564     sn_l1_table = NULL;
 565
 566     /*
 567      * Update QCOW_OFLAG_COPIED in the active L1 table (it may have changed
 568      * when we decreased the refcount of the old snapshot.
 569      */
 570     ret = qcow2_update_snapshot_refcount(bs, s->l1_table_offset, s->l1_size, 0);
 571     if (ret < 0) {
 572         goto fail;
 573     }
 574
 575 #ifdef DEBUG_ALLOC
 576     {
 577         BdrvCheckResult result = {0};
 578         qcow2_check_refcounts(bs, &result, 0);
 579     }
 580 #endif
 581     return 0;
 582
 583 fail:
 584     g_free(sn_l1_table);
 585     return ret;
 586 }
 587
 588 int qcow2_snapshot_delete(BlockDriverState *bs,
 589                           const char *snapshot_id,
 590                           const char *name,
 591                           Error **errp)
 592 {
 593     BDRVQcow2State *s = bs->opaque;
 594     QCowSnapshot sn;
 595     int snapshot_index, ret;
 596
 597     /* Search the snapshot */
 598     snapshot_index = find_snapshot_by_id_and_name(bs, snapshot_id, name);
 599     if (snapshot_index < 0) {
 600         error_setg(errp, "Can't find the snapshot");
 601         return -ENOENT;
 602     }
 603     sn = s->snapshots[snapshot_index];
 604
 605     /* Remove it from the snapshot list */
 606     memmove(s->snapshots + snapshot_index,
 607             s->snapshots + snapshot_index + 1,
 608             (s->nb_snapshots - snapshot_index - 1) * sizeof(sn));
 609     s->nb_snapshots--;
 610     ret = qcow2_write_snapshots(bs);
 611     if (ret < 0) {
 612         error_setg_errno(errp, -ret,
 613                          "Failed to remove snapshot from snapshot list");
 614         return ret;
 615     }
 616
 617     /*
 618      * The snapshot is now unused, clean up. If we fail after this point, we
 619      * won't recover but just leak clusters.
 620      */
 621     g_free(sn.id_str);
 622     g_free(sn.name);
 623
 624     /*
 625      * Now decrease the refcounts of clusters referenced by the snapshot and
 626      * free the L1 table.
 627      */
 628     ret = qcow2_update_snapshot_refcount(bs, sn.l1_table_offset,
 629                                          sn.l1_size, -1);
 630     if (ret < 0) {
 631         error_setg_errno(errp, -ret, "Failed to free the cluster and L1 table");
 632         return ret;
 633     }
 634     qcow2_free_clusters(bs, sn.l1_table_offset, sn.l1_size * sizeof(uint64_t),
 635                         QCOW2_DISCARD_SNAPSHOT);
 636
 637     /* must update the copied flag on the current cluster offsets */
 638     ret = qcow2_update_snapshot_refcount(bs, s->l1_table_offset, s->l1_size, 0);
 639     if (ret < 0) {
 640         error_setg_errno(errp, -ret,
 641                          "Failed to update snapshot status in disk");
 642         return ret;
 643     }
 644
 645 #ifdef DEBUG_ALLOC
 646     {
 647         BdrvCheckResult result = {0};
 648         qcow2_check_refcounts(bs, &result, 0);
 649     }
 650 #endif
 651     return 0;
 652 }
 653
 654 int qcow2_snapshot_list(BlockDriverState *bs, QEMUSnapshotInfo **psn_tab)
 655 {
 656     BDRVQcow2State *s = bs->opaque;
 657     QEMUSnapshotInfo *sn_tab, *sn_info;
 658     QCowSnapshot *sn;
 659     int i;
 660
 661     if (!s->nb_snapshots) {
 662         *psn_tab = NULL;
 663         return s->nb_snapshots;
 664     }
 665
 666     sn_tab = g_new0(QEMUSnapshotInfo, s->nb_snapshots);
 667     for(i = 0; i < s->nb_snapshots; i++) {
 668         sn_info = sn_tab + i;
 669         sn = s->snapshots + i;
 670         pstrcpy(sn_info->id_str, sizeof(sn_info->id_str),
 671                 sn->id_str);
 672         pstrcpy(sn_info->name, sizeof(sn_info->name),
 673                 sn->name);
 674         sn_info->vm_state_size = sn->vm_state_size;
 675         sn_info->date_sec = sn->date_sec;
 676         sn_info->date_nsec = sn->date_nsec;
 677         sn_info->vm_clock_nsec = sn->vm_clock_nsec;
 678     }
 679     *psn_tab = sn_tab;
 680     return s->nb_snapshots;
 681 }
 682
 683 int qcow2_snapshot_load_tmp(BlockDriverState *bs,
 684                             const char *snapshot_id,
 685                             const char *name,
 686                             Error **errp)
 687 {
 688     int i, snapshot_index;
 689     BDRVQcow2State *s = bs->opaque;
 690     QCowSnapshot *sn;
 691     uint64_t *new_l1_table;
 692     int new_l1_bytes;
 693     int ret;
 694
 695     assert(bs->read_only);
 696
 697     /* Search the snapshot */
 698     snapshot_index = find_snapshot_by_id_and_name(bs, snapshot_id, name);
 699     if (snapshot_index < 0) {
 700         error_setg(errp,
 701                    "Can't find snapshot");
 702         return -ENOENT;
 703     }
 704     sn = &s->snapshots[snapshot_index];
 705
 706     /* Allocate and read in the snapshot's L1 table */
 707     if (sn->l1_size > QCOW_MAX_L1_SIZE / sizeof(uint64_t)) {
 708         error_setg(errp, "Snapshot L1 table too large");
 709         return -EFBIG;
 710     }
 711     new_l1_bytes = sn->l1_size * sizeof(uint64_t);
 712     new_l1_table = qemu_try_blockalign(bs->file->bs,
 713                                        align_offset(new_l1_bytes, 512));
 714     if (new_l1_table == NULL) {
 715         return -ENOMEM;
 716     }
 717
 718     ret = bdrv_pread(bs->file->bs, sn->l1_table_offset,
 719                      new_l1_table, new_l1_bytes);
 720     if (ret < 0) {
 721         error_setg(errp, "Failed to read l1 table for snapshot");
 722         qemu_vfree(new_l1_table);
 723         return ret;
 724     }
 725
 726     /* Switch the L1 table */
 727     qemu_vfree(s->l1_table);
 728
 729     s->l1_size = sn->l1_size;
 730     s->l1_table_offset = sn->l1_table_offset;
 731     s->l1_table = new_l1_table;
 732
 733     for(i = 0;i < s->l1_size; i++) {
 734         be64_to_cpus(&s->l1_table[i]);
 735     }
 736
 737     return 0;
 738 }