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