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 "block/block_int.h"
  28 #include "block/qcow2.h"
  29 #include "qemu/bswap.h"
  30 #include "qemu/error-report.h"
  31 #include "qemu/cutils.h"
  32
  33 void qcow2_free_snapshots(BlockDriverState *bs)
  34 {
  35     BDRVQcow2State *s = bs->opaque;
  36     int i;
  37
  38     for(i = 0; i < s->nb_snapshots; i++) {
  39         g_free(s->snapshots[i].name);
  40         g_free(s->snapshots[i].id_str);
  41     }
  42     g_free(s->snapshots);
  43     s->snapshots = NULL;
  44     s->nb_snapshots = 0;
  45 }
  46
  47 int qcow2_read_snapshots(BlockDriverState *bs)
  48 {
  49     BDRVQcow2State *s = bs->opaque;
  50     QCowSnapshotHeader h;
  51     QCowSnapshotExtraData extra;
  52     QCowSnapshot *sn;
  53     int i, id_str_size, name_size;
  54     int64_t offset;
  55     uint32_t extra_data_size;
  56     int ret;
  57
  58     if (!s->nb_snapshots) {
  59         s->snapshots = NULL;
  60         s->snapshots_size = 0;
  61         return 0;
  62     }
  63
  64     offset = s->snapshots_offset;
  65     s->snapshots = g_new0(QCowSnapshot, s->nb_snapshots);
  66
  67     for(i = 0; i < s->nb_snapshots; i++) {
  68         /* Read statically sized part of the snapshot header */
  69         offset = align_offset(offset, 8);
  70         ret = bdrv_pread(bs->file, offset, &h, sizeof(h));
  71         if (ret < 0) {
  72             goto fail;
  73         }
  74
  75         offset += sizeof(h);
  76         sn = s->snapshots + i;
  77         sn->l1_table_offset = be64_to_cpu(h.l1_table_offset);
  78         sn->l1_size = be32_to_cpu(h.l1_size);
  79         sn->vm_state_size = be32_to_cpu(h.vm_state_size);
  80         sn->date_sec = be32_to_cpu(h.date_sec);
  81         sn->date_nsec = be32_to_cpu(h.date_nsec);
  82         sn->vm_clock_nsec = be64_to_cpu(h.vm_clock_nsec);
  83         extra_data_size = be32_to_cpu(h.extra_data_size);
  84
  85         id_str_size = be16_to_cpu(h.id_str_size);
  86         name_size = be16_to_cpu(h.name_size);
  87
  88         /* Read extra data */
  89         ret = bdrv_pread(bs->file, offset, &extra,
  90                          MIN(sizeof(extra), extra_data_size));
  91         if (ret < 0) {
  92             goto fail;
  93         }
  94         offset += extra_data_size;
  95
  96         if (extra_data_size >= 8) {
  97             sn->vm_state_size = be64_to_cpu(extra.vm_state_size_large);
  98         }
  99
 100         if (extra_data_size >= 16) {
 101             sn->disk_size = be64_to_cpu(extra.disk_size);
 102         } else {
 103             sn->disk_size = bs->total_sectors * BDRV_SECTOR_SIZE;
 104         }
 105
 106         /* Read snapshot ID */
 107         sn->id_str = g_malloc(id_str_size + 1);
 108         ret = bdrv_pread(bs->file, offset, sn->id_str, id_str_size);
 109         if (ret < 0) {
 110             goto fail;
 111         }
 112         offset += id_str_size;
 113         sn->id_str[id_str_size] = '\0';
 114
 115         /* Read snapshot name */
 116         sn->name = g_malloc(name_size + 1);
 117         ret = bdrv_pread(bs->file, offset, sn->name, name_size);
 118         if (ret < 0) {
 119             goto fail;
 120         }
 121         offset += name_size;
 122         sn->name[name_size] = '\0';
 123
 124         if (offset - s->snapshots_offset > QCOW_MAX_SNAPSHOTS_SIZE) {
 125             ret = -EFBIG;
 126             goto fail;
 127         }
 128     }
 129
 130     assert(offset - s->snapshots_offset <= INT_MAX);
 131     s->snapshots_size = offset - s->snapshots_offset;
 132     return 0;
 133
 134 fail:
 135     qcow2_free_snapshots(bs);
 136     return ret;
 137 }
 138
 139 /* add at the end of the file a new list of snapshots */
 140 static int qcow2_write_snapshots(BlockDriverState *bs)
 141 {
 142     BDRVQcow2State *s = bs->opaque;
 143     QCowSnapshot *sn;
 144     QCowSnapshotHeader h;
 145     QCowSnapshotExtraData extra;
 146     int i, name_size, id_str_size, snapshots_size;
 147     struct {
 148         uint32_t nb_snapshots;
 149         uint64_t snapshots_offset;
 150     } QEMU_PACKED header_data;
 151     int64_t offset, snapshots_offset = 0;
 152     int ret;
 153
 154     /* compute the size of the snapshots */
 155     offset = 0;
 156     for(i = 0; i < s->nb_snapshots; i++) {
 157         sn = s->snapshots + i;
 158         offset = align_offset(offset, 8);
 159         offset += sizeof(h);
 160         offset += sizeof(extra);
 161         offset += strlen(sn->id_str);
 162         offset += strlen(sn->name);
 163
 164         if (offset > QCOW_MAX_SNAPSHOTS_SIZE) {
 165             ret = -EFBIG;
 166             goto fail;
 167         }
 168     }
 169
 170     assert(offset <= INT_MAX);
 171     snapshots_size = offset;
 172
 173     /* Allocate space for the new snapshot list */
 174     snapshots_offset = qcow2_alloc_clusters(bs, snapshots_size);
 175     offset = snapshots_offset;
 176     if (offset < 0) {
 177         ret = offset;
 178         goto fail;
 179     }
 180     ret = bdrv_flush(bs);
 181     if (ret < 0) {
 182         goto fail;
 183     }
 184
 185     /* The snapshot list position has not yet been updated, so these clusters
 186      * must indeed be completely free */
 187     ret = qcow2_pre_write_overlap_check(bs, 0, offset, snapshots_size);
 188     if (ret < 0) {
 189         goto fail;
 190     }
 191
 192
 193     /* Write all snapshots to the new list */
 194     for(i = 0; i < s->nb_snapshots; i++) {
 195         sn = s->snapshots + i;
 196         memset(&h, 0, sizeof(h));
 197         h.l1_table_offset = cpu_to_be64(sn->l1_table_offset);
 198         h.l1_size = cpu_to_be32(sn->l1_size);
 199         /* If it doesn't fit in 32 bit, older implementations should treat it
 200          * as a disk-only snapshot rather than truncate the VM state */
 201         if (sn->vm_state_size <= 0xffffffff) {
 202             h.vm_state_size = cpu_to_be32(sn->vm_state_size);
 203         }
 204         h.date_sec = cpu_to_be32(sn->date_sec);
 205         h.date_nsec = cpu_to_be32(sn->date_nsec);
 206         h.vm_clock_nsec = cpu_to_be64(sn->vm_clock_nsec);
 207         h.extra_data_size = cpu_to_be32(sizeof(extra));
 208
 209         memset(&extra, 0, sizeof(extra));
 210         extra.vm_state_size_large = cpu_to_be64(sn->vm_state_size);
 211         extra.disk_size = cpu_to_be64(sn->disk_size);
 212
 213         id_str_size = strlen(sn->id_str);
 214         name_size = strlen(sn->name);
 215         assert(id_str_size <= UINT16_MAX && name_size <= UINT16_MAX);
 216         h.id_str_size = cpu_to_be16(id_str_size);
 217         h.name_size = cpu_to_be16(name_size);
 218         offset = align_offset(offset, 8);
 219
 220         ret = bdrv_pwrite(bs->file, offset, &h, sizeof(h));
 221         if (ret < 0) {
 222             goto fail;
 223         }
 224         offset += sizeof(h);
 225
 226         ret = bdrv_pwrite(bs->file, offset, &extra, sizeof(extra));
 227         if (ret < 0) {
 228             goto fail;
 229         }
 230         offset += sizeof(extra);
 231
 232         ret = bdrv_pwrite(bs->file, offset, sn->id_str, id_str_size);
 233         if (ret < 0) {
 234             goto fail;
 235         }
 236         offset += id_str_size;
 237
 238         ret = bdrv_pwrite(bs->file, offset, sn->name, name_size);
 239         if (ret < 0) {
 240             goto fail;
 241         }
 242         offset += name_size;
 243     }
 244
 245     /*
 246      * Update the header to point to the new snapshot table. This requires the
 247      * new table and its refcounts to be stable on disk.
 248      */
 249     ret = bdrv_flush(bs);
 250     if (ret < 0) {
 251         goto fail;
 252     }
 253
 254     QEMU_BUILD_BUG_ON(offsetof(QCowHeader, snapshots_offset) !=
 255         offsetof(QCowHeader, nb_snapshots) + sizeof(header_data.nb_snapshots));
 256
 257     header_data.nb_snapshots        = cpu_to_be32(s->nb_snapshots);
 258     header_data.snapshots_offset    = cpu_to_be64(snapshots_offset);
 259
 260     ret = bdrv_pwrite_sync(bs->file, offsetof(QCowHeader, nb_snapshots),
 261                            &header_data, sizeof(header_data));
 262     if (ret < 0) {
 263         goto fail;
 264     }
 265
 266     /* free the old snapshot table */
 267     qcow2_free_clusters(bs, s->snapshots_offset, s->snapshots_size,
 268                         QCOW2_DISCARD_SNAPSHOT);
 269     s->snapshots_offset = snapshots_offset;
 270     s->snapshots_size = snapshots_size;
 271     return 0;
 272
 273 fail:
 274     if (snapshots_offset > 0) {
 275         qcow2_free_clusters(bs, snapshots_offset, snapshots_size,
 276                             QCOW2_DISCARD_ALWAYS);
 277     }
 278     return ret;
 279 }
 280
 281 static void find_new_snapshot_id(BlockDriverState *bs,
 282                                  char *id_str, int id_str_size)
 283 {
 284     BDRVQcow2State *s = bs->opaque;
 285     QCowSnapshot *sn;
 286     int i;
 287     unsigned long id, id_max = 0;
 288
 289     for(i = 0; i < s->nb_snapshots; i++) {
 290         sn = s->snapshots + i;
 291         id = strtoul(sn->id_str, NULL, 10);
 292         if (id > id_max)
 293             id_max = id;
 294     }
 295     snprintf(id_str, id_str_size, "%lu", id_max + 1);
 296 }
 297
 298 static int find_snapshot_by_id_and_name(BlockDriverState *bs,
 299                                         const char *id,
 300                                         const char *name)
 301 {
 302     BDRVQcow2State *s = bs->opaque;
 303     int i;
 304
 305     if (id && name) {
 306         for (i = 0; i < s->nb_snapshots; i++) {
 307             if (!strcmp(s->snapshots[i].id_str, id) &&
 308                 !strcmp(s->snapshots[i].name, name)) {
 309                 return i;
 310             }
 311         }
 312     } else if (id) {
 313         for (i = 0; i < s->nb_snapshots; i++) {
 314             if (!strcmp(s->snapshots[i].id_str, id)) {
 315                 return i;
 316             }
 317         }
 318     } else if (name) {
 319         for (i = 0; i < s->nb_snapshots; i++) {
 320             if (!strcmp(s->snapshots[i].name, name)) {
 321                 return i;
 322             }
 323         }
 324     }
 325
 326     return -1;
 327 }
 328
 329 static int find_snapshot_by_id_or_name(BlockDriverState *bs,
 330                                        const char *id_or_name)
 331 {
 332     int ret;
 333
 334     ret = find_snapshot_by_id_and_name(bs, id_or_name, NULL);
 335     if (ret >= 0) {
 336         return ret;
 337     }
 338     return find_snapshot_by_id_and_name(bs, NULL, id_or_name);
 339 }
 340
 341 /* if no id is provided, a new one is constructed */
 342 int qcow2_snapshot_create(BlockDriverState *bs, QEMUSnapshotInfo *sn_info)
 343 {
 344     BDRVQcow2State *s = bs->opaque;
 345     QCowSnapshot *new_snapshot_list = NULL;
 346     QCowSnapshot *old_snapshot_list = NULL;
 347     QCowSnapshot sn1, *sn = &sn1;
 348     int i, ret;
 349     uint64_t *l1_table = NULL;
 350     int64_t l1_table_offset;
 351
 352     if (s->nb_snapshots >= QCOW_MAX_SNAPSHOTS) {
 353         return -EFBIG;
 354     }
 355
 356     memset(sn, 0, sizeof(*sn));
 357
 358     /* Generate an ID */
 359     find_new_snapshot_id(bs, sn_info->id_str, sizeof(sn_info->id_str));
 360
 361     /* Check that the ID is unique */
 362     if (find_snapshot_by_id_and_name(bs, sn_info->id_str, NULL) >= 0) {
 363         return -EEXIST;
 364     }
 365
 366     /* Populate sn with passed data */
 367     sn->id_str = g_strdup(sn_info->id_str);
 368     sn->name = g_strdup(sn_info->name);
 369
 370     sn->disk_size = bs->total_sectors * BDRV_SECTOR_SIZE;
 371     sn->vm_state_size = sn_info->vm_state_size;
 372     sn->date_sec = sn_info->date_sec;
 373     sn->date_nsec = sn_info->date_nsec;
 374     sn->vm_clock_nsec = sn_info->vm_clock_nsec;
 375
 376     /* Allocate the L1 table of the snapshot and copy the current one there. */
 377     l1_table_offset = qcow2_alloc_clusters(bs, s->l1_size * sizeof(uint64_t));
 378     if (l1_table_offset < 0) {
 379         ret = l1_table_offset;
 380         goto fail;
 381     }
 382
 383     sn->l1_table_offset = l1_table_offset;
 384     sn->l1_size = s->l1_size;
 385
 386     l1_table = g_try_new(uint64_t, s->l1_size);
 387     if (s->l1_size && l1_table == NULL) {
 388         ret = -ENOMEM;
 389         goto fail;
 390     }
 391
 392     for(i = 0; i < s->l1_size; i++) {
 393         l1_table[i] = cpu_to_be64(s->l1_table[i]);
 394     }
 395
 396     ret = qcow2_pre_write_overlap_check(bs, 0, sn->l1_table_offset,
 397                                         s->l1_size * sizeof(uint64_t));
 398     if (ret < 0) {
 399         goto fail;
 400     }
 401
 402     ret = bdrv_pwrite(bs->file, sn->l1_table_offset, l1_table,
 403                       s->l1_size * sizeof(uint64_t));
 404     if (ret < 0) {
 405         goto fail;
 406     }
 407
 408     g_free(l1_table);
 409     l1_table = NULL;
 410
 411     /*
 412      * Increase the refcounts of all clusters and make sure everything is
 413      * stable on disk before updating the snapshot table to contain a pointer
 414      * to the new L1 table.
 415      */
 416     ret = qcow2_update_snapshot_refcount(bs, s->l1_table_offset, s->l1_size, 1);
 417     if (ret < 0) {
 418         goto fail;
 419     }
 420
 421     /* Append the new snapshot to the snapshot list */
 422     new_snapshot_list = g_new(QCowSnapshot, s->nb_snapshots + 1);
 423     if (s->snapshots) {
 424         memcpy(new_snapshot_list, s->snapshots,
 425                s->nb_snapshots * sizeof(QCowSnapshot));
 426         old_snapshot_list = s->snapshots;
 427     }
 428     s->snapshots = new_snapshot_list;
 429     s->snapshots[s->nb_snapshots++] = *sn;
 430
 431     ret = qcow2_write_snapshots(bs);
 432     if (ret < 0) {
 433         g_free(s->snapshots);
 434         s->snapshots = old_snapshot_list;
 435         s->nb_snapshots--;
 436         goto fail;
 437     }
 438
 439     g_free(old_snapshot_list);
 440
 441     /* The VM state isn't needed any more in the active L1 table; in fact, it
 442      * hurts by causing expensive COW for the next snapshot. */
 443     qcow2_discard_clusters(bs, qcow2_vm_state_offset(s),
 444                            align_offset(sn->vm_state_size, s->cluster_size)
 445                                 >> BDRV_SECTOR_BITS,
 446                            QCOW2_DISCARD_NEVER, false);
 447
 448 #ifdef DEBUG_ALLOC
 449     {
 450       BdrvCheckResult result = {0};
 451       qcow2_check_refcounts(bs, &result, 0);
 452     }
 453 #endif
 454     return 0;
 455
 456 fail:
 457     g_free(sn->id_str);
 458     g_free(sn->name);
 459     g_free(l1_table);
 460
 461     return ret;
 462 }
 463
 464 /* copy the snapshot 'snapshot_name' into the current disk image */
 465 int qcow2_snapshot_goto(BlockDriverState *bs, const char *snapshot_id)
 466 {
 467     BDRVQcow2State *s = bs->opaque;
 468     QCowSnapshot *sn;
 469     int i, snapshot_index;
 470     int cur_l1_bytes, sn_l1_bytes;
 471     int ret;
 472     uint64_t *sn_l1_table = NULL;
 473
 474     /* Search the snapshot */
 475     snapshot_index = find_snapshot_by_id_or_name(bs, snapshot_id);
 476     if (snapshot_index < 0) {
 477         return -ENOENT;
 478     }
 479     sn = &s->snapshots[snapshot_index];
 480
 481     if (sn->disk_size != bs->total_sectors * BDRV_SECTOR_SIZE) {
 482         error_report("qcow2: Loading snapshots with different disk "
 483             "size is not implemented");
 484         ret = -ENOTSUP;
 485         goto fail;
 486     }
 487
 488     /*
 489      * Make sure that the current L1 table is big enough to contain the whole
 490      * L1 table of the snapshot. If the snapshot L1 table is smaller, the
 491      * current one must be padded with zeros.
 492      */
 493     ret = qcow2_grow_l1_table(bs, sn->l1_size, true);
 494     if (ret < 0) {
 495         goto fail;
 496     }
 497
 498     cur_l1_bytes = s->l1_size * sizeof(uint64_t);
 499     sn_l1_bytes = sn->l1_size * sizeof(uint64_t);
 500
 501     /*
 502      * Copy the snapshot L1 table to the current L1 table.
 503      *
 504      * Before overwriting the old current L1 table on disk, make sure to
 505      * increase all refcounts for the clusters referenced by the new one.
 506      * Decrease the refcount referenced by the old one only when the L1
 507      * table is overwritten.
 508      */
 509     sn_l1_table = g_try_malloc0(cur_l1_bytes);
 510     if (cur_l1_bytes && sn_l1_table == NULL) {
 511         ret = -ENOMEM;
 512         goto fail;
 513     }
 514
 515     ret = bdrv_pread(bs->file, sn->l1_table_offset,
 516                      sn_l1_table, sn_l1_bytes);
 517     if (ret < 0) {
 518         goto fail;
 519     }
 520
 521     ret = qcow2_update_snapshot_refcount(bs, sn->l1_table_offset,
 522                                          sn->l1_size, 1);
 523     if (ret < 0) {
 524         goto fail;
 525     }
 526
 527     ret = qcow2_pre_write_overlap_check(bs, QCOW2_OL_ACTIVE_L1,
 528                                         s->l1_table_offset, cur_l1_bytes);
 529     if (ret < 0) {
 530         goto fail;
 531     }
 532
 533     ret = bdrv_pwrite_sync(bs->file, s->l1_table_offset, sn_l1_table,
 534                            cur_l1_bytes);
 535     if (ret < 0) {
 536         goto fail;
 537     }
 538
 539     /*
 540      * Decrease refcount of clusters of current L1 table.
 541      *
 542      * At this point, the in-memory s->l1_table points to the old L1 table,
 543      * whereas on disk we already have the new one.
 544      *
 545      * qcow2_update_snapshot_refcount special cases the current L1 table to use
 546      * the in-memory data instead of really using the offset to load a new one,
 547      * which is why this works.
 548      */
 549     ret = qcow2_update_snapshot_refcount(bs, s->l1_table_offset,
 550                                          s->l1_size, -1);
 551
 552     /*
 553      * Now update the in-memory L1 table to be in sync with the on-disk one. We
 554      * need to do this even if updating refcounts failed.
 555      */
 556     for(i = 0;i < s->l1_size; i++) {
 557         s->l1_table[i] = be64_to_cpu(sn_l1_table[i]);
 558     }
 559
 560     if (ret < 0) {
 561         goto fail;
 562     }
 563
 564     g_free(sn_l1_table);
 565     sn_l1_table = NULL;
 566
 567     /*
 568      * Update QCOW_OFLAG_COPIED in the active L1 table (it may have changed
 569      * when we decreased the refcount of the old snapshot.
 570      */
 571     ret = qcow2_update_snapshot_refcount(bs, s->l1_table_offset, s->l1_size, 0);
 572     if (ret < 0) {
 573         goto fail;
 574     }
 575
 576 #ifdef DEBUG_ALLOC
 577     {
 578         BdrvCheckResult result = {0};
 579         qcow2_check_refcounts(bs, &result, 0);
 580     }
 581 #endif
 582     return 0;
 583
 584 fail:
 585     g_free(sn_l1_table);
 586     return ret;
 587 }
 588
 589 int qcow2_snapshot_delete(BlockDriverState *bs,
 590                           const char *snapshot_id,
 591                           const char *name,
 592                           Error **errp)
 593 {
 594     BDRVQcow2State *s = bs->opaque;
 595     QCowSnapshot sn;
 596     int snapshot_index, ret;
 597
 598     /* Search the snapshot */
 599     snapshot_index = find_snapshot_by_id_and_name(bs, snapshot_id, name);
 600     if (snapshot_index < 0) {
 601         error_setg(errp, "Can't find the snapshot");
 602         return -ENOENT;
 603     }
 604     sn = s->snapshots[snapshot_index];
 605
 606     /* Remove it from the snapshot list */
 607     memmove(s->snapshots + snapshot_index,
 608             s->snapshots + snapshot_index + 1,
 609             (s->nb_snapshots - snapshot_index - 1) * sizeof(sn));
 610     s->nb_snapshots--;
 611     ret = qcow2_write_snapshots(bs);
 612     if (ret < 0) {
 613         error_setg_errno(errp, -ret,
 614                          "Failed to remove snapshot from snapshot list");
 615         return ret;
 616     }
 617
 618     /*
 619      * The snapshot is now unused, clean up. If we fail after this point, we
 620      * won't recover but just leak clusters.
 621      */
 622     g_free(sn.id_str);
 623     g_free(sn.name);
 624
 625     /*
 626      * Now decrease the refcounts of clusters referenced by the snapshot and
 627      * free the L1 table.
 628      */
 629     ret = qcow2_update_snapshot_refcount(bs, sn.l1_table_offset,
 630                                          sn.l1_size, -1);
 631     if (ret < 0) {
 632         error_setg_errno(errp, -ret, "Failed to free the cluster and L1 table");
 633         return ret;
 634     }
 635     qcow2_free_clusters(bs, sn.l1_table_offset, sn.l1_size * sizeof(uint64_t),
 636                         QCOW2_DISCARD_SNAPSHOT);
 637
 638     /* must update the copied flag on the current cluster offsets */
 639     ret = qcow2_update_snapshot_refcount(bs, s->l1_table_offset, s->l1_size, 0);
 640     if (ret < 0) {
 641         error_setg_errno(errp, -ret,
 642                          "Failed to update snapshot status in disk");
 643         return ret;
 644     }
 645
 646 #ifdef DEBUG_ALLOC
 647     {
 648         BdrvCheckResult result = {0};
 649         qcow2_check_refcounts(bs, &result, 0);
 650     }
 651 #endif
 652     return 0;
 653 }
 654
 655 int qcow2_snapshot_list(BlockDriverState *bs, QEMUSnapshotInfo **psn_tab)
 656 {
 657     BDRVQcow2State *s = bs->opaque;
 658     QEMUSnapshotInfo *sn_tab, *sn_info;
 659     QCowSnapshot *sn;
 660     int i;
 661
 662     if (!s->nb_snapshots) {
 663         *psn_tab = NULL;
 664         return s->nb_snapshots;
 665     }
 666
 667     sn_tab = g_new0(QEMUSnapshotInfo, s->nb_snapshots);
 668     for(i = 0; i < s->nb_snapshots; i++) {
 669         sn_info = sn_tab + i;
 670         sn = s->snapshots + i;
 671         pstrcpy(sn_info->id_str, sizeof(sn_info->id_str),
 672                 sn->id_str);
 673         pstrcpy(sn_info->name, sizeof(sn_info->name),
 674                 sn->name);
 675         sn_info->vm_state_size = sn->vm_state_size;
 676         sn_info->date_sec = sn->date_sec;
 677         sn_info->date_nsec = sn->date_nsec;
 678         sn_info->vm_clock_nsec = sn->vm_clock_nsec;
 679     }
 680     *psn_tab = sn_tab;
 681     return s->nb_snapshots;
 682 }
 683
 684 int qcow2_snapshot_load_tmp(BlockDriverState *bs,
 685                             const char *snapshot_id,
 686                             const char *name,
 687                             Error **errp)
 688 {
 689     int i, snapshot_index;
 690     BDRVQcow2State *s = bs->opaque;
 691     QCowSnapshot *sn;
 692     uint64_t *new_l1_table;
 693     int new_l1_bytes;
 694     int ret;
 695
 696     assert(bs->read_only);
 697
 698     /* Search the snapshot */
 699     snapshot_index = find_snapshot_by_id_and_name(bs, snapshot_id, name);
 700     if (snapshot_index < 0) {
 701         error_setg(errp,
 702                    "Can't find snapshot");
 703         return -ENOENT;
 704     }
 705     sn = &s->snapshots[snapshot_index];
 706
 707     /* Allocate and read in the snapshot's L1 table */
 708     if (sn->l1_size > QCOW_MAX_L1_SIZE / sizeof(uint64_t)) {
 709         error_setg(errp, "Snapshot L1 table too large");
 710         return -EFBIG;
 711     }
 712     new_l1_bytes = sn->l1_size * sizeof(uint64_t);
 713     new_l1_table = qemu_try_blockalign(bs->file->bs,
 714                                        align_offset(new_l1_bytes, 512));
 715     if (new_l1_table == NULL) {
 716         return -ENOMEM;
 717     }
 718
 719     ret = bdrv_pread(bs->file, sn->l1_table_offset,
 720                      new_l1_table, new_l1_bytes);
 721     if (ret < 0) {
 722         error_setg(errp, "Failed to read l1 table for snapshot");
 723         qemu_vfree(new_l1_table);
 724         return ret;
 725     }
 726
 727     /* Switch the L1 table */
 728     qemu_vfree(s->l1_table);
 729
 730     s->l1_size = sn->l1_size;
 731     s->l1_table_offset = sn->l1_table_offset;
 732     s->l1_table = new_l1_table;
 733
 734     for(i = 0;i < s->l1_size; i++) {
 735         be64_to_cpus(&s->l1_table[i]);
 736     }
 737
 738     return 0;
 739 }