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_malloc0(s->nb_snapshots * sizeof(QCowSnapshot));
  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
 121     s->snapshots_size = offset - s->snapshots_offset;
 122     return 0;
 123
 124 fail:
 125     qcow2_free_snapshots(bs);
 126     return ret;
 127 }
 128
 129 /* add at the end of the file a new list of snapshots */
 130 static int qcow2_write_snapshots(BlockDriverState *bs)
 131 {
 132     BDRVQcowState *s = bs->opaque;
 133     QCowSnapshot *sn;
 134     QCowSnapshotHeader h;
 135     QCowSnapshotExtraData extra;
 136     int i, name_size, id_str_size, snapshots_size;
 137     struct {
 138         uint32_t nb_snapshots;
 139         uint64_t snapshots_offset;
 140     } QEMU_PACKED header_data;
 141     int64_t offset, snapshots_offset;
 142     int ret;
 143
 144     /* compute the size of the snapshots */
 145     offset = 0;
 146     for(i = 0; i < s->nb_snapshots; i++) {
 147         sn = s->snapshots + i;
 148         offset = align_offset(offset, 8);
 149         offset += sizeof(h);
 150         offset += sizeof(extra);
 151         offset += strlen(sn->id_str);
 152         offset += strlen(sn->name);
 153     }
 154     snapshots_size = offset;
 155
 156     /* Allocate space for the new snapshot list */
 157     snapshots_offset = qcow2_alloc_clusters(bs, snapshots_size);
 158     offset = snapshots_offset;
 159     if (offset < 0) {
 160         ret = offset;
 161         goto fail;
 162     }
 163     ret = bdrv_flush(bs);
 164     if (ret < 0) {
 165         goto fail;
 166     }
 167
 168     /* The snapshot list position has not yet been updated, so these clusters
 169      * must indeed be completely free */
 170     ret = qcow2_pre_write_overlap_check(bs, 0, offset, snapshots_size);
 171     if (ret < 0) {
 172         goto fail;
 173     }
 174
 175
 176     /* Write all snapshots to the new list */
 177     for(i = 0; i < s->nb_snapshots; i++) {
 178         sn = s->snapshots + i;
 179         memset(&h, 0, sizeof(h));
 180         h.l1_table_offset = cpu_to_be64(sn->l1_table_offset);
 181         h.l1_size = cpu_to_be32(sn->l1_size);
 182         /* If it doesn't fit in 32 bit, older implementations should treat it
 183          * as a disk-only snapshot rather than truncate the VM state */
 184         if (sn->vm_state_size <= 0xffffffff) {
 185             h.vm_state_size = cpu_to_be32(sn->vm_state_size);
 186         }
 187         h.date_sec = cpu_to_be32(sn->date_sec);
 188         h.date_nsec = cpu_to_be32(sn->date_nsec);
 189         h.vm_clock_nsec = cpu_to_be64(sn->vm_clock_nsec);
 190         h.extra_data_size = cpu_to_be32(sizeof(extra));
 191
 192         memset(&extra, 0, sizeof(extra));
 193         extra.vm_state_size_large = cpu_to_be64(sn->vm_state_size);
 194         extra.disk_size = cpu_to_be64(sn->disk_size);
 195
 196         id_str_size = strlen(sn->id_str);
 197         name_size = strlen(sn->name);
 198         assert(id_str_size <= UINT16_MAX && name_size <= UINT16_MAX);
 199         h.id_str_size = cpu_to_be16(id_str_size);
 200         h.name_size = cpu_to_be16(name_size);
 201         offset = align_offset(offset, 8);
 202
 203         ret = bdrv_pwrite(bs->file, offset, &h, sizeof(h));
 204         if (ret < 0) {
 205             goto fail;
 206         }
 207         offset += sizeof(h);
 208
 209         ret = bdrv_pwrite(bs->file, offset, &extra, sizeof(extra));
 210         if (ret < 0) {
 211             goto fail;
 212         }
 213         offset += sizeof(extra);
 214
 215         ret = bdrv_pwrite(bs->file, offset, sn->id_str, id_str_size);
 216         if (ret < 0) {
 217             goto fail;
 218         }
 219         offset += id_str_size;
 220
 221         ret = bdrv_pwrite(bs->file, offset, sn->name, name_size);
 222         if (ret < 0) {
 223             goto fail;
 224         }
 225         offset += name_size;
 226     }
 227
 228     /*
 229      * Update the header to point to the new snapshot table. This requires the
 230      * new table and its refcounts to be stable on disk.
 231      */
 232     ret = bdrv_flush(bs);
 233     if (ret < 0) {
 234         goto fail;
 235     }
 236
 237     QEMU_BUILD_BUG_ON(offsetof(QCowHeader, snapshots_offset) !=
 238         offsetof(QCowHeader, nb_snapshots) + sizeof(header_data.nb_snapshots));
 239
 240     header_data.nb_snapshots        = cpu_to_be32(s->nb_snapshots);
 241     header_data.snapshots_offset    = cpu_to_be64(snapshots_offset);
 242
 243     ret = bdrv_pwrite_sync(bs->file, offsetof(QCowHeader, nb_snapshots),
 244                            &header_data, sizeof(header_data));
 245     if (ret < 0) {
 246         goto fail;
 247     }
 248
 249     /* free the old snapshot table */
 250     qcow2_free_clusters(bs, s->snapshots_offset, s->snapshots_size,
 251                         QCOW2_DISCARD_SNAPSHOT);
 252     s->snapshots_offset = snapshots_offset;
 253     s->snapshots_size = snapshots_size;
 254     return 0;
 255
 256 fail:
 257     if (snapshots_offset > 0) {
 258         qcow2_free_clusters(bs, snapshots_offset, snapshots_size,
 259                             QCOW2_DISCARD_ALWAYS);
 260     }
 261     return ret;
 262 }
 263
 264 static void find_new_snapshot_id(BlockDriverState *bs,
 265                                  char *id_str, int id_str_size)
 266 {
 267     BDRVQcowState *s = bs->opaque;
 268     QCowSnapshot *sn;
 269     int i;
 270     unsigned long id, id_max = 0;
 271
 272     for(i = 0; i < s->nb_snapshots; i++) {
 273         sn = s->snapshots + i;
 274         id = strtoul(sn->id_str, NULL, 10);
 275         if (id > id_max)
 276             id_max = id;
 277     }
 278     snprintf(id_str, id_str_size, "%lu", id_max + 1);
 279 }
 280
 281 static int find_snapshot_by_id_and_name(BlockDriverState *bs,
 282                                         const char *id,
 283                                         const char *name)
 284 {
 285     BDRVQcowState *s = bs->opaque;
 286     int i;
 287
 288     if (id && name) {
 289         for (i = 0; i < s->nb_snapshots; i++) {
 290             if (!strcmp(s->snapshots[i].id_str, id) &&
 291                 !strcmp(s->snapshots[i].name, name)) {
 292                 return i;
 293             }
 294         }
 295     } else if (id) {
 296         for (i = 0; i < s->nb_snapshots; i++) {
 297             if (!strcmp(s->snapshots[i].id_str, id)) {
 298                 return i;
 299             }
 300         }
 301     } else if (name) {
 302         for (i = 0; i < s->nb_snapshots; i++) {
 303             if (!strcmp(s->snapshots[i].name, name)) {
 304                 return i;
 305             }
 306         }
 307     }
 308
 309     return -1;
 310 }
 311
 312 static int find_snapshot_by_id_or_name(BlockDriverState *bs,
 313                                        const char *id_or_name)
 314 {
 315     int ret;
 316
 317     ret = find_snapshot_by_id_and_name(bs, id_or_name, NULL);
 318     if (ret >= 0) {
 319         return ret;
 320     }
 321     return find_snapshot_by_id_and_name(bs, NULL, id_or_name);
 322 }
 323
 324 /* if no id is provided, a new one is constructed */
 325 int qcow2_snapshot_create(BlockDriverState *bs, QEMUSnapshotInfo *sn_info)
 326 {
 327     BDRVQcowState *s = bs->opaque;
 328     QCowSnapshot *new_snapshot_list = NULL;
 329     QCowSnapshot *old_snapshot_list = NULL;
 330     QCowSnapshot sn1, *sn = &sn1;
 331     int i, ret;
 332     uint64_t *l1_table = NULL;
 333     int64_t l1_table_offset;
 334
 335     if (s->nb_snapshots >= QCOW_MAX_SNAPSHOTS) {
 336         return -EFBIG;
 337     }
 338
 339     memset(sn, 0, sizeof(*sn));
 340
 341     /* Generate an ID if it wasn't passed */
 342     if (sn_info->id_str[0] == '\0') {
 343         find_new_snapshot_id(bs, sn_info->id_str, sizeof(sn_info->id_str));
 344     }
 345
 346     /* Check that the ID is unique */
 347     if (find_snapshot_by_id_and_name(bs, sn_info->id_str, NULL) >= 0) {
 348         return -EEXIST;
 349     }
 350
 351     /* Populate sn with passed data */
 352     sn->id_str = g_strdup(sn_info->id_str);
 353     sn->name = g_strdup(sn_info->name);
 354
 355     sn->disk_size = bs->total_sectors * BDRV_SECTOR_SIZE;
 356     sn->vm_state_size = sn_info->vm_state_size;
 357     sn->date_sec = sn_info->date_sec;
 358     sn->date_nsec = sn_info->date_nsec;
 359     sn->vm_clock_nsec = sn_info->vm_clock_nsec;
 360
 361     /* Allocate the L1 table of the snapshot and copy the current one there. */
 362     l1_table_offset = qcow2_alloc_clusters(bs, s->l1_size * sizeof(uint64_t));
 363     if (l1_table_offset < 0) {
 364         ret = l1_table_offset;
 365         goto fail;
 366     }
 367
 368     sn->l1_table_offset = l1_table_offset;
 369     sn->l1_size = s->l1_size;
 370
 371     l1_table = g_malloc(s->l1_size * sizeof(uint64_t));
 372     for(i = 0; i < s->l1_size; i++) {
 373         l1_table[i] = cpu_to_be64(s->l1_table[i]);
 374     }
 375
 376     ret = qcow2_pre_write_overlap_check(bs, 0, sn->l1_table_offset,
 377                                         s->l1_size * sizeof(uint64_t));
 378     if (ret < 0) {
 379         goto fail;
 380     }
 381
 382     ret = bdrv_pwrite(bs->file, sn->l1_table_offset, l1_table,
 383                       s->l1_size * sizeof(uint64_t));
 384     if (ret < 0) {
 385         goto fail;
 386     }
 387
 388     g_free(l1_table);
 389     l1_table = NULL;
 390
 391     /*
 392      * Increase the refcounts of all clusters and make sure everything is
 393      * stable on disk before updating the snapshot table to contain a pointer
 394      * to the new L1 table.
 395      */
 396     ret = qcow2_update_snapshot_refcount(bs, s->l1_table_offset, s->l1_size, 1);
 397     if (ret < 0) {
 398         goto fail;
 399     }
 400
 401     /* Append the new snapshot to the snapshot list */
 402     new_snapshot_list = g_malloc((s->nb_snapshots + 1) * sizeof(QCowSnapshot));
 403     if (s->snapshots) {
 404         memcpy(new_snapshot_list, s->snapshots,
 405                s->nb_snapshots * sizeof(QCowSnapshot));
 406         old_snapshot_list = s->snapshots;
 407     }
 408     s->snapshots = new_snapshot_list;
 409     s->snapshots[s->nb_snapshots++] = *sn;
 410
 411     ret = qcow2_write_snapshots(bs);
 412     if (ret < 0) {
 413         g_free(s->snapshots);
 414         s->snapshots = old_snapshot_list;
 415         s->nb_snapshots--;
 416         goto fail;
 417     }
 418
 419     g_free(old_snapshot_list);
 420
 421     /* The VM state isn't needed any more in the active L1 table; in fact, it
 422      * hurts by causing expensive COW for the next snapshot. */
 423     qcow2_discard_clusters(bs, qcow2_vm_state_offset(s),
 424                            align_offset(sn->vm_state_size, s->cluster_size)
 425                                 >> BDRV_SECTOR_BITS,
 426                            QCOW2_DISCARD_NEVER);
 427
 428 #ifdef DEBUG_ALLOC
 429     {
 430       BdrvCheckResult result = {0};
 431       qcow2_check_refcounts(bs, &result, 0);
 432     }
 433 #endif
 434     return 0;
 435
 436 fail:
 437     g_free(sn->id_str);
 438     g_free(sn->name);
 439     g_free(l1_table);
 440
 441     return ret;
 442 }
 443
 444 /* copy the snapshot 'snapshot_name' into the current disk image */
 445 int qcow2_snapshot_goto(BlockDriverState *bs, const char *snapshot_id)
 446 {
 447     BDRVQcowState *s = bs->opaque;
 448     QCowSnapshot *sn;
 449     int i, snapshot_index;
 450     int cur_l1_bytes, sn_l1_bytes;
 451     int ret;
 452     uint64_t *sn_l1_table = NULL;
 453
 454     /* Search the snapshot */
 455     snapshot_index = find_snapshot_by_id_or_name(bs, snapshot_id);
 456     if (snapshot_index < 0) {
 457         return -ENOENT;
 458     }
 459     sn = &s->snapshots[snapshot_index];
 460
 461     if (sn->disk_size != bs->total_sectors * BDRV_SECTOR_SIZE) {
 462         error_report("qcow2: Loading snapshots with different disk "
 463             "size is not implemented");
 464         ret = -ENOTSUP;
 465         goto fail;
 466     }
 467
 468     /*
 469      * Make sure that the current L1 table is big enough to contain the whole
 470      * L1 table of the snapshot. If the snapshot L1 table is smaller, the
 471      * current one must be padded with zeros.
 472      */
 473     ret = qcow2_grow_l1_table(bs, sn->l1_size, true);
 474     if (ret < 0) {
 475         goto fail;
 476     }
 477
 478     cur_l1_bytes = s->l1_size * sizeof(uint64_t);
 479     sn_l1_bytes = sn->l1_size * sizeof(uint64_t);
 480
 481     /*
 482      * Copy the snapshot L1 table to the current L1 table.
 483      *
 484      * Before overwriting the old current L1 table on disk, make sure to
 485      * increase all refcounts for the clusters referenced by the new one.
 486      * Decrease the refcount referenced by the old one only when the L1
 487      * table is overwritten.
 488      */
 489     sn_l1_table = g_malloc0(cur_l1_bytes);
 490
 491     ret = bdrv_pread(bs->file, sn->l1_table_offset, sn_l1_table, sn_l1_bytes);
 492     if (ret < 0) {
 493         goto fail;
 494     }
 495
 496     ret = qcow2_update_snapshot_refcount(bs, sn->l1_table_offset,
 497                                          sn->l1_size, 1);
 498     if (ret < 0) {
 499         goto fail;
 500     }
 501
 502     ret = qcow2_pre_write_overlap_check(bs, QCOW2_OL_ACTIVE_L1,
 503                                         s->l1_table_offset, cur_l1_bytes);
 504     if (ret < 0) {
 505         goto fail;
 506     }
 507
 508     ret = bdrv_pwrite_sync(bs->file, s->l1_table_offset, sn_l1_table,
 509                            cur_l1_bytes);
 510     if (ret < 0) {
 511         goto fail;
 512     }
 513
 514     /*
 515      * Decrease refcount of clusters of current L1 table.
 516      *
 517      * At this point, the in-memory s->l1_table points to the old L1 table,
 518      * whereas on disk we already have the new one.
 519      *
 520      * qcow2_update_snapshot_refcount special cases the current L1 table to use
 521      * the in-memory data instead of really using the offset to load a new one,
 522      * which is why this works.
 523      */
 524     ret = qcow2_update_snapshot_refcount(bs, s->l1_table_offset,
 525                                          s->l1_size, -1);
 526
 527     /*
 528      * Now update the in-memory L1 table to be in sync with the on-disk one. We
 529      * need to do this even if updating refcounts failed.
 530      */
 531     for(i = 0;i < s->l1_size; i++) {
 532         s->l1_table[i] = be64_to_cpu(sn_l1_table[i]);
 533     }
 534
 535     if (ret < 0) {
 536         goto fail;
 537     }
 538
 539     g_free(sn_l1_table);
 540     sn_l1_table = NULL;
 541
 542     /*
 543      * Update QCOW_OFLAG_COPIED in the active L1 table (it may have changed
 544      * when we decreased the refcount of the old snapshot.
 545      */
 546     ret = qcow2_update_snapshot_refcount(bs, s->l1_table_offset, s->l1_size, 0);
 547     if (ret < 0) {
 548         goto fail;
 549     }
 550
 551 #ifdef DEBUG_ALLOC
 552     {
 553         BdrvCheckResult result = {0};
 554         qcow2_check_refcounts(bs, &result, 0);
 555     }
 556 #endif
 557     return 0;
 558
 559 fail:
 560     g_free(sn_l1_table);
 561     return ret;
 562 }
 563
 564 int qcow2_snapshot_delete(BlockDriverState *bs,
 565                           const char *snapshot_id,
 566                           const char *name,
 567                           Error **errp)
 568 {
 569     BDRVQcowState *s = bs->opaque;
 570     QCowSnapshot sn;
 571     int snapshot_index, ret;
 572
 573     /* Search the snapshot */
 574     snapshot_index = find_snapshot_by_id_and_name(bs, snapshot_id, name);
 575     if (snapshot_index < 0) {
 576         error_setg(errp, "Can't find the snapshot");
 577         return -ENOENT;
 578     }
 579     sn = s->snapshots[snapshot_index];
 580
 581     /* Remove it from the snapshot list */
 582     memmove(s->snapshots + snapshot_index,
 583             s->snapshots + snapshot_index + 1,
 584             (s->nb_snapshots - snapshot_index - 1) * sizeof(sn));
 585     s->nb_snapshots--;
 586     ret = qcow2_write_snapshots(bs);
 587     if (ret < 0) {
 588         error_setg_errno(errp, -ret,
 589                          "Failed to remove snapshot from snapshot list");
 590         return ret;
 591     }
 592
 593     /*
 594      * The snapshot is now unused, clean up. If we fail after this point, we
 595      * won't recover but just leak clusters.
 596      */
 597     g_free(sn.id_str);
 598     g_free(sn.name);
 599
 600     /*
 601      * Now decrease the refcounts of clusters referenced by the snapshot and
 602      * free the L1 table.
 603      */
 604     ret = qcow2_update_snapshot_refcount(bs, sn.l1_table_offset,
 605                                          sn.l1_size, -1);
 606     if (ret < 0) {
 607         error_setg_errno(errp, -ret, "Failed to free the cluster and L1 table");
 608         return ret;
 609     }
 610     qcow2_free_clusters(bs, sn.l1_table_offset, sn.l1_size * sizeof(uint64_t),
 611                         QCOW2_DISCARD_SNAPSHOT);
 612
 613     /* must update the copied flag on the current cluster offsets */
 614     ret = qcow2_update_snapshot_refcount(bs, s->l1_table_offset, s->l1_size, 0);
 615     if (ret < 0) {
 616         error_setg_errno(errp, -ret,
 617                          "Failed to update snapshot status in disk");
 618         return ret;
 619     }
 620
 621 #ifdef DEBUG_ALLOC
 622     {
 623         BdrvCheckResult result = {0};
 624         qcow2_check_refcounts(bs, &result, 0);
 625     }
 626 #endif
 627     return 0;
 628 }
 629
 630 int qcow2_snapshot_list(BlockDriverState *bs, QEMUSnapshotInfo **psn_tab)
 631 {
 632     BDRVQcowState *s = bs->opaque;
 633     QEMUSnapshotInfo *sn_tab, *sn_info;
 634     QCowSnapshot *sn;
 635     int i;
 636
 637     if (!s->nb_snapshots) {
 638         *psn_tab = NULL;
 639         return s->nb_snapshots;
 640     }
 641
 642     sn_tab = g_malloc0(s->nb_snapshots * sizeof(QEMUSnapshotInfo));
 643     for(i = 0; i < s->nb_snapshots; i++) {
 644         sn_info = sn_tab + i;
 645         sn = s->snapshots + i;
 646         pstrcpy(sn_info->id_str, sizeof(sn_info->id_str),
 647                 sn->id_str);
 648         pstrcpy(sn_info->name, sizeof(sn_info->name),
 649                 sn->name);
 650         sn_info->vm_state_size = sn->vm_state_size;
 651         sn_info->date_sec = sn->date_sec;
 652         sn_info->date_nsec = sn->date_nsec;
 653         sn_info->vm_clock_nsec = sn->vm_clock_nsec;
 654     }
 655     *psn_tab = sn_tab;
 656     return s->nb_snapshots;
 657 }
 658
 659 int qcow2_snapshot_load_tmp(BlockDriverState *bs,
 660                             const char *snapshot_id,
 661                             const char *name,
 662                             Error **errp)
 663 {
 664     int i, snapshot_index;
 665     BDRVQcowState *s = bs->opaque;
 666     QCowSnapshot *sn;
 667     uint64_t *new_l1_table;
 668     int new_l1_bytes;
 669     int ret;
 670
 671     assert(bs->read_only);
 672
 673     /* Search the snapshot */
 674     snapshot_index = find_snapshot_by_id_and_name(bs, snapshot_id, name);
 675     if (snapshot_index < 0) {
 676         error_setg(errp,
 677                    "Can't find snapshot");
 678         return -ENOENT;
 679     }
 680     sn = &s->snapshots[snapshot_index];
 681
 682     /* Allocate and read in the snapshot's L1 table */
 683     new_l1_bytes = s->l1_size * sizeof(uint64_t);
 684     new_l1_table = g_malloc0(align_offset(new_l1_bytes, 512));
 685
 686     ret = bdrv_pread(bs->file, sn->l1_table_offset, new_l1_table, new_l1_bytes);
 687     if (ret < 0) {
 688         error_setg(errp, "Failed to read l1 table for snapshot");
 689         g_free(new_l1_table);
 690         return ret;
 691     }
 692
 693     /* Switch the L1 table */
 694     g_free(s->l1_table);
 695
 696     s->l1_size = sn->l1_size;
 697     s->l1_table_offset = sn->l1_table_offset;
 698     s->l1_table = new_l1_table;
 699
 700     for(i = 0;i < s->l1_size; i++) {
 701         be64_to_cpus(&s->l1_table[i]);
 702     }
 703
 704     return 0;
 705 }