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 typedef struct QEMU_PACKED QCowSnapshotHeader {
  30     /* header is 8 byte aligned */
  31     uint64_t l1_table_offset;
  32
  33     uint32_t l1_size;
  34     uint16_t id_str_size;
  35     uint16_t name_size;
  36
  37     uint32_t date_sec;
  38     uint32_t date_nsec;
  39
  40     uint64_t vm_clock_nsec;
  41
  42     uint32_t vm_state_size;
  43     uint32_t extra_data_size; /* for extension */
  44     /* extra data follows */
  45     /* id_str follows */
  46     /* name follows  */
  47 } QCowSnapshotHeader;
  48
  49 typedef struct QEMU_PACKED QCowSnapshotExtraData {
  50     uint64_t vm_state_size_large;
  51     uint64_t disk_size;
  52 } QCowSnapshotExtraData;
  53
  54 void qcow2_free_snapshots(BlockDriverState *bs)
  55 {
  56     BDRVQcowState *s = bs->opaque;
  57     int i;
  58
  59     for(i = 0; i < s->nb_snapshots; i++) {
  60         g_free(s->snapshots[i].name);
  61         g_free(s->snapshots[i].id_str);
  62     }
  63     g_free(s->snapshots);
  64     s->snapshots = NULL;
  65     s->nb_snapshots = 0;
  66 }
  67
  68 int qcow2_read_snapshots(BlockDriverState *bs)
  69 {
  70     BDRVQcowState *s = bs->opaque;
  71     QCowSnapshotHeader h;
  72     QCowSnapshotExtraData extra;
  73     QCowSnapshot *sn;
  74     int i, id_str_size, name_size;
  75     int64_t offset;
  76     uint32_t extra_data_size;
  77     int ret;
  78
  79     if (!s->nb_snapshots) {
  80         s->snapshots = NULL;
  81         s->snapshots_size = 0;
  82         return 0;
  83     }
  84
  85     offset = s->snapshots_offset;
  86     s->snapshots = g_malloc0(s->nb_snapshots * sizeof(QCowSnapshot));
  87
  88     for(i = 0; i < s->nb_snapshots; i++) {
  89         /* Read statically sized part of the snapshot header */
  90         offset = align_offset(offset, 8);
  91         ret = bdrv_pread(bs->file, offset, &h, sizeof(h));
  92         if (ret < 0) {
  93             goto fail;
  94         }
  95
  96         offset += sizeof(h);
  97         sn = s->snapshots + i;
  98         sn->l1_table_offset = be64_to_cpu(h.l1_table_offset);
  99         sn->l1_size = be32_to_cpu(h.l1_size);
 100         sn->vm_state_size = be32_to_cpu(h.vm_state_size);
 101         sn->date_sec = be32_to_cpu(h.date_sec);
 102         sn->date_nsec = be32_to_cpu(h.date_nsec);
 103         sn->vm_clock_nsec = be64_to_cpu(h.vm_clock_nsec);
 104         extra_data_size = be32_to_cpu(h.extra_data_size);
 105
 106         id_str_size = be16_to_cpu(h.id_str_size);
 107         name_size = be16_to_cpu(h.name_size);
 108
 109         /* Read extra data */
 110         ret = bdrv_pread(bs->file, offset, &extra,
 111                          MIN(sizeof(extra), extra_data_size));
 112         if (ret < 0) {
 113             goto fail;
 114         }
 115         offset += extra_data_size;
 116
 117         if (extra_data_size >= 8) {
 118             sn->vm_state_size = be64_to_cpu(extra.vm_state_size_large);
 119         }
 120
 121         if (extra_data_size >= 16) {
 122             sn->disk_size = be64_to_cpu(extra.disk_size);
 123         } else {
 124             sn->disk_size = bs->total_sectors * BDRV_SECTOR_SIZE;
 125         }
 126
 127         /* Read snapshot ID */
 128         sn->id_str = g_malloc(id_str_size + 1);
 129         ret = bdrv_pread(bs->file, offset, sn->id_str, id_str_size);
 130         if (ret < 0) {
 131             goto fail;
 132         }
 133         offset += id_str_size;
 134         sn->id_str[id_str_size] = '\0';
 135
 136         /* Read snapshot name */
 137         sn->name = g_malloc(name_size + 1);
 138         ret = bdrv_pread(bs->file, offset, sn->name, name_size);
 139         if (ret < 0) {
 140             goto fail;
 141         }
 142         offset += name_size;
 143         sn->name[name_size] = '\0';
 144     }
 145
 146     s->snapshots_size = offset - s->snapshots_offset;
 147     return 0;
 148
 149 fail:
 150     qcow2_free_snapshots(bs);
 151     return ret;
 152 }
 153
 154 /* add at the end of the file a new list of snapshots */
 155 static int qcow2_write_snapshots(BlockDriverState *bs)
 156 {
 157     BDRVQcowState *s = bs->opaque;
 158     QCowSnapshot *sn;
 159     QCowSnapshotHeader h;
 160     QCowSnapshotExtraData extra;
 161     int i, name_size, id_str_size, snapshots_size;
 162     struct {
 163         uint32_t nb_snapshots;
 164         uint64_t snapshots_offset;
 165     } QEMU_PACKED header_data;
 166     int64_t offset, snapshots_offset;
 167     int ret;
 168
 169     /* compute the size of the snapshots */
 170     offset = 0;
 171     for(i = 0; i < s->nb_snapshots; i++) {
 172         sn = s->snapshots + i;
 173         offset = align_offset(offset, 8);
 174         offset += sizeof(h);
 175         offset += sizeof(extra);
 176         offset += strlen(sn->id_str);
 177         offset += strlen(sn->name);
 178     }
 179     snapshots_size = offset;
 180
 181     /* Allocate space for the new snapshot list */
 182     snapshots_offset = qcow2_alloc_clusters(bs, snapshots_size);
 183     offset = snapshots_offset;
 184     if (offset < 0) {
 185         return offset;
 186     }
 187     ret = bdrv_flush(bs);
 188     if (ret < 0) {
 189         return ret;
 190     }
 191
 192     /* The snapshot list position has not yet been updated, so these clusters
 193      * must indeed be completely free */
 194     ret = qcow2_pre_write_overlap_check(bs, QCOW2_OL_DEFAULT, offset,
 195                                         snapshots_size);
 196     if (ret < 0) {
 197         return ret;
 198     }
 199
 200
 201     /* Write all snapshots to the new list */
 202     for(i = 0; i < s->nb_snapshots; i++) {
 203         sn = s->snapshots + i;
 204         memset(&h, 0, sizeof(h));
 205         h.l1_table_offset = cpu_to_be64(sn->l1_table_offset);
 206         h.l1_size = cpu_to_be32(sn->l1_size);
 207         /* If it doesn't fit in 32 bit, older implementations should treat it
 208          * as a disk-only snapshot rather than truncate the VM state */
 209         if (sn->vm_state_size <= 0xffffffff) {
 210             h.vm_state_size = cpu_to_be32(sn->vm_state_size);
 211         }
 212         h.date_sec = cpu_to_be32(sn->date_sec);
 213         h.date_nsec = cpu_to_be32(sn->date_nsec);
 214         h.vm_clock_nsec = cpu_to_be64(sn->vm_clock_nsec);
 215         h.extra_data_size = cpu_to_be32(sizeof(extra));
 216
 217         memset(&extra, 0, sizeof(extra));
 218         extra.vm_state_size_large = cpu_to_be64(sn->vm_state_size);
 219         extra.disk_size = cpu_to_be64(sn->disk_size);
 220
 221         id_str_size = strlen(sn->id_str);
 222         name_size = strlen(sn->name);
 223         h.id_str_size = cpu_to_be16(id_str_size);
 224         h.name_size = cpu_to_be16(name_size);
 225         offset = align_offset(offset, 8);
 226
 227         ret = bdrv_pwrite(bs->file, offset, &h, sizeof(h));
 228         if (ret < 0) {
 229             goto fail;
 230         }
 231         offset += sizeof(h);
 232
 233         ret = bdrv_pwrite(bs->file, offset, &extra, sizeof(extra));
 234         if (ret < 0) {
 235             goto fail;
 236         }
 237         offset += sizeof(extra);
 238
 239         ret = bdrv_pwrite(bs->file, offset, sn->id_str, id_str_size);
 240         if (ret < 0) {
 241             goto fail;
 242         }
 243         offset += id_str_size;
 244
 245         ret = bdrv_pwrite(bs->file, offset, sn->name, name_size);
 246         if (ret < 0) {
 247             goto fail;
 248         }
 249         offset += name_size;
 250     }
 251
 252     /*
 253      * Update the header to point to the new snapshot table. This requires the
 254      * new table and its refcounts to be stable on disk.
 255      */
 256     ret = bdrv_flush(bs);
 257     if (ret < 0) {
 258         goto fail;
 259     }
 260
 261     QEMU_BUILD_BUG_ON(offsetof(QCowHeader, snapshots_offset) !=
 262         offsetof(QCowHeader, nb_snapshots) + sizeof(header_data.nb_snapshots));
 263
 264     header_data.nb_snapshots        = cpu_to_be32(s->nb_snapshots);
 265     header_data.snapshots_offset    = cpu_to_be64(snapshots_offset);
 266
 267     ret = bdrv_pwrite_sync(bs->file, offsetof(QCowHeader, nb_snapshots),
 268                            &header_data, sizeof(header_data));
 269     if (ret < 0) {
 270         goto fail;
 271     }
 272
 273     /* free the old snapshot table */
 274     qcow2_free_clusters(bs, s->snapshots_offset, s->snapshots_size,
 275                         QCOW2_DISCARD_SNAPSHOT);
 276     s->snapshots_offset = snapshots_offset;
 277     s->snapshots_size = snapshots_size;
 278     return 0;
 279
 280 fail:
 281     return ret;
 282 }
 283
 284 static void find_new_snapshot_id(BlockDriverState *bs,
 285                                  char *id_str, int id_str_size)
 286 {
 287     BDRVQcowState *s = bs->opaque;
 288     QCowSnapshot *sn;
 289     int i, id, id_max = 0;
 290
 291     for(i = 0; i < s->nb_snapshots; i++) {
 292         sn = s->snapshots + i;
 293         id = strtoul(sn->id_str, NULL, 10);
 294         if (id > id_max)
 295             id_max = id;
 296     }
 297     snprintf(id_str, id_str_size, "%d", id_max + 1);
 298 }
 299
 300 static int find_snapshot_by_id_and_name(BlockDriverState *bs,
 301                                         const char *id,
 302                                         const char *name)
 303 {
 304     BDRVQcowState *s = bs->opaque;
 305     int i;
 306
 307     if (id && name) {
 308         for (i = 0; i < s->nb_snapshots; i++) {
 309             if (!strcmp(s->snapshots[i].id_str, id) &&
 310                 !strcmp(s->snapshots[i].name, name)) {
 311                 return i;
 312             }
 313         }
 314     } else if (id) {
 315         for (i = 0; i < s->nb_snapshots; i++) {
 316             if (!strcmp(s->snapshots[i].id_str, id)) {
 317                 return i;
 318             }
 319         }
 320     } else if (name) {
 321         for (i = 0; i < s->nb_snapshots; i++) {
 322             if (!strcmp(s->snapshots[i].name, name)) {
 323                 return i;
 324             }
 325         }
 326     }
 327
 328     return -1;
 329 }
 330
 331 static int find_snapshot_by_id_or_name(BlockDriverState *bs,
 332                                        const char *id_or_name)
 333 {
 334     int ret;
 335
 336     ret = find_snapshot_by_id_and_name(bs, id_or_name, NULL);
 337     if (ret >= 0) {
 338         return ret;
 339     }
 340     return find_snapshot_by_id_and_name(bs, NULL, id_or_name);
 341 }
 342
 343 /* if no id is provided, a new one is constructed */
 344 int qcow2_snapshot_create(BlockDriverState *bs, QEMUSnapshotInfo *sn_info)
 345 {
 346     BDRVQcowState *s = bs->opaque;
 347     QCowSnapshot *new_snapshot_list = NULL;
 348     QCowSnapshot *old_snapshot_list = NULL;
 349     QCowSnapshot sn1, *sn = &sn1;
 350     int i, ret;
 351     uint64_t *l1_table = NULL;
 352     int64_t l1_table_offset;
 353
 354     memset(sn, 0, sizeof(*sn));
 355
 356     /* Generate an ID if it wasn't passed */
 357     if (sn_info->id_str[0] == '\0') {
 358         find_new_snapshot_id(bs, sn_info->id_str, sizeof(sn_info->id_str));
 359     }
 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_malloc(s->l1_size * sizeof(uint64_t));
 387     for(i = 0; i < s->l1_size; i++) {
 388         l1_table[i] = cpu_to_be64(s->l1_table[i]);
 389     }
 390
 391     ret = qcow2_pre_write_overlap_check(bs, QCOW2_OL_DEFAULT,
 392             sn->l1_table_offset, s->l1_size * sizeof(uint64_t));
 393     if (ret < 0) {
 394         goto fail;
 395     }
 396
 397     ret = bdrv_pwrite(bs->file, sn->l1_table_offset, l1_table,
 398                       s->l1_size * sizeof(uint64_t));
 399     if (ret < 0) {
 400         goto fail;
 401     }
 402
 403     g_free(l1_table);
 404     l1_table = NULL;
 405
 406     /*
 407      * Increase the refcounts of all clusters and make sure everything is
 408      * stable on disk before updating the snapshot table to contain a pointer
 409      * to the new L1 table.
 410      */
 411     ret = qcow2_update_snapshot_refcount(bs, s->l1_table_offset, s->l1_size, 1);
 412     if (ret < 0) {
 413         goto fail;
 414     }
 415
 416     /* Append the new snapshot to the snapshot list */
 417     new_snapshot_list = g_malloc((s->nb_snapshots + 1) * sizeof(QCowSnapshot));
 418     if (s->snapshots) {
 419         memcpy(new_snapshot_list, s->snapshots,
 420                s->nb_snapshots * sizeof(QCowSnapshot));
 421         old_snapshot_list = s->snapshots;
 422     }
 423     s->snapshots = new_snapshot_list;
 424     s->snapshots[s->nb_snapshots++] = *sn;
 425
 426     ret = qcow2_write_snapshots(bs);
 427     if (ret < 0) {
 428         g_free(s->snapshots);
 429         s->snapshots = old_snapshot_list;
 430         goto fail;
 431     }
 432
 433     g_free(old_snapshot_list);
 434
 435     /* The VM state isn't needed any more in the active L1 table; in fact, it
 436      * hurts by causing expensive COW for the next snapshot. */
 437     qcow2_discard_clusters(bs, qcow2_vm_state_offset(s),
 438                            align_offset(sn->vm_state_size, s->cluster_size)
 439                                 >> BDRV_SECTOR_BITS,
 440                            QCOW2_DISCARD_NEVER);
 441
 442 #ifdef DEBUG_ALLOC
 443     {
 444       BdrvCheckResult result = {0};
 445       qcow2_check_refcounts(bs, &result, 0);
 446     }
 447 #endif
 448     return 0;
 449
 450 fail:
 451     g_free(sn->id_str);
 452     g_free(sn->name);
 453     g_free(l1_table);
 454
 455     return ret;
 456 }
 457
 458 /* copy the snapshot 'snapshot_name' into the current disk image */
 459 int qcow2_snapshot_goto(BlockDriverState *bs, const char *snapshot_id)
 460 {
 461     BDRVQcowState *s = bs->opaque;
 462     QCowSnapshot *sn;
 463     int i, snapshot_index;
 464     int cur_l1_bytes, sn_l1_bytes;
 465     int ret;
 466     uint64_t *sn_l1_table = NULL;
 467
 468     /* Search the snapshot */
 469     snapshot_index = find_snapshot_by_id_or_name(bs, snapshot_id);
 470     if (snapshot_index < 0) {
 471         return -ENOENT;
 472     }
 473     sn = &s->snapshots[snapshot_index];
 474
 475     if (sn->disk_size != bs->total_sectors * BDRV_SECTOR_SIZE) {
 476         error_report("qcow2: Loading snapshots with different disk "
 477             "size is not implemented");
 478         ret = -ENOTSUP;
 479         goto fail;
 480     }
 481
 482     /*
 483      * Make sure that the current L1 table is big enough to contain the whole
 484      * L1 table of the snapshot. If the snapshot L1 table is smaller, the
 485      * current one must be padded with zeros.
 486      */
 487     ret = qcow2_grow_l1_table(bs, sn->l1_size, true);
 488     if (ret < 0) {
 489         goto fail;
 490     }
 491
 492     cur_l1_bytes = s->l1_size * sizeof(uint64_t);
 493     sn_l1_bytes = sn->l1_size * sizeof(uint64_t);
 494
 495     /*
 496      * Copy the snapshot L1 table to the current L1 table.
 497      *
 498      * Before overwriting the old current L1 table on disk, make sure to
 499      * increase all refcounts for the clusters referenced by the new one.
 500      * Decrease the refcount referenced by the old one only when the L1
 501      * table is overwritten.
 502      */
 503     sn_l1_table = g_malloc0(cur_l1_bytes);
 504
 505     ret = bdrv_pread(bs->file, sn->l1_table_offset, sn_l1_table, sn_l1_bytes);
 506     if (ret < 0) {
 507         goto fail;
 508     }
 509
 510     ret = qcow2_update_snapshot_refcount(bs, sn->l1_table_offset,
 511                                          sn->l1_size, 1);
 512     if (ret < 0) {
 513         goto fail;
 514     }
 515
 516     ret = qcow2_pre_write_overlap_check(bs,
 517             QCOW2_OL_DEFAULT & ~QCOW2_OL_ACTIVE_L1,
 518             s->l1_table_offset, cur_l1_bytes);
 519     if (ret < 0) {
 520         goto fail;
 521     }
 522
 523     ret = bdrv_pwrite_sync(bs->file, s->l1_table_offset, sn_l1_table,
 524                            cur_l1_bytes);
 525     if (ret < 0) {
 526         goto fail;
 527     }
 528
 529     /*
 530      * Decrease refcount of clusters of current L1 table.
 531      *
 532      * At this point, the in-memory s->l1_table points to the old L1 table,
 533      * whereas on disk we already have the new one.
 534      *
 535      * qcow2_update_snapshot_refcount special cases the current L1 table to use
 536      * the in-memory data instead of really using the offset to load a new one,
 537      * which is why this works.
 538      */
 539     ret = qcow2_update_snapshot_refcount(bs, s->l1_table_offset,
 540                                          s->l1_size, -1);
 541
 542     /*
 543      * Now update the in-memory L1 table to be in sync with the on-disk one. We
 544      * need to do this even if updating refcounts failed.
 545      */
 546     for(i = 0;i < s->l1_size; i++) {
 547         s->l1_table[i] = be64_to_cpu(sn_l1_table[i]);
 548     }
 549
 550     if (ret < 0) {
 551         goto fail;
 552     }
 553
 554     g_free(sn_l1_table);
 555     sn_l1_table = NULL;
 556
 557     /*
 558      * Update QCOW_OFLAG_COPIED in the active L1 table (it may have changed
 559      * when we decreased the refcount of the old snapshot.
 560      */
 561     ret = qcow2_update_snapshot_refcount(bs, s->l1_table_offset, s->l1_size, 0);
 562     if (ret < 0) {
 563         goto fail;
 564     }
 565
 566 #ifdef DEBUG_ALLOC
 567     {
 568         BdrvCheckResult result = {0};
 569         qcow2_check_refcounts(bs, &result, 0);
 570     }
 571 #endif
 572     return 0;
 573
 574 fail:
 575     g_free(sn_l1_table);
 576     return ret;
 577 }
 578
 579 int qcow2_snapshot_delete(BlockDriverState *bs,
 580                           const char *snapshot_id,
 581                           const char *name,
 582                           Error **errp)
 583 {
 584     BDRVQcowState *s = bs->opaque;
 585     QCowSnapshot sn;
 586     int snapshot_index, ret;
 587
 588     /* Search the snapshot */
 589     snapshot_index = find_snapshot_by_id_and_name(bs, snapshot_id, name);
 590     if (snapshot_index < 0) {
 591         error_setg(errp, "Can't find the snapshot");
 592         return -ENOENT;
 593     }
 594     sn = s->snapshots[snapshot_index];
 595
 596     /* Remove it from the snapshot list */
 597     memmove(s->snapshots + snapshot_index,
 598             s->snapshots + snapshot_index + 1,
 599             (s->nb_snapshots - snapshot_index - 1) * sizeof(sn));
 600     s->nb_snapshots--;
 601     ret = qcow2_write_snapshots(bs);
 602     if (ret < 0) {
 603         error_setg(errp, "Failed to remove snapshot from snapshot list");
 604         return ret;
 605     }
 606
 607     /*
 608      * The snapshot is now unused, clean up. If we fail after this point, we
 609      * won't recover but just leak clusters.
 610      */
 611     g_free(sn.id_str);
 612     g_free(sn.name);
 613
 614     /*
 615      * Now decrease the refcounts of clusters referenced by the snapshot and
 616      * free the L1 table.
 617      */
 618     ret = qcow2_update_snapshot_refcount(bs, sn.l1_table_offset,
 619                                          sn.l1_size, -1);
 620     if (ret < 0) {
 621         error_setg(errp, "Failed to free the cluster and L1 table");
 622         return ret;
 623     }
 624     qcow2_free_clusters(bs, sn.l1_table_offset, sn.l1_size * sizeof(uint64_t),
 625                         QCOW2_DISCARD_SNAPSHOT);
 626
 627     /* must update the copied flag on the current cluster offsets */
 628     ret = qcow2_update_snapshot_refcount(bs, s->l1_table_offset, s->l1_size, 0);
 629     if (ret < 0) {
 630         error_setg(errp, "Failed to update snapshot status in disk");
 631         return ret;
 632     }
 633
 634 #ifdef DEBUG_ALLOC
 635     {
 636         BdrvCheckResult result = {0};
 637         qcow2_check_refcounts(bs, &result, 0);
 638     }
 639 #endif
 640     return 0;
 641 }
 642
 643 int qcow2_snapshot_list(BlockDriverState *bs, QEMUSnapshotInfo **psn_tab)
 644 {
 645     BDRVQcowState *s = bs->opaque;
 646     QEMUSnapshotInfo *sn_tab, *sn_info;
 647     QCowSnapshot *sn;
 648     int i;
 649
 650     if (!s->nb_snapshots) {
 651         *psn_tab = NULL;
 652         return s->nb_snapshots;
 653     }
 654
 655     sn_tab = g_malloc0(s->nb_snapshots * sizeof(QEMUSnapshotInfo));
 656     for(i = 0; i < s->nb_snapshots; i++) {
 657         sn_info = sn_tab + i;
 658         sn = s->snapshots + i;
 659         pstrcpy(sn_info->id_str, sizeof(sn_info->id_str),
 660                 sn->id_str);
 661         pstrcpy(sn_info->name, sizeof(sn_info->name),
 662                 sn->name);
 663         sn_info->vm_state_size = sn->vm_state_size;
 664         sn_info->date_sec = sn->date_sec;
 665         sn_info->date_nsec = sn->date_nsec;
 666         sn_info->vm_clock_nsec = sn->vm_clock_nsec;
 667     }
 668     *psn_tab = sn_tab;
 669     return s->nb_snapshots;
 670 }
 671
 672 int qcow2_snapshot_load_tmp(BlockDriverState *bs, const char *snapshot_name)
 673 {
 674     int i, snapshot_index;
 675     BDRVQcowState *s = bs->opaque;
 676     QCowSnapshot *sn;
 677     uint64_t *new_l1_table;
 678     int new_l1_bytes;
 679     int ret;
 680
 681     assert(bs->read_only);
 682
 683     /* Search the snapshot */
 684     snapshot_index = find_snapshot_by_id_or_name(bs, snapshot_name);
 685     if (snapshot_index < 0) {
 686         return -ENOENT;
 687     }
 688     sn = &s->snapshots[snapshot_index];
 689
 690     /* Allocate and read in the snapshot's L1 table */
 691     new_l1_bytes = s->l1_size * sizeof(uint64_t);
 692     new_l1_table = g_malloc0(align_offset(new_l1_bytes, 512));
 693
 694     ret = bdrv_pread(bs->file, sn->l1_table_offset, new_l1_table, new_l1_bytes);
 695     if (ret < 0) {
 696         g_free(new_l1_table);
 697         return ret;
 698     }
 699
 700     /* Switch the L1 table */
 701     g_free(s->l1_table);
 702
 703     s->l1_size = sn->l1_size;
 704     s->l1_table_offset = sn->l1_table_offset;
 705     s->l1_table = new_l1_table;
 706
 707     for(i = 0;i < s->l1_size; i++) {
 708         be64_to_cpus(&s->l1_table[i]);
 709     }
 710
 711     return 0;
 712 }