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