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     s->snapshots_offset = snapshots_offset;
 267     s->snapshots_size = snapshots_size;
 268     return 0;
 269
 270 fail:
 271     return ret;
 272 }
 273
 274 static void find_new_snapshot_id(BlockDriverState *bs,
 275                                  char *id_str, int id_str_size)
 276 {
 277     BDRVQcowState *s = bs->opaque;
 278     QCowSnapshot *sn;
 279     int i, id, id_max = 0;
 280
 281     for(i = 0; i < s->nb_snapshots; i++) {
 282         sn = s->snapshots + i;
 283         id = strtoul(sn->id_str, NULL, 10);
 284         if (id > id_max)
 285             id_max = id;
 286     }
 287     snprintf(id_str, id_str_size, "%d", id_max + 1);
 288 }
 289
 290 static int find_snapshot_by_id(BlockDriverState *bs, const char *id_str)
 291 {
 292     BDRVQcowState *s = bs->opaque;
 293     int i;
 294
 295     for(i = 0; i < s->nb_snapshots; i++) {
 296         if (!strcmp(s->snapshots[i].id_str, id_str))
 297             return i;
 298     }
 299     return -1;
 300 }
 301
 302 static int find_snapshot_by_id_or_name(BlockDriverState *bs, const char *name)
 303 {
 304     BDRVQcowState *s = bs->opaque;
 305     int i, ret;
 306
 307     ret = find_snapshot_by_id(bs, name);
 308     if (ret >= 0)
 309         return ret;
 310     for(i = 0; i < s->nb_snapshots; i++) {
 311         if (!strcmp(s->snapshots[i].name, name))
 312             return i;
 313     }
 314     return -1;
 315 }
 316
 317 /* if no id is provided, a new one is constructed */
 318 int qcow2_snapshot_create(BlockDriverState *bs, QEMUSnapshotInfo *sn_info)
 319 {
 320     BDRVQcowState *s = bs->opaque;
 321     QCowSnapshot *new_snapshot_list = NULL;
 322     QCowSnapshot *old_snapshot_list = NULL;
 323     QCowSnapshot sn1, *sn = &sn1;
 324     int i, ret;
 325     uint64_t *l1_table = NULL;
 326     int64_t l1_table_offset;
 327
 328     memset(sn, 0, sizeof(*sn));
 329
 330     /* Generate an ID if it wasn't passed */
 331     if (sn_info->id_str[0] == '\0') {
 332         find_new_snapshot_id(bs, sn_info->id_str, sizeof(sn_info->id_str));
 333     }
 334
 335     /* Check that the ID is unique */
 336     if (find_snapshot_by_id(bs, sn_info->id_str) >= 0) {
 337         return -EEXIST;
 338     }
 339
 340     /* Populate sn with passed data */
 341     sn->id_str = g_strdup(sn_info->id_str);
 342     sn->name = g_strdup(sn_info->name);
 343
 344     sn->disk_size = bs->total_sectors * BDRV_SECTOR_SIZE;
 345     sn->vm_state_size = sn_info->vm_state_size;
 346     sn->date_sec = sn_info->date_sec;
 347     sn->date_nsec = sn_info->date_nsec;
 348     sn->vm_clock_nsec = sn_info->vm_clock_nsec;
 349
 350     /* Allocate the L1 table of the snapshot and copy the current one there. */
 351     l1_table_offset = qcow2_alloc_clusters(bs, s->l1_size * sizeof(uint64_t));
 352     if (l1_table_offset < 0) {
 353         ret = l1_table_offset;
 354         goto fail;
 355     }
 356
 357     sn->l1_table_offset = l1_table_offset;
 358     sn->l1_size = s->l1_size;
 359
 360     l1_table = g_malloc(s->l1_size * sizeof(uint64_t));
 361     for(i = 0; i < s->l1_size; i++) {
 362         l1_table[i] = cpu_to_be64(s->l1_table[i]);
 363     }
 364
 365     ret = bdrv_pwrite(bs->file, sn->l1_table_offset, l1_table,
 366                       s->l1_size * sizeof(uint64_t));
 367     if (ret < 0) {
 368         goto fail;
 369     }
 370
 371     g_free(l1_table);
 372     l1_table = NULL;
 373
 374     /*
 375      * Increase the refcounts of all clusters and make sure everything is
 376      * stable on disk before updating the snapshot table to contain a pointer
 377      * to the new L1 table.
 378      */
 379     ret = qcow2_update_snapshot_refcount(bs, s->l1_table_offset, s->l1_size, 1);
 380     if (ret < 0) {
 381         goto fail;
 382     }
 383
 384     ret = bdrv_flush(bs);
 385     if (ret < 0) {
 386         goto fail;
 387     }
 388
 389     /* Append the new snapshot to the snapshot list */
 390     new_snapshot_list = g_malloc((s->nb_snapshots + 1) * sizeof(QCowSnapshot));
 391     if (s->snapshots) {
 392         memcpy(new_snapshot_list, s->snapshots,
 393                s->nb_snapshots * sizeof(QCowSnapshot));
 394         old_snapshot_list = s->snapshots;
 395     }
 396     s->snapshots = new_snapshot_list;
 397     s->snapshots[s->nb_snapshots++] = *sn;
 398
 399     ret = qcow2_write_snapshots(bs);
 400     if (ret < 0) {
 401         g_free(s->snapshots);
 402         s->snapshots = old_snapshot_list;
 403         goto fail;
 404     }
 405
 406     g_free(old_snapshot_list);
 407
 408 #ifdef DEBUG_ALLOC
 409     {
 410       BdrvCheckResult result = {0};
 411       qcow2_check_refcounts(bs, &result, 0);
 412     }
 413 #endif
 414     return 0;
 415
 416 fail:
 417     g_free(sn->id_str);
 418     g_free(sn->name);
 419     g_free(l1_table);
 420
 421     return ret;
 422 }
 423
 424 /* copy the snapshot 'snapshot_name' into the current disk image */
 425 int qcow2_snapshot_goto(BlockDriverState *bs, const char *snapshot_id)
 426 {
 427     BDRVQcowState *s = bs->opaque;
 428     QCowSnapshot *sn;
 429     int i, snapshot_index;
 430     int cur_l1_bytes, sn_l1_bytes;
 431     int ret;
 432     uint64_t *sn_l1_table = NULL;
 433
 434     /* Search the snapshot */
 435     snapshot_index = find_snapshot_by_id_or_name(bs, snapshot_id);
 436     if (snapshot_index < 0) {
 437         return -ENOENT;
 438     }
 439     sn = &s->snapshots[snapshot_index];
 440
 441     if (sn->disk_size != bs->total_sectors * BDRV_SECTOR_SIZE) {
 442         error_report("qcow2: Loading snapshots with different disk "
 443             "size is not implemented");
 444         ret = -ENOTSUP;
 445         goto fail;
 446     }
 447
 448     /*
 449      * Make sure that the current L1 table is big enough to contain the whole
 450      * L1 table of the snapshot. If the snapshot L1 table is smaller, the
 451      * current one must be padded with zeros.
 452      */
 453     ret = qcow2_grow_l1_table(bs, sn->l1_size, true);
 454     if (ret < 0) {
 455         goto fail;
 456     }
 457
 458     cur_l1_bytes = s->l1_size * sizeof(uint64_t);
 459     sn_l1_bytes = sn->l1_size * sizeof(uint64_t);
 460
 461     /*
 462      * Copy the snapshot L1 table to the current L1 table.
 463      *
 464      * Before overwriting the old current L1 table on disk, make sure to
 465      * increase all refcounts for the clusters referenced by the new one.
 466      * Decrease the refcount referenced by the old one only when the L1
 467      * table is overwritten.
 468      */
 469     sn_l1_table = g_malloc0(cur_l1_bytes);
 470
 471     ret = bdrv_pread(bs->file, sn->l1_table_offset, sn_l1_table, sn_l1_bytes);
 472     if (ret < 0) {
 473         goto fail;
 474     }
 475
 476     ret = qcow2_update_snapshot_refcount(bs, sn->l1_table_offset,
 477                                          sn->l1_size, 1);
 478     if (ret < 0) {
 479         goto fail;
 480     }
 481
 482     ret = bdrv_pwrite_sync(bs->file, s->l1_table_offset, sn_l1_table,
 483                            cur_l1_bytes);
 484     if (ret < 0) {
 485         goto fail;
 486     }
 487
 488     /*
 489      * Decrease refcount of clusters of current L1 table.
 490      *
 491      * At this point, the in-memory s->l1_table points to the old L1 table,
 492      * whereas on disk we already have the new one.
 493      *
 494      * qcow2_update_snapshot_refcount special cases the current L1 table to use
 495      * the in-memory data instead of really using the offset to load a new one,
 496      * which is why this works.
 497      */
 498     ret = qcow2_update_snapshot_refcount(bs, s->l1_table_offset,
 499                                          s->l1_size, -1);
 500
 501     /*
 502      * Now update the in-memory L1 table to be in sync with the on-disk one. We
 503      * need to do this even if updating refcounts failed.
 504      */
 505     for(i = 0;i < s->l1_size; i++) {
 506         s->l1_table[i] = be64_to_cpu(sn_l1_table[i]);
 507     }
 508
 509     if (ret < 0) {
 510         goto fail;
 511     }
 512
 513     g_free(sn_l1_table);
 514     sn_l1_table = NULL;
 515
 516     /*
 517      * Update QCOW_OFLAG_COPIED in the active L1 table (it may have changed
 518      * when we decreased the refcount of the old snapshot.
 519      */
 520     ret = qcow2_update_snapshot_refcount(bs, s->l1_table_offset, s->l1_size, 0);
 521     if (ret < 0) {
 522         goto fail;
 523     }
 524
 525 #ifdef DEBUG_ALLOC
 526     {
 527         BdrvCheckResult result = {0};
 528         qcow2_check_refcounts(bs, &result, 0);
 529     }
 530 #endif
 531     return 0;
 532
 533 fail:
 534     g_free(sn_l1_table);
 535     return ret;
 536 }
 537
 538 int qcow2_snapshot_delete(BlockDriverState *bs, const char *snapshot_id)
 539 {
 540     BDRVQcowState *s = bs->opaque;
 541     QCowSnapshot sn;
 542     int snapshot_index, ret;
 543
 544     /* Search the snapshot */
 545     snapshot_index = find_snapshot_by_id_or_name(bs, snapshot_id);
 546     if (snapshot_index < 0) {
 547         return -ENOENT;
 548     }
 549     sn = s->snapshots[snapshot_index];
 550
 551     /* Remove it from the snapshot list */
 552     memmove(s->snapshots + snapshot_index,
 553             s->snapshots + snapshot_index + 1,
 554             (s->nb_snapshots - snapshot_index - 1) * sizeof(sn));
 555     s->nb_snapshots--;
 556     ret = qcow2_write_snapshots(bs);
 557     if (ret < 0) {
 558         return ret;
 559     }
 560
 561     /*
 562      * The snapshot is now unused, clean up. If we fail after this point, we
 563      * won't recover but just leak clusters.
 564      */
 565     g_free(sn.id_str);
 566     g_free(sn.name);
 567
 568     /*
 569      * Now decrease the refcounts of clusters referenced by the snapshot and
 570      * free the L1 table.
 571      */
 572     ret = qcow2_update_snapshot_refcount(bs, sn.l1_table_offset,
 573                                          sn.l1_size, -1);
 574     if (ret < 0) {
 575         return ret;
 576     }
 577     qcow2_free_clusters(bs, sn.l1_table_offset, sn.l1_size * sizeof(uint64_t));
 578
 579     /* must update the copied flag on the current cluster offsets */
 580     ret = qcow2_update_snapshot_refcount(bs, s->l1_table_offset, s->l1_size, 0);
 581     if (ret < 0) {
 582         return ret;
 583     }
 584
 585 #ifdef DEBUG_ALLOC
 586     {
 587         BdrvCheckResult result = {0};
 588         qcow2_check_refcounts(bs, &result, 0);
 589     }
 590 #endif
 591     return 0;
 592 }
 593
 594 int qcow2_snapshot_list(BlockDriverState *bs, QEMUSnapshotInfo **psn_tab)
 595 {
 596     BDRVQcowState *s = bs->opaque;
 597     QEMUSnapshotInfo *sn_tab, *sn_info;
 598     QCowSnapshot *sn;
 599     int i;
 600
 601     if (!s->nb_snapshots) {
 602         *psn_tab = NULL;
 603         return s->nb_snapshots;
 604     }
 605
 606     sn_tab = g_malloc0(s->nb_snapshots * sizeof(QEMUSnapshotInfo));
 607     for(i = 0; i < s->nb_snapshots; i++) {
 608         sn_info = sn_tab + i;
 609         sn = s->snapshots + i;
 610         pstrcpy(sn_info->id_str, sizeof(sn_info->id_str),
 611                 sn->id_str);
 612         pstrcpy(sn_info->name, sizeof(sn_info->name),
 613                 sn->name);
 614         sn_info->vm_state_size = sn->vm_state_size;
 615         sn_info->date_sec = sn->date_sec;
 616         sn_info->date_nsec = sn->date_nsec;
 617         sn_info->vm_clock_nsec = sn->vm_clock_nsec;
 618     }
 619     *psn_tab = sn_tab;
 620     return s->nb_snapshots;
 621 }
 622
 623 int qcow2_snapshot_load_tmp(BlockDriverState *bs, const char *snapshot_name)
 624 {
 625     int i, snapshot_index;
 626     BDRVQcowState *s = bs->opaque;
 627     QCowSnapshot *sn;
 628     uint64_t *new_l1_table;
 629     int new_l1_bytes;
 630     int ret;
 631
 632     assert(bs->read_only);
 633
 634     /* Search the snapshot */
 635     snapshot_index = find_snapshot_by_id_or_name(bs, snapshot_name);
 636     if (snapshot_index < 0) {
 637         return -ENOENT;
 638     }
 639     sn = &s->snapshots[snapshot_index];
 640
 641     /* Allocate and read in the snapshot's L1 table */
 642     new_l1_bytes = s->l1_size * sizeof(uint64_t);
 643     new_l1_table = g_malloc0(align_offset(new_l1_bytes, 512));
 644
 645     ret = bdrv_pread(bs->file, sn->l1_table_offset, new_l1_table, new_l1_bytes);
 646     if (ret < 0) {
 647         g_free(new_l1_table);
 648         return ret;
 649     }
 650
 651     /* Switch the L1 table */
 652     g_free(s->l1_table);
 653
 654     s->l1_size = sn->l1_size;
 655     s->l1_table_offset = sn->l1_table_offset;
 656     s->l1_table = new_l1_table;
 657
 658     for(i = 0;i < s->l1_size; i++) {
 659         be64_to_cpus(&s->l1_table[i]);
 660     }
 661
 662     return 0;
 663 }