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         ret = offset;
 186         goto fail;
 187     }
 188     ret = bdrv_flush(bs);
 189     if (ret < 0) {
 190         goto fail;
 191     }
 192
 193     /* The snapshot list position has not yet been updated, so these clusters
 194      * must indeed be completely free */
 195     ret = qcow2_pre_write_overlap_check(bs, 0, offset, snapshots_size);
 196     if (ret < 0) {
 197         goto fail;
 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         assert(id_str_size <= UINT16_MAX && name_size <= UINT16_MAX);
 224         h.id_str_size = cpu_to_be16(id_str_size);
 225         h.name_size = cpu_to_be16(name_size);
 226         offset = align_offset(offset, 8);
 227
 228         ret = bdrv_pwrite(bs->file, offset, &h, sizeof(h));
 229         if (ret < 0) {
 230             goto fail;
 231         }
 232         offset += sizeof(h);
 233
 234         ret = bdrv_pwrite(bs->file, offset, &extra, sizeof(extra));
 235         if (ret < 0) {
 236             goto fail;
 237         }
 238         offset += sizeof(extra);
 239
 240         ret = bdrv_pwrite(bs->file, offset, sn->id_str, id_str_size);
 241         if (ret < 0) {
 242             goto fail;
 243         }
 244         offset += id_str_size;
 245
 246         ret = bdrv_pwrite(bs->file, offset, sn->name, name_size);
 247         if (ret < 0) {
 248             goto fail;
 249         }
 250         offset += name_size;
 251     }
 252
 253     /*
 254      * Update the header to point to the new snapshot table. This requires the
 255      * new table and its refcounts to be stable on disk.
 256      */
 257     ret = bdrv_flush(bs);
 258     if (ret < 0) {
 259         goto fail;
 260     }
 261
 262     QEMU_BUILD_BUG_ON(offsetof(QCowHeader, snapshots_offset) !=
 263         offsetof(QCowHeader, nb_snapshots) + sizeof(header_data.nb_snapshots));
 264
 265     header_data.nb_snapshots        = cpu_to_be32(s->nb_snapshots);
 266     header_data.snapshots_offset    = cpu_to_be64(snapshots_offset);
 267
 268     ret = bdrv_pwrite_sync(bs->file, offsetof(QCowHeader, nb_snapshots),
 269                            &header_data, sizeof(header_data));
 270     if (ret < 0) {
 271         goto fail;
 272     }
 273
 274     /* free the old snapshot table */
 275     qcow2_free_clusters(bs, s->snapshots_offset, s->snapshots_size,
 276                         QCOW2_DISCARD_SNAPSHOT);
 277     s->snapshots_offset = snapshots_offset;
 278     s->snapshots_size = snapshots_size;
 279     return 0;
 280
 281 fail:
 282     if (snapshots_offset > 0) {
 283         qcow2_free_clusters(bs, snapshots_offset, snapshots_size,
 284                             QCOW2_DISCARD_ALWAYS);
 285     }
 286     return ret;
 287 }
 288
 289 static void find_new_snapshot_id(BlockDriverState *bs,
 290                                  char *id_str, int id_str_size)
 291 {
 292     BDRVQcowState *s = bs->opaque;
 293     QCowSnapshot *sn;
 294     int i;
 295     unsigned long id, id_max = 0;
 296
 297     for(i = 0; i < s->nb_snapshots; i++) {
 298         sn = s->snapshots + i;
 299         id = strtoul(sn->id_str, NULL, 10);
 300         if (id > id_max)
 301             id_max = id;
 302     }
 303     snprintf(id_str, id_str_size, "%lu", id_max + 1);
 304 }
 305
 306 static int find_snapshot_by_id_and_name(BlockDriverState *bs,
 307                                         const char *id,
 308                                         const char *name)
 309 {
 310     BDRVQcowState *s = bs->opaque;
 311     int i;
 312
 313     if (id && name) {
 314         for (i = 0; i < s->nb_snapshots; i++) {
 315             if (!strcmp(s->snapshots[i].id_str, id) &&
 316                 !strcmp(s->snapshots[i].name, name)) {
 317                 return i;
 318             }
 319         }
 320     } else if (id) {
 321         for (i = 0; i < s->nb_snapshots; i++) {
 322             if (!strcmp(s->snapshots[i].id_str, id)) {
 323                 return i;
 324             }
 325         }
 326     } else if (name) {
 327         for (i = 0; i < s->nb_snapshots; i++) {
 328             if (!strcmp(s->snapshots[i].name, name)) {
 329                 return i;
 330             }
 331         }
 332     }
 333
 334     return -1;
 335 }
 336
 337 static int find_snapshot_by_id_or_name(BlockDriverState *bs,
 338                                        const char *id_or_name)
 339 {
 340     int ret;
 341
 342     ret = find_snapshot_by_id_and_name(bs, id_or_name, NULL);
 343     if (ret >= 0) {
 344         return ret;
 345     }
 346     return find_snapshot_by_id_and_name(bs, NULL, id_or_name);
 347 }
 348
 349 /* if no id is provided, a new one is constructed */
 350 int qcow2_snapshot_create(BlockDriverState *bs, QEMUSnapshotInfo *sn_info)
 351 {
 352     BDRVQcowState *s = bs->opaque;
 353     QCowSnapshot *new_snapshot_list = NULL;
 354     QCowSnapshot *old_snapshot_list = NULL;
 355     QCowSnapshot sn1, *sn = &sn1;
 356     int i, ret;
 357     uint64_t *l1_table = NULL;
 358     int64_t l1_table_offset;
 359
 360     memset(sn, 0, sizeof(*sn));
 361
 362     /* Generate an ID if it wasn't passed */
 363     if (sn_info->id_str[0] == '\0') {
 364         find_new_snapshot_id(bs, sn_info->id_str, sizeof(sn_info->id_str));
 365     }
 366
 367     /* Check that the ID is unique */
 368     if (find_snapshot_by_id_and_name(bs, sn_info->id_str, NULL) >= 0) {
 369         return -EEXIST;
 370     }
 371
 372     /* Populate sn with passed data */
 373     sn->id_str = g_strdup(sn_info->id_str);
 374     sn->name = g_strdup(sn_info->name);
 375
 376     sn->disk_size = bs->total_sectors * BDRV_SECTOR_SIZE;
 377     sn->vm_state_size = sn_info->vm_state_size;
 378     sn->date_sec = sn_info->date_sec;
 379     sn->date_nsec = sn_info->date_nsec;
 380     sn->vm_clock_nsec = sn_info->vm_clock_nsec;
 381
 382     /* Allocate the L1 table of the snapshot and copy the current one there. */
 383     l1_table_offset = qcow2_alloc_clusters(bs, s->l1_size * sizeof(uint64_t));
 384     if (l1_table_offset < 0) {
 385         ret = l1_table_offset;
 386         goto fail;
 387     }
 388
 389     sn->l1_table_offset = l1_table_offset;
 390     sn->l1_size = s->l1_size;
 391
 392     l1_table = g_malloc(s->l1_size * sizeof(uint64_t));
 393     for(i = 0; i < s->l1_size; i++) {
 394         l1_table[i] = cpu_to_be64(s->l1_table[i]);
 395     }
 396
 397     ret = qcow2_pre_write_overlap_check(bs, 0, sn->l1_table_offset,
 398                                         s->l1_size * sizeof(uint64_t));
 399     if (ret < 0) {
 400         goto fail;
 401     }
 402
 403     ret = bdrv_pwrite(bs->file, sn->l1_table_offset, l1_table,
 404                       s->l1_size * sizeof(uint64_t));
 405     if (ret < 0) {
 406         goto fail;
 407     }
 408
 409     g_free(l1_table);
 410     l1_table = NULL;
 411
 412     /*
 413      * Increase the refcounts of all clusters and make sure everything is
 414      * stable on disk before updating the snapshot table to contain a pointer
 415      * to the new L1 table.
 416      */
 417     ret = qcow2_update_snapshot_refcount(bs, s->l1_table_offset, s->l1_size, 1);
 418     if (ret < 0) {
 419         goto fail;
 420     }
 421
 422     /* Append the new snapshot to the snapshot list */
 423     new_snapshot_list = g_malloc((s->nb_snapshots + 1) * sizeof(QCowSnapshot));
 424     if (s->snapshots) {
 425         memcpy(new_snapshot_list, s->snapshots,
 426                s->nb_snapshots * sizeof(QCowSnapshot));
 427         old_snapshot_list = s->snapshots;
 428     }
 429     s->snapshots = new_snapshot_list;
 430     s->snapshots[s->nb_snapshots++] = *sn;
 431
 432     ret = qcow2_write_snapshots(bs);
 433     if (ret < 0) {
 434         g_free(s->snapshots);
 435         s->snapshots = old_snapshot_list;
 436         s->nb_snapshots--;
 437         goto fail;
 438     }
 439
 440     g_free(old_snapshot_list);
 441
 442     /* The VM state isn't needed any more in the active L1 table; in fact, it
 443      * hurts by causing expensive COW for the next snapshot. */
 444     qcow2_discard_clusters(bs, qcow2_vm_state_offset(s),
 445                            align_offset(sn->vm_state_size, s->cluster_size)
 446                                 >> BDRV_SECTOR_BITS,
 447                            QCOW2_DISCARD_NEVER);
 448
 449 #ifdef DEBUG_ALLOC
 450     {
 451       BdrvCheckResult result = {0};
 452       qcow2_check_refcounts(bs, &result, 0);
 453     }
 454 #endif
 455     return 0;
 456
 457 fail:
 458     g_free(sn->id_str);
 459     g_free(sn->name);
 460     g_free(l1_table);
 461
 462     return ret;
 463 }
 464
 465 /* copy the snapshot 'snapshot_name' into the current disk image */
 466 int qcow2_snapshot_goto(BlockDriverState *bs, const char *snapshot_id)
 467 {
 468     BDRVQcowState *s = bs->opaque;
 469     QCowSnapshot *sn;
 470     int i, snapshot_index;
 471     int cur_l1_bytes, sn_l1_bytes;
 472     int ret;
 473     uint64_t *sn_l1_table = NULL;
 474
 475     /* Search the snapshot */
 476     snapshot_index = find_snapshot_by_id_or_name(bs, snapshot_id);
 477     if (snapshot_index < 0) {
 478         return -ENOENT;
 479     }
 480     sn = &s->snapshots[snapshot_index];
 481
 482     if (sn->disk_size != bs->total_sectors * BDRV_SECTOR_SIZE) {
 483         error_report("qcow2: Loading snapshots with different disk "
 484             "size is not implemented");
 485         ret = -ENOTSUP;
 486         goto fail;
 487     }
 488
 489     /*
 490      * Make sure that the current L1 table is big enough to contain the whole
 491      * L1 table of the snapshot. If the snapshot L1 table is smaller, the
 492      * current one must be padded with zeros.
 493      */
 494     ret = qcow2_grow_l1_table(bs, sn->l1_size, true);
 495     if (ret < 0) {
 496         goto fail;
 497     }
 498
 499     cur_l1_bytes = s->l1_size * sizeof(uint64_t);
 500     sn_l1_bytes = sn->l1_size * sizeof(uint64_t);
 501
 502     /*
 503      * Copy the snapshot L1 table to the current L1 table.
 504      *
 505      * Before overwriting the old current L1 table on disk, make sure to
 506      * increase all refcounts for the clusters referenced by the new one.
 507      * Decrease the refcount referenced by the old one only when the L1
 508      * table is overwritten.
 509      */
 510     sn_l1_table = g_malloc0(cur_l1_bytes);
 511
 512     ret = bdrv_pread(bs->file, sn->l1_table_offset, sn_l1_table, sn_l1_bytes);
 513     if (ret < 0) {
 514         goto fail;
 515     }
 516
 517     ret = qcow2_update_snapshot_refcount(bs, sn->l1_table_offset,
 518                                          sn->l1_size, 1);
 519     if (ret < 0) {
 520         goto fail;
 521     }
 522
 523     ret = qcow2_pre_write_overlap_check(bs, QCOW2_OL_ACTIVE_L1,
 524                                         s->l1_table_offset, cur_l1_bytes);
 525     if (ret < 0) {
 526         goto fail;
 527     }
 528
 529     ret = bdrv_pwrite_sync(bs->file, s->l1_table_offset, sn_l1_table,
 530                            cur_l1_bytes);
 531     if (ret < 0) {
 532         goto fail;
 533     }
 534
 535     /*
 536      * Decrease refcount of clusters of current L1 table.
 537      *
 538      * At this point, the in-memory s->l1_table points to the old L1 table,
 539      * whereas on disk we already have the new one.
 540      *
 541      * qcow2_update_snapshot_refcount special cases the current L1 table to use
 542      * the in-memory data instead of really using the offset to load a new one,
 543      * which is why this works.
 544      */
 545     ret = qcow2_update_snapshot_refcount(bs, s->l1_table_offset,
 546                                          s->l1_size, -1);
 547
 548     /*
 549      * Now update the in-memory L1 table to be in sync with the on-disk one. We
 550      * need to do this even if updating refcounts failed.
 551      */
 552     for(i = 0;i < s->l1_size; i++) {
 553         s->l1_table[i] = be64_to_cpu(sn_l1_table[i]);
 554     }
 555
 556     if (ret < 0) {
 557         goto fail;
 558     }
 559
 560     g_free(sn_l1_table);
 561     sn_l1_table = NULL;
 562
 563     /*
 564      * Update QCOW_OFLAG_COPIED in the active L1 table (it may have changed
 565      * when we decreased the refcount of the old snapshot.
 566      */
 567     ret = qcow2_update_snapshot_refcount(bs, s->l1_table_offset, s->l1_size, 0);
 568     if (ret < 0) {
 569         goto fail;
 570     }
 571
 572 #ifdef DEBUG_ALLOC
 573     {
 574         BdrvCheckResult result = {0};
 575         qcow2_check_refcounts(bs, &result, 0);
 576     }
 577 #endif
 578     return 0;
 579
 580 fail:
 581     g_free(sn_l1_table);
 582     return ret;
 583 }
 584
 585 int qcow2_snapshot_delete(BlockDriverState *bs,
 586                           const char *snapshot_id,
 587                           const char *name,
 588                           Error **errp)
 589 {
 590     BDRVQcowState *s = bs->opaque;
 591     QCowSnapshot sn;
 592     int snapshot_index, ret;
 593
 594     /* Search the snapshot */
 595     snapshot_index = find_snapshot_by_id_and_name(bs, snapshot_id, name);
 596     if (snapshot_index < 0) {
 597         error_setg(errp, "Can't find the snapshot");
 598         return -ENOENT;
 599     }
 600     sn = s->snapshots[snapshot_index];
 601
 602     /* Remove it from the snapshot list */
 603     memmove(s->snapshots + snapshot_index,
 604             s->snapshots + snapshot_index + 1,
 605             (s->nb_snapshots - snapshot_index - 1) * sizeof(sn));
 606     s->nb_snapshots--;
 607     ret = qcow2_write_snapshots(bs);
 608     if (ret < 0) {
 609         error_setg(errp, "Failed to remove snapshot from snapshot list");
 610         return ret;
 611     }
 612
 613     /*
 614      * The snapshot is now unused, clean up. If we fail after this point, we
 615      * won't recover but just leak clusters.
 616      */
 617     g_free(sn.id_str);
 618     g_free(sn.name);
 619
 620     /*
 621      * Now decrease the refcounts of clusters referenced by the snapshot and
 622      * free the L1 table.
 623      */
 624     ret = qcow2_update_snapshot_refcount(bs, sn.l1_table_offset,
 625                                          sn.l1_size, -1);
 626     if (ret < 0) {
 627         error_setg(errp, "Failed to free the cluster and L1 table");
 628         return ret;
 629     }
 630     qcow2_free_clusters(bs, sn.l1_table_offset, sn.l1_size * sizeof(uint64_t),
 631                         QCOW2_DISCARD_SNAPSHOT);
 632
 633     /* must update the copied flag on the current cluster offsets */
 634     ret = qcow2_update_snapshot_refcount(bs, s->l1_table_offset, s->l1_size, 0);
 635     if (ret < 0) {
 636         error_setg(errp, "Failed to update snapshot status in disk");
 637         return ret;
 638     }
 639
 640 #ifdef DEBUG_ALLOC
 641     {
 642         BdrvCheckResult result = {0};
 643         qcow2_check_refcounts(bs, &result, 0);
 644     }
 645 #endif
 646     return 0;
 647 }
 648
 649 int qcow2_snapshot_list(BlockDriverState *bs, QEMUSnapshotInfo **psn_tab)
 650 {
 651     BDRVQcowState *s = bs->opaque;
 652     QEMUSnapshotInfo *sn_tab, *sn_info;
 653     QCowSnapshot *sn;
 654     int i;
 655
 656     if (!s->nb_snapshots) {
 657         *psn_tab = NULL;
 658         return s->nb_snapshots;
 659     }
 660
 661     sn_tab = g_malloc0(s->nb_snapshots * sizeof(QEMUSnapshotInfo));
 662     for(i = 0; i < s->nb_snapshots; i++) {
 663         sn_info = sn_tab + i;
 664         sn = s->snapshots + i;
 665         pstrcpy(sn_info->id_str, sizeof(sn_info->id_str),
 666                 sn->id_str);
 667         pstrcpy(sn_info->name, sizeof(sn_info->name),
 668                 sn->name);
 669         sn_info->vm_state_size = sn->vm_state_size;
 670         sn_info->date_sec = sn->date_sec;
 671         sn_info->date_nsec = sn->date_nsec;
 672         sn_info->vm_clock_nsec = sn->vm_clock_nsec;
 673     }
 674     *psn_tab = sn_tab;
 675     return s->nb_snapshots;
 676 }
 677
 678 int qcow2_snapshot_load_tmp(BlockDriverState *bs,
 679                             const char *snapshot_id,
 680                             const char *name,
 681                             Error **errp)
 682 {
 683     int i, snapshot_index;
 684     BDRVQcowState *s = bs->opaque;
 685     QCowSnapshot *sn;
 686     uint64_t *new_l1_table;
 687     int new_l1_bytes;
 688     int ret;
 689
 690     assert(bs->read_only);
 691
 692     /* Search the snapshot */
 693     snapshot_index = find_snapshot_by_id_and_name(bs, snapshot_id, name);
 694     if (snapshot_index < 0) {
 695         error_setg(errp,
 696                    "Can't find snapshot");
 697         return -ENOENT;
 698     }
 699     sn = &s->snapshots[snapshot_index];
 700
 701     /* Allocate and read in the snapshot's L1 table */
 702     new_l1_bytes = s->l1_size * sizeof(uint64_t);
 703     new_l1_table = g_malloc0(align_offset(new_l1_bytes, 512));
 704
 705     ret = bdrv_pread(bs->file, sn->l1_table_offset, new_l1_table, new_l1_bytes);
 706     if (ret < 0) {
 707         error_setg(errp, "Failed to read l1 table for snapshot");
 708         g_free(new_l1_table);
 709         return ret;
 710     }
 711
 712     /* Switch the L1 table */
 713     g_free(s->l1_table);
 714
 715     s->l1_size = sn->l1_size;
 716     s->l1_table_offset = sn->l1_table_offset;
 717     s->l1_table = new_l1_table;
 718
 719     for(i = 0;i < s->l1_size; i++) {
 720         be64_to_cpus(&s->l1_table[i]);
 721     }
 722
 723     return 0;
 724 }