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, QCOW2_OL_DEFAULT, offset,
 196                                         snapshots_size);
 197     if (ret < 0) {
 198         goto fail;
 199     }
 200
 201
 202     /* Write all snapshots to the new list */
 203     for(i = 0; i < s->nb_snapshots; i++) {
 204         sn = s->snapshots + i;
 205         memset(&h, 0, sizeof(h));
 206         h.l1_table_offset = cpu_to_be64(sn->l1_table_offset);
 207         h.l1_size = cpu_to_be32(sn->l1_size);
 208         /* If it doesn't fit in 32 bit, older implementations should treat it
 209          * as a disk-only snapshot rather than truncate the VM state */
 210         if (sn->vm_state_size <= 0xffffffff) {
 211             h.vm_state_size = cpu_to_be32(sn->vm_state_size);
 212         }
 213         h.date_sec = cpu_to_be32(sn->date_sec);
 214         h.date_nsec = cpu_to_be32(sn->date_nsec);
 215         h.vm_clock_nsec = cpu_to_be64(sn->vm_clock_nsec);
 216         h.extra_data_size = cpu_to_be32(sizeof(extra));
 217
 218         memset(&extra, 0, sizeof(extra));
 219         extra.vm_state_size_large = cpu_to_be64(sn->vm_state_size);
 220         extra.disk_size = cpu_to_be64(sn->disk_size);
 221
 222         id_str_size = strlen(sn->id_str);
 223         name_size = strlen(sn->name);
 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     return ret;
 283 }
 284
 285 static void find_new_snapshot_id(BlockDriverState *bs,
 286                                  char *id_str, int id_str_size)
 287 {
 288     BDRVQcowState *s = bs->opaque;
 289     QCowSnapshot *sn;
 290     int i, id, id_max = 0;
 291
 292     for(i = 0; i < s->nb_snapshots; i++) {
 293         sn = s->snapshots + i;
 294         id = strtoul(sn->id_str, NULL, 10);
 295         if (id > id_max)
 296             id_max = id;
 297     }
 298     snprintf(id_str, id_str_size, "%d", id_max + 1);
 299 }
 300
 301 static int find_snapshot_by_id_and_name(BlockDriverState *bs,
 302                                         const char *id,
 303                                         const char *name)
 304 {
 305     BDRVQcowState *s = bs->opaque;
 306     int i;
 307
 308     if (id && name) {
 309         for (i = 0; i < s->nb_snapshots; i++) {
 310             if (!strcmp(s->snapshots[i].id_str, id) &&
 311                 !strcmp(s->snapshots[i].name, name)) {
 312                 return i;
 313             }
 314         }
 315     } else if (id) {
 316         for (i = 0; i < s->nb_snapshots; i++) {
 317             if (!strcmp(s->snapshots[i].id_str, id)) {
 318                 return i;
 319             }
 320         }
 321     } else if (name) {
 322         for (i = 0; i < s->nb_snapshots; i++) {
 323             if (!strcmp(s->snapshots[i].name, name)) {
 324                 return i;
 325             }
 326         }
 327     }
 328
 329     return -1;
 330 }
 331
 332 static int find_snapshot_by_id_or_name(BlockDriverState *bs,
 333                                        const char *id_or_name)
 334 {
 335     int ret;
 336
 337     ret = find_snapshot_by_id_and_name(bs, id_or_name, NULL);
 338     if (ret >= 0) {
 339         return ret;
 340     }
 341     return find_snapshot_by_id_and_name(bs, NULL, id_or_name);
 342 }
 343
 344 /* if no id is provided, a new one is constructed */
 345 int qcow2_snapshot_create(BlockDriverState *bs, QEMUSnapshotInfo *sn_info)
 346 {
 347     BDRVQcowState *s = bs->opaque;
 348     QCowSnapshot *new_snapshot_list = NULL;
 349     QCowSnapshot *old_snapshot_list = NULL;
 350     QCowSnapshot sn1, *sn = &sn1;
 351     int i, ret;
 352     uint64_t *l1_table = NULL;
 353     int64_t l1_table_offset;
 354
 355     memset(sn, 0, sizeof(*sn));
 356
 357     /* Generate an ID if it wasn't passed */
 358     if (sn_info->id_str[0] == '\0') {
 359         find_new_snapshot_id(bs, sn_info->id_str, sizeof(sn_info->id_str));
 360     }
 361
 362     /* Check that the ID is unique */
 363     if (find_snapshot_by_id_and_name(bs, sn_info->id_str, NULL) >= 0) {
 364         return -EEXIST;
 365     }
 366
 367     /* Populate sn with passed data */
 368     sn->id_str = g_strdup(sn_info->id_str);
 369     sn->name = g_strdup(sn_info->name);
 370
 371     sn->disk_size = bs->total_sectors * BDRV_SECTOR_SIZE;
 372     sn->vm_state_size = sn_info->vm_state_size;
 373     sn->date_sec = sn_info->date_sec;
 374     sn->date_nsec = sn_info->date_nsec;
 375     sn->vm_clock_nsec = sn_info->vm_clock_nsec;
 376
 377     /* Allocate the L1 table of the snapshot and copy the current one there. */
 378     l1_table_offset = qcow2_alloc_clusters(bs, s->l1_size * sizeof(uint64_t));
 379     if (l1_table_offset < 0) {
 380         ret = l1_table_offset;
 381         goto fail;
 382     }
 383
 384     sn->l1_table_offset = l1_table_offset;
 385     sn->l1_size = s->l1_size;
 386
 387     l1_table = g_malloc(s->l1_size * sizeof(uint64_t));
 388     for(i = 0; i < s->l1_size; i++) {
 389         l1_table[i] = cpu_to_be64(s->l1_table[i]);
 390     }
 391
 392     ret = qcow2_pre_write_overlap_check(bs, QCOW2_OL_DEFAULT,
 393             sn->l1_table_offset, s->l1_size * sizeof(uint64_t));
 394     if (ret < 0) {
 395         goto fail;
 396     }
 397
 398     ret = bdrv_pwrite(bs->file, sn->l1_table_offset, l1_table,
 399                       s->l1_size * sizeof(uint64_t));
 400     if (ret < 0) {
 401         goto fail;
 402     }
 403
 404     g_free(l1_table);
 405     l1_table = NULL;
 406
 407     /*
 408      * Increase the refcounts of all clusters and make sure everything is
 409      * stable on disk before updating the snapshot table to contain a pointer
 410      * to the new L1 table.
 411      */
 412     ret = qcow2_update_snapshot_refcount(bs, s->l1_table_offset, s->l1_size, 1);
 413     if (ret < 0) {
 414         goto fail;
 415     }
 416
 417     /* Append the new snapshot to the snapshot list */
 418     new_snapshot_list = g_malloc((s->nb_snapshots + 1) * sizeof(QCowSnapshot));
 419     if (s->snapshots) {
 420         memcpy(new_snapshot_list, s->snapshots,
 421                s->nb_snapshots * sizeof(QCowSnapshot));
 422         old_snapshot_list = s->snapshots;
 423     }
 424     s->snapshots = new_snapshot_list;
 425     s->snapshots[s->nb_snapshots++] = *sn;
 426
 427     ret = qcow2_write_snapshots(bs);
 428     if (ret < 0) {
 429         g_free(s->snapshots);
 430         s->snapshots = old_snapshot_list;
 431         goto fail;
 432     }
 433
 434     g_free(old_snapshot_list);
 435
 436     /* The VM state isn't needed any more in the active L1 table; in fact, it
 437      * hurts by causing expensive COW for the next snapshot. */
 438     qcow2_discard_clusters(bs, qcow2_vm_state_offset(s),
 439                            align_offset(sn->vm_state_size, s->cluster_size)
 440                                 >> BDRV_SECTOR_BITS,
 441                            QCOW2_DISCARD_NEVER);
 442
 443 #ifdef DEBUG_ALLOC
 444     {
 445       BdrvCheckResult result = {0};
 446       qcow2_check_refcounts(bs, &result, 0);
 447     }
 448 #endif
 449     return 0;
 450
 451 fail:
 452     g_free(sn->id_str);
 453     g_free(sn->name);
 454     g_free(l1_table);
 455
 456     return ret;
 457 }
 458
 459 /* copy the snapshot 'snapshot_name' into the current disk image */
 460 int qcow2_snapshot_goto(BlockDriverState *bs, const char *snapshot_id)
 461 {
 462     BDRVQcowState *s = bs->opaque;
 463     QCowSnapshot *sn;
 464     int i, snapshot_index;
 465     int cur_l1_bytes, sn_l1_bytes;
 466     int ret;
 467     uint64_t *sn_l1_table = NULL;
 468
 469     /* Search the snapshot */
 470     snapshot_index = find_snapshot_by_id_or_name(bs, snapshot_id);
 471     if (snapshot_index < 0) {
 472         return -ENOENT;
 473     }
 474     sn = &s->snapshots[snapshot_index];
 475
 476     if (sn->disk_size != bs->total_sectors * BDRV_SECTOR_SIZE) {
 477         error_report("qcow2: Loading snapshots with different disk "
 478             "size is not implemented");
 479         ret = -ENOTSUP;
 480         goto fail;
 481     }
 482
 483     /*
 484      * Make sure that the current L1 table is big enough to contain the whole
 485      * L1 table of the snapshot. If the snapshot L1 table is smaller, the
 486      * current one must be padded with zeros.
 487      */
 488     ret = qcow2_grow_l1_table(bs, sn->l1_size, true);
 489     if (ret < 0) {
 490         goto fail;
 491     }
 492
 493     cur_l1_bytes = s->l1_size * sizeof(uint64_t);
 494     sn_l1_bytes = sn->l1_size * sizeof(uint64_t);
 495
 496     /*
 497      * Copy the snapshot L1 table to the current L1 table.
 498      *
 499      * Before overwriting the old current L1 table on disk, make sure to
 500      * increase all refcounts for the clusters referenced by the new one.
 501      * Decrease the refcount referenced by the old one only when the L1
 502      * table is overwritten.
 503      */
 504     sn_l1_table = g_malloc0(cur_l1_bytes);
 505
 506     ret = bdrv_pread(bs->file, sn->l1_table_offset, sn_l1_table, sn_l1_bytes);
 507     if (ret < 0) {
 508         goto fail;
 509     }
 510
 511     ret = qcow2_update_snapshot_refcount(bs, sn->l1_table_offset,
 512                                          sn->l1_size, 1);
 513     if (ret < 0) {
 514         goto fail;
 515     }
 516
 517     ret = qcow2_pre_write_overlap_check(bs,
 518             QCOW2_OL_DEFAULT & ~QCOW2_OL_ACTIVE_L1,
 519             s->l1_table_offset, cur_l1_bytes);
 520     if (ret < 0) {
 521         goto fail;
 522     }
 523
 524     ret = bdrv_pwrite_sync(bs->file, s->l1_table_offset, sn_l1_table,
 525                            cur_l1_bytes);
 526     if (ret < 0) {
 527         goto fail;
 528     }
 529
 530     /*
 531      * Decrease refcount of clusters of current L1 table.
 532      *
 533      * At this point, the in-memory s->l1_table points to the old L1 table,
 534      * whereas on disk we already have the new one.
 535      *
 536      * qcow2_update_snapshot_refcount special cases the current L1 table to use
 537      * the in-memory data instead of really using the offset to load a new one,
 538      * which is why this works.
 539      */
 540     ret = qcow2_update_snapshot_refcount(bs, s->l1_table_offset,
 541                                          s->l1_size, -1);
 542
 543     /*
 544      * Now update the in-memory L1 table to be in sync with the on-disk one. We
 545      * need to do this even if updating refcounts failed.
 546      */
 547     for(i = 0;i < s->l1_size; i++) {
 548         s->l1_table[i] = be64_to_cpu(sn_l1_table[i]);
 549     }
 550
 551     if (ret < 0) {
 552         goto fail;
 553     }
 554
 555     g_free(sn_l1_table);
 556     sn_l1_table = NULL;
 557
 558     /*
 559      * Update QCOW_OFLAG_COPIED in the active L1 table (it may have changed
 560      * when we decreased the refcount of the old snapshot.
 561      */
 562     ret = qcow2_update_snapshot_refcount(bs, s->l1_table_offset, s->l1_size, 0);
 563     if (ret < 0) {
 564         goto fail;
 565     }
 566
 567 #ifdef DEBUG_ALLOC
 568     {
 569         BdrvCheckResult result = {0};
 570         qcow2_check_refcounts(bs, &result, 0);
 571     }
 572 #endif
 573     return 0;
 574
 575 fail:
 576     g_free(sn_l1_table);
 577     return ret;
 578 }
 579
 580 int qcow2_snapshot_delete(BlockDriverState *bs,
 581                           const char *snapshot_id,
 582                           const char *name,
 583                           Error **errp)
 584 {
 585     BDRVQcowState *s = bs->opaque;
 586     QCowSnapshot sn;
 587     int snapshot_index, ret;
 588
 589     /* Search the snapshot */
 590     snapshot_index = find_snapshot_by_id_and_name(bs, snapshot_id, name);
 591     if (snapshot_index < 0) {
 592         error_setg(errp, "Can't find the snapshot");
 593         return -ENOENT;
 594     }
 595     sn = s->snapshots[snapshot_index];
 596
 597     /* Remove it from the snapshot list */
 598     memmove(s->snapshots + snapshot_index,
 599             s->snapshots + snapshot_index + 1,
 600             (s->nb_snapshots - snapshot_index - 1) * sizeof(sn));
 601     s->nb_snapshots--;
 602     ret = qcow2_write_snapshots(bs);
 603     if (ret < 0) {
 604         error_setg(errp, "Failed to remove snapshot from snapshot list");
 605         return ret;
 606     }
 607
 608     /*
 609      * The snapshot is now unused, clean up. If we fail after this point, we
 610      * won't recover but just leak clusters.
 611      */
 612     g_free(sn.id_str);
 613     g_free(sn.name);
 614
 615     /*
 616      * Now decrease the refcounts of clusters referenced by the snapshot and
 617      * free the L1 table.
 618      */
 619     ret = qcow2_update_snapshot_refcount(bs, sn.l1_table_offset,
 620                                          sn.l1_size, -1);
 621     if (ret < 0) {
 622         error_setg(errp, "Failed to free the cluster and L1 table");
 623         return ret;
 624     }
 625     qcow2_free_clusters(bs, sn.l1_table_offset, sn.l1_size * sizeof(uint64_t),
 626                         QCOW2_DISCARD_SNAPSHOT);
 627
 628     /* must update the copied flag on the current cluster offsets */
 629     ret = qcow2_update_snapshot_refcount(bs, s->l1_table_offset, s->l1_size, 0);
 630     if (ret < 0) {
 631         error_setg(errp, "Failed to update snapshot status in disk");
 632         return ret;
 633     }
 634
 635 #ifdef DEBUG_ALLOC
 636     {
 637         BdrvCheckResult result = {0};
 638         qcow2_check_refcounts(bs, &result, 0);
 639     }
 640 #endif
 641     return 0;
 642 }
 643
 644 int qcow2_snapshot_list(BlockDriverState *bs, QEMUSnapshotInfo **psn_tab)
 645 {
 646     BDRVQcowState *s = bs->opaque;
 647     QEMUSnapshotInfo *sn_tab, *sn_info;
 648     QCowSnapshot *sn;
 649     int i;
 650
 651     if (!s->nb_snapshots) {
 652         *psn_tab = NULL;
 653         return s->nb_snapshots;
 654     }
 655
 656     sn_tab = g_malloc0(s->nb_snapshots * sizeof(QEMUSnapshotInfo));
 657     for(i = 0; i < s->nb_snapshots; i++) {
 658         sn_info = sn_tab + i;
 659         sn = s->snapshots + i;
 660         pstrcpy(sn_info->id_str, sizeof(sn_info->id_str),
 661                 sn->id_str);
 662         pstrcpy(sn_info->name, sizeof(sn_info->name),
 663                 sn->name);
 664         sn_info->vm_state_size = sn->vm_state_size;
 665         sn_info->date_sec = sn->date_sec;
 666         sn_info->date_nsec = sn->date_nsec;
 667         sn_info->vm_clock_nsec = sn->vm_clock_nsec;
 668     }
 669     *psn_tab = sn_tab;
 670     return s->nb_snapshots;
 671 }
 672
 673 int qcow2_snapshot_load_tmp(BlockDriverState *bs, const char *snapshot_name)
 674 {
 675     int i, snapshot_index;
 676     BDRVQcowState *s = bs->opaque;
 677     QCowSnapshot *sn;
 678     uint64_t *new_l1_table;
 679     int new_l1_bytes;
 680     int ret;
 681
 682     assert(bs->read_only);
 683
 684     /* Search the snapshot */
 685     snapshot_index = find_snapshot_by_id_or_name(bs, snapshot_name);
 686     if (snapshot_index < 0) {
 687         return -ENOENT;
 688     }
 689     sn = &s->snapshots[snapshot_index];
 690
 691     /* Allocate and read in the snapshot's L1 table */
 692     new_l1_bytes = s->l1_size * sizeof(uint64_t);
 693     new_l1_table = g_malloc0(align_offset(new_l1_bytes, 512));
 694
 695     ret = bdrv_pread(bs->file, sn->l1_table_offset, new_l1_table, new_l1_bytes);
 696     if (ret < 0) {
 697         g_free(new_l1_table);
 698         return ret;
 699     }
 700
 701     /* Switch the L1 table */
 702     g_free(s->l1_table);
 703
 704     s->l1_size = sn->l1_size;
 705     s->l1_table_offset = sn->l1_table_offset;
 706     s->l1_table = new_l1_table;
 707
 708     for(i = 0;i < s->l1_size; i++) {
 709         be64_to_cpus(&s->l1_table[i]);
 710     }
 711
 712     return 0;
 713 }