block/snapshot.c

   1 /*
   2  * Block layer snapshot related functions
   3  *
   4  * Copyright (c) 2003-2008 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/osdep.h"
  26 #include "block/snapshot.h"
  27 #include "block/block_int.h"
  28 #include "block/qdict.h"
  29 #include "qapi/error.h"
  30 #include "qapi/qmp/qdict.h"
  31 #include "qapi/qmp/qerror.h"
  32 #include "qapi/qmp/qstring.h"
  33 #include "qemu/option.h"
  34 #include "sysemu/block-backend.h"
  35
  36 QemuOptsList internal_snapshot_opts = {
  37     .name = "snapshot",
  38     .head = QTAILQ_HEAD_INITIALIZER(internal_snapshot_opts.head),
  39     .desc = {
  40         {
  41             .name = SNAPSHOT_OPT_ID,
  42             .type = QEMU_OPT_STRING,
  43             .help = "snapshot id"
  44         },{
  45             .name = SNAPSHOT_OPT_NAME,
  46             .type = QEMU_OPT_STRING,
  47             .help = "snapshot name"
  48         },{
  49             /* end of list */
  50         }
  51     },
  52 };
  53
  54 int bdrv_snapshot_find(BlockDriverState *bs, QEMUSnapshotInfo *sn_info,
  55                        const char *name)
  56 {
  57     QEMUSnapshotInfo *sn_tab, *sn;
  58     int nb_sns, i, ret;
  59
  60     ret = -ENOENT;
  61     nb_sns = bdrv_snapshot_list(bs, &sn_tab);
  62     if (nb_sns < 0) {
  63         return ret;
  64     }
  65     for (i = 0; i < nb_sns; i++) {
  66         sn = &sn_tab[i];
  67         if (!strcmp(sn->name, name)) {
  68             *sn_info = *sn;
  69             ret = 0;
  70             break;
  71         }
  72     }
  73     g_free(sn_tab);
  74     return ret;
  75 }
  76
  77 /**
  78  * Look up an internal snapshot by @id and @name.
  79  * @bs: block device to search
  80  * @id: unique snapshot ID, or NULL
  81  * @name: snapshot name, or NULL
  82  * @sn_info: location to store information on the snapshot found
  83  * @errp: location to store error, will be set only for exception
  84  *
  85  * This function will traverse snapshot list in @bs to search the matching
  86  * one, @id and @name are the matching condition:
  87  * If both @id and @name are specified, find the first one with id @id and
  88  * name @name.
  89  * If only @id is specified, find the first one with id @id.
  90  * If only @name is specified, find the first one with name @name.
  91  * if none is specified, abort().
  92  *
  93  * Returns: true when a snapshot is found and @sn_info will be filled, false
  94  * when error or not found. If all operation succeed but no matching one is
  95  * found, @errp will NOT be set.
  96  */
  97 bool bdrv_snapshot_find_by_id_and_name(BlockDriverState *bs,
  98                                        const char *id,
  99                                        const char *name,
 100                                        QEMUSnapshotInfo *sn_info,
 101                                        Error **errp)
 102 {
 103     QEMUSnapshotInfo *sn_tab, *sn;
 104     int nb_sns, i;
 105     bool ret = false;
 106
 107     assert(id || name);
 108
 109     nb_sns = bdrv_snapshot_list(bs, &sn_tab);
 110     if (nb_sns < 0) {
 111         error_setg_errno(errp, -nb_sns, "Failed to get a snapshot list");
 112         return false;
 113     } else if (nb_sns == 0) {
 114         return false;
 115     }
 116
 117     if (id && name) {
 118         for (i = 0; i < nb_sns; i++) {
 119             sn = &sn_tab[i];
 120             if (!strcmp(sn->id_str, id) && !strcmp(sn->name, name)) {
 121                 *sn_info = *sn;
 122                 ret = true;
 123                 break;
 124             }
 125         }
 126     } else if (id) {
 127         for (i = 0; i < nb_sns; i++) {
 128             sn = &sn_tab[i];
 129             if (!strcmp(sn->id_str, id)) {
 130                 *sn_info = *sn;
 131                 ret = true;
 132                 break;
 133             }
 134         }
 135     } else if (name) {
 136         for (i = 0; i < nb_sns; i++) {
 137             sn = &sn_tab[i];
 138             if (!strcmp(sn->name, name)) {
 139                 *sn_info = *sn;
 140                 ret = true;
 141                 break;
 142             }
 143         }
 144     }
 145
 146     g_free(sn_tab);
 147     return ret;
 148 }
 149
 150 /**
 151  * Return a pointer to the child BDS pointer to which we can fall
 152  * back if the given BDS does not support snapshots.
 153  * Return NULL if there is no BDS to (safely) fall back to.
 154  *
 155  * We need to return an indirect pointer because bdrv_snapshot_goto()
 156  * has to modify the BdrvChild pointer.
 157  */
 158 static BdrvChild **bdrv_snapshot_fallback_ptr(BlockDriverState *bs)
 159 {
 160     BdrvChild **fallback;
 161     BdrvChild *child;
 162
 163     /*
 164      * The only BdrvChild pointers that are safe to modify (and which
 165      * we can thus return a reference to) are bs->file and
 166      * bs->backing.
 167      */
 168     fallback = &bs->file;
 169     if (!*fallback && bs->drv && bs->drv->is_filter) {
 170         fallback = &bs->backing;
 171     }
 172
 173     if (!*fallback) {
 174         return NULL;
 175     }
 176
 177     /*
 178      * Check that there are no other children that would need to be
 179      * snapshotted.  If there are, it is not safe to fall back to
 180      * *fallback.
 181      */
 182     QLIST_FOREACH(child, &bs->children, next) {
 183         if (child->role & (BDRV_CHILD_DATA | BDRV_CHILD_METADATA |
 184                            BDRV_CHILD_FILTERED) &&
 185             child != *fallback)
 186         {
 187             return NULL;
 188         }
 189     }
 190
 191     return fallback;
 192 }
 193
 194 static BlockDriverState *bdrv_snapshot_fallback(BlockDriverState *bs)
 195 {
 196     BdrvChild **child_ptr = bdrv_snapshot_fallback_ptr(bs);
 197     return child_ptr ? (*child_ptr)->bs : NULL;
 198 }
 199
 200 int bdrv_can_snapshot(BlockDriverState *bs)
 201 {
 202     BlockDriver *drv = bs->drv;
 203     if (!drv || !bdrv_is_inserted(bs) || bdrv_is_read_only(bs)) {
 204         return 0;
 205     }
 206
 207     if (!drv->bdrv_snapshot_create) {
 208         BlockDriverState *fallback_bs = bdrv_snapshot_fallback(bs);
 209         if (fallback_bs) {
 210             return bdrv_can_snapshot(fallback_bs);
 211         }
 212         return 0;
 213     }
 214
 215     return 1;
 216 }
 217
 218 int bdrv_snapshot_create(BlockDriverState *bs,
 219                          QEMUSnapshotInfo *sn_info)
 220 {
 221     BlockDriver *drv = bs->drv;
 222     BlockDriverState *fallback_bs = bdrv_snapshot_fallback(bs);
 223     if (!drv) {
 224         return -ENOMEDIUM;
 225     }
 226     if (drv->bdrv_snapshot_create) {
 227         return drv->bdrv_snapshot_create(bs, sn_info);
 228     }
 229     if (fallback_bs) {
 230         return bdrv_snapshot_create(fallback_bs, sn_info);
 231     }
 232     return -ENOTSUP;
 233 }
 234
 235 int bdrv_snapshot_goto(BlockDriverState *bs,
 236                        const char *snapshot_id,
 237                        Error **errp)
 238 {
 239     BlockDriver *drv = bs->drv;
 240     BdrvChild **fallback_ptr;
 241     int ret, open_ret;
 242
 243     if (!drv) {
 244         error_setg(errp, "Block driver is closed");
 245         return -ENOMEDIUM;
 246     }
 247
 248     if (!QLIST_EMPTY(&bs->dirty_bitmaps)) {
 249         error_setg(errp, "Device has active dirty bitmaps");
 250         return -EBUSY;
 251     }
 252
 253     if (drv->bdrv_snapshot_goto) {
 254         ret = drv->bdrv_snapshot_goto(bs, snapshot_id);
 255         if (ret < 0) {
 256             error_setg_errno(errp, -ret, "Failed to load snapshot");
 257         }
 258         return ret;
 259     }
 260
 261     fallback_ptr = bdrv_snapshot_fallback_ptr(bs);
 262     if (fallback_ptr) {
 263         QDict *options;
 264         QDict *file_options;
 265         Error *local_err = NULL;
 266         BlockDriverState *fallback_bs = (*fallback_ptr)->bs;
 267         char *subqdict_prefix = g_strdup_printf("%s.", (*fallback_ptr)->name);
 268
 269         options = qdict_clone_shallow(bs->options);
 270
 271         /* Prevent it from getting deleted when detached from bs */
 272         bdrv_ref(fallback_bs);
 273
 274         qdict_extract_subqdict(options, &file_options, subqdict_prefix);
 275         qobject_unref(file_options);
 276         g_free(subqdict_prefix);
 277
 278         qdict_put_str(options, (*fallback_ptr)->name,
 279                       bdrv_get_node_name(fallback_bs));
 280
 281         if (drv->bdrv_close) {
 282             drv->bdrv_close(bs);
 283         }
 284
 285         bdrv_unref_child(bs, *fallback_ptr);
 286         *fallback_ptr = NULL;
 287
 288         ret = bdrv_snapshot_goto(fallback_bs, snapshot_id, errp);
 289         open_ret = drv->bdrv_open(bs, options, bs->open_flags, &local_err);
 290         qobject_unref(options);
 291         if (open_ret < 0) {
 292             bdrv_unref(fallback_bs);
 293             bs->drv = NULL;
 294             /* A bdrv_snapshot_goto() error takes precedence */
 295             error_propagate(errp, local_err);
 296             return ret < 0 ? ret : open_ret;
 297         }
 298
 299         assert(fallback_bs == (*fallback_ptr)->bs);
 300         bdrv_unref(fallback_bs);
 301         return ret;
 302     }
 303
 304     error_setg(errp, "Block driver does not support snapshots");
 305     return -ENOTSUP;
 306 }
 307
 308 /**
 309  * Delete an internal snapshot by @snapshot_id and @name.
 310  * @bs: block device used in the operation
 311  * @snapshot_id: unique snapshot ID, or NULL
 312  * @name: snapshot name, or NULL
 313  * @errp: location to store error
 314  *
 315  * If both @snapshot_id and @name are specified, delete the first one with
 316  * id @snapshot_id and name @name.
 317  * If only @snapshot_id is specified, delete the first one with id
 318  * @snapshot_id.
 319  * If only @name is specified, delete the first one with name @name.
 320  * if none is specified, return -EINVAL.
 321  *
 322  * Returns: 0 on success, -errno on failure. If @bs is not inserted, return
 323  * -ENOMEDIUM. If @snapshot_id and @name are both NULL, return -EINVAL. If @bs
 324  * does not support internal snapshot deletion, return -ENOTSUP. If @bs does
 325  * not support parameter @snapshot_id or @name, or one of them is not correctly
 326  * specified, return -EINVAL. If @bs can't find one matching @id and @name,
 327  * return -ENOENT. If @errp != NULL, it will always be filled with error
 328  * message on failure.
 329  */
 330 int bdrv_snapshot_delete(BlockDriverState *bs,
 331                          const char *snapshot_id,
 332                          const char *name,
 333                          Error **errp)
 334 {
 335     BlockDriver *drv = bs->drv;
 336     BlockDriverState *fallback_bs = bdrv_snapshot_fallback(bs);
 337     int ret;
 338
 339     if (!drv) {
 340         error_setg(errp, QERR_DEVICE_HAS_NO_MEDIUM, bdrv_get_device_name(bs));
 341         return -ENOMEDIUM;
 342     }
 343     if (!snapshot_id && !name) {
 344         error_setg(errp, "snapshot_id and name are both NULL");
 345         return -EINVAL;
 346     }
 347
 348     /* drain all pending i/o before deleting snapshot */
 349     bdrv_drained_begin(bs);
 350
 351     if (drv->bdrv_snapshot_delete) {
 352         ret = drv->bdrv_snapshot_delete(bs, snapshot_id, name, errp);
 353     } else if (fallback_bs) {
 354         ret = bdrv_snapshot_delete(fallback_bs, snapshot_id, name, errp);
 355     } else {
 356         error_setg(errp, "Block format '%s' used by device '%s' "
 357                    "does not support internal snapshot deletion",
 358                    drv->format_name, bdrv_get_device_name(bs));
 359         ret = -ENOTSUP;
 360     }
 361
 362     bdrv_drained_end(bs);
 363     return ret;
 364 }
 365
 366 int bdrv_snapshot_list(BlockDriverState *bs,
 367                        QEMUSnapshotInfo **psn_info)
 368 {
 369     BlockDriver *drv = bs->drv;
 370     BlockDriverState *fallback_bs = bdrv_snapshot_fallback(bs);
 371     if (!drv) {
 372         return -ENOMEDIUM;
 373     }
 374     if (drv->bdrv_snapshot_list) {
 375         return drv->bdrv_snapshot_list(bs, psn_info);
 376     }
 377     if (fallback_bs) {
 378         return bdrv_snapshot_list(fallback_bs, psn_info);
 379     }
 380     return -ENOTSUP;
 381 }
 382
 383 /**
 384  * Temporarily load an internal snapshot by @snapshot_id and @name.
 385  * @bs: block device used in the operation
 386  * @snapshot_id: unique snapshot ID, or NULL
 387  * @name: snapshot name, or NULL
 388  * @errp: location to store error
 389  *
 390  * If both @snapshot_id and @name are specified, load the first one with
 391  * id @snapshot_id and name @name.
 392  * If only @snapshot_id is specified, load the first one with id
 393  * @snapshot_id.
 394  * If only @name is specified, load the first one with name @name.
 395  * if none is specified, return -EINVAL.
 396  *
 397  * Returns: 0 on success, -errno on fail. If @bs is not inserted, return
 398  * -ENOMEDIUM. If @bs is not readonly, return -EINVAL. If @bs did not support
 399  * internal snapshot, return -ENOTSUP. If qemu can't find a matching @id and
 400  * @name, return -ENOENT. If @errp != NULL, it will always be filled on
 401  * failure.
 402  */
 403 int bdrv_snapshot_load_tmp(BlockDriverState *bs,
 404                            const char *snapshot_id,
 405                            const char *name,
 406                            Error **errp)
 407 {
 408     BlockDriver *drv = bs->drv;
 409
 410     if (!drv) {
 411         error_setg(errp, QERR_DEVICE_HAS_NO_MEDIUM, bdrv_get_device_name(bs));
 412         return -ENOMEDIUM;
 413     }
 414     if (!snapshot_id && !name) {
 415         error_setg(errp, "snapshot_id and name are both NULL");
 416         return -EINVAL;
 417     }
 418     if (!bdrv_is_read_only(bs)) {
 419         error_setg(errp, "Device is not readonly");
 420         return -EINVAL;
 421     }
 422     if (drv->bdrv_snapshot_load_tmp) {
 423         return drv->bdrv_snapshot_load_tmp(bs, snapshot_id, name, errp);
 424     }
 425     error_setg(errp, "Block format '%s' used by device '%s' "
 426                "does not support temporarily loading internal snapshots",
 427                drv->format_name, bdrv_get_device_name(bs));
 428     return -ENOTSUP;
 429 }
 430
 431 int bdrv_snapshot_load_tmp_by_id_or_name(BlockDriverState *bs,
 432                                          const char *id_or_name,
 433                                          Error **errp)
 434 {
 435     int ret;
 436     Error *local_err = NULL;
 437
 438     ret = bdrv_snapshot_load_tmp(bs, id_or_name, NULL, &local_err);
 439     if (ret == -ENOENT || ret == -EINVAL) {
 440         error_free(local_err);
 441         local_err = NULL;
 442         ret = bdrv_snapshot_load_tmp(bs, NULL, id_or_name, &local_err);
 443     }
 444
 445     error_propagate(errp, local_err);
 446
 447     return ret;
 448 }
 449
 450
 451 static int bdrv_all_get_snapshot_devices(bool has_devices, strList *devices,
 452                                          GList **all_bdrvs,
 453                                          Error **errp)
 454 {
 455     g_autoptr(GList) bdrvs = NULL;
 456
 457     if (has_devices) {
 458         if (!devices) {
 459             error_setg(errp, "At least one device is required for snapshot");
 460             return -1;
 461         }
 462
 463         while (devices) {
 464             BlockDriverState *bs = bdrv_find_node(devices->value);
 465             if (!bs) {
 466                 error_setg(errp, "No block device node '%s'", devices->value);
 467                 return -1;
 468             }
 469             bdrvs = g_list_append(bdrvs, bs);
 470             devices = devices->next;
 471         }
 472     } else {
 473         BlockDriverState *bs;
 474         BdrvNextIterator it;
 475         for (bs = bdrv_first(&it); bs; bs = bdrv_next(&it)) {
 476             bdrvs = g_list_append(bdrvs, bs);
 477         }
 478     }
 479
 480     *all_bdrvs = g_steal_pointer(&bdrvs);
 481     return 0;
 482 }
 483
 484
 485 static bool bdrv_all_snapshots_includes_bs(BlockDriverState *bs)
 486 {
 487     if (!bdrv_is_inserted(bs) || bdrv_is_read_only(bs)) {
 488         return false;
 489     }
 490
 491     /* Include all nodes that are either in use by a BlockBackend, or that
 492      * aren't attached to any node, but owned by the monitor. */
 493     return bdrv_has_blk(bs) || QLIST_EMPTY(&bs->parents);
 494 }
 495
 496 /* Group operations. All block drivers are involved.
 497  * These functions will properly handle dataplane (take aio_context_acquire
 498  * when appropriate for appropriate block drivers) */
 499
 500 bool bdrv_all_can_snapshot(bool has_devices, strList *devices,
 501                            Error **errp)
 502 {
 503     g_autoptr(GList) bdrvs = NULL;
 504     GList *iterbdrvs;
 505
 506     if (bdrv_all_get_snapshot_devices(has_devices, devices, &bdrvs, errp) < 0) {
 507         return false;
 508     }
 509
 510     iterbdrvs = bdrvs;
 511     while (iterbdrvs) {
 512         BlockDriverState *bs = iterbdrvs->data;
 513         AioContext *ctx = bdrv_get_aio_context(bs);
 514         bool ok = true;
 515
 516         aio_context_acquire(ctx);
 517         if (devices || bdrv_all_snapshots_includes_bs(bs)) {
 518             ok = bdrv_can_snapshot(bs);
 519         }
 520         aio_context_release(ctx);
 521         if (!ok) {
 522             error_setg(errp, "Device '%s' is writable but does not support "
 523                        "snapshots", bdrv_get_device_or_node_name(bs));
 524             return false;
 525         }
 526
 527         iterbdrvs = iterbdrvs->next;
 528     }
 529
 530     return true;
 531 }
 532
 533 int bdrv_all_delete_snapshot(const char *name,
 534                              bool has_devices, strList *devices,
 535                              Error **errp)
 536 {
 537     g_autoptr(GList) bdrvs = NULL;
 538     GList *iterbdrvs;
 539
 540     if (bdrv_all_get_snapshot_devices(has_devices, devices, &bdrvs, errp) < 0) {
 541         return -1;
 542     }
 543
 544     iterbdrvs = bdrvs;
 545     while (iterbdrvs) {
 546         BlockDriverState *bs = iterbdrvs->data;
 547         AioContext *ctx = bdrv_get_aio_context(bs);
 548         QEMUSnapshotInfo sn1, *snapshot = &sn1;
 549         int ret = 0;
 550
 551         aio_context_acquire(ctx);
 552         if ((devices || bdrv_all_snapshots_includes_bs(bs)) &&
 553             bdrv_snapshot_find(bs, snapshot, name) >= 0)
 554         {
 555             ret = bdrv_snapshot_delete(bs, snapshot->id_str,
 556                                        snapshot->name, errp);
 557         }
 558         aio_context_release(ctx);
 559         if (ret < 0) {
 560             error_prepend(errp, "Could not delete snapshot '%s' on '%s': ",
 561                           name, bdrv_get_device_or_node_name(bs));
 562             return -1;
 563         }
 564
 565         iterbdrvs = iterbdrvs->next;
 566     }
 567
 568     return 0;
 569 }
 570
 571
 572 int bdrv_all_goto_snapshot(const char *name,
 573                            bool has_devices, strList *devices,
 574                            Error **errp)
 575 {
 576     g_autoptr(GList) bdrvs = NULL;
 577     GList *iterbdrvs;
 578
 579     if (bdrv_all_get_snapshot_devices(has_devices, devices, &bdrvs, errp) < 0) {
 580         return -1;
 581     }
 582
 583     iterbdrvs = bdrvs;
 584     while (iterbdrvs) {
 585         BlockDriverState *bs = iterbdrvs->data;
 586         AioContext *ctx = bdrv_get_aio_context(bs);
 587         int ret = 0;
 588
 589         aio_context_acquire(ctx);
 590         if (devices || bdrv_all_snapshots_includes_bs(bs)) {
 591             ret = bdrv_snapshot_goto(bs, name, errp);
 592         }
 593         aio_context_release(ctx);
 594         if (ret < 0) {
 595             error_prepend(errp, "Could not load snapshot '%s' on '%s': ",
 596                           name, bdrv_get_device_or_node_name(bs));
 597             return -1;
 598         }
 599
 600         iterbdrvs = iterbdrvs->next;
 601     }
 602
 603     return 0;
 604 }
 605
 606 int bdrv_all_has_snapshot(const char *name,
 607                           bool has_devices, strList *devices,
 608                           Error **errp)
 609 {
 610     g_autoptr(GList) bdrvs = NULL;
 611     GList *iterbdrvs;
 612
 613     if (bdrv_all_get_snapshot_devices(has_devices, devices, &bdrvs, errp) < 0) {
 614         return -1;
 615     }
 616
 617     iterbdrvs = bdrvs;
 618     while (iterbdrvs) {
 619         BlockDriverState *bs = iterbdrvs->data;
 620         AioContext *ctx = bdrv_get_aio_context(bs);
 621         QEMUSnapshotInfo sn;
 622         int ret = 0;
 623
 624         aio_context_acquire(ctx);
 625         if (devices || bdrv_all_snapshots_includes_bs(bs)) {
 626             ret = bdrv_snapshot_find(bs, &sn, name);
 627         }
 628         aio_context_release(ctx);
 629         if (ret < 0) {
 630             if (ret == -ENOENT) {
 631                 return 0;
 632             } else {
 633                 error_setg_errno(errp, errno,
 634                                  "Could not check snapshot '%s' on '%s'",
 635                                  name, bdrv_get_device_or_node_name(bs));
 636                 return -1;
 637             }
 638         }
 639
 640         iterbdrvs = iterbdrvs->next;
 641     }
 642
 643     return 1;
 644 }
 645
 646 int bdrv_all_create_snapshot(QEMUSnapshotInfo *sn,
 647                              BlockDriverState *vm_state_bs,
 648                              uint64_t vm_state_size,
 649                              bool has_devices, strList *devices,
 650                              Error **errp)
 651 {
 652     g_autoptr(GList) bdrvs = NULL;
 653     GList *iterbdrvs;
 654
 655     if (bdrv_all_get_snapshot_devices(has_devices, devices, &bdrvs, errp) < 0) {
 656         return -1;
 657     }
 658
 659     iterbdrvs = bdrvs;
 660     while (iterbdrvs) {
 661         BlockDriverState *bs = iterbdrvs->data;
 662         AioContext *ctx = bdrv_get_aio_context(bs);
 663         int ret = 0;
 664
 665         aio_context_acquire(ctx);
 666         if (bs == vm_state_bs) {
 667             sn->vm_state_size = vm_state_size;
 668             ret = bdrv_snapshot_create(bs, sn);
 669         } else if (devices || bdrv_all_snapshots_includes_bs(bs)) {
 670             sn->vm_state_size = 0;
 671             ret = bdrv_snapshot_create(bs, sn);
 672         }
 673         aio_context_release(ctx);
 674         if (ret < 0) {
 675             error_setg(errp, "Could not create snapshot '%s' on '%s'",
 676                        sn->name, bdrv_get_device_or_node_name(bs));
 677             return -1;
 678         }
 679
 680         iterbdrvs = iterbdrvs->next;
 681     }
 682
 683     return 0;
 684 }
 685
 686
 687 BlockDriverState *bdrv_all_find_vmstate_bs(const char *vmstate_bs,
 688                                            bool has_devices, strList *devices,
 689                                            Error **errp)
 690 {
 691     g_autoptr(GList) bdrvs = NULL;
 692     GList *iterbdrvs;
 693
 694     if (bdrv_all_get_snapshot_devices(has_devices, devices, &bdrvs, errp) < 0) {
 695         return NULL;
 696     }
 697
 698     iterbdrvs = bdrvs;
 699     while (iterbdrvs) {
 700         BlockDriverState *bs = iterbdrvs->data;
 701         AioContext *ctx = bdrv_get_aio_context(bs);
 702         bool found = false;
 703
 704         aio_context_acquire(ctx);
 705         found = (devices || bdrv_all_snapshots_includes_bs(bs)) &&
 706             bdrv_can_snapshot(bs);
 707         aio_context_release(ctx);
 708
 709         if (vmstate_bs) {
 710             if (g_str_equal(vmstate_bs,
 711                             bdrv_get_node_name(bs))) {
 712                 if (found) {
 713                     return bs;
 714                 } else {
 715                     error_setg(errp,
 716                                "vmstate block device '%s' does not support snapshots",
 717                                vmstate_bs);
 718                     return NULL;
 719                 }
 720             }
 721         } else if (found) {
 722             return bs;
 723         }
 724
 725         iterbdrvs = iterbdrvs->next;
 726     }
 727
 728     if (vmstate_bs) {
 729         error_setg(errp,
 730                    "vmstate block device '%s' does not exist", vmstate_bs);
 731     } else {
 732         error_setg(errp,
 733                    "no block device can store vmstate for snapshot");
 734     }
 735     return NULL;
 736 }