block/backup.c

   1 /*
   2  * QEMU backup
   3  *
   4  * Copyright (C) 2013 Proxmox Server Solutions
   5  *
   6  * Authors:
   7  *  Dietmar Maurer ([email protected])
   8  *
   9  * This work is licensed under the terms of the GNU GPL, version 2 or later.
  10  * See the COPYING file in the top-level directory.
  11  *
  12  */
  13
  14 #include "qemu/osdep.h"
  15
  16 #include "trace.h"
  17 #include "block/block.h"
  18 #include "block/block_int.h"
  19 #include "block/blockjob_int.h"
  20 #include "block/block_backup.h"
  21 #include "qapi/error.h"
  22 #include "qapi/qmp/qerror.h"
  23 #include "qemu/ratelimit.h"
  24 #include "qemu/cutils.h"
  25 #include "sysemu/block-backend.h"
  26 #include "qemu/bitmap.h"
  27 #include "qemu/error-report.h"
  28
  29 #define BACKUP_CLUSTER_SIZE_DEFAULT (1 << 16)
  30
  31 typedef struct CowRequest {
  32     int64_t start_byte;
  33     int64_t end_byte;
  34     QLIST_ENTRY(CowRequest) list;
  35     CoQueue wait_queue; /* coroutines blocked on this request */
  36 } CowRequest;
  37
  38 typedef struct BackupBlockJob {
  39     BlockJob common;
  40     BlockBackend *target;
  41     /* bitmap for sync=incremental */
  42     BdrvDirtyBitmap *sync_bitmap;
  43     MirrorSyncMode sync_mode;
  44     BlockdevOnError on_source_error;
  45     BlockdevOnError on_target_error;
  46     CoRwlock flush_rwlock;
  47     uint64_t len;
  48     uint64_t bytes_read;
  49     int64_t cluster_size;
  50     bool compress;
  51     NotifierWithReturn before_write;
  52     QLIST_HEAD(, CowRequest) inflight_reqs;
  53
  54     HBitmap *copy_bitmap;
  55     bool use_copy_range;
  56     int64_t copy_range_size;
  57
  58     bool serialize_target_writes;
  59 } BackupBlockJob;
  60
  61 static const BlockJobDriver backup_job_driver;
  62
  63 /* See if in-flight requests overlap and wait for them to complete */
  64 static void coroutine_fn wait_for_overlapping_requests(BackupBlockJob *job,
  65                                                        int64_t start,
  66                                                        int64_t end)
  67 {
  68     CowRequest *req;
  69     bool retry;
  70
  71     do {
  72         retry = false;
  73         QLIST_FOREACH(req, &job->inflight_reqs, list) {
  74             if (end > req->start_byte && start < req->end_byte) {
  75                 qemu_co_queue_wait(&req->wait_queue, NULL);
  76                 retry = true;
  77                 break;
  78             }
  79         }
  80     } while (retry);
  81 }
  82
  83 /* Keep track of an in-flight request */
  84 static void cow_request_begin(CowRequest *req, BackupBlockJob *job,
  85                               int64_t start, int64_t end)
  86 {
  87     req->start_byte = start;
  88     req->end_byte = end;
  89     qemu_co_queue_init(&req->wait_queue);
  90     QLIST_INSERT_HEAD(&job->inflight_reqs, req, list);
  91 }
  92
  93 /* Forget about a completed request */
  94 static void cow_request_end(CowRequest *req)
  95 {
  96     QLIST_REMOVE(req, list);
  97     qemu_co_queue_restart_all(&req->wait_queue);
  98 }
  99
 100 /* Copy range to target with a bounce buffer and return the bytes copied. If
 101  * error occurred, return a negative error number */
 102 static int coroutine_fn backup_cow_with_bounce_buffer(BackupBlockJob *job,
 103                                                       int64_t start,
 104                                                       int64_t end,
 105                                                       bool is_write_notifier,
 106                                                       bool *error_is_read,
 107                                                       void **bounce_buffer)
 108 {
 109     int ret;
 110     BlockBackend *blk = job->common.blk;
 111     int nbytes;
 112     int read_flags = is_write_notifier ? BDRV_REQ_NO_SERIALISING : 0;
 113     int write_flags = job->serialize_target_writes ? BDRV_REQ_SERIALISING : 0;
 114
 115     assert(QEMU_IS_ALIGNED(start, job->cluster_size));
 116     hbitmap_reset(job->copy_bitmap, start, job->cluster_size);
 117     nbytes = MIN(job->cluster_size, job->len - start);
 118     if (!*bounce_buffer) {
 119         *bounce_buffer = blk_blockalign(blk, job->cluster_size);
 120     }
 121
 122     ret = blk_co_pread(blk, start, nbytes, *bounce_buffer, read_flags);
 123     if (ret < 0) {
 124         trace_backup_do_cow_read_fail(job, start, ret);
 125         if (error_is_read) {
 126             *error_is_read = true;
 127         }
 128         goto fail;
 129     }
 130
 131     if (buffer_is_zero(*bounce_buffer, nbytes)) {
 132         ret = blk_co_pwrite_zeroes(job->target, start,
 133                                    nbytes, write_flags | BDRV_REQ_MAY_UNMAP);
 134     } else {
 135         ret = blk_co_pwrite(job->target, start,
 136                             nbytes, *bounce_buffer, write_flags |
 137                             (job->compress ? BDRV_REQ_WRITE_COMPRESSED : 0));
 138     }
 139     if (ret < 0) {
 140         trace_backup_do_cow_write_fail(job, start, ret);
 141         if (error_is_read) {
 142             *error_is_read = false;
 143         }
 144         goto fail;
 145     }
 146
 147     return nbytes;
 148 fail:
 149     hbitmap_set(job->copy_bitmap, start, job->cluster_size);
 150     return ret;
 151
 152 }
 153
 154 /* Copy range to target and return the bytes copied. If error occurred, return a
 155  * negative error number. */
 156 static int coroutine_fn backup_cow_with_offload(BackupBlockJob *job,
 157                                                 int64_t start,
 158                                                 int64_t end,
 159                                                 bool is_write_notifier)
 160 {
 161     int ret;
 162     int nr_clusters;
 163     BlockBackend *blk = job->common.blk;
 164     int nbytes;
 165     int read_flags = is_write_notifier ? BDRV_REQ_NO_SERIALISING : 0;
 166     int write_flags = job->serialize_target_writes ? BDRV_REQ_SERIALISING : 0;
 167
 168     assert(QEMU_IS_ALIGNED(job->copy_range_size, job->cluster_size));
 169     assert(QEMU_IS_ALIGNED(start, job->cluster_size));
 170     nbytes = MIN(job->copy_range_size, end - start);
 171     nr_clusters = DIV_ROUND_UP(nbytes, job->cluster_size);
 172     hbitmap_reset(job->copy_bitmap, start, job->cluster_size * nr_clusters);
 173     ret = blk_co_copy_range(blk, start, job->target, start, nbytes,
 174                             read_flags, write_flags);
 175     if (ret < 0) {
 176         trace_backup_do_cow_copy_range_fail(job, start, ret);
 177         hbitmap_set(job->copy_bitmap, start, job->cluster_size * nr_clusters);
 178         return ret;
 179     }
 180
 181     return nbytes;
 182 }
 183
 184 static int coroutine_fn backup_do_cow(BackupBlockJob *job,
 185                                       int64_t offset, uint64_t bytes,
 186                                       bool *error_is_read,
 187                                       bool is_write_notifier)
 188 {
 189     CowRequest cow_request;
 190     int ret = 0;
 191     int64_t start, end; /* bytes */
 192     void *bounce_buffer = NULL;
 193
 194     qemu_co_rwlock_rdlock(&job->flush_rwlock);
 195
 196     start = QEMU_ALIGN_DOWN(offset, job->cluster_size);
 197     end = QEMU_ALIGN_UP(bytes + offset, job->cluster_size);
 198
 199     trace_backup_do_cow_enter(job, start, offset, bytes);
 200
 201     wait_for_overlapping_requests(job, start, end);
 202     cow_request_begin(&cow_request, job, start, end);
 203
 204     while (start < end) {
 205         if (!hbitmap_get(job->copy_bitmap, start)) {
 206             trace_backup_do_cow_skip(job, start);
 207             start += job->cluster_size;
 208             continue; /* already copied */
 209         }
 210
 211         trace_backup_do_cow_process(job, start);
 212
 213         if (job->use_copy_range) {
 214             ret = backup_cow_with_offload(job, start, end, is_write_notifier);
 215             if (ret < 0) {
 216                 job->use_copy_range = false;
 217             }
 218         }
 219         if (!job->use_copy_range) {
 220             ret = backup_cow_with_bounce_buffer(job, start, end, is_write_notifier,
 221                                                 error_is_read, &bounce_buffer);
 222         }
 223         if (ret < 0) {
 224             break;
 225         }
 226
 227         /* Publish progress, guest I/O counts as progress too.  Note that the
 228          * offset field is an opaque progress value, it is not a disk offset.
 229          */
 230         start += ret;
 231         job->bytes_read += ret;
 232         job_progress_update(&job->common.job, ret);
 233         ret = 0;
 234     }
 235
 236     if (bounce_buffer) {
 237         qemu_vfree(bounce_buffer);
 238     }
 239
 240     cow_request_end(&cow_request);
 241
 242     trace_backup_do_cow_return(job, offset, bytes, ret);
 243
 244     qemu_co_rwlock_unlock(&job->flush_rwlock);
 245
 246     return ret;
 247 }
 248
 249 static int coroutine_fn backup_before_write_notify(
 250         NotifierWithReturn *notifier,
 251         void *opaque)
 252 {
 253     BackupBlockJob *job = container_of(notifier, BackupBlockJob, before_write);
 254     BdrvTrackedRequest *req = opaque;
 255
 256     assert(req->bs == blk_bs(job->common.blk));
 257     assert(QEMU_IS_ALIGNED(req->offset, BDRV_SECTOR_SIZE));
 258     assert(QEMU_IS_ALIGNED(req->bytes, BDRV_SECTOR_SIZE));
 259
 260     return backup_do_cow(job, req->offset, req->bytes, NULL, true);
 261 }
 262
 263 static void backup_cleanup_sync_bitmap(BackupBlockJob *job, int ret)
 264 {
 265     BdrvDirtyBitmap *bm;
 266     BlockDriverState *bs = blk_bs(job->common.blk);
 267
 268     if (ret < 0) {
 269         /* Merge the successor back into the parent, delete nothing. */
 270         bm = bdrv_reclaim_dirty_bitmap(bs, job->sync_bitmap, NULL);
 271         assert(bm);
 272     } else {
 273         /* Everything is fine, delete this bitmap and install the backup. */
 274         bm = bdrv_dirty_bitmap_abdicate(bs, job->sync_bitmap, NULL);
 275         assert(bm);
 276     }
 277 }
 278
 279 static void backup_commit(Job *job)
 280 {
 281     BackupBlockJob *s = container_of(job, BackupBlockJob, common.job);
 282     if (s->sync_bitmap) {
 283         backup_cleanup_sync_bitmap(s, 0);
 284     }
 285 }
 286
 287 static void backup_abort(Job *job)
 288 {
 289     BackupBlockJob *s = container_of(job, BackupBlockJob, common.job);
 290     if (s->sync_bitmap) {
 291         backup_cleanup_sync_bitmap(s, -1);
 292     }
 293 }
 294
 295 static void backup_clean(Job *job)
 296 {
 297     BackupBlockJob *s = container_of(job, BackupBlockJob, common.job);
 298     assert(s->target);
 299     blk_unref(s->target);
 300     s->target = NULL;
 301
 302     if (s->copy_bitmap) {
 303         hbitmap_free(s->copy_bitmap);
 304         s->copy_bitmap = NULL;
 305     }
 306 }
 307
 308 void backup_do_checkpoint(BlockJob *job, Error **errp)
 309 {
 310     BackupBlockJob *backup_job = container_of(job, BackupBlockJob, common);
 311
 312     assert(block_job_driver(job) == &backup_job_driver);
 313
 314     if (backup_job->sync_mode != MIRROR_SYNC_MODE_NONE) {
 315         error_setg(errp, "The backup job only supports block checkpoint in"
 316                    " sync=none mode");
 317         return;
 318     }
 319
 320     hbitmap_set(backup_job->copy_bitmap, 0, backup_job->len);
 321 }
 322
 323 static void backup_drain(BlockJob *job)
 324 {
 325     BackupBlockJob *s = container_of(job, BackupBlockJob, common);
 326
 327     /* Need to keep a reference in case blk_drain triggers execution
 328      * of backup_complete...
 329      */
 330     if (s->target) {
 331         BlockBackend *target = s->target;
 332         blk_ref(target);
 333         blk_drain(target);
 334         blk_unref(target);
 335     }
 336 }
 337
 338 static BlockErrorAction backup_error_action(BackupBlockJob *job,
 339                                             bool read, int error)
 340 {
 341     if (read) {
 342         return block_job_error_action(&job->common, job->on_source_error,
 343                                       true, error);
 344     } else {
 345         return block_job_error_action(&job->common, job->on_target_error,
 346                                       false, error);
 347     }
 348 }
 349
 350 static bool coroutine_fn yield_and_check(BackupBlockJob *job)
 351 {
 352     uint64_t delay_ns;
 353
 354     if (job_is_cancelled(&job->common.job)) {
 355         return true;
 356     }
 357
 358     /* We need to yield even for delay_ns = 0 so that bdrv_drain_all() can
 359      * return. Without a yield, the VM would not reboot. */
 360     delay_ns = block_job_ratelimit_get_delay(&job->common, job->bytes_read);
 361     job->bytes_read = 0;
 362     job_sleep_ns(&job->common.job, delay_ns);
 363
 364     if (job_is_cancelled(&job->common.job)) {
 365         return true;
 366     }
 367
 368     return false;
 369 }
 370
 371 static bool bdrv_is_unallocated_range(BlockDriverState *bs,
 372                                       int64_t offset, int64_t bytes)
 373 {
 374     int64_t end = offset + bytes;
 375
 376     while (offset < end && !bdrv_is_allocated(bs, offset, bytes, &bytes)) {
 377         if (bytes == 0) {
 378             return true;
 379         }
 380         offset += bytes;
 381         bytes = end - offset;
 382     }
 383
 384     return offset >= end;
 385 }
 386
 387 static int coroutine_fn backup_loop(BackupBlockJob *job)
 388 {
 389     int ret;
 390     bool error_is_read;
 391     int64_t offset;
 392     HBitmapIter hbi;
 393     BlockDriverState *bs = blk_bs(job->common.blk);
 394
 395     hbitmap_iter_init(&hbi, job->copy_bitmap, 0);
 396     while ((offset = hbitmap_iter_next(&hbi)) != -1) {
 397         if (job->sync_mode == MIRROR_SYNC_MODE_TOP &&
 398             bdrv_is_unallocated_range(bs, offset, job->cluster_size))
 399         {
 400             hbitmap_reset(job->copy_bitmap, offset, job->cluster_size);
 401             continue;
 402         }
 403
 404         do {
 405             if (yield_and_check(job)) {
 406                 return 0;
 407             }
 408             ret = backup_do_cow(job, offset,
 409                                 job->cluster_size, &error_is_read, false);
 410             if (ret < 0 && backup_error_action(job, error_is_read, -ret) ==
 411                            BLOCK_ERROR_ACTION_REPORT)
 412             {
 413                 return ret;
 414             }
 415         } while (ret < 0);
 416     }
 417
 418     return 0;
 419 }
 420
 421 /* init copy_bitmap from sync_bitmap */
 422 static void backup_incremental_init_copy_bitmap(BackupBlockJob *job)
 423 {
 424     uint64_t offset = 0;
 425     uint64_t bytes = job->len;
 426
 427     while (bdrv_dirty_bitmap_next_dirty_area(job->sync_bitmap,
 428                                              &offset, &bytes))
 429     {
 430         hbitmap_set(job->copy_bitmap, offset, bytes);
 431
 432         offset += bytes;
 433         if (offset >= job->len) {
 434             break;
 435         }
 436         bytes = job->len - offset;
 437     }
 438
 439     /* TODO job_progress_set_remaining() would make more sense */
 440     job_progress_update(&job->common.job,
 441         job->len - hbitmap_count(job->copy_bitmap));
 442 }
 443
 444 static int coroutine_fn backup_run(Job *job, Error **errp)
 445 {
 446     BackupBlockJob *s = container_of(job, BackupBlockJob, common.job);
 447     BlockDriverState *bs = blk_bs(s->common.blk);
 448     int ret = 0;
 449
 450     QLIST_INIT(&s->inflight_reqs);
 451     qemu_co_rwlock_init(&s->flush_rwlock);
 452
 453     job_progress_set_remaining(job, s->len);
 454
 455     if (s->sync_mode == MIRROR_SYNC_MODE_INCREMENTAL) {
 456         backup_incremental_init_copy_bitmap(s);
 457     } else {
 458         hbitmap_set(s->copy_bitmap, 0, s->len);
 459     }
 460
 461     s->before_write.notify = backup_before_write_notify;
 462     bdrv_add_before_write_notifier(bs, &s->before_write);
 463
 464     if (s->sync_mode == MIRROR_SYNC_MODE_NONE) {
 465         /* All bits are set in copy_bitmap to allow any cluster to be copied.
 466          * This does not actually require them to be copied. */
 467         while (!job_is_cancelled(job)) {
 468             /* Yield until the job is cancelled.  We just let our before_write
 469              * notify callback service CoW requests. */
 470             job_yield(job);
 471         }
 472     } else {
 473         ret = backup_loop(s);
 474     }
 475
 476     notifier_with_return_remove(&s->before_write);
 477
 478     /* wait until pending backup_do_cow() calls have completed */
 479     qemu_co_rwlock_wrlock(&s->flush_rwlock);
 480     qemu_co_rwlock_unlock(&s->flush_rwlock);
 481
 482     return ret;
 483 }
 484
 485 static const BlockJobDriver backup_job_driver = {
 486     .job_driver = {
 487         .instance_size          = sizeof(BackupBlockJob),
 488         .job_type               = JOB_TYPE_BACKUP,
 489         .free                   = block_job_free,
 490         .user_resume            = block_job_user_resume,
 491         .drain                  = block_job_drain,
 492         .run                    = backup_run,
 493         .commit                 = backup_commit,
 494         .abort                  = backup_abort,
 495         .clean                  = backup_clean,
 496     },
 497     .drain                  = backup_drain,
 498 };
 499
 500 static int64_t backup_calculate_cluster_size(BlockDriverState *target,
 501                                              Error **errp)
 502 {
 503     int ret;
 504     BlockDriverInfo bdi;
 505
 506     /*
 507      * If there is no backing file on the target, we cannot rely on COW if our
 508      * backup cluster size is smaller than the target cluster size. Even for
 509      * targets with a backing file, try to avoid COW if possible.
 510      */
 511     ret = bdrv_get_info(target, &bdi);
 512     if (ret == -ENOTSUP && !target->backing) {
 513         /* Cluster size is not defined */
 514         warn_report("The target block device doesn't provide "
 515                     "information about the block size and it doesn't have a "
 516                     "backing file. The default block size of %u bytes is "
 517                     "used. If the actual block size of the target exceeds "
 518                     "this default, the backup may be unusable",
 519                     BACKUP_CLUSTER_SIZE_DEFAULT);
 520         return BACKUP_CLUSTER_SIZE_DEFAULT;
 521     } else if (ret < 0 && !target->backing) {
 522         error_setg_errno(errp, -ret,
 523             "Couldn't determine the cluster size of the target image, "
 524             "which has no backing file");
 525         error_append_hint(errp,
 526             "Aborting, since this may create an unusable destination image\n");
 527         return ret;
 528     } else if (ret < 0 && target->backing) {
 529         /* Not fatal; just trudge on ahead. */
 530         return BACKUP_CLUSTER_SIZE_DEFAULT;
 531     }
 532
 533     return MAX(BACKUP_CLUSTER_SIZE_DEFAULT, bdi.cluster_size);
 534 }
 535
 536 BlockJob *backup_job_create(const char *job_id, BlockDriverState *bs,
 537                   BlockDriverState *target, int64_t speed,
 538                   MirrorSyncMode sync_mode, BdrvDirtyBitmap *sync_bitmap,
 539                   bool compress,
 540                   BlockdevOnError on_source_error,
 541                   BlockdevOnError on_target_error,
 542                   int creation_flags,
 543                   BlockCompletionFunc *cb, void *opaque,
 544                   JobTxn *txn, Error **errp)
 545 {
 546     int64_t len;
 547     BackupBlockJob *job = NULL;
 548     int ret;
 549     int64_t cluster_size;
 550     HBitmap *copy_bitmap = NULL;
 551
 552     assert(bs);
 553     assert(target);
 554
 555     if (bs == target) {
 556         error_setg(errp, "Source and target cannot be the same");
 557         return NULL;
 558     }
 559
 560     if (!bdrv_is_inserted(bs)) {
 561         error_setg(errp, "Device is not inserted: %s",
 562                    bdrv_get_device_name(bs));
 563         return NULL;
 564     }
 565
 566     if (!bdrv_is_inserted(target)) {
 567         error_setg(errp, "Device is not inserted: %s",
 568                    bdrv_get_device_name(target));
 569         return NULL;
 570     }
 571
 572     if (compress && target->drv->bdrv_co_pwritev_compressed == NULL) {
 573         error_setg(errp, "Compression is not supported for this drive %s",
 574                    bdrv_get_device_name(target));
 575         return NULL;
 576     }
 577
 578     if (bdrv_op_is_blocked(bs, BLOCK_OP_TYPE_BACKUP_SOURCE, errp)) {
 579         return NULL;
 580     }
 581
 582     if (bdrv_op_is_blocked(target, BLOCK_OP_TYPE_BACKUP_TARGET, errp)) {
 583         return NULL;
 584     }
 585
 586     if (sync_mode == MIRROR_SYNC_MODE_INCREMENTAL) {
 587         if (!sync_bitmap) {
 588             error_setg(errp, "must provide a valid bitmap name for "
 589                              "\"incremental\" sync mode");
 590             return NULL;
 591         }
 592
 593         /* Create a new bitmap, and freeze/disable this one. */
 594         if (bdrv_dirty_bitmap_create_successor(bs, sync_bitmap, errp) < 0) {
 595             return NULL;
 596         }
 597     } else if (sync_bitmap) {
 598         error_setg(errp,
 599                    "a sync_bitmap was provided to backup_run, "
 600                    "but received an incompatible sync_mode (%s)",
 601                    MirrorSyncMode_str(sync_mode));
 602         return NULL;
 603     }
 604
 605     len = bdrv_getlength(bs);
 606     if (len < 0) {
 607         error_setg_errno(errp, -len, "unable to get length for '%s'",
 608                          bdrv_get_device_name(bs));
 609         goto error;
 610     }
 611
 612     cluster_size = backup_calculate_cluster_size(target, errp);
 613     if (cluster_size < 0) {
 614         goto error;
 615     }
 616
 617     copy_bitmap = hbitmap_alloc(len, ctz32(cluster_size));
 618
 619     /* job->len is fixed, so we can't allow resize */
 620     job = block_job_create(job_id, &backup_job_driver, txn, bs,
 621                            BLK_PERM_CONSISTENT_READ,
 622                            BLK_PERM_CONSISTENT_READ | BLK_PERM_WRITE |
 623                            BLK_PERM_WRITE_UNCHANGED | BLK_PERM_GRAPH_MOD,
 624                            speed, creation_flags, cb, opaque, errp);
 625     if (!job) {
 626         goto error;
 627     }
 628
 629     /* The target must match the source in size, so no resize here either */
 630     job->target = blk_new(BLK_PERM_WRITE,
 631                           BLK_PERM_CONSISTENT_READ | BLK_PERM_WRITE |
 632                           BLK_PERM_WRITE_UNCHANGED | BLK_PERM_GRAPH_MOD);
 633     ret = blk_insert_bs(job->target, target, errp);
 634     if (ret < 0) {
 635         goto error;
 636     }
 637
 638     job->on_source_error = on_source_error;
 639     job->on_target_error = on_target_error;
 640     job->sync_mode = sync_mode;
 641     job->sync_bitmap = sync_mode == MIRROR_SYNC_MODE_INCREMENTAL ?
 642                        sync_bitmap : NULL;
 643     job->compress = compress;
 644
 645     /* Detect image-fleecing (and similar) schemes */
 646     job->serialize_target_writes = bdrv_chain_contains(target, bs);
 647     job->cluster_size = cluster_size;
 648     job->copy_bitmap = copy_bitmap;
 649     copy_bitmap = NULL;
 650     job->use_copy_range = true;
 651     job->copy_range_size = MIN_NON_ZERO(blk_get_max_transfer(job->common.blk),
 652                                         blk_get_max_transfer(job->target));
 653     job->copy_range_size = MAX(job->cluster_size,
 654                                QEMU_ALIGN_UP(job->copy_range_size,
 655                                              job->cluster_size));
 656
 657     /* Required permissions are already taken with target's blk_new() */
 658     block_job_add_bdrv(&job->common, "target", target, 0, BLK_PERM_ALL,
 659                        &error_abort);
 660     job->len = len;
 661
 662     return &job->common;
 663
 664  error:
 665     if (copy_bitmap) {
 666         assert(!job || !job->copy_bitmap);
 667         hbitmap_free(copy_bitmap);
 668     }
 669     if (sync_bitmap) {
 670         bdrv_reclaim_dirty_bitmap(bs, sync_bitmap, NULL);
 671     }
 672     if (job) {
 673         backup_clean(&job->common.job);
 674         job_early_fail(&job->common.job);
 675     }
 676
 677     return NULL;
 678 }