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     BdrvDirtyBitmap *sync_bitmap;
  42     MirrorSyncMode sync_mode;
  43     BitmapSyncMode bitmap_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         int64_t dirty_end;
 206
 207         if (!hbitmap_get(job->copy_bitmap, start)) {
 208             trace_backup_do_cow_skip(job, start);
 209             start += job->cluster_size;
 210             continue; /* already copied */
 211         }
 212
 213         dirty_end = hbitmap_next_zero(job->copy_bitmap, start, (end - start));
 214         if (dirty_end < 0) {
 215             dirty_end = end;
 216         }
 217
 218         trace_backup_do_cow_process(job, start);
 219
 220         if (job->use_copy_range) {
 221             ret = backup_cow_with_offload(job, start, dirty_end,
 222                                           is_write_notifier);
 223             if (ret < 0) {
 224                 job->use_copy_range = false;
 225             }
 226         }
 227         if (!job->use_copy_range) {
 228             ret = backup_cow_with_bounce_buffer(job, start, dirty_end,
 229                                                 is_write_notifier,
 230                                                 error_is_read, &bounce_buffer);
 231         }
 232         if (ret < 0) {
 233             break;
 234         }
 235
 236         /* Publish progress, guest I/O counts as progress too.  Note that the
 237          * offset field is an opaque progress value, it is not a disk offset.
 238          */
 239         start += ret;
 240         job->bytes_read += ret;
 241         job_progress_update(&job->common.job, ret);
 242         ret = 0;
 243     }
 244
 245     if (bounce_buffer) {
 246         qemu_vfree(bounce_buffer);
 247     }
 248
 249     cow_request_end(&cow_request);
 250
 251     trace_backup_do_cow_return(job, offset, bytes, ret);
 252
 253     qemu_co_rwlock_unlock(&job->flush_rwlock);
 254
 255     return ret;
 256 }
 257
 258 static int coroutine_fn backup_before_write_notify(
 259         NotifierWithReturn *notifier,
 260         void *opaque)
 261 {
 262     BackupBlockJob *job = container_of(notifier, BackupBlockJob, before_write);
 263     BdrvTrackedRequest *req = opaque;
 264
 265     assert(req->bs == blk_bs(job->common.blk));
 266     assert(QEMU_IS_ALIGNED(req->offset, BDRV_SECTOR_SIZE));
 267     assert(QEMU_IS_ALIGNED(req->bytes, BDRV_SECTOR_SIZE));
 268
 269     return backup_do_cow(job, req->offset, req->bytes, NULL, true);
 270 }
 271
 272 static void backup_cleanup_sync_bitmap(BackupBlockJob *job, int ret)
 273 {
 274     BdrvDirtyBitmap *bm;
 275     BlockDriverState *bs = blk_bs(job->common.blk);
 276
 277     if (ret < 0 || job->bitmap_mode == BITMAP_SYNC_MODE_NEVER) {
 278         /*
 279          * Failure, or we don't want to synchronize the bitmap.
 280          * Merge the successor back into the parent, delete nothing.
 281          */
 282         bm = bdrv_reclaim_dirty_bitmap(bs, job->sync_bitmap, NULL);
 283         assert(bm);
 284     } else {
 285         /* Everything is fine, delete this bitmap and install the backup. */
 286         bm = bdrv_dirty_bitmap_abdicate(bs, job->sync_bitmap, NULL);
 287         assert(bm);
 288     }
 289 }
 290
 291 static void backup_commit(Job *job)
 292 {
 293     BackupBlockJob *s = container_of(job, BackupBlockJob, common.job);
 294     if (s->sync_bitmap) {
 295         backup_cleanup_sync_bitmap(s, 0);
 296     }
 297 }
 298
 299 static void backup_abort(Job *job)
 300 {
 301     BackupBlockJob *s = container_of(job, BackupBlockJob, common.job);
 302     if (s->sync_bitmap) {
 303         backup_cleanup_sync_bitmap(s, -1);
 304     }
 305 }
 306
 307 static void backup_clean(Job *job)
 308 {
 309     BackupBlockJob *s = container_of(job, BackupBlockJob, common.job);
 310     assert(s->target);
 311     blk_unref(s->target);
 312     s->target = NULL;
 313
 314     if (s->copy_bitmap) {
 315         hbitmap_free(s->copy_bitmap);
 316         s->copy_bitmap = NULL;
 317     }
 318 }
 319
 320 void backup_do_checkpoint(BlockJob *job, Error **errp)
 321 {
 322     BackupBlockJob *backup_job = container_of(job, BackupBlockJob, common);
 323
 324     assert(block_job_driver(job) == &backup_job_driver);
 325
 326     if (backup_job->sync_mode != MIRROR_SYNC_MODE_NONE) {
 327         error_setg(errp, "The backup job only supports block checkpoint in"
 328                    " sync=none mode");
 329         return;
 330     }
 331
 332     hbitmap_set(backup_job->copy_bitmap, 0, backup_job->len);
 333 }
 334
 335 static void backup_drain(BlockJob *job)
 336 {
 337     BackupBlockJob *s = container_of(job, BackupBlockJob, common);
 338
 339     /* Need to keep a reference in case blk_drain triggers execution
 340      * of backup_complete...
 341      */
 342     if (s->target) {
 343         BlockBackend *target = s->target;
 344         blk_ref(target);
 345         blk_drain(target);
 346         blk_unref(target);
 347     }
 348 }
 349
 350 static BlockErrorAction backup_error_action(BackupBlockJob *job,
 351                                             bool read, int error)
 352 {
 353     if (read) {
 354         return block_job_error_action(&job->common, job->on_source_error,
 355                                       true, error);
 356     } else {
 357         return block_job_error_action(&job->common, job->on_target_error,
 358                                       false, error);
 359     }
 360 }
 361
 362 static bool coroutine_fn yield_and_check(BackupBlockJob *job)
 363 {
 364     uint64_t delay_ns;
 365
 366     if (job_is_cancelled(&job->common.job)) {
 367         return true;
 368     }
 369
 370     /* We need to yield even for delay_ns = 0 so that bdrv_drain_all() can
 371      * return. Without a yield, the VM would not reboot. */
 372     delay_ns = block_job_ratelimit_get_delay(&job->common, job->bytes_read);
 373     job->bytes_read = 0;
 374     job_sleep_ns(&job->common.job, delay_ns);
 375
 376     if (job_is_cancelled(&job->common.job)) {
 377         return true;
 378     }
 379
 380     return false;
 381 }
 382
 383 static bool bdrv_is_unallocated_range(BlockDriverState *bs,
 384                                       int64_t offset, int64_t bytes)
 385 {
 386     int64_t end = offset + bytes;
 387
 388     while (offset < end && !bdrv_is_allocated(bs, offset, bytes, &bytes)) {
 389         if (bytes == 0) {
 390             return true;
 391         }
 392         offset += bytes;
 393         bytes = end - offset;
 394     }
 395
 396     return offset >= end;
 397 }
 398
 399 static int coroutine_fn backup_loop(BackupBlockJob *job)
 400 {
 401     int ret;
 402     bool error_is_read;
 403     int64_t offset;
 404     HBitmapIter hbi;
 405     BlockDriverState *bs = blk_bs(job->common.blk);
 406
 407     hbitmap_iter_init(&hbi, job->copy_bitmap, 0);
 408     while ((offset = hbitmap_iter_next(&hbi)) != -1) {
 409         if (job->sync_mode == MIRROR_SYNC_MODE_TOP &&
 410             bdrv_is_unallocated_range(bs, offset, job->cluster_size))
 411         {
 412             hbitmap_reset(job->copy_bitmap, offset, job->cluster_size);
 413             continue;
 414         }
 415
 416         do {
 417             if (yield_and_check(job)) {
 418                 return 0;
 419             }
 420             ret = backup_do_cow(job, offset,
 421                                 job->cluster_size, &error_is_read, false);
 422             if (ret < 0 && backup_error_action(job, error_is_read, -ret) ==
 423                            BLOCK_ERROR_ACTION_REPORT)
 424             {
 425                 return ret;
 426             }
 427         } while (ret < 0);
 428     }
 429
 430     return 0;
 431 }
 432
 433 /* init copy_bitmap from sync_bitmap */
 434 static void backup_incremental_init_copy_bitmap(BackupBlockJob *job)
 435 {
 436     uint64_t offset = 0;
 437     uint64_t bytes = job->len;
 438
 439     while (bdrv_dirty_bitmap_next_dirty_area(job->sync_bitmap,
 440                                              &offset, &bytes))
 441     {
 442         hbitmap_set(job->copy_bitmap, offset, bytes);
 443
 444         offset += bytes;
 445         if (offset >= job->len) {
 446             break;
 447         }
 448         bytes = job->len - offset;
 449     }
 450
 451     /* TODO job_progress_set_remaining() would make more sense */
 452     job_progress_update(&job->common.job,
 453         job->len - hbitmap_count(job->copy_bitmap));
 454 }
 455
 456 static int coroutine_fn backup_run(Job *job, Error **errp)
 457 {
 458     BackupBlockJob *s = container_of(job, BackupBlockJob, common.job);
 459     BlockDriverState *bs = blk_bs(s->common.blk);
 460     int ret = 0;
 461
 462     QLIST_INIT(&s->inflight_reqs);
 463     qemu_co_rwlock_init(&s->flush_rwlock);
 464
 465     job_progress_set_remaining(job, s->len);
 466
 467     if (s->sync_mode == MIRROR_SYNC_MODE_BITMAP) {
 468         backup_incremental_init_copy_bitmap(s);
 469     } else {
 470         hbitmap_set(s->copy_bitmap, 0, s->len);
 471     }
 472
 473     s->before_write.notify = backup_before_write_notify;
 474     bdrv_add_before_write_notifier(bs, &s->before_write);
 475
 476     if (s->sync_mode == MIRROR_SYNC_MODE_NONE) {
 477         /* All bits are set in copy_bitmap to allow any cluster to be copied.
 478          * This does not actually require them to be copied. */
 479         while (!job_is_cancelled(job)) {
 480             /* Yield until the job is cancelled.  We just let our before_write
 481              * notify callback service CoW requests. */
 482             job_yield(job);
 483         }
 484     } else {
 485         ret = backup_loop(s);
 486     }
 487
 488     notifier_with_return_remove(&s->before_write);
 489
 490     /* wait until pending backup_do_cow() calls have completed */
 491     qemu_co_rwlock_wrlock(&s->flush_rwlock);
 492     qemu_co_rwlock_unlock(&s->flush_rwlock);
 493
 494     return ret;
 495 }
 496
 497 static const BlockJobDriver backup_job_driver = {
 498     .job_driver = {
 499         .instance_size          = sizeof(BackupBlockJob),
 500         .job_type               = JOB_TYPE_BACKUP,
 501         .free                   = block_job_free,
 502         .user_resume            = block_job_user_resume,
 503         .drain                  = block_job_drain,
 504         .run                    = backup_run,
 505         .commit                 = backup_commit,
 506         .abort                  = backup_abort,
 507         .clean                  = backup_clean,
 508     },
 509     .drain                  = backup_drain,
 510 };
 511
 512 static int64_t backup_calculate_cluster_size(BlockDriverState *target,
 513                                              Error **errp)
 514 {
 515     int ret;
 516     BlockDriverInfo bdi;
 517
 518     /*
 519      * If there is no backing file on the target, we cannot rely on COW if our
 520      * backup cluster size is smaller than the target cluster size. Even for
 521      * targets with a backing file, try to avoid COW if possible.
 522      */
 523     ret = bdrv_get_info(target, &bdi);
 524     if (ret == -ENOTSUP && !target->backing) {
 525         /* Cluster size is not defined */
 526         warn_report("The target block device doesn't provide "
 527                     "information about the block size and it doesn't have a "
 528                     "backing file. The default block size of %u bytes is "
 529                     "used. If the actual block size of the target exceeds "
 530                     "this default, the backup may be unusable",
 531                     BACKUP_CLUSTER_SIZE_DEFAULT);
 532         return BACKUP_CLUSTER_SIZE_DEFAULT;
 533     } else if (ret < 0 && !target->backing) {
 534         error_setg_errno(errp, -ret,
 535             "Couldn't determine the cluster size of the target image, "
 536             "which has no backing file");
 537         error_append_hint(errp,
 538             "Aborting, since this may create an unusable destination image\n");
 539         return ret;
 540     } else if (ret < 0 && target->backing) {
 541         /* Not fatal; just trudge on ahead. */
 542         return BACKUP_CLUSTER_SIZE_DEFAULT;
 543     }
 544
 545     return MAX(BACKUP_CLUSTER_SIZE_DEFAULT, bdi.cluster_size);
 546 }
 547
 548 BlockJob *backup_job_create(const char *job_id, BlockDriverState *bs,
 549                   BlockDriverState *target, int64_t speed,
 550                   MirrorSyncMode sync_mode, BdrvDirtyBitmap *sync_bitmap,
 551                   BitmapSyncMode bitmap_mode,
 552                   bool compress,
 553                   BlockdevOnError on_source_error,
 554                   BlockdevOnError on_target_error,
 555                   int creation_flags,
 556                   BlockCompletionFunc *cb, void *opaque,
 557                   JobTxn *txn, Error **errp)
 558 {
 559     int64_t len;
 560     BackupBlockJob *job = NULL;
 561     int ret;
 562     int64_t cluster_size;
 563     HBitmap *copy_bitmap = NULL;
 564
 565     assert(bs);
 566     assert(target);
 567
 568     if (bs == target) {
 569         error_setg(errp, "Source and target cannot be the same");
 570         return NULL;
 571     }
 572
 573     if (!bdrv_is_inserted(bs)) {
 574         error_setg(errp, "Device is not inserted: %s",
 575                    bdrv_get_device_name(bs));
 576         return NULL;
 577     }
 578
 579     if (!bdrv_is_inserted(target)) {
 580         error_setg(errp, "Device is not inserted: %s",
 581                    bdrv_get_device_name(target));
 582         return NULL;
 583     }
 584
 585     if (compress && target->drv->bdrv_co_pwritev_compressed == NULL) {
 586         error_setg(errp, "Compression is not supported for this drive %s",
 587                    bdrv_get_device_name(target));
 588         return NULL;
 589     }
 590
 591     if (bdrv_op_is_blocked(bs, BLOCK_OP_TYPE_BACKUP_SOURCE, errp)) {
 592         return NULL;
 593     }
 594
 595     if (bdrv_op_is_blocked(target, BLOCK_OP_TYPE_BACKUP_TARGET, errp)) {
 596         return NULL;
 597     }
 598
 599     /* QMP interface should have handled translating this to bitmap mode */
 600     assert(sync_mode != MIRROR_SYNC_MODE_INCREMENTAL);
 601
 602     if (sync_mode == MIRROR_SYNC_MODE_BITMAP) {
 603         if (!sync_bitmap) {
 604             error_setg(errp, "must provide a valid bitmap name for "
 605                        "'%s' sync mode", MirrorSyncMode_str(sync_mode));
 606             return NULL;
 607         }
 608
 609         /* Create a new bitmap, and freeze/disable this one. */
 610         if (bdrv_dirty_bitmap_create_successor(bs, sync_bitmap, errp) < 0) {
 611             return NULL;
 612         }
 613     } else if (sync_bitmap) {
 614         error_setg(errp,
 615                    "a bitmap was given to backup_job_create, "
 616                    "but it received an incompatible sync_mode (%s)",
 617                    MirrorSyncMode_str(sync_mode));
 618         return NULL;
 619     }
 620
 621     len = bdrv_getlength(bs);
 622     if (len < 0) {
 623         error_setg_errno(errp, -len, "unable to get length for '%s'",
 624                          bdrv_get_device_name(bs));
 625         goto error;
 626     }
 627
 628     cluster_size = backup_calculate_cluster_size(target, errp);
 629     if (cluster_size < 0) {
 630         goto error;
 631     }
 632
 633     copy_bitmap = hbitmap_alloc(len, ctz32(cluster_size));
 634
 635     /* job->len is fixed, so we can't allow resize */
 636     job = block_job_create(job_id, &backup_job_driver, txn, bs,
 637                            BLK_PERM_CONSISTENT_READ,
 638                            BLK_PERM_CONSISTENT_READ | BLK_PERM_WRITE |
 639                            BLK_PERM_WRITE_UNCHANGED | BLK_PERM_GRAPH_MOD,
 640                            speed, creation_flags, cb, opaque, errp);
 641     if (!job) {
 642         goto error;
 643     }
 644
 645     /* The target must match the source in size, so no resize here either */
 646     job->target = blk_new(job->common.job.aio_context,
 647                           BLK_PERM_WRITE,
 648                           BLK_PERM_CONSISTENT_READ | BLK_PERM_WRITE |
 649                           BLK_PERM_WRITE_UNCHANGED | BLK_PERM_GRAPH_MOD);
 650     ret = blk_insert_bs(job->target, target, errp);
 651     if (ret < 0) {
 652         goto error;
 653     }
 654     blk_set_disable_request_queuing(job->target, true);
 655
 656     job->on_source_error = on_source_error;
 657     job->on_target_error = on_target_error;
 658     job->sync_mode = sync_mode;
 659     job->sync_bitmap = sync_bitmap;
 660     job->bitmap_mode = bitmap_mode;
 661     job->compress = compress;
 662
 663     /* Detect image-fleecing (and similar) schemes */
 664     job->serialize_target_writes = bdrv_chain_contains(target, bs);
 665     job->cluster_size = cluster_size;
 666     job->copy_bitmap = copy_bitmap;
 667     copy_bitmap = NULL;
 668     job->use_copy_range = !compress; /* compression isn't supported for it */
 669     job->copy_range_size = MIN_NON_ZERO(blk_get_max_transfer(job->common.blk),
 670                                         blk_get_max_transfer(job->target));
 671     job->copy_range_size = MAX(job->cluster_size,
 672                                QEMU_ALIGN_UP(job->copy_range_size,
 673                                              job->cluster_size));
 674
 675     /* Required permissions are already taken with target's blk_new() */
 676     block_job_add_bdrv(&job->common, "target", target, 0, BLK_PERM_ALL,
 677                        &error_abort);
 678     job->len = len;
 679
 680     return &job->common;
 681
 682  error:
 683     if (copy_bitmap) {
 684         assert(!job || !job->copy_bitmap);
 685         hbitmap_free(copy_bitmap);
 686     }
 687     if (sync_bitmap) {
 688         bdrv_reclaim_dirty_bitmap(bs, sync_bitmap, NULL);
 689     }
 690     if (job) {
 691         backup_clean(&job->common.job);
 692         job_early_fail(&job->common.job);
 693     }
 694
 695     return NULL;
 696 }