block/backup.c

   1 /*
   2  * QEMU backup
   3  *
   4  * Copyright (C) 2013 Proxmox Server Solutions
   5  *
   6  * Authors:
   7  *  Dietmar Maurer (dietmar@proxmox.com)
   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
  42     BdrvDirtyBitmap *sync_bitmap;
  43     BdrvDirtyBitmap *copy_bitmap;
  44
  45     MirrorSyncMode sync_mode;
  46     BitmapSyncMode bitmap_mode;
  47     BlockdevOnError on_source_error;
  48     BlockdevOnError on_target_error;
  49     CoRwlock flush_rwlock;
  50     uint64_t len;
  51     uint64_t bytes_read;
  52     int64_t cluster_size;
  53     bool compress;
  54     NotifierWithReturn before_write;
  55     QLIST_HEAD(, CowRequest) inflight_reqs;
  56
  57     bool use_copy_range;
  58     int64_t copy_range_size;
  59
  60     bool serialize_target_writes;
  61 } BackupBlockJob;
  62
  63 static const BlockJobDriver backup_job_driver;
  64
  65 /* See if in-flight requests overlap and wait for them to complete */
  66 static void coroutine_fn wait_for_overlapping_requests(BackupBlockJob *job,
  67                                                        int64_t start,
  68                                                        int64_t end)
  69 {
  70     CowRequest *req;
  71     bool retry;
  72
  73     do {
  74         retry = false;
  75         QLIST_FOREACH(req, &job->inflight_reqs, list) {
  76             if (end > req->start_byte && start < req->end_byte) {
  77                 qemu_co_queue_wait(&req->wait_queue, NULL);
  78                 retry = true;
  79                 break;
  80             }
  81         }
  82     } while (retry);
  83 }
  84
  85 /* Keep track of an in-flight request */
  86 static void cow_request_begin(CowRequest *req, BackupBlockJob *job,
  87                               int64_t start, int64_t end)
  88 {
  89     req->start_byte = start;
  90     req->end_byte = end;
  91     qemu_co_queue_init(&req->wait_queue);
  92     QLIST_INSERT_HEAD(&job->inflight_reqs, req, list);
  93 }
  94
  95 /* Forget about a completed request */
  96 static void cow_request_end(CowRequest *req)
  97 {
  98     QLIST_REMOVE(req, list);
  99     qemu_co_queue_restart_all(&req->wait_queue);
 100 }
 101
 102 /* Copy range to target with a bounce buffer and return the bytes copied. If
 103  * error occurred, return a negative error number */
 104 static int coroutine_fn backup_cow_with_bounce_buffer(BackupBlockJob *job,
 105                                                       int64_t start,
 106                                                       int64_t end,
 107                                                       bool is_write_notifier,
 108                                                       bool *error_is_read,
 109                                                       void **bounce_buffer)
 110 {
 111     int ret;
 112     BlockBackend *blk = job->common.blk;
 113     int nbytes;
 114     int read_flags = is_write_notifier ? BDRV_REQ_NO_SERIALISING : 0;
 115     int write_flags = job->serialize_target_writes ? BDRV_REQ_SERIALISING : 0;
 116
 117     assert(QEMU_IS_ALIGNED(start, job->cluster_size));
 118     bdrv_reset_dirty_bitmap(job->copy_bitmap, start, job->cluster_size);
 119     nbytes = MIN(job->cluster_size, job->len - start);
 120     if (!*bounce_buffer) {
 121         *bounce_buffer = blk_blockalign(blk, job->cluster_size);
 122     }
 123
 124     ret = blk_co_pread(blk, start, nbytes, *bounce_buffer, read_flags);
 125     if (ret < 0) {
 126         trace_backup_do_cow_read_fail(job, start, ret);
 127         if (error_is_read) {
 128             *error_is_read = true;
 129         }
 130         goto fail;
 131     }
 132
 133     if (buffer_is_zero(*bounce_buffer, nbytes)) {
 134         ret = blk_co_pwrite_zeroes(job->target, start,
 135                                    nbytes, write_flags | BDRV_REQ_MAY_UNMAP);
 136     } else {
 137         ret = blk_co_pwrite(job->target, start,
 138                             nbytes, *bounce_buffer, write_flags |
 139                             (job->compress ? BDRV_REQ_WRITE_COMPRESSED : 0));
 140     }
 141     if (ret < 0) {
 142         trace_backup_do_cow_write_fail(job, start, ret);
 143         if (error_is_read) {
 144             *error_is_read = false;
 145         }
 146         goto fail;
 147     }
 148
 149     return nbytes;
 150 fail:
 151     bdrv_set_dirty_bitmap(job->copy_bitmap, start, job->cluster_size);
 152     return ret;
 153
 154 }
 155
 156 /* Copy range to target and return the bytes copied. If error occurred, return a
 157  * negative error number. */
 158 static int coroutine_fn backup_cow_with_offload(BackupBlockJob *job,
 159                                                 int64_t start,
 160                                                 int64_t end,
 161                                                 bool is_write_notifier)
 162 {
 163     int ret;
 164     int nr_clusters;
 165     BlockBackend *blk = job->common.blk;
 166     int nbytes;
 167     int read_flags = is_write_notifier ? BDRV_REQ_NO_SERIALISING : 0;
 168     int write_flags = job->serialize_target_writes ? BDRV_REQ_SERIALISING : 0;
 169
 170     assert(QEMU_IS_ALIGNED(job->copy_range_size, job->cluster_size));
 171     assert(QEMU_IS_ALIGNED(start, job->cluster_size));
 172     nbytes = MIN(job->copy_range_size, end - start);
 173     nr_clusters = DIV_ROUND_UP(nbytes, job->cluster_size);
 174     bdrv_reset_dirty_bitmap(job->copy_bitmap, start,
 175                             job->cluster_size * nr_clusters);
 176     ret = blk_co_copy_range(blk, start, job->target, start, nbytes,
 177                             read_flags, write_flags);
 178     if (ret < 0) {
 179         trace_backup_do_cow_copy_range_fail(job, start, ret);
 180         bdrv_set_dirty_bitmap(job->copy_bitmap, start,
 181                               job->cluster_size * nr_clusters);
 182         return ret;
 183     }
 184
 185     return nbytes;
 186 }
 187
 188 /*
 189  * Check if the cluster starting at offset is allocated or not.
 190  * return via pnum the number of contiguous clusters sharing this allocation.
 191  */
 192 static int backup_is_cluster_allocated(BackupBlockJob *s, int64_t offset,
 193                                        int64_t *pnum)
 194 {
 195     BlockDriverState *bs = blk_bs(s->common.blk);
 196     int64_t count, total_count = 0;
 197     int64_t bytes = s->len - offset;
 198     int ret;
 199
 200     assert(QEMU_IS_ALIGNED(offset, s->cluster_size));
 201
 202     while (true) {
 203         ret = bdrv_is_allocated(bs, offset, bytes, &count);
 204         if (ret < 0) {
 205             return ret;
 206         }
 207
 208         total_count += count;
 209
 210         if (ret || count == 0) {
 211             /*
 212              * ret: partial segment(s) are considered allocated.
 213              * otherwise: unallocated tail is treated as an entire segment.
 214              */
 215             *pnum = DIV_ROUND_UP(total_count, s->cluster_size);
 216             return ret;
 217         }
 218
 219         /* Unallocated segment(s) with uncertain following segment(s) */
 220         if (total_count >= s->cluster_size) {
 221             *pnum = total_count / s->cluster_size;
 222             return 0;
 223         }
 224
 225         offset += count;
 226         bytes -= count;
 227     }
 228 }
 229
 230 static int coroutine_fn backup_do_cow(BackupBlockJob *job,
 231                                       int64_t offset, uint64_t bytes,
 232                                       bool *error_is_read,
 233                                       bool is_write_notifier)
 234 {
 235     CowRequest cow_request;
 236     int ret = 0;
 237     int64_t start, end; /* bytes */
 238     void *bounce_buffer = NULL;
 239
 240     qemu_co_rwlock_rdlock(&job->flush_rwlock);
 241
 242     start = QEMU_ALIGN_DOWN(offset, job->cluster_size);
 243     end = QEMU_ALIGN_UP(bytes + offset, job->cluster_size);
 244
 245     trace_backup_do_cow_enter(job, start, offset, bytes);
 246
 247     wait_for_overlapping_requests(job, start, end);
 248     cow_request_begin(&cow_request, job, start, end);
 249
 250     while (start < end) {
 251         int64_t dirty_end;
 252
 253         if (!bdrv_dirty_bitmap_get(job->copy_bitmap, start)) {
 254             trace_backup_do_cow_skip(job, start);
 255             start += job->cluster_size;
 256             continue; /* already copied */
 257         }
 258
 259         dirty_end = bdrv_dirty_bitmap_next_zero(job->copy_bitmap, start,
 260                                                 (end - start));
 261         if (dirty_end < 0) {
 262             dirty_end = end;
 263         }
 264
 265         trace_backup_do_cow_process(job, start);
 266
 267         if (job->use_copy_range) {
 268             ret = backup_cow_with_offload(job, start, dirty_end,
 269                                           is_write_notifier);
 270             if (ret < 0) {
 271                 job->use_copy_range = false;
 272             }
 273         }
 274         if (!job->use_copy_range) {
 275             ret = backup_cow_with_bounce_buffer(job, start, dirty_end,
 276                                                 is_write_notifier,
 277                                                 error_is_read, &bounce_buffer);
 278         }
 279         if (ret < 0) {
 280             break;
 281         }
 282
 283         /* Publish progress, guest I/O counts as progress too.  Note that the
 284          * offset field is an opaque progress value, it is not a disk offset.
 285          */
 286         start += ret;
 287         job->bytes_read += ret;
 288         job_progress_update(&job->common.job, ret);
 289         ret = 0;
 290     }
 291
 292     if (bounce_buffer) {
 293         qemu_vfree(bounce_buffer);
 294     }
 295
 296     cow_request_end(&cow_request);
 297
 298     trace_backup_do_cow_return(job, offset, bytes, ret);
 299
 300     qemu_co_rwlock_unlock(&job->flush_rwlock);
 301
 302     return ret;
 303 }
 304
 305 static int coroutine_fn backup_before_write_notify(
 306         NotifierWithReturn *notifier,
 307         void *opaque)
 308 {
 309     BackupBlockJob *job = container_of(notifier, BackupBlockJob, before_write);
 310     BdrvTrackedRequest *req = opaque;
 311
 312     assert(req->bs == blk_bs(job->common.blk));
 313     assert(QEMU_IS_ALIGNED(req->offset, BDRV_SECTOR_SIZE));
 314     assert(QEMU_IS_ALIGNED(req->bytes, BDRV_SECTOR_SIZE));
 315
 316     return backup_do_cow(job, req->offset, req->bytes, NULL, true);
 317 }
 318
 319 static void backup_cleanup_sync_bitmap(BackupBlockJob *job, int ret)
 320 {
 321     BdrvDirtyBitmap *bm;
 322     BlockDriverState *bs = blk_bs(job->common.blk);
 323     bool sync = (((ret == 0) || (job->bitmap_mode == BITMAP_SYNC_MODE_ALWAYS)) \
 324                  && (job->bitmap_mode != BITMAP_SYNC_MODE_NEVER));
 325
 326     if (sync) {
 327         /*
 328          * We succeeded, or we always intended to sync the bitmap.
 329          * Delete this bitmap and install the child.
 330          */
 331         bm = bdrv_dirty_bitmap_abdicate(bs, job->sync_bitmap, NULL);
 332     } else {
 333         /*
 334          * We failed, or we never intended to sync the bitmap anyway.
 335          * Merge the successor back into the parent, keeping all data.
 336          */
 337         bm = bdrv_reclaim_dirty_bitmap(bs, job->sync_bitmap, NULL);
 338     }
 339
 340     assert(bm);
 341
 342     if (ret < 0 && job->bitmap_mode == BITMAP_SYNC_MODE_ALWAYS) {
 343         /* If we failed and synced, merge in the bits we didn't copy: */
 344         bdrv_dirty_bitmap_merge_internal(bm, job->copy_bitmap,
 345                                          NULL, true);
 346     }
 347 }
 348
 349 static void backup_commit(Job *job)
 350 {
 351     BackupBlockJob *s = container_of(job, BackupBlockJob, common.job);
 352     if (s->sync_bitmap) {
 353         backup_cleanup_sync_bitmap(s, 0);
 354     }
 355 }
 356
 357 static void backup_abort(Job *job)
 358 {
 359     BackupBlockJob *s = container_of(job, BackupBlockJob, common.job);
 360     if (s->sync_bitmap) {
 361         backup_cleanup_sync_bitmap(s, -1);
 362     }
 363 }
 364
 365 static void backup_clean(Job *job)
 366 {
 367     BackupBlockJob *s = container_of(job, BackupBlockJob, common.job);
 368     BlockDriverState *bs = blk_bs(s->common.blk);
 369
 370     if (s->copy_bitmap) {
 371         bdrv_release_dirty_bitmap(bs, s->copy_bitmap);
 372         s->copy_bitmap = NULL;
 373     }
 374
 375     assert(s->target);
 376     blk_unref(s->target);
 377     s->target = NULL;
 378 }
 379
 380 void backup_do_checkpoint(BlockJob *job, Error **errp)
 381 {
 382     BackupBlockJob *backup_job = container_of(job, BackupBlockJob, common);
 383
 384     assert(block_job_driver(job) == &backup_job_driver);
 385
 386     if (backup_job->sync_mode != MIRROR_SYNC_MODE_NONE) {
 387         error_setg(errp, "The backup job only supports block checkpoint in"
 388                    " sync=none mode");
 389         return;
 390     }
 391
 392     bdrv_set_dirty_bitmap(backup_job->copy_bitmap, 0, backup_job->len);
 393 }
 394
 395 static void backup_drain(BlockJob *job)
 396 {
 397     BackupBlockJob *s = container_of(job, BackupBlockJob, common);
 398
 399     /* Need to keep a reference in case blk_drain triggers execution
 400      * of backup_complete...
 401      */
 402     if (s->target) {
 403         BlockBackend *target = s->target;
 404         blk_ref(target);
 405         blk_drain(target);
 406         blk_unref(target);
 407     }
 408 }
 409
 410 static BlockErrorAction backup_error_action(BackupBlockJob *job,
 411                                             bool read, int error)
 412 {
 413     if (read) {
 414         return block_job_error_action(&job->common, job->on_source_error,
 415                                       true, error);
 416     } else {
 417         return block_job_error_action(&job->common, job->on_target_error,
 418                                       false, error);
 419     }
 420 }
 421
 422 static bool coroutine_fn yield_and_check(BackupBlockJob *job)
 423 {
 424     uint64_t delay_ns;
 425
 426     if (job_is_cancelled(&job->common.job)) {
 427         return true;
 428     }
 429
 430     /* We need to yield even for delay_ns = 0 so that bdrv_drain_all() can
 431      * return. Without a yield, the VM would not reboot. */
 432     delay_ns = block_job_ratelimit_get_delay(&job->common, job->bytes_read);
 433     job->bytes_read = 0;
 434     job_sleep_ns(&job->common.job, delay_ns);
 435
 436     if (job_is_cancelled(&job->common.job)) {
 437         return true;
 438     }
 439
 440     return false;
 441 }
 442
 443 static int coroutine_fn backup_loop(BackupBlockJob *job)
 444 {
 445     bool error_is_read;
 446     int64_t offset;
 447     BdrvDirtyBitmapIter *bdbi;
 448     int ret = 0;
 449     int64_t dummy;
 450
 451     bdbi = bdrv_dirty_iter_new(job->copy_bitmap);
 452     while ((offset = bdrv_dirty_iter_next(bdbi)) != -1) {
 453         if (job->sync_mode == MIRROR_SYNC_MODE_TOP &&
 454             !backup_is_cluster_allocated(job, offset, &dummy))
 455         {
 456             bdrv_reset_dirty_bitmap(job->copy_bitmap, offset,
 457                                     job->cluster_size);
 458             continue;
 459         }
 460
 461         do {
 462             if (yield_and_check(job)) {
 463                 goto out;
 464             }
 465             ret = backup_do_cow(job, offset,
 466                                 job->cluster_size, &error_is_read, false);
 467             if (ret < 0 && backup_error_action(job, error_is_read, -ret) ==
 468                            BLOCK_ERROR_ACTION_REPORT)
 469             {
 470                 goto out;
 471             }
 472         } while (ret < 0);
 473     }
 474
 475  out:
 476     bdrv_dirty_iter_free(bdbi);
 477     return ret;
 478 }
 479
 480 static void backup_init_copy_bitmap(BackupBlockJob *job)
 481 {
 482     bool ret;
 483     uint64_t estimate;
 484
 485     if (job->sync_mode == MIRROR_SYNC_MODE_BITMAP) {
 486         ret = bdrv_dirty_bitmap_merge_internal(job->copy_bitmap,
 487                                                job->sync_bitmap,
 488                                                NULL, true);
 489         assert(ret);
 490     } else {
 491         bdrv_set_dirty_bitmap(job->copy_bitmap, 0, job->len);
 492     }
 493
 494     estimate = bdrv_get_dirty_count(job->copy_bitmap);
 495     job_progress_set_remaining(&job->common.job, estimate);
 496 }
 497
 498 static int coroutine_fn backup_run(Job *job, Error **errp)
 499 {
 500     BackupBlockJob *s = container_of(job, BackupBlockJob, common.job);
 501     BlockDriverState *bs = blk_bs(s->common.blk);
 502     int ret = 0;
 503
 504     QLIST_INIT(&s->inflight_reqs);
 505     qemu_co_rwlock_init(&s->flush_rwlock);
 506
 507     backup_init_copy_bitmap(s);
 508
 509     s->before_write.notify = backup_before_write_notify;
 510     bdrv_add_before_write_notifier(bs, &s->before_write);
 511
 512     if (s->sync_mode == MIRROR_SYNC_MODE_NONE) {
 513         /* All bits are set in copy_bitmap to allow any cluster to be copied.
 514          * This does not actually require them to be copied. */
 515         while (!job_is_cancelled(job)) {
 516             /* Yield until the job is cancelled.  We just let our before_write
 517              * notify callback service CoW requests. */
 518             job_yield(job);
 519         }
 520     } else {
 521         ret = backup_loop(s);
 522     }
 523
 524     notifier_with_return_remove(&s->before_write);
 525
 526     /* wait until pending backup_do_cow() calls have completed */
 527     qemu_co_rwlock_wrlock(&s->flush_rwlock);
 528     qemu_co_rwlock_unlock(&s->flush_rwlock);
 529
 530     return ret;
 531 }
 532
 533 static const BlockJobDriver backup_job_driver = {
 534     .job_driver = {
 535         .instance_size          = sizeof(BackupBlockJob),
 536         .job_type               = JOB_TYPE_BACKUP,
 537         .free                   = block_job_free,
 538         .user_resume            = block_job_user_resume,
 539         .drain                  = block_job_drain,
 540         .run                    = backup_run,
 541         .commit                 = backup_commit,
 542         .abort                  = backup_abort,
 543         .clean                  = backup_clean,
 544     },
 545     .drain                  = backup_drain,
 546 };
 547
 548 static int64_t backup_calculate_cluster_size(BlockDriverState *target,
 549                                              Error **errp)
 550 {
 551     int ret;
 552     BlockDriverInfo bdi;
 553
 554     /*
 555      * If there is no backing file on the target, we cannot rely on COW if our
 556      * backup cluster size is smaller than the target cluster size. Even for
 557      * targets with a backing file, try to avoid COW if possible.
 558      */
 559     ret = bdrv_get_info(target, &bdi);
 560     if (ret == -ENOTSUP && !target->backing) {
 561         /* Cluster size is not defined */
 562         warn_report("The target block device doesn't provide "
 563                     "information about the block size and it doesn't have a "
 564                     "backing file. The default block size of %u bytes is "
 565                     "used. If the actual block size of the target exceeds "
 566                     "this default, the backup may be unusable",
 567                     BACKUP_CLUSTER_SIZE_DEFAULT);
 568         return BACKUP_CLUSTER_SIZE_DEFAULT;
 569     } else if (ret < 0 && !target->backing) {
 570         error_setg_errno(errp, -ret,
 571             "Couldn't determine the cluster size of the target image, "
 572             "which has no backing file");
 573         error_append_hint(errp,
 574             "Aborting, since this may create an unusable destination image\n");
 575         return ret;
 576     } else if (ret < 0 && target->backing) {
 577         /* Not fatal; just trudge on ahead. */
 578         return BACKUP_CLUSTER_SIZE_DEFAULT;
 579     }
 580
 581     return MAX(BACKUP_CLUSTER_SIZE_DEFAULT, bdi.cluster_size);
 582 }
 583
 584 BlockJob *backup_job_create(const char *job_id, BlockDriverState *bs,
 585                   BlockDriverState *target, int64_t speed,
 586                   MirrorSyncMode sync_mode, BdrvDirtyBitmap *sync_bitmap,
 587                   BitmapSyncMode bitmap_mode,
 588                   bool compress,
 589                   BlockdevOnError on_source_error,
 590                   BlockdevOnError on_target_error,
 591                   int creation_flags,
 592                   BlockCompletionFunc *cb, void *opaque,
 593                   JobTxn *txn, Error **errp)
 594 {
 595     int64_t len;
 596     BackupBlockJob *job = NULL;
 597     int ret;
 598     int64_t cluster_size;
 599     BdrvDirtyBitmap *copy_bitmap = NULL;
 600
 601     assert(bs);
 602     assert(target);
 603
 604     /* QMP interface protects us from these cases */
 605     assert(sync_mode != MIRROR_SYNC_MODE_INCREMENTAL);
 606     assert(sync_bitmap || sync_mode != MIRROR_SYNC_MODE_BITMAP);
 607
 608     if (bs == target) {
 609         error_setg(errp, "Source and target cannot be the same");
 610         return NULL;
 611     }
 612
 613     if (!bdrv_is_inserted(bs)) {
 614         error_setg(errp, "Device is not inserted: %s",
 615                    bdrv_get_device_name(bs));
 616         return NULL;
 617     }
 618
 619     if (!bdrv_is_inserted(target)) {
 620         error_setg(errp, "Device is not inserted: %s",
 621                    bdrv_get_device_name(target));
 622         return NULL;
 623     }
 624
 625     if (compress && target->drv->bdrv_co_pwritev_compressed == NULL) {
 626         error_setg(errp, "Compression is not supported for this drive %s",
 627                    bdrv_get_device_name(target));
 628         return NULL;
 629     }
 630
 631     if (bdrv_op_is_blocked(bs, BLOCK_OP_TYPE_BACKUP_SOURCE, errp)) {
 632         return NULL;
 633     }
 634
 635     if (bdrv_op_is_blocked(target, BLOCK_OP_TYPE_BACKUP_TARGET, errp)) {
 636         return NULL;
 637     }
 638
 639     if (sync_mode == MIRROR_SYNC_MODE_BITMAP) {
 640         /* If we need to write to this bitmap, check that we can: */
 641         if (bitmap_mode != BITMAP_SYNC_MODE_NEVER &&
 642             bdrv_dirty_bitmap_check(sync_bitmap, BDRV_BITMAP_DEFAULT, errp)) {
 643             return NULL;
 644         }
 645
 646         /* Create a new bitmap, and freeze/disable this one. */
 647         if (bdrv_dirty_bitmap_create_successor(bs, sync_bitmap, errp) < 0) {
 648             return NULL;
 649         }
 650     } else if (sync_bitmap) {
 651         error_setg(errp,
 652                    "a bitmap was given to backup_job_create, "
 653                    "but it received an incompatible sync_mode (%s)",
 654                    MirrorSyncMode_str(sync_mode));
 655         return NULL;
 656     }
 657
 658     len = bdrv_getlength(bs);
 659     if (len < 0) {
 660         error_setg_errno(errp, -len, "unable to get length for '%s'",
 661                          bdrv_get_device_name(bs));
 662         goto error;
 663     }
 664
 665     cluster_size = backup_calculate_cluster_size(target, errp);
 666     if (cluster_size < 0) {
 667         goto error;
 668     }
 669
 670     copy_bitmap = bdrv_create_dirty_bitmap(bs, cluster_size, NULL, errp);
 671     if (!copy_bitmap) {
 672         goto error;
 673     }
 674     bdrv_disable_dirty_bitmap(copy_bitmap);
 675
 676     /* job->len is fixed, so we can't allow resize */
 677     job = block_job_create(job_id, &backup_job_driver, txn, bs,
 678                            BLK_PERM_CONSISTENT_READ,
 679                            BLK_PERM_CONSISTENT_READ | BLK_PERM_WRITE |
 680                            BLK_PERM_WRITE_UNCHANGED | BLK_PERM_GRAPH_MOD,
 681                            speed, creation_flags, cb, opaque, errp);
 682     if (!job) {
 683         goto error;
 684     }
 685
 686     /* The target must match the source in size, so no resize here either */
 687     job->target = blk_new(job->common.job.aio_context,
 688                           BLK_PERM_WRITE,
 689                           BLK_PERM_CONSISTENT_READ | BLK_PERM_WRITE |
 690                           BLK_PERM_WRITE_UNCHANGED | BLK_PERM_GRAPH_MOD);
 691     ret = blk_insert_bs(job->target, target, errp);
 692     if (ret < 0) {
 693         goto error;
 694     }
 695     blk_set_disable_request_queuing(job->target, true);
 696
 697     job->on_source_error = on_source_error;
 698     job->on_target_error = on_target_error;
 699     job->sync_mode = sync_mode;
 700     job->sync_bitmap = sync_bitmap;
 701     job->bitmap_mode = bitmap_mode;
 702     job->compress = compress;
 703
 704     /* Detect image-fleecing (and similar) schemes */
 705     job->serialize_target_writes = bdrv_chain_contains(target, bs);
 706     job->cluster_size = cluster_size;
 707     job->copy_bitmap = copy_bitmap;
 708     copy_bitmap = NULL;
 709     job->use_copy_range = !compress; /* compression isn't supported for it */
 710     job->copy_range_size = MIN_NON_ZERO(blk_get_max_transfer(job->common.blk),
 711                                         blk_get_max_transfer(job->target));
 712     job->copy_range_size = MAX(job->cluster_size,
 713                                QEMU_ALIGN_UP(job->copy_range_size,
 714                                              job->cluster_size));
 715
 716     /* Required permissions are already taken with target's blk_new() */
 717     block_job_add_bdrv(&job->common, "target", target, 0, BLK_PERM_ALL,
 718                        &error_abort);
 719     job->len = len;
 720
 721     return &job->common;
 722
 723  error:
 724     if (copy_bitmap) {
 725         assert(!job || !job->copy_bitmap);
 726         bdrv_release_dirty_bitmap(bs, copy_bitmap);
 727     }
 728     if (sync_bitmap) {
 729         bdrv_reclaim_dirty_bitmap(bs, sync_bitmap, NULL);
 730     }
 731     if (job) {
 732         backup_clean(&job->common.job);
 733         job_early_fail(&job->common.job);
 734     }
 735
 736     return NULL;
 737 }