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     NotifierWithReturn before_write;
  54     QLIST_HEAD(, CowRequest) inflight_reqs;
  55
  56     bool use_copy_range;
  57     int64_t copy_range_size;
  58
  59     BdrvRequestFlags write_flags;
  60     bool initializing_bitmap;
  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
 116     assert(QEMU_IS_ALIGNED(start, job->cluster_size));
 117     bdrv_reset_dirty_bitmap(job->copy_bitmap, start, job->cluster_size);
 118     nbytes = MIN(job->cluster_size, job->len - start);
 119     if (!*bounce_buffer) {
 120         *bounce_buffer = blk_blockalign(blk, job->cluster_size);
 121     }
 122
 123     ret = blk_co_pread(blk, start, nbytes, *bounce_buffer, read_flags);
 124     if (ret < 0) {
 125         trace_backup_do_cow_read_fail(job, start, ret);
 126         if (error_is_read) {
 127             *error_is_read = true;
 128         }
 129         goto fail;
 130     }
 131
 132     ret = blk_co_pwrite(job->target, start, nbytes, *bounce_buffer,
 133                         job->write_flags);
 134     if (ret < 0) {
 135         trace_backup_do_cow_write_fail(job, start, ret);
 136         if (error_is_read) {
 137             *error_is_read = false;
 138         }
 139         goto fail;
 140     }
 141
 142     return nbytes;
 143 fail:
 144     bdrv_set_dirty_bitmap(job->copy_bitmap, start, job->cluster_size);
 145     return ret;
 146
 147 }
 148
 149 /* Copy range to target and return the bytes copied. If error occurred, return a
 150  * negative error number. */
 151 static int coroutine_fn backup_cow_with_offload(BackupBlockJob *job,
 152                                                 int64_t start,
 153                                                 int64_t end,
 154                                                 bool is_write_notifier)
 155 {
 156     int ret;
 157     int nr_clusters;
 158     BlockBackend *blk = job->common.blk;
 159     int nbytes;
 160     int read_flags = is_write_notifier ? BDRV_REQ_NO_SERIALISING : 0;
 161
 162     assert(QEMU_IS_ALIGNED(job->copy_range_size, job->cluster_size));
 163     assert(QEMU_IS_ALIGNED(start, job->cluster_size));
 164     nbytes = MIN(job->copy_range_size, end - start);
 165     nr_clusters = DIV_ROUND_UP(nbytes, job->cluster_size);
 166     bdrv_reset_dirty_bitmap(job->copy_bitmap, start,
 167                             job->cluster_size * nr_clusters);
 168     ret = blk_co_copy_range(blk, start, job->target, start, nbytes,
 169                             read_flags, job->write_flags);
 170     if (ret < 0) {
 171         trace_backup_do_cow_copy_range_fail(job, start, ret);
 172         bdrv_set_dirty_bitmap(job->copy_bitmap, start,
 173                               job->cluster_size * nr_clusters);
 174         return ret;
 175     }
 176
 177     return nbytes;
 178 }
 179
 180 /*
 181  * Check if the cluster starting at offset is allocated or not.
 182  * return via pnum the number of contiguous clusters sharing this allocation.
 183  */
 184 static int backup_is_cluster_allocated(BackupBlockJob *s, int64_t offset,
 185                                        int64_t *pnum)
 186 {
 187     BlockDriverState *bs = blk_bs(s->common.blk);
 188     int64_t count, total_count = 0;
 189     int64_t bytes = s->len - offset;
 190     int ret;
 191
 192     assert(QEMU_IS_ALIGNED(offset, s->cluster_size));
 193
 194     while (true) {
 195         ret = bdrv_is_allocated(bs, offset, bytes, &count);
 196         if (ret < 0) {
 197             return ret;
 198         }
 199
 200         total_count += count;
 201
 202         if (ret || count == 0) {
 203             /*
 204              * ret: partial segment(s) are considered allocated.
 205              * otherwise: unallocated tail is treated as an entire segment.
 206              */
 207             *pnum = DIV_ROUND_UP(total_count, s->cluster_size);
 208             return ret;
 209         }
 210
 211         /* Unallocated segment(s) with uncertain following segment(s) */
 212         if (total_count >= s->cluster_size) {
 213             *pnum = total_count / s->cluster_size;
 214             return 0;
 215         }
 216
 217         offset += count;
 218         bytes -= count;
 219     }
 220 }
 221
 222 /**
 223  * Reset bits in copy_bitmap starting at offset if they represent unallocated
 224  * data in the image. May reset subsequent contiguous bits.
 225  * @return 0 when the cluster at @offset was unallocated,
 226  *         1 otherwise, and -ret on error.
 227  */
 228 static int64_t backup_bitmap_reset_unallocated(BackupBlockJob *s,
 229                                                int64_t offset, int64_t *count)
 230 {
 231     int ret;
 232     int64_t clusters, bytes, estimate;
 233
 234     ret = backup_is_cluster_allocated(s, offset, &clusters);
 235     if (ret < 0) {
 236         return ret;
 237     }
 238
 239     bytes = clusters * s->cluster_size;
 240
 241     if (!ret) {
 242         bdrv_reset_dirty_bitmap(s->copy_bitmap, offset, bytes);
 243         estimate = bdrv_get_dirty_count(s->copy_bitmap);
 244         job_progress_set_remaining(&s->common.job, estimate);
 245     }
 246
 247     *count = bytes;
 248     return ret;
 249 }
 250
 251 static int coroutine_fn backup_do_cow(BackupBlockJob *job,
 252                                       int64_t offset, uint64_t bytes,
 253                                       bool *error_is_read,
 254                                       bool is_write_notifier)
 255 {
 256     CowRequest cow_request;
 257     int ret = 0;
 258     int64_t start, end; /* bytes */
 259     void *bounce_buffer = NULL;
 260     int64_t status_bytes;
 261
 262     qemu_co_rwlock_rdlock(&job->flush_rwlock);
 263
 264     start = QEMU_ALIGN_DOWN(offset, job->cluster_size);
 265     end = QEMU_ALIGN_UP(bytes + offset, job->cluster_size);
 266
 267     trace_backup_do_cow_enter(job, start, offset, bytes);
 268
 269     wait_for_overlapping_requests(job, start, end);
 270     cow_request_begin(&cow_request, job, start, end);
 271
 272     while (start < end) {
 273         int64_t dirty_end;
 274
 275         if (!bdrv_dirty_bitmap_get(job->copy_bitmap, start)) {
 276             trace_backup_do_cow_skip(job, start);
 277             start += job->cluster_size;
 278             continue; /* already copied */
 279         }
 280
 281         dirty_end = bdrv_dirty_bitmap_next_zero(job->copy_bitmap, start,
 282                                                 (end - start));
 283         if (dirty_end < 0) {
 284             dirty_end = end;
 285         }
 286
 287         if (job->initializing_bitmap) {
 288             ret = backup_bitmap_reset_unallocated(job, start, &status_bytes);
 289             if (ret == 0) {
 290                 trace_backup_do_cow_skip_range(job, start, status_bytes);
 291                 start += status_bytes;
 292                 continue;
 293             }
 294             /* Clamp to known allocated region */
 295             dirty_end = MIN(dirty_end, start + status_bytes);
 296         }
 297
 298         trace_backup_do_cow_process(job, start);
 299
 300         if (job->use_copy_range) {
 301             ret = backup_cow_with_offload(job, start, dirty_end,
 302                                           is_write_notifier);
 303             if (ret < 0) {
 304                 job->use_copy_range = false;
 305             }
 306         }
 307         if (!job->use_copy_range) {
 308             ret = backup_cow_with_bounce_buffer(job, start, dirty_end,
 309                                                 is_write_notifier,
 310                                                 error_is_read, &bounce_buffer);
 311         }
 312         if (ret < 0) {
 313             break;
 314         }
 315
 316         /* Publish progress, guest I/O counts as progress too.  Note that the
 317          * offset field is an opaque progress value, it is not a disk offset.
 318          */
 319         start += ret;
 320         job->bytes_read += ret;
 321         job_progress_update(&job->common.job, ret);
 322         ret = 0;
 323     }
 324
 325     if (bounce_buffer) {
 326         qemu_vfree(bounce_buffer);
 327     }
 328
 329     cow_request_end(&cow_request);
 330
 331     trace_backup_do_cow_return(job, offset, bytes, ret);
 332
 333     qemu_co_rwlock_unlock(&job->flush_rwlock);
 334
 335     return ret;
 336 }
 337
 338 static int coroutine_fn backup_before_write_notify(
 339         NotifierWithReturn *notifier,
 340         void *opaque)
 341 {
 342     BackupBlockJob *job = container_of(notifier, BackupBlockJob, before_write);
 343     BdrvTrackedRequest *req = opaque;
 344
 345     assert(req->bs == blk_bs(job->common.blk));
 346     assert(QEMU_IS_ALIGNED(req->offset, BDRV_SECTOR_SIZE));
 347     assert(QEMU_IS_ALIGNED(req->bytes, BDRV_SECTOR_SIZE));
 348
 349     return backup_do_cow(job, req->offset, req->bytes, NULL, true);
 350 }
 351
 352 static void backup_cleanup_sync_bitmap(BackupBlockJob *job, int ret)
 353 {
 354     BdrvDirtyBitmap *bm;
 355     BlockDriverState *bs = blk_bs(job->common.blk);
 356     bool sync = (((ret == 0) || (job->bitmap_mode == BITMAP_SYNC_MODE_ALWAYS)) \
 357                  && (job->bitmap_mode != BITMAP_SYNC_MODE_NEVER));
 358
 359     if (sync) {
 360         /*
 361          * We succeeded, or we always intended to sync the bitmap.
 362          * Delete this bitmap and install the child.
 363          */
 364         bm = bdrv_dirty_bitmap_abdicate(bs, job->sync_bitmap, NULL);
 365     } else {
 366         /*
 367          * We failed, or we never intended to sync the bitmap anyway.
 368          * Merge the successor back into the parent, keeping all data.
 369          */
 370         bm = bdrv_reclaim_dirty_bitmap(bs, job->sync_bitmap, NULL);
 371     }
 372
 373     assert(bm);
 374
 375     if (ret < 0 && job->bitmap_mode == BITMAP_SYNC_MODE_ALWAYS) {
 376         /* If we failed and synced, merge in the bits we didn't copy: */
 377         bdrv_dirty_bitmap_merge_internal(bm, job->copy_bitmap,
 378                                          NULL, true);
 379     }
 380 }
 381
 382 static void backup_commit(Job *job)
 383 {
 384     BackupBlockJob *s = container_of(job, BackupBlockJob, common.job);
 385     if (s->sync_bitmap) {
 386         backup_cleanup_sync_bitmap(s, 0);
 387     }
 388 }
 389
 390 static void backup_abort(Job *job)
 391 {
 392     BackupBlockJob *s = container_of(job, BackupBlockJob, common.job);
 393     if (s->sync_bitmap) {
 394         backup_cleanup_sync_bitmap(s, -1);
 395     }
 396 }
 397
 398 static void backup_clean(Job *job)
 399 {
 400     BackupBlockJob *s = container_of(job, BackupBlockJob, common.job);
 401     BlockDriverState *bs = blk_bs(s->common.blk);
 402
 403     if (s->copy_bitmap) {
 404         bdrv_release_dirty_bitmap(bs, s->copy_bitmap);
 405         s->copy_bitmap = NULL;
 406     }
 407
 408     assert(s->target);
 409     blk_unref(s->target);
 410     s->target = NULL;
 411 }
 412
 413 void backup_do_checkpoint(BlockJob *job, Error **errp)
 414 {
 415     BackupBlockJob *backup_job = container_of(job, BackupBlockJob, common);
 416
 417     assert(block_job_driver(job) == &backup_job_driver);
 418
 419     if (backup_job->sync_mode != MIRROR_SYNC_MODE_NONE) {
 420         error_setg(errp, "The backup job only supports block checkpoint in"
 421                    " sync=none mode");
 422         return;
 423     }
 424
 425     bdrv_set_dirty_bitmap(backup_job->copy_bitmap, 0, backup_job->len);
 426 }
 427
 428 static BlockErrorAction backup_error_action(BackupBlockJob *job,
 429                                             bool read, int error)
 430 {
 431     if (read) {
 432         return block_job_error_action(&job->common, job->on_source_error,
 433                                       true, error);
 434     } else {
 435         return block_job_error_action(&job->common, job->on_target_error,
 436                                       false, error);
 437     }
 438 }
 439
 440 static bool coroutine_fn yield_and_check(BackupBlockJob *job)
 441 {
 442     uint64_t delay_ns;
 443
 444     if (job_is_cancelled(&job->common.job)) {
 445         return true;
 446     }
 447
 448     /* We need to yield even for delay_ns = 0 so that bdrv_drain_all() can
 449      * return. Without a yield, the VM would not reboot. */
 450     delay_ns = block_job_ratelimit_get_delay(&job->common, job->bytes_read);
 451     job->bytes_read = 0;
 452     job_sleep_ns(&job->common.job, delay_ns);
 453
 454     if (job_is_cancelled(&job->common.job)) {
 455         return true;
 456     }
 457
 458     return false;
 459 }
 460
 461 static int coroutine_fn backup_loop(BackupBlockJob *job)
 462 {
 463     bool error_is_read;
 464     int64_t offset;
 465     BdrvDirtyBitmapIter *bdbi;
 466     int ret = 0;
 467
 468     bdbi = bdrv_dirty_iter_new(job->copy_bitmap);
 469     while ((offset = bdrv_dirty_iter_next(bdbi)) != -1) {
 470         do {
 471             if (yield_and_check(job)) {
 472                 goto out;
 473             }
 474             ret = backup_do_cow(job, offset,
 475                                 job->cluster_size, &error_is_read, false);
 476             if (ret < 0 && backup_error_action(job, error_is_read, -ret) ==
 477                            BLOCK_ERROR_ACTION_REPORT)
 478             {
 479                 goto out;
 480             }
 481         } while (ret < 0);
 482     }
 483
 484  out:
 485     bdrv_dirty_iter_free(bdbi);
 486     return ret;
 487 }
 488
 489 static void backup_init_copy_bitmap(BackupBlockJob *job)
 490 {
 491     bool ret;
 492     uint64_t estimate;
 493
 494     if (job->sync_mode == MIRROR_SYNC_MODE_BITMAP) {
 495         ret = bdrv_dirty_bitmap_merge_internal(job->copy_bitmap,
 496                                                job->sync_bitmap,
 497                                                NULL, true);
 498         assert(ret);
 499     } else {
 500         if (job->sync_mode == MIRROR_SYNC_MODE_TOP) {
 501             /*
 502              * We can't hog the coroutine to initialize this thoroughly.
 503              * Set a flag and resume work when we are able to yield safely.
 504              */
 505             job->initializing_bitmap = true;
 506         }
 507         bdrv_set_dirty_bitmap(job->copy_bitmap, 0, job->len);
 508     }
 509
 510     estimate = bdrv_get_dirty_count(job->copy_bitmap);
 511     job_progress_set_remaining(&job->common.job, estimate);
 512 }
 513
 514 static int coroutine_fn backup_run(Job *job, Error **errp)
 515 {
 516     BackupBlockJob *s = container_of(job, BackupBlockJob, common.job);
 517     BlockDriverState *bs = blk_bs(s->common.blk);
 518     int ret = 0;
 519
 520     QLIST_INIT(&s->inflight_reqs);
 521     qemu_co_rwlock_init(&s->flush_rwlock);
 522
 523     backup_init_copy_bitmap(s);
 524
 525     s->before_write.notify = backup_before_write_notify;
 526     bdrv_add_before_write_notifier(bs, &s->before_write);
 527
 528     if (s->sync_mode == MIRROR_SYNC_MODE_TOP) {
 529         int64_t offset = 0;
 530         int64_t count;
 531
 532         for (offset = 0; offset < s->len; ) {
 533             if (yield_and_check(s)) {
 534                 ret = -ECANCELED;
 535                 goto out;
 536             }
 537
 538             ret = backup_bitmap_reset_unallocated(s, offset, &count);
 539             if (ret < 0) {
 540                 goto out;
 541             }
 542
 543             offset += count;
 544         }
 545         s->initializing_bitmap = false;
 546     }
 547
 548     if (s->sync_mode == MIRROR_SYNC_MODE_NONE) {
 549         /* All bits are set in copy_bitmap to allow any cluster to be copied.
 550          * This does not actually require them to be copied. */
 551         while (!job_is_cancelled(job)) {
 552             /* Yield until the job is cancelled.  We just let our before_write
 553              * notify callback service CoW requests. */
 554             job_yield(job);
 555         }
 556     } else {
 557         ret = backup_loop(s);
 558     }
 559
 560  out:
 561     notifier_with_return_remove(&s->before_write);
 562
 563     /* wait until pending backup_do_cow() calls have completed */
 564     qemu_co_rwlock_wrlock(&s->flush_rwlock);
 565     qemu_co_rwlock_unlock(&s->flush_rwlock);
 566
 567     return ret;
 568 }
 569
 570 static const BlockJobDriver backup_job_driver = {
 571     .job_driver = {
 572         .instance_size          = sizeof(BackupBlockJob),
 573         .job_type               = JOB_TYPE_BACKUP,
 574         .free                   = block_job_free,
 575         .user_resume            = block_job_user_resume,
 576         .run                    = backup_run,
 577         .commit                 = backup_commit,
 578         .abort                  = backup_abort,
 579         .clean                  = backup_clean,
 580     }
 581 };
 582
 583 static int64_t backup_calculate_cluster_size(BlockDriverState *target,
 584                                              Error **errp)
 585 {
 586     int ret;
 587     BlockDriverInfo bdi;
 588
 589     /*
 590      * If there is no backing file on the target, we cannot rely on COW if our
 591      * backup cluster size is smaller than the target cluster size. Even for
 592      * targets with a backing file, try to avoid COW if possible.
 593      */
 594     ret = bdrv_get_info(target, &bdi);
 595     if (ret == -ENOTSUP && !target->backing) {
 596         /* Cluster size is not defined */
 597         warn_report("The target block device doesn't provide "
 598                     "information about the block size and it doesn't have a "
 599                     "backing file. The default block size of %u bytes is "
 600                     "used. If the actual block size of the target exceeds "
 601                     "this default, the backup may be unusable",
 602                     BACKUP_CLUSTER_SIZE_DEFAULT);
 603         return BACKUP_CLUSTER_SIZE_DEFAULT;
 604     } else if (ret < 0 && !target->backing) {
 605         error_setg_errno(errp, -ret,
 606             "Couldn't determine the cluster size of the target image, "
 607             "which has no backing file");
 608         error_append_hint(errp,
 609             "Aborting, since this may create an unusable destination image\n");
 610         return ret;
 611     } else if (ret < 0 && target->backing) {
 612         /* Not fatal; just trudge on ahead. */
 613         return BACKUP_CLUSTER_SIZE_DEFAULT;
 614     }
 615
 616     return MAX(BACKUP_CLUSTER_SIZE_DEFAULT, bdi.cluster_size);
 617 }
 618
 619 BlockJob *backup_job_create(const char *job_id, BlockDriverState *bs,
 620                   BlockDriverState *target, int64_t speed,
 621                   MirrorSyncMode sync_mode, BdrvDirtyBitmap *sync_bitmap,
 622                   BitmapSyncMode bitmap_mode,
 623                   bool compress,
 624                   BlockdevOnError on_source_error,
 625                   BlockdevOnError on_target_error,
 626                   int creation_flags,
 627                   BlockCompletionFunc *cb, void *opaque,
 628                   JobTxn *txn, Error **errp)
 629 {
 630     int64_t len;
 631     BackupBlockJob *job = NULL;
 632     int ret;
 633     int64_t cluster_size;
 634     BdrvDirtyBitmap *copy_bitmap = NULL;
 635
 636     assert(bs);
 637     assert(target);
 638
 639     /* QMP interface protects us from these cases */
 640     assert(sync_mode != MIRROR_SYNC_MODE_INCREMENTAL);
 641     assert(sync_bitmap || sync_mode != MIRROR_SYNC_MODE_BITMAP);
 642
 643     if (bs == target) {
 644         error_setg(errp, "Source and target cannot be the same");
 645         return NULL;
 646     }
 647
 648     if (!bdrv_is_inserted(bs)) {
 649         error_setg(errp, "Device is not inserted: %s",
 650                    bdrv_get_device_name(bs));
 651         return NULL;
 652     }
 653
 654     if (!bdrv_is_inserted(target)) {
 655         error_setg(errp, "Device is not inserted: %s",
 656                    bdrv_get_device_name(target));
 657         return NULL;
 658     }
 659
 660     if (compress && !block_driver_can_compress(target->drv)) {
 661         error_setg(errp, "Compression is not supported for this drive %s",
 662                    bdrv_get_device_name(target));
 663         return NULL;
 664     }
 665
 666     if (bdrv_op_is_blocked(bs, BLOCK_OP_TYPE_BACKUP_SOURCE, errp)) {
 667         return NULL;
 668     }
 669
 670     if (bdrv_op_is_blocked(target, BLOCK_OP_TYPE_BACKUP_TARGET, errp)) {
 671         return NULL;
 672     }
 673
 674     if (sync_bitmap) {
 675         /* If we need to write to this bitmap, check that we can: */
 676         if (bitmap_mode != BITMAP_SYNC_MODE_NEVER &&
 677             bdrv_dirty_bitmap_check(sync_bitmap, BDRV_BITMAP_DEFAULT, errp)) {
 678             return NULL;
 679         }
 680
 681         /* Create a new bitmap, and freeze/disable this one. */
 682         if (bdrv_dirty_bitmap_create_successor(bs, sync_bitmap, errp) < 0) {
 683             return NULL;
 684         }
 685     }
 686
 687     len = bdrv_getlength(bs);
 688     if (len < 0) {
 689         error_setg_errno(errp, -len, "unable to get length for '%s'",
 690                          bdrv_get_device_name(bs));
 691         goto error;
 692     }
 693
 694     cluster_size = backup_calculate_cluster_size(target, errp);
 695     if (cluster_size < 0) {
 696         goto error;
 697     }
 698
 699     copy_bitmap = bdrv_create_dirty_bitmap(bs, cluster_size, NULL, errp);
 700     if (!copy_bitmap) {
 701         goto error;
 702     }
 703     bdrv_disable_dirty_bitmap(copy_bitmap);
 704
 705     /* job->len is fixed, so we can't allow resize */
 706     job = block_job_create(job_id, &backup_job_driver, txn, bs,
 707                            BLK_PERM_CONSISTENT_READ,
 708                            BLK_PERM_CONSISTENT_READ | BLK_PERM_WRITE |
 709                            BLK_PERM_WRITE_UNCHANGED | BLK_PERM_GRAPH_MOD,
 710                            speed, creation_flags, cb, opaque, errp);
 711     if (!job) {
 712         goto error;
 713     }
 714
 715     /* The target must match the source in size, so no resize here either */
 716     job->target = blk_new(job->common.job.aio_context,
 717                           BLK_PERM_WRITE,
 718                           BLK_PERM_CONSISTENT_READ | BLK_PERM_WRITE |
 719                           BLK_PERM_WRITE_UNCHANGED | BLK_PERM_GRAPH_MOD);
 720     ret = blk_insert_bs(job->target, target, errp);
 721     if (ret < 0) {
 722         goto error;
 723     }
 724     blk_set_disable_request_queuing(job->target, true);
 725
 726     job->on_source_error = on_source_error;
 727     job->on_target_error = on_target_error;
 728     job->sync_mode = sync_mode;
 729     job->sync_bitmap = sync_bitmap;
 730     job->bitmap_mode = bitmap_mode;
 731
 732     /*
 733      * Set write flags:
 734      * 1. Detect image-fleecing (and similar) schemes
 735      * 2. Handle compression
 736      */
 737     job->write_flags =
 738         (bdrv_chain_contains(target, bs) ? BDRV_REQ_SERIALISING : 0) |
 739         (compress ? BDRV_REQ_WRITE_COMPRESSED : 0);
 740
 741     job->cluster_size = cluster_size;
 742     job->copy_bitmap = copy_bitmap;
 743     copy_bitmap = NULL;
 744     job->use_copy_range = !compress; /* compression isn't supported for it */
 745     job->copy_range_size = MIN_NON_ZERO(blk_get_max_transfer(job->common.blk),
 746                                         blk_get_max_transfer(job->target));
 747     job->copy_range_size = MAX(job->cluster_size,
 748                                QEMU_ALIGN_UP(job->copy_range_size,
 749                                              job->cluster_size));
 750
 751     /* Required permissions are already taken with target's blk_new() */
 752     block_job_add_bdrv(&job->common, "target", target, 0, BLK_PERM_ALL,
 753                        &error_abort);
 754     job->len = len;
 755
 756     return &job->common;
 757
 758  error:
 759     if (copy_bitmap) {
 760         assert(!job || !job->copy_bitmap);
 761         bdrv_release_dirty_bitmap(bs, copy_bitmap);
 762     }
 763     if (sync_bitmap) {
 764         bdrv_reclaim_dirty_bitmap(bs, sync_bitmap, NULL);
 765     }
 766     if (job) {
 767         backup_clean(&job->common.job);
 768         job_early_fail(&job->common.job);
 769     }
 770
 771     return NULL;
 772 }