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 static int coroutine_fn backup_do_cow(BackupBlockJob *job,
 189                                       int64_t offset, uint64_t bytes,
 190                                       bool *error_is_read,
 191                                       bool is_write_notifier)
 192 {
 193     CowRequest cow_request;
 194     int ret = 0;
 195     int64_t start, end; /* bytes */
 196     void *bounce_buffer = NULL;
 197
 198     qemu_co_rwlock_rdlock(&job->flush_rwlock);
 199
 200     start = QEMU_ALIGN_DOWN(offset, job->cluster_size);
 201     end = QEMU_ALIGN_UP(bytes + offset, job->cluster_size);
 202
 203     trace_backup_do_cow_enter(job, start, offset, bytes);
 204
 205     wait_for_overlapping_requests(job, start, end);
 206     cow_request_begin(&cow_request, job, start, end);
 207
 208     while (start < end) {
 209         int64_t dirty_end;
 210
 211         if (!bdrv_dirty_bitmap_get(job->copy_bitmap, start)) {
 212             trace_backup_do_cow_skip(job, start);
 213             start += job->cluster_size;
 214             continue; /* already copied */
 215         }
 216
 217         dirty_end = bdrv_dirty_bitmap_next_zero(job->copy_bitmap, start,
 218                                                 (end - start));
 219         if (dirty_end < 0) {
 220             dirty_end = end;
 221         }
 222
 223         trace_backup_do_cow_process(job, start);
 224
 225         if (job->use_copy_range) {
 226             ret = backup_cow_with_offload(job, start, dirty_end,
 227                                           is_write_notifier);
 228             if (ret < 0) {
 229                 job->use_copy_range = false;
 230             }
 231         }
 232         if (!job->use_copy_range) {
 233             ret = backup_cow_with_bounce_buffer(job, start, dirty_end,
 234                                                 is_write_notifier,
 235                                                 error_is_read, &bounce_buffer);
 236         }
 237         if (ret < 0) {
 238             break;
 239         }
 240
 241         /* Publish progress, guest I/O counts as progress too.  Note that the
 242          * offset field is an opaque progress value, it is not a disk offset.
 243          */
 244         start += ret;
 245         job->bytes_read += ret;
 246         job_progress_update(&job->common.job, ret);
 247         ret = 0;
 248     }
 249
 250     if (bounce_buffer) {
 251         qemu_vfree(bounce_buffer);
 252     }
 253
 254     cow_request_end(&cow_request);
 255
 256     trace_backup_do_cow_return(job, offset, bytes, ret);
 257
 258     qemu_co_rwlock_unlock(&job->flush_rwlock);
 259
 260     return ret;
 261 }
 262
 263 static int coroutine_fn backup_before_write_notify(
 264         NotifierWithReturn *notifier,
 265         void *opaque)
 266 {
 267     BackupBlockJob *job = container_of(notifier, BackupBlockJob, before_write);
 268     BdrvTrackedRequest *req = opaque;
 269
 270     assert(req->bs == blk_bs(job->common.blk));
 271     assert(QEMU_IS_ALIGNED(req->offset, BDRV_SECTOR_SIZE));
 272     assert(QEMU_IS_ALIGNED(req->bytes, BDRV_SECTOR_SIZE));
 273
 274     return backup_do_cow(job, req->offset, req->bytes, NULL, true);
 275 }
 276
 277 static void backup_cleanup_sync_bitmap(BackupBlockJob *job, int ret)
 278 {
 279     BdrvDirtyBitmap *bm;
 280     BlockDriverState *bs = blk_bs(job->common.blk);
 281     bool sync = (((ret == 0) || (job->bitmap_mode == BITMAP_SYNC_MODE_ALWAYS)) \
 282                  && (job->bitmap_mode != BITMAP_SYNC_MODE_NEVER));
 283
 284     if (sync) {
 285         /*
 286          * We succeeded, or we always intended to sync the bitmap.
 287          * Delete this bitmap and install the child.
 288          */
 289         bm = bdrv_dirty_bitmap_abdicate(bs, job->sync_bitmap, NULL);
 290     } else {
 291         /*
 292          * We failed, or we never intended to sync the bitmap anyway.
 293          * Merge the successor back into the parent, keeping all data.
 294          */
 295         bm = bdrv_reclaim_dirty_bitmap(bs, job->sync_bitmap, NULL);
 296     }
 297
 298     assert(bm);
 299
 300     if (ret < 0 && job->bitmap_mode == BITMAP_SYNC_MODE_ALWAYS) {
 301         /* If we failed and synced, merge in the bits we didn't copy: */
 302         bdrv_dirty_bitmap_merge_internal(bm, job->copy_bitmap,
 303                                          NULL, true);
 304     }
 305 }
 306
 307 static void backup_commit(Job *job)
 308 {
 309     BackupBlockJob *s = container_of(job, BackupBlockJob, common.job);
 310     if (s->sync_bitmap) {
 311         backup_cleanup_sync_bitmap(s, 0);
 312     }
 313 }
 314
 315 static void backup_abort(Job *job)
 316 {
 317     BackupBlockJob *s = container_of(job, BackupBlockJob, common.job);
 318     if (s->sync_bitmap) {
 319         backup_cleanup_sync_bitmap(s, -1);
 320     }
 321 }
 322
 323 static void backup_clean(Job *job)
 324 {
 325     BackupBlockJob *s = container_of(job, BackupBlockJob, common.job);
 326     BlockDriverState *bs = blk_bs(s->common.blk);
 327
 328     if (s->copy_bitmap) {
 329         bdrv_release_dirty_bitmap(bs, s->copy_bitmap);
 330         s->copy_bitmap = NULL;
 331     }
 332
 333     assert(s->target);
 334     blk_unref(s->target);
 335     s->target = NULL;
 336 }
 337
 338 void backup_do_checkpoint(BlockJob *job, Error **errp)
 339 {
 340     BackupBlockJob *backup_job = container_of(job, BackupBlockJob, common);
 341
 342     assert(block_job_driver(job) == &backup_job_driver);
 343
 344     if (backup_job->sync_mode != MIRROR_SYNC_MODE_NONE) {
 345         error_setg(errp, "The backup job only supports block checkpoint in"
 346                    " sync=none mode");
 347         return;
 348     }
 349
 350     bdrv_set_dirty_bitmap(backup_job->copy_bitmap, 0, backup_job->len);
 351 }
 352
 353 static void backup_drain(BlockJob *job)
 354 {
 355     BackupBlockJob *s = container_of(job, BackupBlockJob, common);
 356
 357     /* Need to keep a reference in case blk_drain triggers execution
 358      * of backup_complete...
 359      */
 360     if (s->target) {
 361         BlockBackend *target = s->target;
 362         blk_ref(target);
 363         blk_drain(target);
 364         blk_unref(target);
 365     }
 366 }
 367
 368 static BlockErrorAction backup_error_action(BackupBlockJob *job,
 369                                             bool read, int error)
 370 {
 371     if (read) {
 372         return block_job_error_action(&job->common, job->on_source_error,
 373                                       true, error);
 374     } else {
 375         return block_job_error_action(&job->common, job->on_target_error,
 376                                       false, error);
 377     }
 378 }
 379
 380 static bool coroutine_fn yield_and_check(BackupBlockJob *job)
 381 {
 382     uint64_t delay_ns;
 383
 384     if (job_is_cancelled(&job->common.job)) {
 385         return true;
 386     }
 387
 388     /* We need to yield even for delay_ns = 0 so that bdrv_drain_all() can
 389      * return. Without a yield, the VM would not reboot. */
 390     delay_ns = block_job_ratelimit_get_delay(&job->common, job->bytes_read);
 391     job->bytes_read = 0;
 392     job_sleep_ns(&job->common.job, delay_ns);
 393
 394     if (job_is_cancelled(&job->common.job)) {
 395         return true;
 396     }
 397
 398     return false;
 399 }
 400
 401 static bool bdrv_is_unallocated_range(BlockDriverState *bs,
 402                                       int64_t offset, int64_t bytes)
 403 {
 404     int64_t end = offset + bytes;
 405
 406     while (offset < end && !bdrv_is_allocated(bs, offset, bytes, &bytes)) {
 407         if (bytes == 0) {
 408             return true;
 409         }
 410         offset += bytes;
 411         bytes = end - offset;
 412     }
 413
 414     return offset >= end;
 415 }
 416
 417 static int coroutine_fn backup_loop(BackupBlockJob *job)
 418 {
 419     bool error_is_read;
 420     int64_t offset;
 421     BdrvDirtyBitmapIter *bdbi;
 422     BlockDriverState *bs = blk_bs(job->common.blk);
 423     int ret = 0;
 424
 425     bdbi = bdrv_dirty_iter_new(job->copy_bitmap);
 426     while ((offset = bdrv_dirty_iter_next(bdbi)) != -1) {
 427         if (job->sync_mode == MIRROR_SYNC_MODE_TOP &&
 428             bdrv_is_unallocated_range(bs, offset, job->cluster_size))
 429         {
 430             bdrv_reset_dirty_bitmap(job->copy_bitmap, offset,
 431                                     job->cluster_size);
 432             continue;
 433         }
 434
 435         do {
 436             if (yield_and_check(job)) {
 437                 goto out;
 438             }
 439             ret = backup_do_cow(job, offset,
 440                                 job->cluster_size, &error_is_read, false);
 441             if (ret < 0 && backup_error_action(job, error_is_read, -ret) ==
 442                            BLOCK_ERROR_ACTION_REPORT)
 443             {
 444                 goto out;
 445             }
 446         } while (ret < 0);
 447     }
 448
 449  out:
 450     bdrv_dirty_iter_free(bdbi);
 451     return ret;
 452 }
 453
 454 /* init copy_bitmap from sync_bitmap */
 455 static void backup_incremental_init_copy_bitmap(BackupBlockJob *job)
 456 {
 457     bool ret = bdrv_dirty_bitmap_merge_internal(job->copy_bitmap,
 458                                                 job->sync_bitmap,
 459                                                 NULL, true);
 460     assert(ret);
 461
 462     /* TODO job_progress_set_remaining() would make more sense */
 463     job_progress_update(&job->common.job,
 464                         job->len - bdrv_get_dirty_count(job->copy_bitmap));
 465 }
 466
 467 static int coroutine_fn backup_run(Job *job, Error **errp)
 468 {
 469     BackupBlockJob *s = container_of(job, BackupBlockJob, common.job);
 470     BlockDriverState *bs = blk_bs(s->common.blk);
 471     int ret = 0;
 472
 473     QLIST_INIT(&s->inflight_reqs);
 474     qemu_co_rwlock_init(&s->flush_rwlock);
 475
 476     job_progress_set_remaining(job, s->len);
 477
 478     if (s->sync_mode == MIRROR_SYNC_MODE_BITMAP) {
 479         backup_incremental_init_copy_bitmap(s);
 480     } else {
 481         bdrv_set_dirty_bitmap(s->copy_bitmap, 0, s->len);
 482     }
 483
 484     s->before_write.notify = backup_before_write_notify;
 485     bdrv_add_before_write_notifier(bs, &s->before_write);
 486
 487     if (s->sync_mode == MIRROR_SYNC_MODE_NONE) {
 488         /* All bits are set in copy_bitmap to allow any cluster to be copied.
 489          * This does not actually require them to be copied. */
 490         while (!job_is_cancelled(job)) {
 491             /* Yield until the job is cancelled.  We just let our before_write
 492              * notify callback service CoW requests. */
 493             job_yield(job);
 494         }
 495     } else {
 496         ret = backup_loop(s);
 497     }
 498
 499     notifier_with_return_remove(&s->before_write);
 500
 501     /* wait until pending backup_do_cow() calls have completed */
 502     qemu_co_rwlock_wrlock(&s->flush_rwlock);
 503     qemu_co_rwlock_unlock(&s->flush_rwlock);
 504
 505     return ret;
 506 }
 507
 508 static const BlockJobDriver backup_job_driver = {
 509     .job_driver = {
 510         .instance_size          = sizeof(BackupBlockJob),
 511         .job_type               = JOB_TYPE_BACKUP,
 512         .free                   = block_job_free,
 513         .user_resume            = block_job_user_resume,
 514         .drain                  = block_job_drain,
 515         .run                    = backup_run,
 516         .commit                 = backup_commit,
 517         .abort                  = backup_abort,
 518         .clean                  = backup_clean,
 519     },
 520     .drain                  = backup_drain,
 521 };
 522
 523 static int64_t backup_calculate_cluster_size(BlockDriverState *target,
 524                                              Error **errp)
 525 {
 526     int ret;
 527     BlockDriverInfo bdi;
 528
 529     /*
 530      * If there is no backing file on the target, we cannot rely on COW if our
 531      * backup cluster size is smaller than the target cluster size. Even for
 532      * targets with a backing file, try to avoid COW if possible.
 533      */
 534     ret = bdrv_get_info(target, &bdi);
 535     if (ret == -ENOTSUP && !target->backing) {
 536         /* Cluster size is not defined */
 537         warn_report("The target block device doesn't provide "
 538                     "information about the block size and it doesn't have a "
 539                     "backing file. The default block size of %u bytes is "
 540                     "used. If the actual block size of the target exceeds "
 541                     "this default, the backup may be unusable",
 542                     BACKUP_CLUSTER_SIZE_DEFAULT);
 543         return BACKUP_CLUSTER_SIZE_DEFAULT;
 544     } else if (ret < 0 && !target->backing) {
 545         error_setg_errno(errp, -ret,
 546             "Couldn't determine the cluster size of the target image, "
 547             "which has no backing file");
 548         error_append_hint(errp,
 549             "Aborting, since this may create an unusable destination image\n");
 550         return ret;
 551     } else if (ret < 0 && target->backing) {
 552         /* Not fatal; just trudge on ahead. */
 553         return BACKUP_CLUSTER_SIZE_DEFAULT;
 554     }
 555
 556     return MAX(BACKUP_CLUSTER_SIZE_DEFAULT, bdi.cluster_size);
 557 }
 558
 559 BlockJob *backup_job_create(const char *job_id, BlockDriverState *bs,
 560                   BlockDriverState *target, int64_t speed,
 561                   MirrorSyncMode sync_mode, BdrvDirtyBitmap *sync_bitmap,
 562                   BitmapSyncMode bitmap_mode,
 563                   bool compress,
 564                   BlockdevOnError on_source_error,
 565                   BlockdevOnError on_target_error,
 566                   int creation_flags,
 567                   BlockCompletionFunc *cb, void *opaque,
 568                   JobTxn *txn, Error **errp)
 569 {
 570     int64_t len;
 571     BackupBlockJob *job = NULL;
 572     int ret;
 573     int64_t cluster_size;
 574     BdrvDirtyBitmap *copy_bitmap = NULL;
 575
 576     assert(bs);
 577     assert(target);
 578
 579     if (bs == target) {
 580         error_setg(errp, "Source and target cannot be the same");
 581         return NULL;
 582     }
 583
 584     if (!bdrv_is_inserted(bs)) {
 585         error_setg(errp, "Device is not inserted: %s",
 586                    bdrv_get_device_name(bs));
 587         return NULL;
 588     }
 589
 590     if (!bdrv_is_inserted(target)) {
 591         error_setg(errp, "Device is not inserted: %s",
 592                    bdrv_get_device_name(target));
 593         return NULL;
 594     }
 595
 596     if (compress && target->drv->bdrv_co_pwritev_compressed == NULL) {
 597         error_setg(errp, "Compression is not supported for this drive %s",
 598                    bdrv_get_device_name(target));
 599         return NULL;
 600     }
 601
 602     if (bdrv_op_is_blocked(bs, BLOCK_OP_TYPE_BACKUP_SOURCE, errp)) {
 603         return NULL;
 604     }
 605
 606     if (bdrv_op_is_blocked(target, BLOCK_OP_TYPE_BACKUP_TARGET, errp)) {
 607         return NULL;
 608     }
 609
 610     /* QMP interface should have handled translating this to bitmap mode */
 611     assert(sync_mode != MIRROR_SYNC_MODE_INCREMENTAL);
 612
 613     if (sync_mode == MIRROR_SYNC_MODE_BITMAP) {
 614         if (!sync_bitmap) {
 615             error_setg(errp, "must provide a valid bitmap name for "
 616                        "'%s' sync mode", MirrorSyncMode_str(sync_mode));
 617             return NULL;
 618         }
 619
 620         /* Create a new bitmap, and freeze/disable this one. */
 621         if (bdrv_dirty_bitmap_create_successor(bs, sync_bitmap, errp) < 0) {
 622             return NULL;
 623         }
 624     } else if (sync_bitmap) {
 625         error_setg(errp,
 626                    "a bitmap was given to backup_job_create, "
 627                    "but it received an incompatible sync_mode (%s)",
 628                    MirrorSyncMode_str(sync_mode));
 629         return NULL;
 630     }
 631
 632     len = bdrv_getlength(bs);
 633     if (len < 0) {
 634         error_setg_errno(errp, -len, "unable to get length for '%s'",
 635                          bdrv_get_device_name(bs));
 636         goto error;
 637     }
 638
 639     cluster_size = backup_calculate_cluster_size(target, errp);
 640     if (cluster_size < 0) {
 641         goto error;
 642     }
 643
 644     copy_bitmap = bdrv_create_dirty_bitmap(bs, cluster_size, NULL, errp);
 645     if (!copy_bitmap) {
 646         goto error;
 647     }
 648     bdrv_disable_dirty_bitmap(copy_bitmap);
 649
 650     /* job->len is fixed, so we can't allow resize */
 651     job = block_job_create(job_id, &backup_job_driver, txn, bs,
 652                            BLK_PERM_CONSISTENT_READ,
 653                            BLK_PERM_CONSISTENT_READ | BLK_PERM_WRITE |
 654                            BLK_PERM_WRITE_UNCHANGED | BLK_PERM_GRAPH_MOD,
 655                            speed, creation_flags, cb, opaque, errp);
 656     if (!job) {
 657         goto error;
 658     }
 659
 660     /* The target must match the source in size, so no resize here either */
 661     job->target = blk_new(job->common.job.aio_context,
 662                           BLK_PERM_WRITE,
 663                           BLK_PERM_CONSISTENT_READ | BLK_PERM_WRITE |
 664                           BLK_PERM_WRITE_UNCHANGED | BLK_PERM_GRAPH_MOD);
 665     ret = blk_insert_bs(job->target, target, errp);
 666     if (ret < 0) {
 667         goto error;
 668     }
 669     blk_set_disable_request_queuing(job->target, true);
 670
 671     job->on_source_error = on_source_error;
 672     job->on_target_error = on_target_error;
 673     job->sync_mode = sync_mode;
 674     job->sync_bitmap = sync_bitmap;
 675     job->bitmap_mode = bitmap_mode;
 676     job->compress = compress;
 677
 678     /* Detect image-fleecing (and similar) schemes */
 679     job->serialize_target_writes = bdrv_chain_contains(target, bs);
 680     job->cluster_size = cluster_size;
 681     job->copy_bitmap = copy_bitmap;
 682     copy_bitmap = NULL;
 683     job->use_copy_range = !compress; /* compression isn't supported for it */
 684     job->copy_range_size = MIN_NON_ZERO(blk_get_max_transfer(job->common.blk),
 685                                         blk_get_max_transfer(job->target));
 686     job->copy_range_size = MAX(job->cluster_size,
 687                                QEMU_ALIGN_UP(job->copy_range_size,
 688                                              job->cluster_size));
 689
 690     /* Required permissions are already taken with target's blk_new() */
 691     block_job_add_bdrv(&job->common, "target", target, 0, BLK_PERM_ALL,
 692                        &error_abort);
 693     job->len = len;
 694
 695     return &job->common;
 696
 697  error:
 698     if (copy_bitmap) {
 699         assert(!job || !job->copy_bitmap);
 700         bdrv_release_dirty_bitmap(bs, copy_bitmap);
 701     }
 702     if (sync_bitmap) {
 703         bdrv_reclaim_dirty_bitmap(bs, sync_bitmap, NULL);
 704     }
 705     if (job) {
 706         backup_clean(&job->common.job);
 707         job_early_fail(&job->common.job);
 708     }
 709
 710     return NULL;
 711 }