block/backup.c

   1 /*
   2  * QEMU backup
   3  *
   4  * Copyright (C) 2013 Proxmox Server Solutions
   5  *
   6  * Authors:
   7  *  Dietmar Maurer ([email protected])
   8  *
   9  * This work is licensed under the terms of the GNU GPL, version 2 or later.
  10  * See the COPYING file in the top-level directory.
  11  *
  12  */
  13
  14 #include "qemu/osdep.h"
  15
  16 #include "trace.h"
  17 #include "block/block.h"
  18 #include "block/block_int.h"
  19 #include "block/blockjob_int.h"
  20 #include "block/block_backup.h"
  21 #include "qapi/error.h"
  22 #include "qapi/qmp/qerror.h"
  23 #include "qemu/ratelimit.h"
  24 #include "qemu/cutils.h"
  25 #include "sysemu/block-backend.h"
  26 #include "qemu/bitmap.h"
  27 #include "qemu/error-report.h"
  28
  29 #define BACKUP_CLUSTER_SIZE_DEFAULT (1 << 16)
  30
  31 typedef struct CowRequest {
  32     int64_t start_byte;
  33     int64_t end_byte;
  34     QLIST_ENTRY(CowRequest) list;
  35     CoQueue wait_queue; /* coroutines blocked on this request */
  36 } CowRequest;
  37
  38 typedef struct BackupBlockJob {
  39     BlockJob common;
  40     BlockBackend *target;
  41     /* bitmap for sync=incremental */
  42     BdrvDirtyBitmap *sync_bitmap;
  43     MirrorSyncMode sync_mode;
  44     BlockdevOnError on_source_error;
  45     BlockdevOnError on_target_error;
  46     CoRwlock flush_rwlock;
  47     uint64_t len;
  48     uint64_t bytes_read;
  49     int64_t cluster_size;
  50     bool compress;
  51     NotifierWithReturn before_write;
  52     QLIST_HEAD(, CowRequest) inflight_reqs;
  53
  54     HBitmap *copy_bitmap;
  55     bool use_copy_range;
  56     int64_t copy_range_size;
  57
  58     bool serialize_target_writes;
  59 } BackupBlockJob;
  60
  61 static const BlockJobDriver backup_job_driver;
  62
  63 /* See if in-flight requests overlap and wait for them to complete */
  64 static void coroutine_fn wait_for_overlapping_requests(BackupBlockJob *job,
  65                                                        int64_t start,
  66                                                        int64_t end)
  67 {
  68     CowRequest *req;
  69     bool retry;
  70
  71     do {
  72         retry = false;
  73         QLIST_FOREACH(req, &job->inflight_reqs, list) {
  74             if (end > req->start_byte && start < req->end_byte) {
  75                 qemu_co_queue_wait(&req->wait_queue, NULL);
  76                 retry = true;
  77                 break;
  78             }
  79         }
  80     } while (retry);
  81 }
  82
  83 /* Keep track of an in-flight request */
  84 static void cow_request_begin(CowRequest *req, BackupBlockJob *job,
  85                               int64_t start, int64_t end)
  86 {
  87     req->start_byte = start;
  88     req->end_byte = end;
  89     qemu_co_queue_init(&req->wait_queue);
  90     QLIST_INSERT_HEAD(&job->inflight_reqs, req, list);
  91 }
  92
  93 /* Forget about a completed request */
  94 static void cow_request_end(CowRequest *req)
  95 {
  96     QLIST_REMOVE(req, list);
  97     qemu_co_queue_restart_all(&req->wait_queue);
  98 }
  99
 100 /* Copy range to target with a bounce buffer and return the bytes copied. If
 101  * error occurred, return a negative error number */
 102 static int coroutine_fn backup_cow_with_bounce_buffer(BackupBlockJob *job,
 103                                                       int64_t start,
 104                                                       int64_t end,
 105                                                       bool is_write_notifier,
 106                                                       bool *error_is_read,
 107                                                       void **bounce_buffer)
 108 {
 109     int ret;
 110     struct iovec iov;
 111     QEMUIOVector qiov;
 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     hbitmap_reset(job->copy_bitmap, start / job->cluster_size, 1);
 118     nbytes = MIN(job->cluster_size, job->len - start);
 119     if (!*bounce_buffer) {
 120         *bounce_buffer = blk_blockalign(blk, job->cluster_size);
 121     }
 122     iov.iov_base = *bounce_buffer;
 123     iov.iov_len = nbytes;
 124     qemu_iovec_init_external(&qiov, &iov, 1);
 125
 126     ret = blk_co_preadv(blk, start, qiov.size, &qiov, read_flags);
 127     if (ret < 0) {
 128         trace_backup_do_cow_read_fail(job, start, ret);
 129         if (error_is_read) {
 130             *error_is_read = true;
 131         }
 132         goto fail;
 133     }
 134
 135     if (qemu_iovec_is_zero(&qiov)) {
 136         ret = blk_co_pwrite_zeroes(job->target, start,
 137                                    qiov.size, write_flags | BDRV_REQ_MAY_UNMAP);
 138     } else {
 139         ret = blk_co_pwritev(job->target, start,
 140                              qiov.size, &qiov, write_flags |
 141                              (job->compress ? BDRV_REQ_WRITE_COMPRESSED : 0));
 142     }
 143     if (ret < 0) {
 144         trace_backup_do_cow_write_fail(job, start, ret);
 145         if (error_is_read) {
 146             *error_is_read = false;
 147         }
 148         goto fail;
 149     }
 150
 151     return nbytes;
 152 fail:
 153     hbitmap_set(job->copy_bitmap, start / job->cluster_size, 1);
 154     return ret;
 155
 156 }
 157
 158 /* Copy range to target and return the bytes copied. If error occurred, return a
 159  * negative error number. */
 160 static int coroutine_fn backup_cow_with_offload(BackupBlockJob *job,
 161                                                 int64_t start,
 162                                                 int64_t end,
 163                                                 bool is_write_notifier)
 164 {
 165     int ret;
 166     int nr_clusters;
 167     BlockBackend *blk = job->common.blk;
 168     int nbytes;
 169     int read_flags = is_write_notifier ? BDRV_REQ_NO_SERIALISING : 0;
 170     int write_flags = job->serialize_target_writes ? BDRV_REQ_SERIALISING : 0;
 171
 172     assert(QEMU_IS_ALIGNED(job->copy_range_size, job->cluster_size));
 173     nbytes = MIN(job->copy_range_size, end - start);
 174     nr_clusters = DIV_ROUND_UP(nbytes, job->cluster_size);
 175     hbitmap_reset(job->copy_bitmap, start / job->cluster_size,
 176                   nr_clusters);
 177     ret = blk_co_copy_range(blk, start, job->target, start, nbytes,
 178                             read_flags, write_flags);
 179     if (ret < 0) {
 180         trace_backup_do_cow_copy_range_fail(job, start, ret);
 181         hbitmap_set(job->copy_bitmap, start / job->cluster_size,
 182                     nr_clusters);
 183         return ret;
 184     }
 185
 186     return nbytes;
 187 }
 188
 189 static int coroutine_fn backup_do_cow(BackupBlockJob *job,
 190                                       int64_t offset, uint64_t bytes,
 191                                       bool *error_is_read,
 192                                       bool is_write_notifier)
 193 {
 194     CowRequest cow_request;
 195     int ret = 0;
 196     int64_t start, end; /* bytes */
 197     void *bounce_buffer = NULL;
 198
 199     qemu_co_rwlock_rdlock(&job->flush_rwlock);
 200
 201     start = QEMU_ALIGN_DOWN(offset, job->cluster_size);
 202     end = QEMU_ALIGN_UP(bytes + offset, job->cluster_size);
 203
 204     trace_backup_do_cow_enter(job, start, offset, bytes);
 205
 206     wait_for_overlapping_requests(job, start, end);
 207     cow_request_begin(&cow_request, job, start, end);
 208
 209     while (start < end) {
 210         if (!hbitmap_get(job->copy_bitmap, start / job->cluster_size)) {
 211             trace_backup_do_cow_skip(job, start);
 212             start += job->cluster_size;
 213             continue; /* already copied */
 214         }
 215
 216         trace_backup_do_cow_process(job, start);
 217
 218         if (job->use_copy_range) {
 219             ret = backup_cow_with_offload(job, start, end, is_write_notifier);
 220             if (ret < 0) {
 221                 job->use_copy_range = false;
 222             }
 223         }
 224         if (!job->use_copy_range) {
 225             ret = backup_cow_with_bounce_buffer(job, start, end, is_write_notifier,
 226                                                 error_is_read, &bounce_buffer);
 227         }
 228         if (ret < 0) {
 229             break;
 230         }
 231
 232         /* Publish progress, guest I/O counts as progress too.  Note that the
 233          * offset field is an opaque progress value, it is not a disk offset.
 234          */
 235         start += ret;
 236         job->bytes_read += ret;
 237         job_progress_update(&job->common.job, ret);
 238         ret = 0;
 239     }
 240
 241     if (bounce_buffer) {
 242         qemu_vfree(bounce_buffer);
 243     }
 244
 245     cow_request_end(&cow_request);
 246
 247     trace_backup_do_cow_return(job, offset, bytes, ret);
 248
 249     qemu_co_rwlock_unlock(&job->flush_rwlock);
 250
 251     return ret;
 252 }
 253
 254 static int coroutine_fn backup_before_write_notify(
 255         NotifierWithReturn *notifier,
 256         void *opaque)
 257 {
 258     BackupBlockJob *job = container_of(notifier, BackupBlockJob, before_write);
 259     BdrvTrackedRequest *req = opaque;
 260
 261     assert(req->bs == blk_bs(job->common.blk));
 262     assert(QEMU_IS_ALIGNED(req->offset, BDRV_SECTOR_SIZE));
 263     assert(QEMU_IS_ALIGNED(req->bytes, BDRV_SECTOR_SIZE));
 264
 265     return backup_do_cow(job, req->offset, req->bytes, NULL, true);
 266 }
 267
 268 static void backup_cleanup_sync_bitmap(BackupBlockJob *job, int ret)
 269 {
 270     BdrvDirtyBitmap *bm;
 271     BlockDriverState *bs = blk_bs(job->common.blk);
 272
 273     if (ret < 0) {
 274         /* Merge the successor back into the parent, delete nothing. */
 275         bm = bdrv_reclaim_dirty_bitmap(bs, job->sync_bitmap, NULL);
 276         assert(bm);
 277     } else {
 278         /* Everything is fine, delete this bitmap and install the backup. */
 279         bm = bdrv_dirty_bitmap_abdicate(bs, job->sync_bitmap, NULL);
 280         assert(bm);
 281     }
 282 }
 283
 284 static void backup_commit(Job *job)
 285 {
 286     BackupBlockJob *s = container_of(job, BackupBlockJob, common.job);
 287     if (s->sync_bitmap) {
 288         backup_cleanup_sync_bitmap(s, 0);
 289     }
 290 }
 291
 292 static void backup_abort(Job *job)
 293 {
 294     BackupBlockJob *s = container_of(job, BackupBlockJob, common.job);
 295     if (s->sync_bitmap) {
 296         backup_cleanup_sync_bitmap(s, -1);
 297     }
 298 }
 299
 300 static void backup_clean(Job *job)
 301 {
 302     BackupBlockJob *s = container_of(job, BackupBlockJob, common.job);
 303     assert(s->target);
 304     blk_unref(s->target);
 305     s->target = NULL;
 306 }
 307
 308 static void backup_attached_aio_context(BlockJob *job, AioContext *aio_context)
 309 {
 310     BackupBlockJob *s = container_of(job, BackupBlockJob, common);
 311
 312     blk_set_aio_context(s->target, aio_context);
 313 }
 314
 315 void backup_do_checkpoint(BlockJob *job, Error **errp)
 316 {
 317     BackupBlockJob *backup_job = container_of(job, BackupBlockJob, common);
 318     int64_t len;
 319
 320     assert(block_job_driver(job) == &backup_job_driver);
 321
 322     if (backup_job->sync_mode != MIRROR_SYNC_MODE_NONE) {
 323         error_setg(errp, "The backup job only supports block checkpoint in"
 324                    " sync=none mode");
 325         return;
 326     }
 327
 328     len = DIV_ROUND_UP(backup_job->len, backup_job->cluster_size);
 329     hbitmap_set(backup_job->copy_bitmap, 0, len);
 330 }
 331
 332 static void backup_drain(BlockJob *job)
 333 {
 334     BackupBlockJob *s = container_of(job, BackupBlockJob, common);
 335
 336     /* Need to keep a reference in case blk_drain triggers execution
 337      * of backup_complete...
 338      */
 339     if (s->target) {
 340         BlockBackend *target = s->target;
 341         blk_ref(target);
 342         blk_drain(target);
 343         blk_unref(target);
 344     }
 345 }
 346
 347 static BlockErrorAction backup_error_action(BackupBlockJob *job,
 348                                             bool read, int error)
 349 {
 350     if (read) {
 351         return block_job_error_action(&job->common, job->on_source_error,
 352                                       true, error);
 353     } else {
 354         return block_job_error_action(&job->common, job->on_target_error,
 355                                       false, error);
 356     }
 357 }
 358
 359 static bool coroutine_fn yield_and_check(BackupBlockJob *job)
 360 {
 361     uint64_t delay_ns;
 362
 363     if (job_is_cancelled(&job->common.job)) {
 364         return true;
 365     }
 366
 367     /* We need to yield even for delay_ns = 0 so that bdrv_drain_all() can
 368      * return. Without a yield, the VM would not reboot. */
 369     delay_ns = block_job_ratelimit_get_delay(&job->common, job->bytes_read);
 370     job->bytes_read = 0;
 371     job_sleep_ns(&job->common.job, delay_ns);
 372
 373     if (job_is_cancelled(&job->common.job)) {
 374         return true;
 375     }
 376
 377     return false;
 378 }
 379
 380 static int coroutine_fn backup_run_incremental(BackupBlockJob *job)
 381 {
 382     int ret;
 383     bool error_is_read;
 384     int64_t cluster;
 385     HBitmapIter hbi;
 386
 387     hbitmap_iter_init(&hbi, job->copy_bitmap, 0);
 388     while ((cluster = hbitmap_iter_next(&hbi, true)) != -1) {
 389         do {
 390             if (yield_and_check(job)) {
 391                 return 0;
 392             }
 393             ret = backup_do_cow(job, cluster * job->cluster_size,
 394                                 job->cluster_size, &error_is_read, false);
 395             if (ret < 0 && backup_error_action(job, error_is_read, -ret) ==
 396                            BLOCK_ERROR_ACTION_REPORT)
 397             {
 398                 return ret;
 399             }
 400         } while (ret < 0);
 401     }
 402
 403     return 0;
 404 }
 405
 406 /* init copy_bitmap from sync_bitmap */
 407 static void backup_incremental_init_copy_bitmap(BackupBlockJob *job)
 408 {
 409     BdrvDirtyBitmapIter *dbi;
 410     int64_t offset;
 411     int64_t end = DIV_ROUND_UP(bdrv_dirty_bitmap_size(job->sync_bitmap),
 412                                job->cluster_size);
 413
 414     dbi = bdrv_dirty_iter_new(job->sync_bitmap);
 415     while ((offset = bdrv_dirty_iter_next(dbi)) != -1) {
 416         int64_t cluster = offset / job->cluster_size;
 417         int64_t next_cluster;
 418
 419         offset += bdrv_dirty_bitmap_granularity(job->sync_bitmap);
 420         if (offset >= bdrv_dirty_bitmap_size(job->sync_bitmap)) {
 421             hbitmap_set(job->copy_bitmap, cluster, end - cluster);
 422             break;
 423         }
 424
 425         offset = bdrv_dirty_bitmap_next_zero(job->sync_bitmap, offset);
 426         if (offset == -1) {
 427             hbitmap_set(job->copy_bitmap, cluster, end - cluster);
 428             break;
 429         }
 430
 431         next_cluster = DIV_ROUND_UP(offset, job->cluster_size);
 432         hbitmap_set(job->copy_bitmap, cluster, next_cluster - cluster);
 433         if (next_cluster >= end) {
 434             break;
 435         }
 436
 437         bdrv_set_dirty_iter(dbi, next_cluster * job->cluster_size);
 438     }
 439
 440     /* TODO job_progress_set_remaining() would make more sense */
 441     job_progress_update(&job->common.job,
 442         job->len - hbitmap_count(job->copy_bitmap) * job->cluster_size);
 443
 444     bdrv_dirty_iter_free(dbi);
 445 }
 446
 447 static int coroutine_fn backup_run(Job *job, Error **errp)
 448 {
 449     BackupBlockJob *s = container_of(job, BackupBlockJob, common.job);
 450     BlockDriverState *bs = blk_bs(s->common.blk);
 451     int64_t offset, nb_clusters;
 452     int ret = 0;
 453
 454     QLIST_INIT(&s->inflight_reqs);
 455     qemu_co_rwlock_init(&s->flush_rwlock);
 456
 457     nb_clusters = DIV_ROUND_UP(s->len, s->cluster_size);
 458     job_progress_set_remaining(job, s->len);
 459
 460     s->copy_bitmap = hbitmap_alloc(nb_clusters, 0);
 461     if (s->sync_mode == MIRROR_SYNC_MODE_INCREMENTAL) {
 462         backup_incremental_init_copy_bitmap(s);
 463     } else {
 464         hbitmap_set(s->copy_bitmap, 0, nb_clusters);
 465     }
 466
 467
 468     s->before_write.notify = backup_before_write_notify;
 469     bdrv_add_before_write_notifier(bs, &s->before_write);
 470
 471     if (s->sync_mode == MIRROR_SYNC_MODE_NONE) {
 472         /* All bits are set in copy_bitmap to allow any cluster to be copied.
 473          * This does not actually require them to be copied. */
 474         while (!job_is_cancelled(job)) {
 475             /* Yield until the job is cancelled.  We just let our before_write
 476              * notify callback service CoW requests. */
 477             job_yield(job);
 478         }
 479     } else if (s->sync_mode == MIRROR_SYNC_MODE_INCREMENTAL) {
 480         ret = backup_run_incremental(s);
 481     } else {
 482         /* Both FULL and TOP SYNC_MODE's require copying.. */
 483         for (offset = 0; offset < s->len;
 484              offset += s->cluster_size) {
 485             bool error_is_read;
 486             int alloced = 0;
 487
 488             if (yield_and_check(s)) {
 489                 break;
 490             }
 491
 492             if (s->sync_mode == MIRROR_SYNC_MODE_TOP) {
 493                 int i;
 494                 int64_t n;
 495
 496                 /* Check to see if these blocks are already in the
 497                  * backing file. */
 498
 499                 for (i = 0; i < s->cluster_size;) {
 500                     /* bdrv_is_allocated() only returns true/false based
 501                      * on the first set of sectors it comes across that
 502                      * are are all in the same state.
 503                      * For that reason we must verify each sector in the
 504                      * backup cluster length.  We end up copying more than
 505                      * needed but at some point that is always the case. */
 506                     alloced =
 507                         bdrv_is_allocated(bs, offset + i,
 508                                           s->cluster_size - i, &n);
 509                     i += n;
 510
 511                     if (alloced || n == 0) {
 512                         break;
 513                     }
 514                 }
 515
 516                 /* If the above loop never found any sectors that are in
 517                  * the topmost image, skip this backup. */
 518                 if (alloced == 0) {
 519                     continue;
 520                 }
 521             }
 522             /* FULL sync mode we copy the whole drive. */
 523             if (alloced < 0) {
 524                 ret = alloced;
 525             } else {
 526                 ret = backup_do_cow(s, offset, s->cluster_size,
 527                                     &error_is_read, false);
 528             }
 529             if (ret < 0) {
 530                 /* Depending on error action, fail now or retry cluster */
 531                 BlockErrorAction action =
 532                     backup_error_action(s, error_is_read, -ret);
 533                 if (action == BLOCK_ERROR_ACTION_REPORT) {
 534                     break;
 535                 } else {
 536                     offset -= s->cluster_size;
 537                     continue;
 538                 }
 539             }
 540         }
 541     }
 542
 543     notifier_with_return_remove(&s->before_write);
 544
 545     /* wait until pending backup_do_cow() calls have completed */
 546     qemu_co_rwlock_wrlock(&s->flush_rwlock);
 547     qemu_co_rwlock_unlock(&s->flush_rwlock);
 548     hbitmap_free(s->copy_bitmap);
 549
 550     return ret;
 551 }
 552
 553 static const BlockJobDriver backup_job_driver = {
 554     .job_driver = {
 555         .instance_size          = sizeof(BackupBlockJob),
 556         .job_type               = JOB_TYPE_BACKUP,
 557         .free                   = block_job_free,
 558         .user_resume            = block_job_user_resume,
 559         .drain                  = block_job_drain,
 560         .run                    = backup_run,
 561         .commit                 = backup_commit,
 562         .abort                  = backup_abort,
 563         .clean                  = backup_clean,
 564     },
 565     .attached_aio_context   = backup_attached_aio_context,
 566     .drain                  = backup_drain,
 567 };
 568
 569 BlockJob *backup_job_create(const char *job_id, BlockDriverState *bs,
 570                   BlockDriverState *target, int64_t speed,
 571                   MirrorSyncMode sync_mode, BdrvDirtyBitmap *sync_bitmap,
 572                   bool compress,
 573                   BlockdevOnError on_source_error,
 574                   BlockdevOnError on_target_error,
 575                   int creation_flags,
 576                   BlockCompletionFunc *cb, void *opaque,
 577                   JobTxn *txn, Error **errp)
 578 {
 579     int64_t len;
 580     BlockDriverInfo bdi;
 581     BackupBlockJob *job = NULL;
 582     int ret;
 583
 584     assert(bs);
 585     assert(target);
 586
 587     if (bs == target) {
 588         error_setg(errp, "Source and target cannot be the same");
 589         return NULL;
 590     }
 591
 592     if (!bdrv_is_inserted(bs)) {
 593         error_setg(errp, "Device is not inserted: %s",
 594                    bdrv_get_device_name(bs));
 595         return NULL;
 596     }
 597
 598     if (!bdrv_is_inserted(target)) {
 599         error_setg(errp, "Device is not inserted: %s",
 600                    bdrv_get_device_name(target));
 601         return NULL;
 602     }
 603
 604     if (compress && target->drv->bdrv_co_pwritev_compressed == NULL) {
 605         error_setg(errp, "Compression is not supported for this drive %s",
 606                    bdrv_get_device_name(target));
 607         return NULL;
 608     }
 609
 610     if (bdrv_op_is_blocked(bs, BLOCK_OP_TYPE_BACKUP_SOURCE, errp)) {
 611         return NULL;
 612     }
 613
 614     if (bdrv_op_is_blocked(target, BLOCK_OP_TYPE_BACKUP_TARGET, errp)) {
 615         return NULL;
 616     }
 617
 618     if (sync_mode == MIRROR_SYNC_MODE_INCREMENTAL) {
 619         if (!sync_bitmap) {
 620             error_setg(errp, "must provide a valid bitmap name for "
 621                              "\"incremental\" sync mode");
 622             return NULL;
 623         }
 624
 625         /* Create a new bitmap, and freeze/disable this one. */
 626         if (bdrv_dirty_bitmap_create_successor(bs, sync_bitmap, errp) < 0) {
 627             return NULL;
 628         }
 629     } else if (sync_bitmap) {
 630         error_setg(errp,
 631                    "a sync_bitmap was provided to backup_run, "
 632                    "but received an incompatible sync_mode (%s)",
 633                    MirrorSyncMode_str(sync_mode));
 634         return NULL;
 635     }
 636
 637     len = bdrv_getlength(bs);
 638     if (len < 0) {
 639         error_setg_errno(errp, -len, "unable to get length for '%s'",
 640                          bdrv_get_device_name(bs));
 641         goto error;
 642     }
 643
 644     /* job->len is fixed, so we can't allow resize */
 645     job = block_job_create(job_id, &backup_job_driver, txn, bs,
 646                            BLK_PERM_CONSISTENT_READ,
 647                            BLK_PERM_CONSISTENT_READ | BLK_PERM_WRITE |
 648                            BLK_PERM_WRITE_UNCHANGED | BLK_PERM_GRAPH_MOD,
 649                            speed, creation_flags, cb, opaque, errp);
 650     if (!job) {
 651         goto error;
 652     }
 653
 654     /* The target must match the source in size, so no resize here either */
 655     job->target = blk_new(BLK_PERM_WRITE,
 656                           BLK_PERM_CONSISTENT_READ | BLK_PERM_WRITE |
 657                           BLK_PERM_WRITE_UNCHANGED | BLK_PERM_GRAPH_MOD);
 658     ret = blk_insert_bs(job->target, target, errp);
 659     if (ret < 0) {
 660         goto error;
 661     }
 662
 663     job->on_source_error = on_source_error;
 664     job->on_target_error = on_target_error;
 665     job->sync_mode = sync_mode;
 666     job->sync_bitmap = sync_mode == MIRROR_SYNC_MODE_INCREMENTAL ?
 667                        sync_bitmap : NULL;
 668     job->compress = compress;
 669
 670     /* Detect image-fleecing (and similar) schemes */
 671     job->serialize_target_writes = bdrv_chain_contains(target, bs);
 672
 673     /* If there is no backing file on the target, we cannot rely on COW if our
 674      * backup cluster size is smaller than the target cluster size. Even for
 675      * targets with a backing file, try to avoid COW if possible. */
 676     ret = bdrv_get_info(target, &bdi);
 677     if (ret == -ENOTSUP && !target->backing) {
 678         /* Cluster size is not defined */
 679         warn_report("The target block device doesn't provide "
 680                     "information about the block size and it doesn't have a "
 681                     "backing file. The default block size of %u bytes is "
 682                     "used. If the actual block size of the target exceeds "
 683                     "this default, the backup may be unusable",
 684                     BACKUP_CLUSTER_SIZE_DEFAULT);
 685         job->cluster_size = BACKUP_CLUSTER_SIZE_DEFAULT;
 686     } else if (ret < 0 && !target->backing) {
 687         error_setg_errno(errp, -ret,
 688             "Couldn't determine the cluster size of the target image, "
 689             "which has no backing file");
 690         error_append_hint(errp,
 691             "Aborting, since this may create an unusable destination image\n");
 692         goto error;
 693     } else if (ret < 0 && target->backing) {
 694         /* Not fatal; just trudge on ahead. */
 695         job->cluster_size = BACKUP_CLUSTER_SIZE_DEFAULT;
 696     } else {
 697         job->cluster_size = MAX(BACKUP_CLUSTER_SIZE_DEFAULT, bdi.cluster_size);
 698     }
 699     job->use_copy_range = true;
 700     job->copy_range_size = MIN_NON_ZERO(blk_get_max_transfer(job->common.blk),
 701                                         blk_get_max_transfer(job->target));
 702     job->copy_range_size = MAX(job->cluster_size,
 703                                QEMU_ALIGN_UP(job->copy_range_size,
 704                                              job->cluster_size));
 705
 706     /* Required permissions are already taken with target's blk_new() */
 707     block_job_add_bdrv(&job->common, "target", target, 0, BLK_PERM_ALL,
 708                        &error_abort);
 709     job->len = len;
 710
 711     return &job->common;
 712
 713  error:
 714     if (sync_bitmap) {
 715         bdrv_reclaim_dirty_bitmap(bs, sync_bitmap, NULL);
 716     }
 717     if (job) {
 718         backup_clean(&job->common.job);
 719         job_early_fail(&job->common.job);
 720     }
 721
 722     return NULL;
 723 }