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
  28 #define BACKUP_CLUSTER_SIZE_DEFAULT (1 << 16)
  29 #define SLICE_TIME 100000000ULL /* ns */
  30
  31 typedef struct BackupBlockJob {
  32     BlockJob common;
  33     BlockBackend *target;
  34     /* bitmap for sync=incremental */
  35     BdrvDirtyBitmap *sync_bitmap;
  36     MirrorSyncMode sync_mode;
  37     RateLimit limit;
  38     BlockdevOnError on_source_error;
  39     BlockdevOnError on_target_error;
  40     CoRwlock flush_rwlock;
  41     uint64_t sectors_read;
  42     unsigned long *done_bitmap;
  43     int64_t cluster_size;
  44     bool compress;
  45     NotifierWithReturn before_write;
  46     QLIST_HEAD(, CowRequest) inflight_reqs;
  47 } BackupBlockJob;
  48
  49 /* Size of a cluster in sectors, instead of bytes. */
  50 static inline int64_t cluster_size_sectors(BackupBlockJob *job)
  51 {
  52   return job->cluster_size / BDRV_SECTOR_SIZE;
  53 }
  54
  55 /* See if in-flight requests overlap and wait for them to complete */
  56 static void coroutine_fn wait_for_overlapping_requests(BackupBlockJob *job,
  57                                                        int64_t start,
  58                                                        int64_t end)
  59 {
  60     CowRequest *req;
  61     bool retry;
  62
  63     do {
  64         retry = false;
  65         QLIST_FOREACH(req, &job->inflight_reqs, list) {
  66             if (end > req->start && start < req->end) {
  67                 qemu_co_queue_wait(&req->wait_queue);
  68                 retry = true;
  69                 break;
  70             }
  71         }
  72     } while (retry);
  73 }
  74
  75 /* Keep track of an in-flight request */
  76 static void cow_request_begin(CowRequest *req, BackupBlockJob *job,
  77                                      int64_t start, int64_t end)
  78 {
  79     req->start = start;
  80     req->end = end;
  81     qemu_co_queue_init(&req->wait_queue);
  82     QLIST_INSERT_HEAD(&job->inflight_reqs, req, list);
  83 }
  84
  85 /* Forget about a completed request */
  86 static void cow_request_end(CowRequest *req)
  87 {
  88     QLIST_REMOVE(req, list);
  89     qemu_co_queue_restart_all(&req->wait_queue);
  90 }
  91
  92 static int coroutine_fn backup_do_cow(BackupBlockJob *job,
  93                                       int64_t sector_num, int nb_sectors,
  94                                       bool *error_is_read,
  95                                       bool is_write_notifier)
  96 {
  97     BlockBackend *blk = job->common.blk;
  98     CowRequest cow_request;
  99     struct iovec iov;
 100     QEMUIOVector bounce_qiov;
 101     void *bounce_buffer = NULL;
 102     int ret = 0;
 103     int64_t sectors_per_cluster = cluster_size_sectors(job);
 104     int64_t start, end;
 105     int n;
 106
 107     qemu_co_rwlock_rdlock(&job->flush_rwlock);
 108
 109     start = sector_num / sectors_per_cluster;
 110     end = DIV_ROUND_UP(sector_num + nb_sectors, sectors_per_cluster);
 111
 112     trace_backup_do_cow_enter(job, start, sector_num, nb_sectors);
 113
 114     wait_for_overlapping_requests(job, start, end);
 115     cow_request_begin(&cow_request, job, start, end);
 116
 117     for (; start < end; start++) {
 118         if (test_bit(start, job->done_bitmap)) {
 119             trace_backup_do_cow_skip(job, start);
 120             continue; /* already copied */
 121         }
 122
 123         trace_backup_do_cow_process(job, start);
 124
 125         n = MIN(sectors_per_cluster,
 126                 job->common.len / BDRV_SECTOR_SIZE -
 127                 start * sectors_per_cluster);
 128
 129         if (!bounce_buffer) {
 130             bounce_buffer = blk_blockalign(blk, job->cluster_size);
 131         }
 132         iov.iov_base = bounce_buffer;
 133         iov.iov_len = n * BDRV_SECTOR_SIZE;
 134         qemu_iovec_init_external(&bounce_qiov, &iov, 1);
 135
 136         ret = blk_co_preadv(blk, start * job->cluster_size,
 137                             bounce_qiov.size, &bounce_qiov,
 138                             is_write_notifier ? BDRV_REQ_NO_SERIALISING : 0);
 139         if (ret < 0) {
 140             trace_backup_do_cow_read_fail(job, start, ret);
 141             if (error_is_read) {
 142                 *error_is_read = true;
 143             }
 144             goto out;
 145         }
 146
 147         if (buffer_is_zero(iov.iov_base, iov.iov_len)) {
 148             ret = blk_co_pwrite_zeroes(job->target, start * job->cluster_size,
 149                                        bounce_qiov.size, BDRV_REQ_MAY_UNMAP);
 150         } else {
 151             ret = blk_co_pwritev(job->target, start * job->cluster_size,
 152                                  bounce_qiov.size, &bounce_qiov,
 153                                  job->compress ? BDRV_REQ_WRITE_COMPRESSED : 0);
 154         }
 155         if (ret < 0) {
 156             trace_backup_do_cow_write_fail(job, start, ret);
 157             if (error_is_read) {
 158                 *error_is_read = false;
 159             }
 160             goto out;
 161         }
 162
 163         set_bit(start, job->done_bitmap);
 164
 165         /* Publish progress, guest I/O counts as progress too.  Note that the
 166          * offset field is an opaque progress value, it is not a disk offset.
 167          */
 168         job->sectors_read += n;
 169         job->common.offset += n * BDRV_SECTOR_SIZE;
 170     }
 171
 172 out:
 173     if (bounce_buffer) {
 174         qemu_vfree(bounce_buffer);
 175     }
 176
 177     cow_request_end(&cow_request);
 178
 179     trace_backup_do_cow_return(job, sector_num, nb_sectors, ret);
 180
 181     qemu_co_rwlock_unlock(&job->flush_rwlock);
 182
 183     return ret;
 184 }
 185
 186 static int coroutine_fn backup_before_write_notify(
 187         NotifierWithReturn *notifier,
 188         void *opaque)
 189 {
 190     BackupBlockJob *job = container_of(notifier, BackupBlockJob, before_write);
 191     BdrvTrackedRequest *req = opaque;
 192     int64_t sector_num = req->offset >> BDRV_SECTOR_BITS;
 193     int nb_sectors = req->bytes >> BDRV_SECTOR_BITS;
 194
 195     assert(req->bs == blk_bs(job->common.blk));
 196     assert((req->offset & (BDRV_SECTOR_SIZE - 1)) == 0);
 197     assert((req->bytes & (BDRV_SECTOR_SIZE - 1)) == 0);
 198
 199     return backup_do_cow(job, sector_num, nb_sectors, NULL, true);
 200 }
 201
 202 static void backup_set_speed(BlockJob *job, int64_t speed, Error **errp)
 203 {
 204     BackupBlockJob *s = container_of(job, BackupBlockJob, common);
 205
 206     if (speed < 0) {
 207         error_setg(errp, QERR_INVALID_PARAMETER, "speed");
 208         return;
 209     }
 210     ratelimit_set_speed(&s->limit, speed / BDRV_SECTOR_SIZE, SLICE_TIME);
 211 }
 212
 213 static void backup_cleanup_sync_bitmap(BackupBlockJob *job, int ret)
 214 {
 215     BdrvDirtyBitmap *bm;
 216     BlockDriverState *bs = blk_bs(job->common.blk);
 217
 218     if (ret < 0 || block_job_is_cancelled(&job->common)) {
 219         /* Merge the successor back into the parent, delete nothing. */
 220         bm = bdrv_reclaim_dirty_bitmap(bs, job->sync_bitmap, NULL);
 221         assert(bm);
 222     } else {
 223         /* Everything is fine, delete this bitmap and install the backup. */
 224         bm = bdrv_dirty_bitmap_abdicate(bs, job->sync_bitmap, NULL);
 225         assert(bm);
 226     }
 227 }
 228
 229 static void backup_commit(BlockJob *job)
 230 {
 231     BackupBlockJob *s = container_of(job, BackupBlockJob, common);
 232     if (s->sync_bitmap) {
 233         backup_cleanup_sync_bitmap(s, 0);
 234     }
 235 }
 236
 237 static void backup_abort(BlockJob *job)
 238 {
 239     BackupBlockJob *s = container_of(job, BackupBlockJob, common);
 240     if (s->sync_bitmap) {
 241         backup_cleanup_sync_bitmap(s, -1);
 242     }
 243 }
 244
 245 static void backup_clean(BlockJob *job)
 246 {
 247     BackupBlockJob *s = container_of(job, BackupBlockJob, common);
 248     assert(s->target);
 249     blk_unref(s->target);
 250     s->target = NULL;
 251 }
 252
 253 static void backup_attached_aio_context(BlockJob *job, AioContext *aio_context)
 254 {
 255     BackupBlockJob *s = container_of(job, BackupBlockJob, common);
 256
 257     blk_set_aio_context(s->target, aio_context);
 258 }
 259
 260 void backup_do_checkpoint(BlockJob *job, Error **errp)
 261 {
 262     BackupBlockJob *backup_job = container_of(job, BackupBlockJob, common);
 263     int64_t len;
 264
 265     assert(job->driver->job_type == BLOCK_JOB_TYPE_BACKUP);
 266
 267     if (backup_job->sync_mode != MIRROR_SYNC_MODE_NONE) {
 268         error_setg(errp, "The backup job only supports block checkpoint in"
 269                    " sync=none mode");
 270         return;
 271     }
 272
 273     len = DIV_ROUND_UP(backup_job->common.len, backup_job->cluster_size);
 274     bitmap_zero(backup_job->done_bitmap, len);
 275 }
 276
 277 void backup_wait_for_overlapping_requests(BlockJob *job, int64_t sector_num,
 278                                           int nb_sectors)
 279 {
 280     BackupBlockJob *backup_job = container_of(job, BackupBlockJob, common);
 281     int64_t sectors_per_cluster = cluster_size_sectors(backup_job);
 282     int64_t start, end;
 283
 284     assert(job->driver->job_type == BLOCK_JOB_TYPE_BACKUP);
 285
 286     start = sector_num / sectors_per_cluster;
 287     end = DIV_ROUND_UP(sector_num + nb_sectors, sectors_per_cluster);
 288     wait_for_overlapping_requests(backup_job, start, end);
 289 }
 290
 291 void backup_cow_request_begin(CowRequest *req, BlockJob *job,
 292                               int64_t sector_num,
 293                               int nb_sectors)
 294 {
 295     BackupBlockJob *backup_job = container_of(job, BackupBlockJob, common);
 296     int64_t sectors_per_cluster = cluster_size_sectors(backup_job);
 297     int64_t start, end;
 298
 299     assert(job->driver->job_type == BLOCK_JOB_TYPE_BACKUP);
 300
 301     start = sector_num / sectors_per_cluster;
 302     end = DIV_ROUND_UP(sector_num + nb_sectors, sectors_per_cluster);
 303     cow_request_begin(req, backup_job, start, end);
 304 }
 305
 306 void backup_cow_request_end(CowRequest *req)
 307 {
 308     cow_request_end(req);
 309 }
 310
 311 static void backup_drain(BlockJob *job)
 312 {
 313     BackupBlockJob *s = container_of(job, BackupBlockJob, common);
 314
 315     /* Need to keep a reference in case blk_drain triggers execution
 316      * of backup_complete...
 317      */
 318     if (s->target) {
 319         BlockBackend *target = s->target;
 320         blk_ref(target);
 321         blk_drain(target);
 322         blk_unref(target);
 323     }
 324 }
 325
 326 static BlockErrorAction backup_error_action(BackupBlockJob *job,
 327                                             bool read, int error)
 328 {
 329     if (read) {
 330         return block_job_error_action(&job->common, job->on_source_error,
 331                                       true, error);
 332     } else {
 333         return block_job_error_action(&job->common, job->on_target_error,
 334                                       false, error);
 335     }
 336 }
 337
 338 typedef struct {
 339     int ret;
 340 } BackupCompleteData;
 341
 342 static void backup_complete(BlockJob *job, void *opaque)
 343 {
 344     BackupCompleteData *data = opaque;
 345
 346     block_job_completed(job, data->ret);
 347     g_free(data);
 348 }
 349
 350 static bool coroutine_fn yield_and_check(BackupBlockJob *job)
 351 {
 352     if (block_job_is_cancelled(&job->common)) {
 353         return true;
 354     }
 355
 356     /* we need to yield so that bdrv_drain_all() returns.
 357      * (without, VM does not reboot)
 358      */
 359     if (job->common.speed) {
 360         uint64_t delay_ns = ratelimit_calculate_delay(&job->limit,
 361                                                       job->sectors_read);
 362         job->sectors_read = 0;
 363         block_job_sleep_ns(&job->common, QEMU_CLOCK_REALTIME, delay_ns);
 364     } else {
 365         block_job_sleep_ns(&job->common, QEMU_CLOCK_REALTIME, 0);
 366     }
 367
 368     if (block_job_is_cancelled(&job->common)) {
 369         return true;
 370     }
 371
 372     return false;
 373 }
 374
 375 static int coroutine_fn backup_run_incremental(BackupBlockJob *job)
 376 {
 377     bool error_is_read;
 378     int ret = 0;
 379     int clusters_per_iter;
 380     uint32_t granularity;
 381     int64_t sector;
 382     int64_t cluster;
 383     int64_t end;
 384     int64_t last_cluster = -1;
 385     int64_t sectors_per_cluster = cluster_size_sectors(job);
 386     BdrvDirtyBitmapIter *dbi;
 387
 388     granularity = bdrv_dirty_bitmap_granularity(job->sync_bitmap);
 389     clusters_per_iter = MAX((granularity / job->cluster_size), 1);
 390     dbi = bdrv_dirty_iter_new(job->sync_bitmap, 0);
 391
 392     /* Find the next dirty sector(s) */
 393     while ((sector = bdrv_dirty_iter_next(dbi)) != -1) {
 394         cluster = sector / sectors_per_cluster;
 395
 396         /* Fake progress updates for any clusters we skipped */
 397         if (cluster != last_cluster + 1) {
 398             job->common.offset += ((cluster - last_cluster - 1) *
 399                                    job->cluster_size);
 400         }
 401
 402         for (end = cluster + clusters_per_iter; cluster < end; cluster++) {
 403             do {
 404                 if (yield_and_check(job)) {
 405                     goto out;
 406                 }
 407                 ret = backup_do_cow(job, cluster * sectors_per_cluster,
 408                                     sectors_per_cluster, &error_is_read,
 409                                     false);
 410                 if ((ret < 0) &&
 411                     backup_error_action(job, error_is_read, -ret) ==
 412                     BLOCK_ERROR_ACTION_REPORT) {
 413                     goto out;
 414                 }
 415             } while (ret < 0);
 416         }
 417
 418         /* If the bitmap granularity is smaller than the backup granularity,
 419          * we need to advance the iterator pointer to the next cluster. */
 420         if (granularity < job->cluster_size) {
 421             bdrv_set_dirty_iter(dbi, cluster * sectors_per_cluster);
 422         }
 423
 424         last_cluster = cluster - 1;
 425     }
 426
 427     /* Play some final catchup with the progress meter */
 428     end = DIV_ROUND_UP(job->common.len, job->cluster_size);
 429     if (last_cluster + 1 < end) {
 430         job->common.offset += ((end - last_cluster - 1) * job->cluster_size);
 431     }
 432
 433 out:
 434     bdrv_dirty_iter_free(dbi);
 435     return ret;
 436 }
 437
 438 static void coroutine_fn backup_run(void *opaque)
 439 {
 440     BackupBlockJob *job = opaque;
 441     BackupCompleteData *data;
 442     BlockDriverState *bs = blk_bs(job->common.blk);
 443     int64_t start, end;
 444     int64_t sectors_per_cluster = cluster_size_sectors(job);
 445     int ret = 0;
 446
 447     QLIST_INIT(&job->inflight_reqs);
 448     qemu_co_rwlock_init(&job->flush_rwlock);
 449
 450     start = 0;
 451     end = DIV_ROUND_UP(job->common.len, job->cluster_size);
 452
 453     job->done_bitmap = bitmap_new(end);
 454
 455     job->before_write.notify = backup_before_write_notify;
 456     bdrv_add_before_write_notifier(bs, &job->before_write);
 457
 458     if (job->sync_mode == MIRROR_SYNC_MODE_NONE) {
 459         while (!block_job_is_cancelled(&job->common)) {
 460             /* Yield until the job is cancelled.  We just let our before_write
 461              * notify callback service CoW requests. */
 462             block_job_yield(&job->common);
 463         }
 464     } else if (job->sync_mode == MIRROR_SYNC_MODE_INCREMENTAL) {
 465         ret = backup_run_incremental(job);
 466     } else {
 467         /* Both FULL and TOP SYNC_MODE's require copying.. */
 468         for (; start < end; start++) {
 469             bool error_is_read;
 470             if (yield_and_check(job)) {
 471                 break;
 472             }
 473
 474             if (job->sync_mode == MIRROR_SYNC_MODE_TOP) {
 475                 int i, n;
 476                 int alloced = 0;
 477
 478                 /* Check to see if these blocks are already in the
 479                  * backing file. */
 480
 481                 for (i = 0; i < sectors_per_cluster;) {
 482                     /* bdrv_is_allocated() only returns true/false based
 483                      * on the first set of sectors it comes across that
 484                      * are are all in the same state.
 485                      * For that reason we must verify each sector in the
 486                      * backup cluster length.  We end up copying more than
 487                      * needed but at some point that is always the case. */
 488                     alloced =
 489                         bdrv_is_allocated(bs,
 490                                 start * sectors_per_cluster + i,
 491                                 sectors_per_cluster - i, &n);
 492                     i += n;
 493
 494                     if (alloced == 1 || n == 0) {
 495                         break;
 496                     }
 497                 }
 498
 499                 /* If the above loop never found any sectors that are in
 500                  * the topmost image, skip this backup. */
 501                 if (alloced == 0) {
 502                     continue;
 503                 }
 504             }
 505             /* FULL sync mode we copy the whole drive. */
 506             ret = backup_do_cow(job, start * sectors_per_cluster,
 507                                 sectors_per_cluster, &error_is_read, false);
 508             if (ret < 0) {
 509                 /* Depending on error action, fail now or retry cluster */
 510                 BlockErrorAction action =
 511                     backup_error_action(job, error_is_read, -ret);
 512                 if (action == BLOCK_ERROR_ACTION_REPORT) {
 513                     break;
 514                 } else {
 515                     start--;
 516                     continue;
 517                 }
 518             }
 519         }
 520     }
 521
 522     notifier_with_return_remove(&job->before_write);
 523
 524     /* wait until pending backup_do_cow() calls have completed */
 525     qemu_co_rwlock_wrlock(&job->flush_rwlock);
 526     qemu_co_rwlock_unlock(&job->flush_rwlock);
 527     g_free(job->done_bitmap);
 528
 529     data = g_malloc(sizeof(*data));
 530     data->ret = ret;
 531     block_job_defer_to_main_loop(&job->common, backup_complete, data);
 532 }
 533
 534 static const BlockJobDriver backup_job_driver = {
 535     .instance_size          = sizeof(BackupBlockJob),
 536     .job_type               = BLOCK_JOB_TYPE_BACKUP,
 537     .start                  = backup_run,
 538     .set_speed              = backup_set_speed,
 539     .commit                 = backup_commit,
 540     .abort                  = backup_abort,
 541     .clean                  = backup_clean,
 542     .attached_aio_context   = backup_attached_aio_context,
 543     .drain                  = backup_drain,
 544 };
 545
 546 BlockJob *backup_job_create(const char *job_id, BlockDriverState *bs,
 547                   BlockDriverState *target, int64_t speed,
 548                   MirrorSyncMode sync_mode, BdrvDirtyBitmap *sync_bitmap,
 549                   bool compress,
 550                   BlockdevOnError on_source_error,
 551                   BlockdevOnError on_target_error,
 552                   int creation_flags,
 553                   BlockCompletionFunc *cb, void *opaque,
 554                   BlockJobTxn *txn, Error **errp)
 555 {
 556     int64_t len;
 557     BlockDriverInfo bdi;
 558     BackupBlockJob *job = NULL;
 559     int ret;
 560
 561     assert(bs);
 562     assert(target);
 563
 564     if (bs == target) {
 565         error_setg(errp, "Source and target cannot be the same");
 566         return NULL;
 567     }
 568
 569     if (!bdrv_is_inserted(bs)) {
 570         error_setg(errp, "Device is not inserted: %s",
 571                    bdrv_get_device_name(bs));
 572         return NULL;
 573     }
 574
 575     if (!bdrv_is_inserted(target)) {
 576         error_setg(errp, "Device is not inserted: %s",
 577                    bdrv_get_device_name(target));
 578         return NULL;
 579     }
 580
 581     if (compress && target->drv->bdrv_co_pwritev_compressed == NULL) {
 582         error_setg(errp, "Compression is not supported for this drive %s",
 583                    bdrv_get_device_name(target));
 584         return NULL;
 585     }
 586
 587     if (bdrv_op_is_blocked(bs, BLOCK_OP_TYPE_BACKUP_SOURCE, errp)) {
 588         return NULL;
 589     }
 590
 591     if (bdrv_op_is_blocked(target, BLOCK_OP_TYPE_BACKUP_TARGET, errp)) {
 592         return NULL;
 593     }
 594
 595     if (sync_mode == MIRROR_SYNC_MODE_INCREMENTAL) {
 596         if (!sync_bitmap) {
 597             error_setg(errp, "must provide a valid bitmap name for "
 598                              "\"incremental\" sync mode");
 599             return NULL;
 600         }
 601
 602         /* Create a new bitmap, and freeze/disable this one. */
 603         if (bdrv_dirty_bitmap_create_successor(bs, sync_bitmap, errp) < 0) {
 604             return NULL;
 605         }
 606     } else if (sync_bitmap) {
 607         error_setg(errp,
 608                    "a sync_bitmap was provided to backup_run, "
 609                    "but received an incompatible sync_mode (%s)",
 610                    MirrorSyncMode_lookup[sync_mode]);
 611         return NULL;
 612     }
 613
 614     len = bdrv_getlength(bs);
 615     if (len < 0) {
 616         error_setg_errno(errp, -len, "unable to get length for '%s'",
 617                          bdrv_get_device_name(bs));
 618         goto error;
 619     }
 620
 621     job = block_job_create(job_id, &backup_job_driver, bs, speed,
 622                            creation_flags, cb, opaque, errp);
 623     if (!job) {
 624         goto error;
 625     }
 626
 627     job->target = blk_new();
 628     blk_insert_bs(job->target, target);
 629
 630     job->on_source_error = on_source_error;
 631     job->on_target_error = on_target_error;
 632     job->sync_mode = sync_mode;
 633     job->sync_bitmap = sync_mode == MIRROR_SYNC_MODE_INCREMENTAL ?
 634                        sync_bitmap : NULL;
 635     job->compress = compress;
 636
 637     /* If there is no backing file on the target, we cannot rely on COW if our
 638      * backup cluster size is smaller than the target cluster size. Even for
 639      * targets with a backing file, try to avoid COW if possible. */
 640     ret = bdrv_get_info(target, &bdi);
 641     if (ret < 0 && !target->backing) {
 642         error_setg_errno(errp, -ret,
 643             "Couldn't determine the cluster size of the target image, "
 644             "which has no backing file");
 645         error_append_hint(errp,
 646             "Aborting, since this may create an unusable destination image\n");
 647         goto error;
 648     } else if (ret < 0 && target->backing) {
 649         /* Not fatal; just trudge on ahead. */
 650         job->cluster_size = BACKUP_CLUSTER_SIZE_DEFAULT;
 651     } else {
 652         job->cluster_size = MAX(BACKUP_CLUSTER_SIZE_DEFAULT, bdi.cluster_size);
 653     }
 654
 655     block_job_add_bdrv(&job->common, target);
 656     job->common.len = len;
 657     block_job_txn_add_job(txn, &job->common);
 658
 659     return &job->common;
 660
 661  error:
 662     if (sync_bitmap) {
 663         bdrv_reclaim_dirty_bitmap(bs, sync_bitmap, NULL);
 664     }
 665     if (job) {
 666         backup_clean(&job->common);
 667         block_job_unref(&job->common);
 668     }
 669
 670     return NULL;
 671 }