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 BackupBlockJob {
  32     BlockJob common;
  33     BlockBackend *target;
  34     /* bitmap for sync=incremental */
  35     BdrvDirtyBitmap *sync_bitmap;
  36     MirrorSyncMode sync_mode;
  37     BlockdevOnError on_source_error;
  38     BlockdevOnError on_target_error;
  39     CoRwlock flush_rwlock;
  40     uint64_t len;
  41     uint64_t bytes_read;
  42     int64_t cluster_size;
  43     bool compress;
  44     NotifierWithReturn before_write;
  45     QLIST_HEAD(, CowRequest) inflight_reqs;
  46
  47     HBitmap *copy_bitmap;
  48     bool use_copy_range;
  49     int64_t copy_range_size;
  50
  51     bool serialize_target_writes;
  52 } BackupBlockJob;
  53
  54 static const BlockJobDriver backup_job_driver;
  55
  56 /* See if in-flight requests overlap and wait for them to complete */
  57 static void coroutine_fn wait_for_overlapping_requests(BackupBlockJob *job,
  58                                                        int64_t start,
  59                                                        int64_t end)
  60 {
  61     CowRequest *req;
  62     bool retry;
  63
  64     do {
  65         retry = false;
  66         QLIST_FOREACH(req, &job->inflight_reqs, list) {
  67             if (end > req->start_byte && start < req->end_byte) {
  68                 qemu_co_queue_wait(&req->wait_queue, NULL);
  69                 retry = true;
  70                 break;
  71             }
  72         }
  73     } while (retry);
  74 }
  75
  76 /* Keep track of an in-flight request */
  77 static void cow_request_begin(CowRequest *req, BackupBlockJob *job,
  78                               int64_t start, int64_t end)
  79 {
  80     req->start_byte = start;
  81     req->end_byte = end;
  82     qemu_co_queue_init(&req->wait_queue);
  83     QLIST_INSERT_HEAD(&job->inflight_reqs, req, list);
  84 }
  85
  86 /* Forget about a completed request */
  87 static void cow_request_end(CowRequest *req)
  88 {
  89     QLIST_REMOVE(req, list);
  90     qemu_co_queue_restart_all(&req->wait_queue);
  91 }
  92
  93 /* Copy range to target with a bounce buffer and return the bytes copied. If
  94  * error occurred, return a negative error number */
  95 static int coroutine_fn backup_cow_with_bounce_buffer(BackupBlockJob *job,
  96                                                       int64_t start,
  97                                                       int64_t end,
  98                                                       bool is_write_notifier,
  99                                                       bool *error_is_read,
 100                                                       void **bounce_buffer)
 101 {
 102     int ret;
 103     struct iovec iov;
 104     QEMUIOVector qiov;
 105     BlockBackend *blk = job->common.blk;
 106     int nbytes;
 107     int read_flags = is_write_notifier ? BDRV_REQ_NO_SERIALISING : 0;
 108     int write_flags = job->serialize_target_writes ? BDRV_REQ_SERIALISING : 0;
 109
 110     hbitmap_reset(job->copy_bitmap, start / job->cluster_size, 1);
 111     nbytes = MIN(job->cluster_size, job->len - start);
 112     if (!*bounce_buffer) {
 113         *bounce_buffer = blk_blockalign(blk, job->cluster_size);
 114     }
 115     iov.iov_base = *bounce_buffer;
 116     iov.iov_len = nbytes;
 117     qemu_iovec_init_external(&qiov, &iov, 1);
 118
 119     ret = blk_co_preadv(blk, start, qiov.size, &qiov, read_flags);
 120     if (ret < 0) {
 121         trace_backup_do_cow_read_fail(job, start, ret);
 122         if (error_is_read) {
 123             *error_is_read = true;
 124         }
 125         goto fail;
 126     }
 127
 128     if (qemu_iovec_is_zero(&qiov)) {
 129         ret = blk_co_pwrite_zeroes(job->target, start,
 130                                    qiov.size, write_flags | BDRV_REQ_MAY_UNMAP);
 131     } else {
 132         ret = blk_co_pwritev(job->target, start,
 133                              qiov.size, &qiov, write_flags |
 134                              (job->compress ? BDRV_REQ_WRITE_COMPRESSED : 0));
 135     }
 136     if (ret < 0) {
 137         trace_backup_do_cow_write_fail(job, start, ret);
 138         if (error_is_read) {
 139             *error_is_read = false;
 140         }
 141         goto fail;
 142     }
 143
 144     return nbytes;
 145 fail:
 146     hbitmap_set(job->copy_bitmap, start / job->cluster_size, 1);
 147     return ret;
 148
 149 }
 150
 151 /* Copy range to target and return the bytes copied. If error occurred, return a
 152  * negative error number. */
 153 static int coroutine_fn backup_cow_with_offload(BackupBlockJob *job,
 154                                                 int64_t start,
 155                                                 int64_t end,
 156                                                 bool is_write_notifier)
 157 {
 158     int ret;
 159     int nr_clusters;
 160     BlockBackend *blk = job->common.blk;
 161     int nbytes;
 162     int read_flags = is_write_notifier ? BDRV_REQ_NO_SERIALISING : 0;
 163     int write_flags = job->serialize_target_writes ? BDRV_REQ_SERIALISING : 0;
 164
 165     assert(QEMU_IS_ALIGNED(job->copy_range_size, job->cluster_size));
 166     nbytes = MIN(job->copy_range_size, end - start);
 167     nr_clusters = DIV_ROUND_UP(nbytes, job->cluster_size);
 168     hbitmap_reset(job->copy_bitmap, start / job->cluster_size,
 169                   nr_clusters);
 170     ret = blk_co_copy_range(blk, start, job->target, start, nbytes,
 171                             read_flags, write_flags);
 172     if (ret < 0) {
 173         trace_backup_do_cow_copy_range_fail(job, start, ret);
 174         hbitmap_set(job->copy_bitmap, start / job->cluster_size,
 175                     nr_clusters);
 176         return ret;
 177     }
 178
 179     return nbytes;
 180 }
 181
 182 static int coroutine_fn backup_do_cow(BackupBlockJob *job,
 183                                       int64_t offset, uint64_t bytes,
 184                                       bool *error_is_read,
 185                                       bool is_write_notifier)
 186 {
 187     CowRequest cow_request;
 188     int ret = 0;
 189     int64_t start, end; /* bytes */
 190     void *bounce_buffer = NULL;
 191
 192     qemu_co_rwlock_rdlock(&job->flush_rwlock);
 193
 194     start = QEMU_ALIGN_DOWN(offset, job->cluster_size);
 195     end = QEMU_ALIGN_UP(bytes + offset, job->cluster_size);
 196
 197     trace_backup_do_cow_enter(job, start, offset, bytes);
 198
 199     wait_for_overlapping_requests(job, start, end);
 200     cow_request_begin(&cow_request, job, start, end);
 201
 202     while (start < end) {
 203         if (!hbitmap_get(job->copy_bitmap, start / job->cluster_size)) {
 204             trace_backup_do_cow_skip(job, start);
 205             start += job->cluster_size;
 206             continue; /* already copied */
 207         }
 208
 209         trace_backup_do_cow_process(job, start);
 210
 211         if (job->use_copy_range) {
 212             ret = backup_cow_with_offload(job, start, end, is_write_notifier);
 213             if (ret < 0) {
 214                 job->use_copy_range = false;
 215             }
 216         }
 217         if (!job->use_copy_range) {
 218             ret = backup_cow_with_bounce_buffer(job, start, end, is_write_notifier,
 219                                                 error_is_read, &bounce_buffer);
 220         }
 221         if (ret < 0) {
 222             break;
 223         }
 224
 225         /* Publish progress, guest I/O counts as progress too.  Note that the
 226          * offset field is an opaque progress value, it is not a disk offset.
 227          */
 228         start += ret;
 229         job->bytes_read += ret;
 230         job_progress_update(&job->common.job, ret);
 231         ret = 0;
 232     }
 233
 234     if (bounce_buffer) {
 235         qemu_vfree(bounce_buffer);
 236     }
 237
 238     cow_request_end(&cow_request);
 239
 240     trace_backup_do_cow_return(job, offset, bytes, ret);
 241
 242     qemu_co_rwlock_unlock(&job->flush_rwlock);
 243
 244     return ret;
 245 }
 246
 247 static int coroutine_fn backup_before_write_notify(
 248         NotifierWithReturn *notifier,
 249         void *opaque)
 250 {
 251     BackupBlockJob *job = container_of(notifier, BackupBlockJob, before_write);
 252     BdrvTrackedRequest *req = opaque;
 253
 254     assert(req->bs == blk_bs(job->common.blk));
 255     assert(QEMU_IS_ALIGNED(req->offset, BDRV_SECTOR_SIZE));
 256     assert(QEMU_IS_ALIGNED(req->bytes, BDRV_SECTOR_SIZE));
 257
 258     return backup_do_cow(job, req->offset, req->bytes, NULL, true);
 259 }
 260
 261 static void backup_cleanup_sync_bitmap(BackupBlockJob *job, int ret)
 262 {
 263     BdrvDirtyBitmap *bm;
 264     BlockDriverState *bs = blk_bs(job->common.blk);
 265
 266     if (ret < 0) {
 267         /* Merge the successor back into the parent, delete nothing. */
 268         bm = bdrv_reclaim_dirty_bitmap(bs, job->sync_bitmap, NULL);
 269         assert(bm);
 270     } else {
 271         /* Everything is fine, delete this bitmap and install the backup. */
 272         bm = bdrv_dirty_bitmap_abdicate(bs, job->sync_bitmap, NULL);
 273         assert(bm);
 274     }
 275 }
 276
 277 static void backup_commit(Job *job)
 278 {
 279     BackupBlockJob *s = container_of(job, BackupBlockJob, common.job);
 280     if (s->sync_bitmap) {
 281         backup_cleanup_sync_bitmap(s, 0);
 282     }
 283 }
 284
 285 static void backup_abort(Job *job)
 286 {
 287     BackupBlockJob *s = container_of(job, BackupBlockJob, common.job);
 288     if (s->sync_bitmap) {
 289         backup_cleanup_sync_bitmap(s, -1);
 290     }
 291 }
 292
 293 static void backup_clean(Job *job)
 294 {
 295     BackupBlockJob *s = container_of(job, BackupBlockJob, common.job);
 296     assert(s->target);
 297     blk_unref(s->target);
 298     s->target = NULL;
 299 }
 300
 301 static void backup_attached_aio_context(BlockJob *job, AioContext *aio_context)
 302 {
 303     BackupBlockJob *s = container_of(job, BackupBlockJob, common);
 304
 305     blk_set_aio_context(s->target, aio_context);
 306 }
 307
 308 void backup_do_checkpoint(BlockJob *job, Error **errp)
 309 {
 310     BackupBlockJob *backup_job = container_of(job, BackupBlockJob, common);
 311     int64_t len;
 312
 313     assert(block_job_driver(job) == &backup_job_driver);
 314
 315     if (backup_job->sync_mode != MIRROR_SYNC_MODE_NONE) {
 316         error_setg(errp, "The backup job only supports block checkpoint in"
 317                    " sync=none mode");
 318         return;
 319     }
 320
 321     len = DIV_ROUND_UP(backup_job->len, backup_job->cluster_size);
 322     hbitmap_set(backup_job->copy_bitmap, 0, len);
 323 }
 324
 325 void backup_wait_for_overlapping_requests(BlockJob *job, int64_t offset,
 326                                           uint64_t bytes)
 327 {
 328     BackupBlockJob *backup_job = container_of(job, BackupBlockJob, common);
 329     int64_t start, end;
 330
 331     assert(block_job_driver(job) == &backup_job_driver);
 332
 333     start = QEMU_ALIGN_DOWN(offset, backup_job->cluster_size);
 334     end = QEMU_ALIGN_UP(offset + bytes, backup_job->cluster_size);
 335     wait_for_overlapping_requests(backup_job, start, end);
 336 }
 337
 338 void backup_cow_request_begin(CowRequest *req, BlockJob *job,
 339                               int64_t offset, uint64_t bytes)
 340 {
 341     BackupBlockJob *backup_job = container_of(job, BackupBlockJob, common);
 342     int64_t start, end;
 343
 344     assert(block_job_driver(job) == &backup_job_driver);
 345
 346     start = QEMU_ALIGN_DOWN(offset, backup_job->cluster_size);
 347     end = QEMU_ALIGN_UP(offset + bytes, backup_job->cluster_size);
 348     cow_request_begin(req, backup_job, start, end);
 349 }
 350
 351 void backup_cow_request_end(CowRequest *req)
 352 {
 353     cow_request_end(req);
 354 }
 355
 356 static void backup_drain(BlockJob *job)
 357 {
 358     BackupBlockJob *s = container_of(job, BackupBlockJob, common);
 359
 360     /* Need to keep a reference in case blk_drain triggers execution
 361      * of backup_complete...
 362      */
 363     if (s->target) {
 364         BlockBackend *target = s->target;
 365         blk_ref(target);
 366         blk_drain(target);
 367         blk_unref(target);
 368     }
 369 }
 370
 371 static BlockErrorAction backup_error_action(BackupBlockJob *job,
 372                                             bool read, int error)
 373 {
 374     if (read) {
 375         return block_job_error_action(&job->common, job->on_source_error,
 376                                       true, error);
 377     } else {
 378         return block_job_error_action(&job->common, job->on_target_error,
 379                                       false, error);
 380     }
 381 }
 382
 383 typedef struct {
 384     int ret;
 385 } BackupCompleteData;
 386
 387 static void backup_complete(Job *job, void *opaque)
 388 {
 389     BackupCompleteData *data = opaque;
 390
 391     job_completed(job, data->ret, NULL);
 392     g_free(data);
 393 }
 394
 395 static bool coroutine_fn yield_and_check(BackupBlockJob *job)
 396 {
 397     uint64_t delay_ns;
 398
 399     if (job_is_cancelled(&job->common.job)) {
 400         return true;
 401     }
 402
 403     /* We need to yield even for delay_ns = 0 so that bdrv_drain_all() can
 404      * return. Without a yield, the VM would not reboot. */
 405     delay_ns = block_job_ratelimit_get_delay(&job->common, job->bytes_read);
 406     job->bytes_read = 0;
 407     job_sleep_ns(&job->common.job, delay_ns);
 408
 409     if (job_is_cancelled(&job->common.job)) {
 410         return true;
 411     }
 412
 413     return false;
 414 }
 415
 416 static int coroutine_fn backup_run_incremental(BackupBlockJob *job)
 417 {
 418     int ret;
 419     bool error_is_read;
 420     int64_t cluster;
 421     HBitmapIter hbi;
 422
 423     hbitmap_iter_init(&hbi, job->copy_bitmap, 0);
 424     while ((cluster = hbitmap_iter_next(&hbi, true)) != -1) {
 425         do {
 426             if (yield_and_check(job)) {
 427                 return 0;
 428             }
 429             ret = backup_do_cow(job, cluster * job->cluster_size,
 430                                 job->cluster_size, &error_is_read, false);
 431             if (ret < 0 && backup_error_action(job, error_is_read, -ret) ==
 432                            BLOCK_ERROR_ACTION_REPORT)
 433             {
 434                 return ret;
 435             }
 436         } while (ret < 0);
 437     }
 438
 439     return 0;
 440 }
 441
 442 /* init copy_bitmap from sync_bitmap */
 443 static void backup_incremental_init_copy_bitmap(BackupBlockJob *job)
 444 {
 445     BdrvDirtyBitmapIter *dbi;
 446     int64_t offset;
 447     int64_t end = DIV_ROUND_UP(bdrv_dirty_bitmap_size(job->sync_bitmap),
 448                                job->cluster_size);
 449
 450     dbi = bdrv_dirty_iter_new(job->sync_bitmap);
 451     while ((offset = bdrv_dirty_iter_next(dbi)) != -1) {
 452         int64_t cluster = offset / job->cluster_size;
 453         int64_t next_cluster;
 454
 455         offset += bdrv_dirty_bitmap_granularity(job->sync_bitmap);
 456         if (offset >= bdrv_dirty_bitmap_size(job->sync_bitmap)) {
 457             hbitmap_set(job->copy_bitmap, cluster, end - cluster);
 458             break;
 459         }
 460
 461         offset = bdrv_dirty_bitmap_next_zero(job->sync_bitmap, offset);
 462         if (offset == -1) {
 463             hbitmap_set(job->copy_bitmap, cluster, end - cluster);
 464             break;
 465         }
 466
 467         next_cluster = DIV_ROUND_UP(offset, job->cluster_size);
 468         hbitmap_set(job->copy_bitmap, cluster, next_cluster - cluster);
 469         if (next_cluster >= end) {
 470             break;
 471         }
 472
 473         bdrv_set_dirty_iter(dbi, next_cluster * job->cluster_size);
 474     }
 475
 476     /* TODO job_progress_set_remaining() would make more sense */
 477     job_progress_update(&job->common.job,
 478         job->len - hbitmap_count(job->copy_bitmap) * job->cluster_size);
 479
 480     bdrv_dirty_iter_free(dbi);
 481 }
 482
 483 static void coroutine_fn backup_run(void *opaque)
 484 {
 485     BackupBlockJob *job = opaque;
 486     BackupCompleteData *data;
 487     BlockDriverState *bs = blk_bs(job->common.blk);
 488     int64_t offset, nb_clusters;
 489     int ret = 0;
 490
 491     QLIST_INIT(&job->inflight_reqs);
 492     qemu_co_rwlock_init(&job->flush_rwlock);
 493
 494     nb_clusters = DIV_ROUND_UP(job->len, job->cluster_size);
 495     job_progress_set_remaining(&job->common.job, job->len);
 496
 497     job->copy_bitmap = hbitmap_alloc(nb_clusters, 0);
 498     if (job->sync_mode == MIRROR_SYNC_MODE_INCREMENTAL) {
 499         backup_incremental_init_copy_bitmap(job);
 500     } else {
 501         hbitmap_set(job->copy_bitmap, 0, nb_clusters);
 502     }
 503
 504
 505     job->before_write.notify = backup_before_write_notify;
 506     bdrv_add_before_write_notifier(bs, &job->before_write);
 507
 508     if (job->sync_mode == MIRROR_SYNC_MODE_NONE) {
 509         /* All bits are set in copy_bitmap to allow any cluster to be copied.
 510          * This does not actually require them to be copied. */
 511         while (!job_is_cancelled(&job->common.job)) {
 512             /* Yield until the job is cancelled.  We just let our before_write
 513              * notify callback service CoW requests. */
 514             job_yield(&job->common.job);
 515         }
 516     } else if (job->sync_mode == MIRROR_SYNC_MODE_INCREMENTAL) {
 517         ret = backup_run_incremental(job);
 518     } else {
 519         /* Both FULL and TOP SYNC_MODE's require copying.. */
 520         for (offset = 0; offset < job->len;
 521              offset += job->cluster_size) {
 522             bool error_is_read;
 523             int alloced = 0;
 524
 525             if (yield_and_check(job)) {
 526                 break;
 527             }
 528
 529             if (job->sync_mode == MIRROR_SYNC_MODE_TOP) {
 530                 int i;
 531                 int64_t n;
 532
 533                 /* Check to see if these blocks are already in the
 534                  * backing file. */
 535
 536                 for (i = 0; i < job->cluster_size;) {
 537                     /* bdrv_is_allocated() only returns true/false based
 538                      * on the first set of sectors it comes across that
 539                      * are are all in the same state.
 540                      * For that reason we must verify each sector in the
 541                      * backup cluster length.  We end up copying more than
 542                      * needed but at some point that is always the case. */
 543                     alloced =
 544                         bdrv_is_allocated(bs, offset + i,
 545                                           job->cluster_size - i, &n);
 546                     i += n;
 547
 548                     if (alloced || n == 0) {
 549                         break;
 550                     }
 551                 }
 552
 553                 /* If the above loop never found any sectors that are in
 554                  * the topmost image, skip this backup. */
 555                 if (alloced == 0) {
 556                     continue;
 557                 }
 558             }
 559             /* FULL sync mode we copy the whole drive. */
 560             if (alloced < 0) {
 561                 ret = alloced;
 562             } else {
 563                 ret = backup_do_cow(job, offset, job->cluster_size,
 564                                     &error_is_read, false);
 565             }
 566             if (ret < 0) {
 567                 /* Depending on error action, fail now or retry cluster */
 568                 BlockErrorAction action =
 569                     backup_error_action(job, error_is_read, -ret);
 570                 if (action == BLOCK_ERROR_ACTION_REPORT) {
 571                     break;
 572                 } else {
 573                     offset -= job->cluster_size;
 574                     continue;
 575                 }
 576             }
 577         }
 578     }
 579
 580     notifier_with_return_remove(&job->before_write);
 581
 582     /* wait until pending backup_do_cow() calls have completed */
 583     qemu_co_rwlock_wrlock(&job->flush_rwlock);
 584     qemu_co_rwlock_unlock(&job->flush_rwlock);
 585     hbitmap_free(job->copy_bitmap);
 586
 587     data = g_malloc(sizeof(*data));
 588     data->ret = ret;
 589     job_defer_to_main_loop(&job->common.job, backup_complete, data);
 590 }
 591
 592 static const BlockJobDriver backup_job_driver = {
 593     .job_driver = {
 594         .instance_size          = sizeof(BackupBlockJob),
 595         .job_type               = JOB_TYPE_BACKUP,
 596         .free                   = block_job_free,
 597         .user_resume            = block_job_user_resume,
 598         .drain                  = block_job_drain,
 599         .start                  = backup_run,
 600         .commit                 = backup_commit,
 601         .abort                  = backup_abort,
 602         .clean                  = backup_clean,
 603     },
 604     .attached_aio_context   = backup_attached_aio_context,
 605     .drain                  = backup_drain,
 606 };
 607
 608 BlockJob *backup_job_create(const char *job_id, BlockDriverState *bs,
 609                   BlockDriverState *target, int64_t speed,
 610                   MirrorSyncMode sync_mode, BdrvDirtyBitmap *sync_bitmap,
 611                   bool compress,
 612                   BlockdevOnError on_source_error,
 613                   BlockdevOnError on_target_error,
 614                   int creation_flags,
 615                   BlockCompletionFunc *cb, void *opaque,
 616                   JobTxn *txn, Error **errp)
 617 {
 618     int64_t len;
 619     BlockDriverInfo bdi;
 620     BackupBlockJob *job = NULL;
 621     int ret;
 622
 623     assert(bs);
 624     assert(target);
 625
 626     if (bs == target) {
 627         error_setg(errp, "Source and target cannot be the same");
 628         return NULL;
 629     }
 630
 631     if (!bdrv_is_inserted(bs)) {
 632         error_setg(errp, "Device is not inserted: %s",
 633                    bdrv_get_device_name(bs));
 634         return NULL;
 635     }
 636
 637     if (!bdrv_is_inserted(target)) {
 638         error_setg(errp, "Device is not inserted: %s",
 639                    bdrv_get_device_name(target));
 640         return NULL;
 641     }
 642
 643     if (compress && target->drv->bdrv_co_pwritev_compressed == NULL) {
 644         error_setg(errp, "Compression is not supported for this drive %s",
 645                    bdrv_get_device_name(target));
 646         return NULL;
 647     }
 648
 649     if (bdrv_op_is_blocked(bs, BLOCK_OP_TYPE_BACKUP_SOURCE, errp)) {
 650         return NULL;
 651     }
 652
 653     if (bdrv_op_is_blocked(target, BLOCK_OP_TYPE_BACKUP_TARGET, errp)) {
 654         return NULL;
 655     }
 656
 657     if (sync_mode == MIRROR_SYNC_MODE_INCREMENTAL) {
 658         if (!sync_bitmap) {
 659             error_setg(errp, "must provide a valid bitmap name for "
 660                              "\"incremental\" sync mode");
 661             return NULL;
 662         }
 663
 664         /* Create a new bitmap, and freeze/disable this one. */
 665         if (bdrv_dirty_bitmap_create_successor(bs, sync_bitmap, errp) < 0) {
 666             return NULL;
 667         }
 668     } else if (sync_bitmap) {
 669         error_setg(errp,
 670                    "a sync_bitmap was provided to backup_run, "
 671                    "but received an incompatible sync_mode (%s)",
 672                    MirrorSyncMode_str(sync_mode));
 673         return NULL;
 674     }
 675
 676     len = bdrv_getlength(bs);
 677     if (len < 0) {
 678         error_setg_errno(errp, -len, "unable to get length for '%s'",
 679                          bdrv_get_device_name(bs));
 680         goto error;
 681     }
 682
 683     /* job->len is fixed, so we can't allow resize */
 684     job = block_job_create(job_id, &backup_job_driver, txn, bs,
 685                            BLK_PERM_CONSISTENT_READ,
 686                            BLK_PERM_CONSISTENT_READ | BLK_PERM_WRITE |
 687                            BLK_PERM_WRITE_UNCHANGED | BLK_PERM_GRAPH_MOD,
 688                            speed, creation_flags, cb, opaque, errp);
 689     if (!job) {
 690         goto error;
 691     }
 692
 693     /* The target must match the source in size, so no resize here either */
 694     job->target = blk_new(BLK_PERM_WRITE,
 695                           BLK_PERM_CONSISTENT_READ | BLK_PERM_WRITE |
 696                           BLK_PERM_WRITE_UNCHANGED | BLK_PERM_GRAPH_MOD);
 697     ret = blk_insert_bs(job->target, target, errp);
 698     if (ret < 0) {
 699         goto error;
 700     }
 701
 702     job->on_source_error = on_source_error;
 703     job->on_target_error = on_target_error;
 704     job->sync_mode = sync_mode;
 705     job->sync_bitmap = sync_mode == MIRROR_SYNC_MODE_INCREMENTAL ?
 706                        sync_bitmap : NULL;
 707     job->compress = compress;
 708
 709     /* Detect image-fleecing (and similar) schemes */
 710     job->serialize_target_writes = bdrv_chain_contains(target, bs);
 711
 712     /* If there is no backing file on the target, we cannot rely on COW if our
 713      * backup cluster size is smaller than the target cluster size. Even for
 714      * targets with a backing file, try to avoid COW if possible. */
 715     ret = bdrv_get_info(target, &bdi);
 716     if (ret == -ENOTSUP && !target->backing) {
 717         /* Cluster size is not defined */
 718         warn_report("The target block device doesn't provide "
 719                     "information about the block size and it doesn't have a "
 720                     "backing file. The default block size of %u bytes is "
 721                     "used. If the actual block size of the target exceeds "
 722                     "this default, the backup may be unusable",
 723                     BACKUP_CLUSTER_SIZE_DEFAULT);
 724         job->cluster_size = BACKUP_CLUSTER_SIZE_DEFAULT;
 725     } else if (ret < 0 && !target->backing) {
 726         error_setg_errno(errp, -ret,
 727             "Couldn't determine the cluster size of the target image, "
 728             "which has no backing file");
 729         error_append_hint(errp,
 730             "Aborting, since this may create an unusable destination image\n");
 731         goto error;
 732     } else if (ret < 0 && target->backing) {
 733         /* Not fatal; just trudge on ahead. */
 734         job->cluster_size = BACKUP_CLUSTER_SIZE_DEFAULT;
 735     } else {
 736         job->cluster_size = MAX(BACKUP_CLUSTER_SIZE_DEFAULT, bdi.cluster_size);
 737     }
 738     job->use_copy_range = true;
 739     job->copy_range_size = MIN_NON_ZERO(blk_get_max_transfer(job->common.blk),
 740                                         blk_get_max_transfer(job->target));
 741     job->copy_range_size = MAX(job->cluster_size,
 742                                QEMU_ALIGN_UP(job->copy_range_size,
 743                                              job->cluster_size));
 744
 745     /* Required permissions are already taken with target's blk_new() */
 746     block_job_add_bdrv(&job->common, "target", target, 0, BLK_PERM_ALL,
 747                        &error_abort);
 748     job->len = len;
 749
 750     return &job->common;
 751
 752  error:
 753     if (sync_bitmap) {
 754         bdrv_reclaim_dirty_bitmap(bs, sync_bitmap, NULL);
 755     }
 756     if (job) {
 757         backup_clean(&job->common.job);
 758         job_early_fail(&job->common.job);
 759     }
 760
 761     return NULL;
 762 }