block/mirror.c

   1 /*
   2  * Image mirroring
   3  *
   4  * Copyright Red Hat, Inc. 2012
   5  *
   6  * Authors:
   7  *  Paolo Bonzini  <pbonzini@redhat.com>
   8  *
   9  * This work is licensed under the terms of the GNU LGPL, version 2 or later.
  10  * See the COPYING.LIB file in the top-level directory.
  11  *
  12  */
  13
  14 #include "trace.h"
  15 #include "block/blockjob.h"
  16 #include "block/block_int.h"
  17 #include "qemu/ratelimit.h"
  18 #include "qemu/bitmap.h"
  19
  20 #define SLICE_TIME    100000000ULL /* ns */
  21 #define MAX_IN_FLIGHT 16
  22
  23 /* The mirroring buffer is a list of granularity-sized chunks.
  24  * Free chunks are organized in a list.
  25  */
  26 typedef struct MirrorBuffer {
  27     QSIMPLEQ_ENTRY(MirrorBuffer) next;
  28 } MirrorBuffer;
  29
  30 typedef struct MirrorBlockJob {
  31     BlockJob common;
  32     RateLimit limit;
  33     BlockDriverState *target;
  34     BlockDriverState *base;
  35     bool is_none_mode;
  36     BlockdevOnError on_source_error, on_target_error;
  37     bool synced;
  38     bool should_complete;
  39     int64_t sector_num;
  40     int64_t granularity;
  41     size_t buf_size;
  42     unsigned long *cow_bitmap;
  43     BdrvDirtyBitmap *dirty_bitmap;
  44     HBitmapIter hbi;
  45     uint8_t *buf;
  46     QSIMPLEQ_HEAD(, MirrorBuffer) buf_free;
  47     int buf_free_count;
  48
  49     unsigned long *in_flight_bitmap;
  50     int in_flight;
  51     int ret;
  52 } MirrorBlockJob;
  53
  54 typedef struct MirrorOp {
  55     MirrorBlockJob *s;
  56     QEMUIOVector qiov;
  57     int64_t sector_num;
  58     int nb_sectors;
  59 } MirrorOp;
  60
  61 static BlockErrorAction mirror_error_action(MirrorBlockJob *s, bool read,
  62                                             int error)
  63 {
  64     s->synced = false;
  65     if (read) {
  66         return block_job_error_action(&s->common, s->common.bs,
  67                                       s->on_source_error, true, error);
  68     } else {
  69         return block_job_error_action(&s->common, s->target,
  70                                       s->on_target_error, false, error);
  71     }
  72 }
  73
  74 static void mirror_iteration_done(MirrorOp *op, int ret)
  75 {
  76     MirrorBlockJob *s = op->s;
  77     struct iovec *iov;
  78     int64_t chunk_num;
  79     int i, nb_chunks, sectors_per_chunk;
  80
  81     trace_mirror_iteration_done(s, op->sector_num, op->nb_sectors, ret);
  82
  83     s->in_flight--;
  84     iov = op->qiov.iov;
  85     for (i = 0; i < op->qiov.niov; i++) {
  86         MirrorBuffer *buf = (MirrorBuffer *) iov[i].iov_base;
  87         QSIMPLEQ_INSERT_TAIL(&s->buf_free, buf, next);
  88         s->buf_free_count++;
  89     }
  90
  91     sectors_per_chunk = s->granularity >> BDRV_SECTOR_BITS;
  92     chunk_num = op->sector_num / sectors_per_chunk;
  93     nb_chunks = op->nb_sectors / sectors_per_chunk;
  94     bitmap_clear(s->in_flight_bitmap, chunk_num, nb_chunks);
  95     if (s->cow_bitmap && ret >= 0) {
  96         bitmap_set(s->cow_bitmap, chunk_num, nb_chunks);
  97     }
  98
  99     qemu_iovec_destroy(&op->qiov);
 100     g_slice_free(MirrorOp, op);
 101     qemu_coroutine_enter(s->common.co, NULL);
 102 }
 103
 104 static void mirror_write_complete(void *opaque, int ret)
 105 {
 106     MirrorOp *op = opaque;
 107     MirrorBlockJob *s = op->s;
 108     if (ret < 0) {
 109         BlockDriverState *source = s->common.bs;
 110         BlockErrorAction action;
 111
 112         bdrv_set_dirty(source, op->sector_num, op->nb_sectors);
 113         action = mirror_error_action(s, false, -ret);
 114         if (action == BDRV_ACTION_REPORT && s->ret >= 0) {
 115             s->ret = ret;
 116         }
 117     }
 118     mirror_iteration_done(op, ret);
 119 }
 120
 121 static void mirror_read_complete(void *opaque, int ret)
 122 {
 123     MirrorOp *op = opaque;
 124     MirrorBlockJob *s = op->s;
 125     if (ret < 0) {
 126         BlockDriverState *source = s->common.bs;
 127         BlockErrorAction action;
 128
 129         bdrv_set_dirty(source, op->sector_num, op->nb_sectors);
 130         action = mirror_error_action(s, true, -ret);
 131         if (action == BDRV_ACTION_REPORT && s->ret >= 0) {
 132             s->ret = ret;
 133         }
 134
 135         mirror_iteration_done(op, ret);
 136         return;
 137     }
 138     bdrv_aio_writev(s->target, op->sector_num, &op->qiov, op->nb_sectors,
 139                     mirror_write_complete, op);
 140 }
 141
 142 static void coroutine_fn mirror_iteration(MirrorBlockJob *s)
 143 {
 144     BlockDriverState *source = s->common.bs;
 145     int nb_sectors, sectors_per_chunk, nb_chunks;
 146     int64_t end, sector_num, next_chunk, next_sector, hbitmap_next_sector;
 147     MirrorOp *op;
 148
 149     s->sector_num = hbitmap_iter_next(&s->hbi);
 150     if (s->sector_num < 0) {
 151         bdrv_dirty_iter_init(source, s->dirty_bitmap, &s->hbi);
 152         s->sector_num = hbitmap_iter_next(&s->hbi);
 153         trace_mirror_restart_iter(s,
 154                                   bdrv_get_dirty_count(source, s->dirty_bitmap));
 155         assert(s->sector_num >= 0);
 156     }
 157
 158     hbitmap_next_sector = s->sector_num;
 159     sector_num = s->sector_num;
 160     sectors_per_chunk = s->granularity >> BDRV_SECTOR_BITS;
 161     end = s->common.len >> BDRV_SECTOR_BITS;
 162
 163     /* Extend the QEMUIOVector to include all adjacent blocks that will
 164      * be copied in this operation.
 165      *
 166      * We have to do this if we have no backing file yet in the destination,
 167      * and the cluster size is very large.  Then we need to do COW ourselves.
 168      * The first time a cluster is copied, copy it entirely.  Note that,
 169      * because both the granularity and the cluster size are powers of two,
 170      * the number of sectors to copy cannot exceed one cluster.
 171      *
 172      * We also want to extend the QEMUIOVector to include more adjacent
 173      * dirty blocks if possible, to limit the number of I/O operations and
 174      * run efficiently even with a small granularity.
 175      */
 176     nb_chunks = 0;
 177     nb_sectors = 0;
 178     next_sector = sector_num;
 179     next_chunk = sector_num / sectors_per_chunk;
 180
 181     /* Wait for I/O to this cluster (from a previous iteration) to be done.  */
 182     while (test_bit(next_chunk, s->in_flight_bitmap)) {
 183         trace_mirror_yield_in_flight(s, sector_num, s->in_flight);
 184         qemu_coroutine_yield();
 185     }
 186
 187     do {
 188         int added_sectors, added_chunks;
 189
 190         if (!bdrv_get_dirty(source, s->dirty_bitmap, next_sector) ||
 191             test_bit(next_chunk, s->in_flight_bitmap)) {
 192             assert(nb_sectors > 0);
 193             break;
 194         }
 195
 196         added_sectors = sectors_per_chunk;
 197         if (s->cow_bitmap && !test_bit(next_chunk, s->cow_bitmap)) {
 198             bdrv_round_to_clusters(s->target,
 199                                    next_sector, added_sectors,
 200                                    &next_sector, &added_sectors);
 201
 202             /* On the first iteration, the rounding may make us copy
 203              * sectors before the first dirty one.
 204              */
 205             if (next_sector < sector_num) {
 206                 assert(nb_sectors == 0);
 207                 sector_num = next_sector;
 208                 next_chunk = next_sector / sectors_per_chunk;
 209             }
 210         }
 211
 212         added_sectors = MIN(added_sectors, end - (sector_num + nb_sectors));
 213         added_chunks = (added_sectors + sectors_per_chunk - 1) / sectors_per_chunk;
 214
 215         /* When doing COW, it may happen that there is not enough space for
 216          * a full cluster.  Wait if that is the case.
 217          */
 218         while (nb_chunks == 0 && s->buf_free_count < added_chunks) {
 219             trace_mirror_yield_buf_busy(s, nb_chunks, s->in_flight);
 220             qemu_coroutine_yield();
 221         }
 222         if (s->buf_free_count < nb_chunks + added_chunks) {
 223             trace_mirror_break_buf_busy(s, nb_chunks, s->in_flight);
 224             break;
 225         }
 226
 227         /* We have enough free space to copy these sectors.  */
 228         bitmap_set(s->in_flight_bitmap, next_chunk, added_chunks);
 229
 230         nb_sectors += added_sectors;
 231         nb_chunks += added_chunks;
 232         next_sector += added_sectors;
 233         next_chunk += added_chunks;
 234     } while (next_sector < end);
 235
 236     /* Allocate a MirrorOp that is used as an AIO callback.  */
 237     op = g_slice_new(MirrorOp);
 238     op->s = s;
 239     op->sector_num = sector_num;
 240     op->nb_sectors = nb_sectors;
 241
 242     /* Now make a QEMUIOVector taking enough granularity-sized chunks
 243      * from s->buf_free.
 244      */
 245     qemu_iovec_init(&op->qiov, nb_chunks);
 246     next_sector = sector_num;
 247     while (nb_chunks-- > 0) {
 248         MirrorBuffer *buf = QSIMPLEQ_FIRST(&s->buf_free);
 249         QSIMPLEQ_REMOVE_HEAD(&s->buf_free, next);
 250         s->buf_free_count--;
 251         qemu_iovec_add(&op->qiov, buf, s->granularity);
 252
 253         /* Advance the HBitmapIter in parallel, so that we do not examine
 254          * the same sector twice.
 255          */
 256         if (next_sector > hbitmap_next_sector
 257             && bdrv_get_dirty(source, s->dirty_bitmap, next_sector)) {
 258             hbitmap_next_sector = hbitmap_iter_next(&s->hbi);
 259         }
 260
 261         next_sector += sectors_per_chunk;
 262     }
 263
 264     bdrv_reset_dirty(source, sector_num, nb_sectors);
 265
 266     /* Copy the dirty cluster.  */
 267     s->in_flight++;
 268     trace_mirror_one_iteration(s, sector_num, nb_sectors);
 269     bdrv_aio_readv(source, sector_num, &op->qiov, nb_sectors,
 270                    mirror_read_complete, op);
 271 }
 272
 273 static void mirror_free_init(MirrorBlockJob *s)
 274 {
 275     int granularity = s->granularity;
 276     size_t buf_size = s->buf_size;
 277     uint8_t *buf = s->buf;
 278
 279     assert(s->buf_free_count == 0);
 280     QSIMPLEQ_INIT(&s->buf_free);
 281     while (buf_size != 0) {
 282         MirrorBuffer *cur = (MirrorBuffer *)buf;
 283         QSIMPLEQ_INSERT_TAIL(&s->buf_free, cur, next);
 284         s->buf_free_count++;
 285         buf_size -= granularity;
 286         buf += granularity;
 287     }
 288 }
 289
 290 static void mirror_drain(MirrorBlockJob *s)
 291 {
 292     while (s->in_flight > 0) {
 293         qemu_coroutine_yield();
 294     }
 295 }
 296
 297 static void coroutine_fn mirror_run(void *opaque)
 298 {
 299     MirrorBlockJob *s = opaque;
 300     BlockDriverState *bs = s->common.bs;
 301     int64_t sector_num, end, sectors_per_chunk, length;
 302     uint64_t last_pause_ns;
 303     BlockDriverInfo bdi;
 304     char backing_filename[1024];
 305     int ret = 0;
 306     int n;
 307
 308     if (block_job_is_cancelled(&s->common)) {
 309         goto immediate_exit;
 310     }
 311
 312     s->common.len = bdrv_getlength(bs);
 313     if (s->common.len <= 0) {
 314         block_job_completed(&s->common, s->common.len);
 315         return;
 316     }
 317
 318     length = (bdrv_getlength(bs) + s->granularity - 1) / s->granularity;
 319     s->in_flight_bitmap = bitmap_new(length);
 320
 321     /* If we have no backing file yet in the destination, we cannot let
 322      * the destination do COW.  Instead, we copy sectors around the
 323      * dirty data if needed.  We need a bitmap to do that.
 324      */
 325     bdrv_get_backing_filename(s->target, backing_filename,
 326                               sizeof(backing_filename));
 327     if (backing_filename[0] && !s->target->backing_hd) {
 328         bdrv_get_info(s->target, &bdi);
 329         if (s->granularity < bdi.cluster_size) {
 330             s->buf_size = MAX(s->buf_size, bdi.cluster_size);
 331             s->cow_bitmap = bitmap_new(length);
 332         }
 333     }
 334
 335     end = s->common.len >> BDRV_SECTOR_BITS;
 336     s->buf = qemu_blockalign(bs, s->buf_size);
 337     sectors_per_chunk = s->granularity >> BDRV_SECTOR_BITS;
 338     mirror_free_init(s);
 339
 340     if (!s->is_none_mode) {
 341         /* First part, loop on the sectors and initialize the dirty bitmap.  */
 342         BlockDriverState *base = s->base;
 343         for (sector_num = 0; sector_num < end; ) {
 344             int64_t next = (sector_num | (sectors_per_chunk - 1)) + 1;
 345             ret = bdrv_is_allocated_above(bs, base,
 346                                           sector_num, next - sector_num, &n);
 347
 348             if (ret < 0) {
 349                 goto immediate_exit;
 350             }
 351
 352             assert(n > 0);
 353             if (ret == 1) {
 354                 bdrv_set_dirty(bs, sector_num, n);
 355                 sector_num = next;
 356             } else {
 357                 sector_num += n;
 358             }
 359         }
 360     }
 361
 362     bdrv_dirty_iter_init(bs, s->dirty_bitmap, &s->hbi);
 363     last_pause_ns = qemu_clock_get_ns(QEMU_CLOCK_REALTIME);
 364     for (;;) {
 365         uint64_t delay_ns;
 366         int64_t cnt;
 367         bool should_complete;
 368
 369         if (s->ret < 0) {
 370             ret = s->ret;
 371             goto immediate_exit;
 372         }
 373
 374         cnt = bdrv_get_dirty_count(bs, s->dirty_bitmap);
 375
 376         /* Note that even when no rate limit is applied we need to yield
 377          * periodically with no pending I/O so that qemu_aio_flush() returns.
 378          * We do so every SLICE_TIME nanoseconds, or when there is an error,
 379          * or when the source is clean, whichever comes first.
 380          */
 381         if (qemu_clock_get_ns(QEMU_CLOCK_REALTIME) - last_pause_ns < SLICE_TIME &&
 382             s->common.iostatus == BLOCK_DEVICE_IO_STATUS_OK) {
 383             if (s->in_flight == MAX_IN_FLIGHT || s->buf_free_count == 0 ||
 384                 (cnt == 0 && s->in_flight > 0)) {
 385                 trace_mirror_yield(s, s->in_flight, s->buf_free_count, cnt);
 386                 qemu_coroutine_yield();
 387                 continue;
 388             } else if (cnt != 0) {
 389                 mirror_iteration(s);
 390                 continue;
 391             }
 392         }
 393
 394         should_complete = false;
 395         if (s->in_flight == 0 && cnt == 0) {
 396             trace_mirror_before_flush(s);
 397             ret = bdrv_flush(s->target);
 398             if (ret < 0) {
 399                 if (mirror_error_action(s, false, -ret) == BDRV_ACTION_REPORT) {
 400                     goto immediate_exit;
 401                 }
 402             } else {
 403                 /* We're out of the streaming phase.  From now on, if the job
 404                  * is cancelled we will actually complete all pending I/O and
 405                  * report completion.  This way, block-job-cancel will leave
 406                  * the target in a consistent state.
 407                  */
 408                 s->common.offset = end * BDRV_SECTOR_SIZE;
 409                 if (!s->synced) {
 410                     block_job_ready(&s->common);
 411                     s->synced = true;
 412                 }
 413
 414                 should_complete = s->should_complete ||
 415                     block_job_is_cancelled(&s->common);
 416                 cnt = bdrv_get_dirty_count(bs, s->dirty_bitmap);
 417             }
 418         }
 419
 420         if (cnt == 0 && should_complete) {
 421             /* The dirty bitmap is not updated while operations are pending.
 422              * If we're about to exit, wait for pending operations before
 423              * calling bdrv_get_dirty_count(bs), or we may exit while the
 424              * source has dirty data to copy!
 425              *
 426              * Note that I/O can be submitted by the guest while
 427              * mirror_populate runs.
 428              */
 429             trace_mirror_before_drain(s, cnt);
 430             bdrv_drain_all();
 431             cnt = bdrv_get_dirty_count(bs, s->dirty_bitmap);
 432         }
 433
 434         ret = 0;
 435         trace_mirror_before_sleep(s, cnt, s->synced);
 436         if (!s->synced) {
 437             /* Publish progress */
 438             s->common.offset = (end - cnt) * BDRV_SECTOR_SIZE;
 439
 440             if (s->common.speed) {
 441                 delay_ns = ratelimit_calculate_delay(&s->limit, sectors_per_chunk);
 442             } else {
 443                 delay_ns = 0;
 444             }
 445
 446             block_job_sleep_ns(&s->common, QEMU_CLOCK_REALTIME, delay_ns);
 447             if (block_job_is_cancelled(&s->common)) {
 448                 break;
 449             }
 450         } else if (!should_complete) {
 451             delay_ns = (s->in_flight == 0 && cnt == 0 ? SLICE_TIME : 0);
 452             block_job_sleep_ns(&s->common, QEMU_CLOCK_REALTIME, delay_ns);
 453         } else if (cnt == 0) {
 454             /* The two disks are in sync.  Exit and report successful
 455              * completion.
 456              */
 457             assert(QLIST_EMPTY(&bs->tracked_requests));
 458             s->common.cancelled = false;
 459             break;
 460         }
 461         last_pause_ns = qemu_clock_get_ns(QEMU_CLOCK_REALTIME);
 462     }
 463
 464 immediate_exit:
 465     if (s->in_flight > 0) {
 466         /* We get here only if something went wrong.  Either the job failed,
 467          * or it was cancelled prematurely so that we do not guarantee that
 468          * the target is a copy of the source.
 469          */
 470         assert(ret < 0 || (!s->synced && block_job_is_cancelled(&s->common)));
 471         mirror_drain(s);
 472     }
 473
 474     assert(s->in_flight == 0);
 475     qemu_vfree(s->buf);
 476     g_free(s->cow_bitmap);
 477     g_free(s->in_flight_bitmap);
 478     bdrv_release_dirty_bitmap(bs, s->dirty_bitmap);
 479     bdrv_iostatus_disable(s->target);
 480     if (s->should_complete && ret == 0) {
 481         if (bdrv_get_flags(s->target) != bdrv_get_flags(s->common.bs)) {
 482             bdrv_reopen(s->target, bdrv_get_flags(s->common.bs), NULL);
 483         }
 484         bdrv_swap(s->target, s->common.bs);
 485         if (s->common.driver->job_type == BLOCK_JOB_TYPE_COMMIT) {
 486             /* drop the bs loop chain formed by the swap: break the loop then
 487              * trigger the unref from the top one */
 488             BlockDriverState *p = s->base->backing_hd;
 489             s->base->backing_hd = NULL;
 490             bdrv_unref(p);
 491         }
 492     }
 493     bdrv_unref(s->target);
 494     block_job_completed(&s->common, ret);
 495 }
 496
 497 static void mirror_set_speed(BlockJob *job, int64_t speed, Error **errp)
 498 {
 499     MirrorBlockJob *s = container_of(job, MirrorBlockJob, common);
 500
 501     if (speed < 0) {
 502         error_set(errp, QERR_INVALID_PARAMETER, "speed");
 503         return;
 504     }
 505     ratelimit_set_speed(&s->limit, speed / BDRV_SECTOR_SIZE, SLICE_TIME);
 506 }
 507
 508 static void mirror_iostatus_reset(BlockJob *job)
 509 {
 510     MirrorBlockJob *s = container_of(job, MirrorBlockJob, common);
 511
 512     bdrv_iostatus_reset(s->target);
 513 }
 514
 515 static void mirror_complete(BlockJob *job, Error **errp)
 516 {
 517     MirrorBlockJob *s = container_of(job, MirrorBlockJob, common);
 518     Error *local_err = NULL;
 519     int ret;
 520
 521     ret = bdrv_open_backing_file(s->target, NULL, &local_err);
 522     if (ret < 0) {
 523         char backing_filename[PATH_MAX];
 524         bdrv_get_full_backing_filename(s->target, backing_filename,
 525                                        sizeof(backing_filename));
 526         error_propagate(errp, local_err);
 527         return;
 528     }
 529     if (!s->synced) {
 530         error_set(errp, QERR_BLOCK_JOB_NOT_READY, job->bs->device_name);
 531         return;
 532     }
 533
 534     s->should_complete = true;
 535     block_job_resume(job);
 536 }
 537
 538 static const BlockJobDriver mirror_job_driver = {
 539     .instance_size = sizeof(MirrorBlockJob),
 540     .job_type      = BLOCK_JOB_TYPE_MIRROR,
 541     .set_speed     = mirror_set_speed,
 542     .iostatus_reset= mirror_iostatus_reset,
 543     .complete      = mirror_complete,
 544 };
 545
 546 static const BlockJobDriver commit_active_job_driver = {
 547     .instance_size = sizeof(MirrorBlockJob),
 548     .job_type      = BLOCK_JOB_TYPE_COMMIT,
 549     .set_speed     = mirror_set_speed,
 550     .iostatus_reset
 551                    = mirror_iostatus_reset,
 552     .complete      = mirror_complete,
 553 };
 554
 555 static void mirror_start_job(BlockDriverState *bs, BlockDriverState *target,
 556                             int64_t speed, int64_t granularity,
 557                             int64_t buf_size,
 558                             BlockdevOnError on_source_error,
 559                             BlockdevOnError on_target_error,
 560                             BlockDriverCompletionFunc *cb,
 561                             void *opaque, Error **errp,
 562                             const BlockJobDriver *driver,
 563                             bool is_none_mode, BlockDriverState *base)
 564 {
 565     MirrorBlockJob *s;
 566
 567     if (granularity == 0) {
 568         /* Choose the default granularity based on the target file's cluster
 569          * size, clamped between 4k and 64k.  */
 570         BlockDriverInfo bdi;
 571         if (bdrv_get_info(target, &bdi) >= 0 && bdi.cluster_size != 0) {
 572             granularity = MAX(4096, bdi.cluster_size);
 573             granularity = MIN(65536, granularity);
 574         } else {
 575             granularity = 65536;
 576         }
 577     }
 578
 579     assert ((granularity & (granularity - 1)) == 0);
 580
 581     if ((on_source_error == BLOCKDEV_ON_ERROR_STOP ||
 582          on_source_error == BLOCKDEV_ON_ERROR_ENOSPC) &&
 583         !bdrv_iostatus_is_enabled(bs)) {
 584         error_set(errp, QERR_INVALID_PARAMETER, "on-source-error");
 585         return;
 586     }
 587
 588
 589     s = block_job_create(driver, bs, speed, cb, opaque, errp);
 590     if (!s) {
 591         return;
 592     }
 593
 594     s->on_source_error = on_source_error;
 595     s->on_target_error = on_target_error;
 596     s->target = target;
 597     s->is_none_mode = is_none_mode;
 598     s->base = base;
 599     s->granularity = granularity;
 600     s->buf_size = MAX(buf_size, granularity);
 601
 602     s->dirty_bitmap = bdrv_create_dirty_bitmap(bs, granularity);
 603     bdrv_set_enable_write_cache(s->target, true);
 604     bdrv_set_on_error(s->target, on_target_error, on_target_error);
 605     bdrv_iostatus_enable(s->target);
 606     s->common.co = qemu_coroutine_create(mirror_run);
 607     trace_mirror_start(bs, s, s->common.co, opaque);
 608     qemu_coroutine_enter(s->common.co, s);
 609 }
 610
 611 void mirror_start(BlockDriverState *bs, BlockDriverState *target,
 612                   int64_t speed, int64_t granularity, int64_t buf_size,
 613                   MirrorSyncMode mode, BlockdevOnError on_source_error,
 614                   BlockdevOnError on_target_error,
 615                   BlockDriverCompletionFunc *cb,
 616                   void *opaque, Error **errp)
 617 {
 618     bool is_none_mode;
 619     BlockDriverState *base;
 620
 621     is_none_mode = mode == MIRROR_SYNC_MODE_NONE;
 622     base = mode == MIRROR_SYNC_MODE_TOP ? bs->backing_hd : NULL;
 623     mirror_start_job(bs, target, speed, granularity, buf_size,
 624                      on_source_error, on_target_error, cb, opaque, errp,
 625                      &mirror_job_driver, is_none_mode, base);
 626 }
 627
 628 void commit_active_start(BlockDriverState *bs, BlockDriverState *base,
 629                          int64_t speed,
 630                          BlockdevOnError on_error,
 631                          BlockDriverCompletionFunc *cb,
 632                          void *opaque, Error **errp)
 633 {
 634     int64_t length, base_length;
 635     int orig_base_flags;
 636     int ret;
 637     Error *local_err = NULL;
 638
 639     orig_base_flags = bdrv_get_flags(base);
 640
 641     if (bdrv_reopen(base, bs->open_flags, errp)) {
 642         return;
 643     }
 644
 645     length = bdrv_getlength(bs);
 646     if (length < 0) {
 647         error_setg_errno(errp, -length,
 648                          "Unable to determine length of %s", bs->filename);
 649         goto error_restore_flags;
 650     }
 651
 652     base_length = bdrv_getlength(base);
 653     if (base_length < 0) {
 654         error_setg_errno(errp, -base_length,
 655                          "Unable to determine length of %s", base->filename);
 656         goto error_restore_flags;
 657     }
 658
 659     if (length > base_length) {
 660         ret = bdrv_truncate(base, length);
 661         if (ret < 0) {
 662             error_setg_errno(errp, -ret,
 663                             "Top image %s is larger than base image %s, and "
 664                              "resize of base image failed",
 665                              bs->filename, base->filename);
 666             goto error_restore_flags;
 667         }
 668     }
 669
 670     bdrv_ref(base);
 671     mirror_start_job(bs, base, speed, 0, 0,
 672                      on_error, on_error, cb, opaque, &local_err,
 673                      &commit_active_job_driver, false, base);
 674     if (error_is_set(&local_err)) {
 675         error_propagate(errp, local_err);
 676         goto error_restore_flags;
 677     }
 678
 679     return;
 680
 681 error_restore_flags:
 682     /* ignore error and errp for bdrv_reopen, because we want to propagate
 683      * the original error */
 684     bdrv_reopen(base, orig_base_flags, NULL);
 685     return;
 686 }