block/replication.c

   1 /*
   2  * Replication Block filter
   3  *
   4  * Copyright (c) 2016 HUAWEI TECHNOLOGIES CO., LTD.
   5  * Copyright (c) 2016 Intel Corporation
   6  * Copyright (c) 2016 FUJITSU LIMITED
   7  *
   8  * Author:
   9  *   Wen Congyang <[email protected]>
  10  *
  11  * This work is licensed under the terms of the GNU GPL, version 2 or later.
  12  * See the COPYING file in the top-level directory.
  13  */
  14
  15 #include "qemu/osdep.h"
  16 #include "qemu-common.h"
  17 #include "block/nbd.h"
  18 #include "block/blockjob.h"
  19 #include "block/block_int.h"
  20 #include "block/block_backup.h"
  21 #include "sysemu/block-backend.h"
  22 #include "qapi/error.h"
  23 #include "replication.h"
  24
  25 typedef enum {
  26     BLOCK_REPLICATION_NONE,             /* block replication is not started */
  27     BLOCK_REPLICATION_RUNNING,          /* block replication is running */
  28     BLOCK_REPLICATION_FAILOVER,         /* failover is running in background */
  29     BLOCK_REPLICATION_FAILOVER_FAILED,  /* failover failed */
  30     BLOCK_REPLICATION_DONE,             /* block replication is done */
  31 } ReplicationStage;
  32
  33 typedef struct BDRVReplicationState {
  34     ReplicationMode mode;
  35     ReplicationStage stage;
  36     BdrvChild *active_disk;
  37     BdrvChild *hidden_disk;
  38     BdrvChild *secondary_disk;
  39     char *top_id;
  40     ReplicationState *rs;
  41     Error *blocker;
  42     int orig_hidden_flags;
  43     int orig_secondary_flags;
  44     int error;
  45 } BDRVReplicationState;
  46
  47 static void replication_start(ReplicationState *rs, ReplicationMode mode,
  48                               Error **errp);
  49 static void replication_do_checkpoint(ReplicationState *rs, Error **errp);
  50 static void replication_get_error(ReplicationState *rs, Error **errp);
  51 static void replication_stop(ReplicationState *rs, bool failover,
  52                              Error **errp);
  53
  54 #define REPLICATION_MODE        "mode"
  55 #define REPLICATION_TOP_ID      "top-id"
  56 static QemuOptsList replication_runtime_opts = {
  57     .name = "replication",
  58     .head = QTAILQ_HEAD_INITIALIZER(replication_runtime_opts.head),
  59     .desc = {
  60         {
  61             .name = REPLICATION_MODE,
  62             .type = QEMU_OPT_STRING,
  63         },
  64         {
  65             .name = REPLICATION_TOP_ID,
  66             .type = QEMU_OPT_STRING,
  67         },
  68         { /* end of list */ }
  69     },
  70 };
  71
  72 static ReplicationOps replication_ops = {
  73     .start = replication_start,
  74     .checkpoint = replication_do_checkpoint,
  75     .get_error = replication_get_error,
  76     .stop = replication_stop,
  77 };
  78
  79 static int replication_open(BlockDriverState *bs, QDict *options,
  80                             int flags, Error **errp)
  81 {
  82     int ret;
  83     BDRVReplicationState *s = bs->opaque;
  84     Error *local_err = NULL;
  85     QemuOpts *opts = NULL;
  86     const char *mode;
  87     const char *top_id;
  88
  89     bs->file = bdrv_open_child(NULL, options, "file", bs, &child_file,
  90                                false, errp);
  91     if (!bs->file) {
  92         return -EINVAL;
  93     }
  94
  95     ret = -EINVAL;
  96     opts = qemu_opts_create(&replication_runtime_opts, NULL, 0, &error_abort);
  97     qemu_opts_absorb_qdict(opts, options, &local_err);
  98     if (local_err) {
  99         goto fail;
 100     }
 101
 102     mode = qemu_opt_get(opts, REPLICATION_MODE);
 103     if (!mode) {
 104         error_setg(&local_err, "Missing the option mode");
 105         goto fail;
 106     }
 107
 108     if (!strcmp(mode, "primary")) {
 109         s->mode = REPLICATION_MODE_PRIMARY;
 110         top_id = qemu_opt_get(opts, REPLICATION_TOP_ID);
 111         if (top_id) {
 112             error_setg(&local_err, "The primary side does not support option top-id");
 113             goto fail;
 114         }
 115     } else if (!strcmp(mode, "secondary")) {
 116         s->mode = REPLICATION_MODE_SECONDARY;
 117         top_id = qemu_opt_get(opts, REPLICATION_TOP_ID);
 118         s->top_id = g_strdup(top_id);
 119         if (!s->top_id) {
 120             error_setg(&local_err, "Missing the option top-id");
 121             goto fail;
 122         }
 123     } else {
 124         error_setg(&local_err,
 125                    "The option mode's value should be primary or secondary");
 126         goto fail;
 127     }
 128
 129     s->rs = replication_new(bs, &replication_ops);
 130
 131     ret = 0;
 132
 133 fail:
 134     qemu_opts_del(opts);
 135     error_propagate(errp, local_err);
 136
 137     return ret;
 138 }
 139
 140 static void replication_close(BlockDriverState *bs)
 141 {
 142     BDRVReplicationState *s = bs->opaque;
 143
 144     if (s->stage == BLOCK_REPLICATION_RUNNING) {
 145         replication_stop(s->rs, false, NULL);
 146     }
 147     if (s->stage == BLOCK_REPLICATION_FAILOVER) {
 148         block_job_cancel_sync(s->active_disk->bs->job);
 149     }
 150
 151     if (s->mode == REPLICATION_MODE_SECONDARY) {
 152         g_free(s->top_id);
 153     }
 154
 155     replication_remove(s->rs);
 156 }
 157
 158 static void replication_child_perm(BlockDriverState *bs, BdrvChild *c,
 159                                    const BdrvChildRole *role,
 160                                    uint64_t perm, uint64_t shared,
 161                                    uint64_t *nperm, uint64_t *nshared)
 162 {
 163     *nperm = *nshared = BLK_PERM_CONSISTENT_READ \
 164                         | BLK_PERM_WRITE \
 165                         | BLK_PERM_WRITE_UNCHANGED;
 166
 167     return;
 168 }
 169
 170 static int64_t replication_getlength(BlockDriverState *bs)
 171 {
 172     return bdrv_getlength(bs->file->bs);
 173 }
 174
 175 static int replication_get_io_status(BDRVReplicationState *s)
 176 {
 177     switch (s->stage) {
 178     case BLOCK_REPLICATION_NONE:
 179         return -EIO;
 180     case BLOCK_REPLICATION_RUNNING:
 181         return 0;
 182     case BLOCK_REPLICATION_FAILOVER:
 183         return s->mode == REPLICATION_MODE_PRIMARY ? -EIO : 0;
 184     case BLOCK_REPLICATION_FAILOVER_FAILED:
 185         return s->mode == REPLICATION_MODE_PRIMARY ? -EIO : 1;
 186     case BLOCK_REPLICATION_DONE:
 187         /*
 188          * active commit job completes, and active disk and secondary_disk
 189          * is swapped, so we can operate bs->file directly
 190          */
 191         return s->mode == REPLICATION_MODE_PRIMARY ? -EIO : 0;
 192     default:
 193         abort();
 194     }
 195 }
 196
 197 static int replication_return_value(BDRVReplicationState *s, int ret)
 198 {
 199     if (s->mode == REPLICATION_MODE_SECONDARY) {
 200         return ret;
 201     }
 202
 203     if (ret < 0) {
 204         s->error = ret;
 205         ret = 0;
 206     }
 207
 208     return ret;
 209 }
 210
 211 static coroutine_fn int replication_co_readv(BlockDriverState *bs,
 212                                              int64_t sector_num,
 213                                              int remaining_sectors,
 214                                              QEMUIOVector *qiov)
 215 {
 216     BDRVReplicationState *s = bs->opaque;
 217     BdrvChild *child = s->secondary_disk;
 218     BlockJob *job = NULL;
 219     CowRequest req;
 220     int ret;
 221
 222     if (s->mode == REPLICATION_MODE_PRIMARY) {
 223         /* We only use it to forward primary write requests */
 224         return -EIO;
 225     }
 226
 227     ret = replication_get_io_status(s);
 228     if (ret < 0) {
 229         return ret;
 230     }
 231
 232     if (child && child->bs) {
 233         job = child->bs->job;
 234     }
 235
 236     if (job) {
 237         uint64_t remaining_bytes = remaining_sectors * BDRV_SECTOR_SIZE;
 238
 239         backup_wait_for_overlapping_requests(child->bs->job,
 240                                              sector_num * BDRV_SECTOR_SIZE,
 241                                              remaining_bytes);
 242         backup_cow_request_begin(&req, child->bs->job,
 243                                  sector_num * BDRV_SECTOR_SIZE,
 244                                  remaining_bytes);
 245         ret = bdrv_co_readv(bs->file, sector_num, remaining_sectors,
 246                             qiov);
 247         backup_cow_request_end(&req);
 248         goto out;
 249     }
 250
 251     ret = bdrv_co_readv(bs->file, sector_num, remaining_sectors, qiov);
 252 out:
 253     return replication_return_value(s, ret);
 254 }
 255
 256 static coroutine_fn int replication_co_writev(BlockDriverState *bs,
 257                                               int64_t sector_num,
 258                                               int remaining_sectors,
 259                                               QEMUIOVector *qiov)
 260 {
 261     BDRVReplicationState *s = bs->opaque;
 262     QEMUIOVector hd_qiov;
 263     uint64_t bytes_done = 0;
 264     BdrvChild *top = bs->file;
 265     BdrvChild *base = s->secondary_disk;
 266     BdrvChild *target;
 267     int ret;
 268     int64_t n;
 269
 270     ret = replication_get_io_status(s);
 271     if (ret < 0) {
 272         goto out;
 273     }
 274
 275     if (ret == 0) {
 276         ret = bdrv_co_writev(top, sector_num,
 277                              remaining_sectors, qiov);
 278         return replication_return_value(s, ret);
 279     }
 280
 281     /*
 282      * Failover failed, only write to active disk if the sectors
 283      * have already been allocated in active disk/hidden disk.
 284      */
 285     qemu_iovec_init(&hd_qiov, qiov->niov);
 286     while (remaining_sectors > 0) {
 287         int64_t count;
 288
 289         ret = bdrv_is_allocated_above(top->bs, base->bs,
 290                                       sector_num * BDRV_SECTOR_SIZE,
 291                                       remaining_sectors * BDRV_SECTOR_SIZE,
 292                                       &count);
 293         if (ret < 0) {
 294             goto out1;
 295         }
 296
 297         assert(QEMU_IS_ALIGNED(count, BDRV_SECTOR_SIZE));
 298         n = count >> BDRV_SECTOR_BITS;
 299         qemu_iovec_reset(&hd_qiov);
 300         qemu_iovec_concat(&hd_qiov, qiov, bytes_done, count);
 301
 302         target = ret ? top : base;
 303         ret = bdrv_co_writev(target, sector_num, n, &hd_qiov);
 304         if (ret < 0) {
 305             goto out1;
 306         }
 307
 308         remaining_sectors -= n;
 309         sector_num += n;
 310         bytes_done += count;
 311     }
 312
 313 out1:
 314     qemu_iovec_destroy(&hd_qiov);
 315 out:
 316     return ret;
 317 }
 318
 319 static bool replication_recurse_is_first_non_filter(BlockDriverState *bs,
 320                                                     BlockDriverState *candidate)
 321 {
 322     return bdrv_recurse_is_first_non_filter(bs->file->bs, candidate);
 323 }
 324
 325 static void secondary_do_checkpoint(BDRVReplicationState *s, Error **errp)
 326 {
 327     Error *local_err = NULL;
 328     int ret;
 329
 330     if (!s->secondary_disk->bs->job) {
 331         error_setg(errp, "Backup job was cancelled unexpectedly");
 332         return;
 333     }
 334
 335     backup_do_checkpoint(s->secondary_disk->bs->job, &local_err);
 336     if (local_err) {
 337         error_propagate(errp, local_err);
 338         return;
 339     }
 340
 341     ret = s->active_disk->bs->drv->bdrv_make_empty(s->active_disk->bs);
 342     if (ret < 0) {
 343         error_setg(errp, "Cannot make active disk empty");
 344         return;
 345     }
 346
 347     ret = s->hidden_disk->bs->drv->bdrv_make_empty(s->hidden_disk->bs);
 348     if (ret < 0) {
 349         error_setg(errp, "Cannot make hidden disk empty");
 350         return;
 351     }
 352 }
 353
 354 static void reopen_backing_file(BlockDriverState *bs, bool writable,
 355                                 Error **errp)
 356 {
 357     BDRVReplicationState *s = bs->opaque;
 358     BlockReopenQueue *reopen_queue = NULL;
 359     int orig_hidden_flags, orig_secondary_flags;
 360     int new_hidden_flags, new_secondary_flags;
 361     Error *local_err = NULL;
 362
 363     if (writable) {
 364         orig_hidden_flags = s->orig_hidden_flags =
 365                                 bdrv_get_flags(s->hidden_disk->bs);
 366         new_hidden_flags = (orig_hidden_flags | BDRV_O_RDWR) &
 367                                                     ~BDRV_O_INACTIVE;
 368         orig_secondary_flags = s->orig_secondary_flags =
 369                                 bdrv_get_flags(s->secondary_disk->bs);
 370         new_secondary_flags = (orig_secondary_flags | BDRV_O_RDWR) &
 371                                                      ~BDRV_O_INACTIVE;
 372     } else {
 373         orig_hidden_flags = (s->orig_hidden_flags | BDRV_O_RDWR) &
 374                                                     ~BDRV_O_INACTIVE;
 375         new_hidden_flags = s->orig_hidden_flags;
 376         orig_secondary_flags = (s->orig_secondary_flags | BDRV_O_RDWR) &
 377                                                     ~BDRV_O_INACTIVE;
 378         new_secondary_flags = s->orig_secondary_flags;
 379     }
 380
 381     if (orig_hidden_flags != new_hidden_flags) {
 382         reopen_queue = bdrv_reopen_queue(reopen_queue, s->hidden_disk->bs, NULL,
 383                                          new_hidden_flags);
 384     }
 385
 386     if (!(orig_secondary_flags & BDRV_O_RDWR)) {
 387         reopen_queue = bdrv_reopen_queue(reopen_queue, s->secondary_disk->bs,
 388                                          NULL, new_secondary_flags);
 389     }
 390
 391     if (reopen_queue) {
 392         bdrv_reopen_multiple(bdrv_get_aio_context(bs),
 393                              reopen_queue, &local_err);
 394         error_propagate(errp, local_err);
 395     }
 396 }
 397
 398 static void backup_job_cleanup(BlockDriverState *bs)
 399 {
 400     BDRVReplicationState *s = bs->opaque;
 401     BlockDriverState *top_bs;
 402
 403     top_bs = bdrv_lookup_bs(s->top_id, s->top_id, NULL);
 404     if (!top_bs) {
 405         return;
 406     }
 407     bdrv_op_unblock_all(top_bs, s->blocker);
 408     error_free(s->blocker);
 409     reopen_backing_file(bs, false, NULL);
 410 }
 411
 412 static void backup_job_completed(void *opaque, int ret)
 413 {
 414     BlockDriverState *bs = opaque;
 415     BDRVReplicationState *s = bs->opaque;
 416
 417     if (s->stage != BLOCK_REPLICATION_FAILOVER) {
 418         /* The backup job is cancelled unexpectedly */
 419         s->error = -EIO;
 420     }
 421
 422     backup_job_cleanup(bs);
 423 }
 424
 425 static bool check_top_bs(BlockDriverState *top_bs, BlockDriverState *bs)
 426 {
 427     BdrvChild *child;
 428
 429     /* The bs itself is the top_bs */
 430     if (top_bs == bs) {
 431         return true;
 432     }
 433
 434     /* Iterate over top_bs's children */
 435     QLIST_FOREACH(child, &top_bs->children, next) {
 436         if (child->bs == bs || check_top_bs(child->bs, bs)) {
 437             return true;
 438         }
 439     }
 440
 441     return false;
 442 }
 443
 444 static void replication_start(ReplicationState *rs, ReplicationMode mode,
 445                               Error **errp)
 446 {
 447     BlockDriverState *bs = rs->opaque;
 448     BDRVReplicationState *s;
 449     BlockDriverState *top_bs;
 450     int64_t active_length, hidden_length, disk_length;
 451     AioContext *aio_context;
 452     Error *local_err = NULL;
 453     BlockJob *job;
 454
 455     aio_context = bdrv_get_aio_context(bs);
 456     aio_context_acquire(aio_context);
 457     s = bs->opaque;
 458
 459     if (s->stage != BLOCK_REPLICATION_NONE) {
 460         error_setg(errp, "Block replication is running or done");
 461         aio_context_release(aio_context);
 462         return;
 463     }
 464
 465     if (s->mode != mode) {
 466         error_setg(errp, "The parameter mode's value is invalid, needs %d,"
 467                    " but got %d", s->mode, mode);
 468         aio_context_release(aio_context);
 469         return;
 470     }
 471
 472     switch (s->mode) {
 473     case REPLICATION_MODE_PRIMARY:
 474         break;
 475     case REPLICATION_MODE_SECONDARY:
 476         s->active_disk = bs->file;
 477         if (!s->active_disk || !s->active_disk->bs ||
 478                                     !s->active_disk->bs->backing) {
 479             error_setg(errp, "Active disk doesn't have backing file");
 480             aio_context_release(aio_context);
 481             return;
 482         }
 483
 484         s->hidden_disk = s->active_disk->bs->backing;
 485         if (!s->hidden_disk->bs || !s->hidden_disk->bs->backing) {
 486             error_setg(errp, "Hidden disk doesn't have backing file");
 487             aio_context_release(aio_context);
 488             return;
 489         }
 490
 491         s->secondary_disk = s->hidden_disk->bs->backing;
 492         if (!s->secondary_disk->bs || !bdrv_has_blk(s->secondary_disk->bs)) {
 493             error_setg(errp, "The secondary disk doesn't have block backend");
 494             aio_context_release(aio_context);
 495             return;
 496         }
 497
 498         /* verify the length */
 499         active_length = bdrv_getlength(s->active_disk->bs);
 500         hidden_length = bdrv_getlength(s->hidden_disk->bs);
 501         disk_length = bdrv_getlength(s->secondary_disk->bs);
 502         if (active_length < 0 || hidden_length < 0 || disk_length < 0 ||
 503             active_length != hidden_length || hidden_length != disk_length) {
 504             error_setg(errp, "Active disk, hidden disk, secondary disk's length"
 505                        " are not the same");
 506             aio_context_release(aio_context);
 507             return;
 508         }
 509
 510         if (!s->active_disk->bs->drv->bdrv_make_empty ||
 511             !s->hidden_disk->bs->drv->bdrv_make_empty) {
 512             error_setg(errp,
 513                        "Active disk or hidden disk doesn't support make_empty");
 514             aio_context_release(aio_context);
 515             return;
 516         }
 517
 518         /* reopen the backing file in r/w mode */
 519         reopen_backing_file(bs, true, &local_err);
 520         if (local_err) {
 521             error_propagate(errp, local_err);
 522             aio_context_release(aio_context);
 523             return;
 524         }
 525
 526         /* start backup job now */
 527         error_setg(&s->blocker,
 528                    "Block device is in use by internal backup job");
 529
 530         top_bs = bdrv_lookup_bs(s->top_id, s->top_id, NULL);
 531         if (!top_bs || !bdrv_is_root_node(top_bs) ||
 532             !check_top_bs(top_bs, bs)) {
 533             error_setg(errp, "No top_bs or it is invalid");
 534             reopen_backing_file(bs, false, NULL);
 535             aio_context_release(aio_context);
 536             return;
 537         }
 538         bdrv_op_block_all(top_bs, s->blocker);
 539         bdrv_op_unblock(top_bs, BLOCK_OP_TYPE_DATAPLANE, s->blocker);
 540
 541         job = backup_job_create(NULL, s->secondary_disk->bs, s->hidden_disk->bs,
 542                                 0, MIRROR_SYNC_MODE_NONE, NULL, false,
 543                                 BLOCKDEV_ON_ERROR_REPORT,
 544                                 BLOCKDEV_ON_ERROR_REPORT, BLOCK_JOB_INTERNAL,
 545                                 backup_job_completed, bs, NULL, &local_err);
 546         if (local_err) {
 547             error_propagate(errp, local_err);
 548             backup_job_cleanup(bs);
 549             aio_context_release(aio_context);
 550             return;
 551         }
 552         block_job_start(job);
 553         break;
 554     default:
 555         aio_context_release(aio_context);
 556         abort();
 557     }
 558
 559     s->stage = BLOCK_REPLICATION_RUNNING;
 560
 561     if (s->mode == REPLICATION_MODE_SECONDARY) {
 562         secondary_do_checkpoint(s, errp);
 563     }
 564
 565     s->error = 0;
 566     aio_context_release(aio_context);
 567 }
 568
 569 static void replication_do_checkpoint(ReplicationState *rs, Error **errp)
 570 {
 571     BlockDriverState *bs = rs->opaque;
 572     BDRVReplicationState *s;
 573     AioContext *aio_context;
 574
 575     aio_context = bdrv_get_aio_context(bs);
 576     aio_context_acquire(aio_context);
 577     s = bs->opaque;
 578
 579     if (s->mode == REPLICATION_MODE_SECONDARY) {
 580         secondary_do_checkpoint(s, errp);
 581     }
 582     aio_context_release(aio_context);
 583 }
 584
 585 static void replication_get_error(ReplicationState *rs, Error **errp)
 586 {
 587     BlockDriverState *bs = rs->opaque;
 588     BDRVReplicationState *s;
 589     AioContext *aio_context;
 590
 591     aio_context = bdrv_get_aio_context(bs);
 592     aio_context_acquire(aio_context);
 593     s = bs->opaque;
 594
 595     if (s->stage != BLOCK_REPLICATION_RUNNING) {
 596         error_setg(errp, "Block replication is not running");
 597         aio_context_release(aio_context);
 598         return;
 599     }
 600
 601     if (s->error) {
 602         error_setg(errp, "I/O error occurred");
 603         aio_context_release(aio_context);
 604         return;
 605     }
 606     aio_context_release(aio_context);
 607 }
 608
 609 static void replication_done(void *opaque, int ret)
 610 {
 611     BlockDriverState *bs = opaque;
 612     BDRVReplicationState *s = bs->opaque;
 613
 614     if (ret == 0) {
 615         s->stage = BLOCK_REPLICATION_DONE;
 616
 617         /* refresh top bs's filename */
 618         bdrv_refresh_filename(bs);
 619         s->active_disk = NULL;
 620         s->secondary_disk = NULL;
 621         s->hidden_disk = NULL;
 622         s->error = 0;
 623     } else {
 624         s->stage = BLOCK_REPLICATION_FAILOVER_FAILED;
 625         s->error = -EIO;
 626     }
 627 }
 628
 629 static void replication_stop(ReplicationState *rs, bool failover, Error **errp)
 630 {
 631     BlockDriverState *bs = rs->opaque;
 632     BDRVReplicationState *s;
 633     AioContext *aio_context;
 634
 635     aio_context = bdrv_get_aio_context(bs);
 636     aio_context_acquire(aio_context);
 637     s = bs->opaque;
 638
 639     if (s->stage != BLOCK_REPLICATION_RUNNING) {
 640         error_setg(errp, "Block replication is not running");
 641         aio_context_release(aio_context);
 642         return;
 643     }
 644
 645     switch (s->mode) {
 646     case REPLICATION_MODE_PRIMARY:
 647         s->stage = BLOCK_REPLICATION_DONE;
 648         s->error = 0;
 649         break;
 650     case REPLICATION_MODE_SECONDARY:
 651         /*
 652          * This BDS will be closed, and the job should be completed
 653          * before the BDS is closed, because we will access hidden
 654          * disk, secondary disk in backup_job_completed().
 655          */
 656         if (s->secondary_disk->bs->job) {
 657             block_job_cancel_sync(s->secondary_disk->bs->job);
 658         }
 659
 660         if (!failover) {
 661             secondary_do_checkpoint(s, errp);
 662             s->stage = BLOCK_REPLICATION_DONE;
 663             aio_context_release(aio_context);
 664             return;
 665         }
 666
 667         s->stage = BLOCK_REPLICATION_FAILOVER;
 668         commit_active_start(NULL, s->active_disk->bs, s->secondary_disk->bs,
 669                             BLOCK_JOB_INTERNAL, 0, BLOCKDEV_ON_ERROR_REPORT,
 670                             NULL, replication_done, bs, true, errp);
 671         break;
 672     default:
 673         aio_context_release(aio_context);
 674         abort();
 675     }
 676     aio_context_release(aio_context);
 677 }
 678
 679 BlockDriver bdrv_replication = {
 680     .format_name                = "replication",
 681     .protocol_name              = "replication",
 682     .instance_size              = sizeof(BDRVReplicationState),
 683
 684     .bdrv_open                  = replication_open,
 685     .bdrv_close                 = replication_close,
 686     .bdrv_child_perm            = replication_child_perm,
 687
 688     .bdrv_getlength             = replication_getlength,
 689     .bdrv_co_readv              = replication_co_readv,
 690     .bdrv_co_writev             = replication_co_writev,
 691
 692     .is_filter                  = true,
 693     .bdrv_recurse_is_first_non_filter = replication_recurse_is_first_non_filter,
 694
 695     .has_variable_length        = true,
 696 };
 697
 698 static void bdrv_replication_init(void)
 699 {
 700     bdrv_register(&bdrv_replication);
 701 }
 702
 703 block_init(bdrv_replication_init);