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 <wency@cn.fujitsu.com>
  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                                    BlockReopenQueue *reopen_queue,
 161                                    uint64_t perm, uint64_t shared,
 162                                    uint64_t *nperm, uint64_t *nshared)
 163 {
 164     *nperm = *nshared = BLK_PERM_CONSISTENT_READ \
 165                         | BLK_PERM_WRITE \
 166                         | BLK_PERM_WRITE_UNCHANGED;
 167
 168     return;
 169 }
 170
 171 static int64_t replication_getlength(BlockDriverState *bs)
 172 {
 173     return bdrv_getlength(bs->file->bs);
 174 }
 175
 176 static int replication_get_io_status(BDRVReplicationState *s)
 177 {
 178     switch (s->stage) {
 179     case BLOCK_REPLICATION_NONE:
 180         return -EIO;
 181     case BLOCK_REPLICATION_RUNNING:
 182         return 0;
 183     case BLOCK_REPLICATION_FAILOVER:
 184         return s->mode == REPLICATION_MODE_PRIMARY ? -EIO : 0;
 185     case BLOCK_REPLICATION_FAILOVER_FAILED:
 186         return s->mode == REPLICATION_MODE_PRIMARY ? -EIO : 1;
 187     case BLOCK_REPLICATION_DONE:
 188         /*
 189          * active commit job completes, and active disk and secondary_disk
 190          * is swapped, so we can operate bs->file directly
 191          */
 192         return s->mode == REPLICATION_MODE_PRIMARY ? -EIO : 0;
 193     default:
 194         abort();
 195     }
 196 }
 197
 198 static int replication_return_value(BDRVReplicationState *s, int ret)
 199 {
 200     if (s->mode == REPLICATION_MODE_SECONDARY) {
 201         return ret;
 202     }
 203
 204     if (ret < 0) {
 205         s->error = ret;
 206         ret = 0;
 207     }
 208
 209     return ret;
 210 }
 211
 212 static coroutine_fn int replication_co_readv(BlockDriverState *bs,
 213                                              int64_t sector_num,
 214                                              int remaining_sectors,
 215                                              QEMUIOVector *qiov)
 216 {
 217     BDRVReplicationState *s = bs->opaque;
 218     BdrvChild *child = s->secondary_disk;
 219     BlockJob *job = NULL;
 220     CowRequest req;
 221     int ret;
 222
 223     if (s->mode == REPLICATION_MODE_PRIMARY) {
 224         /* We only use it to forward primary write requests */
 225         return -EIO;
 226     }
 227
 228     ret = replication_get_io_status(s);
 229     if (ret < 0) {
 230         return ret;
 231     }
 232
 233     if (child && child->bs) {
 234         job = child->bs->job;
 235     }
 236
 237     if (job) {
 238         uint64_t remaining_bytes = remaining_sectors * BDRV_SECTOR_SIZE;
 239
 240         backup_wait_for_overlapping_requests(child->bs->job,
 241                                              sector_num * BDRV_SECTOR_SIZE,
 242                                              remaining_bytes);
 243         backup_cow_request_begin(&req, child->bs->job,
 244                                  sector_num * BDRV_SECTOR_SIZE,
 245                                  remaining_bytes);
 246         ret = bdrv_co_readv(bs->file, sector_num, remaining_sectors,
 247                             qiov);
 248         backup_cow_request_end(&req);
 249         goto out;
 250     }
 251
 252     ret = bdrv_co_readv(bs->file, sector_num, remaining_sectors, qiov);
 253 out:
 254     return replication_return_value(s, ret);
 255 }
 256
 257 static coroutine_fn int replication_co_writev(BlockDriverState *bs,
 258                                               int64_t sector_num,
 259                                               int remaining_sectors,
 260                                               QEMUIOVector *qiov)
 261 {
 262     BDRVReplicationState *s = bs->opaque;
 263     QEMUIOVector hd_qiov;
 264     uint64_t bytes_done = 0;
 265     BdrvChild *top = bs->file;
 266     BdrvChild *base = s->secondary_disk;
 267     BdrvChild *target;
 268     int ret;
 269     int64_t n;
 270
 271     ret = replication_get_io_status(s);
 272     if (ret < 0) {
 273         goto out;
 274     }
 275
 276     if (ret == 0) {
 277         ret = bdrv_co_writev(top, sector_num,
 278                              remaining_sectors, qiov);
 279         return replication_return_value(s, ret);
 280     }
 281
 282     /*
 283      * Failover failed, only write to active disk if the sectors
 284      * have already been allocated in active disk/hidden disk.
 285      */
 286     qemu_iovec_init(&hd_qiov, qiov->niov);
 287     while (remaining_sectors > 0) {
 288         int64_t count;
 289
 290         ret = bdrv_is_allocated_above(top->bs, base->bs,
 291                                       sector_num * BDRV_SECTOR_SIZE,
 292                                       remaining_sectors * BDRV_SECTOR_SIZE,
 293                                       &count);
 294         if (ret < 0) {
 295             goto out1;
 296         }
 297
 298         assert(QEMU_IS_ALIGNED(count, BDRV_SECTOR_SIZE));
 299         n = count >> BDRV_SECTOR_BITS;
 300         qemu_iovec_reset(&hd_qiov);
 301         qemu_iovec_concat(&hd_qiov, qiov, bytes_done, count);
 302
 303         target = ret ? top : base;
 304         ret = bdrv_co_writev(target, sector_num, n, &hd_qiov);
 305         if (ret < 0) {
 306             goto out1;
 307         }
 308
 309         remaining_sectors -= n;
 310         sector_num += n;
 311         bytes_done += count;
 312     }
 313
 314 out1:
 315     qemu_iovec_destroy(&hd_qiov);
 316 out:
 317     return ret;
 318 }
 319
 320 static bool replication_recurse_is_first_non_filter(BlockDriverState *bs,
 321                                                     BlockDriverState *candidate)
 322 {
 323     return bdrv_recurse_is_first_non_filter(bs->file->bs, candidate);
 324 }
 325
 326 static void secondary_do_checkpoint(BDRVReplicationState *s, Error **errp)
 327 {
 328     Error *local_err = NULL;
 329     int ret;
 330
 331     if (!s->secondary_disk->bs->job) {
 332         error_setg(errp, "Backup job was cancelled unexpectedly");
 333         return;
 334     }
 335
 336     backup_do_checkpoint(s->secondary_disk->bs->job, &local_err);
 337     if (local_err) {
 338         error_propagate(errp, local_err);
 339         return;
 340     }
 341
 342     ret = s->active_disk->bs->drv->bdrv_make_empty(s->active_disk->bs);
 343     if (ret < 0) {
 344         error_setg(errp, "Cannot make active disk empty");
 345         return;
 346     }
 347
 348     ret = s->hidden_disk->bs->drv->bdrv_make_empty(s->hidden_disk->bs);
 349     if (ret < 0) {
 350         error_setg(errp, "Cannot make hidden disk empty");
 351         return;
 352     }
 353 }
 354
 355 static void reopen_backing_file(BlockDriverState *bs, bool writable,
 356                                 Error **errp)
 357 {
 358     BDRVReplicationState *s = bs->opaque;
 359     BlockReopenQueue *reopen_queue = NULL;
 360     int orig_hidden_flags, orig_secondary_flags;
 361     int new_hidden_flags, new_secondary_flags;
 362     Error *local_err = NULL;
 363
 364     if (writable) {
 365         orig_hidden_flags = s->orig_hidden_flags =
 366                                 bdrv_get_flags(s->hidden_disk->bs);
 367         new_hidden_flags = (orig_hidden_flags | BDRV_O_RDWR) &
 368                                                     ~BDRV_O_INACTIVE;
 369         orig_secondary_flags = s->orig_secondary_flags =
 370                                 bdrv_get_flags(s->secondary_disk->bs);
 371         new_secondary_flags = (orig_secondary_flags | BDRV_O_RDWR) &
 372                                                      ~BDRV_O_INACTIVE;
 373     } else {
 374         orig_hidden_flags = (s->orig_hidden_flags | BDRV_O_RDWR) &
 375                                                     ~BDRV_O_INACTIVE;
 376         new_hidden_flags = s->orig_hidden_flags;
 377         orig_secondary_flags = (s->orig_secondary_flags | BDRV_O_RDWR) &
 378                                                     ~BDRV_O_INACTIVE;
 379         new_secondary_flags = s->orig_secondary_flags;
 380     }
 381
 382     if (orig_hidden_flags != new_hidden_flags) {
 383         reopen_queue = bdrv_reopen_queue(reopen_queue, s->hidden_disk->bs, NULL,
 384                                          new_hidden_flags);
 385     }
 386
 387     if (!(orig_secondary_flags & BDRV_O_RDWR)) {
 388         reopen_queue = bdrv_reopen_queue(reopen_queue, s->secondary_disk->bs,
 389                                          NULL, new_secondary_flags);
 390     }
 391
 392     if (reopen_queue) {
 393         bdrv_reopen_multiple(bdrv_get_aio_context(bs),
 394                              reopen_queue, &local_err);
 395         error_propagate(errp, local_err);
 396     }
 397 }
 398
 399 static void backup_job_cleanup(BlockDriverState *bs)
 400 {
 401     BDRVReplicationState *s = bs->opaque;
 402     BlockDriverState *top_bs;
 403
 404     top_bs = bdrv_lookup_bs(s->top_id, s->top_id, NULL);
 405     if (!top_bs) {
 406         return;
 407     }
 408     bdrv_op_unblock_all(top_bs, s->blocker);
 409     error_free(s->blocker);
 410     reopen_backing_file(bs, false, NULL);
 411 }
 412
 413 static void backup_job_completed(void *opaque, int ret)
 414 {
 415     BlockDriverState *bs = opaque;
 416     BDRVReplicationState *s = bs->opaque;
 417
 418     if (s->stage != BLOCK_REPLICATION_FAILOVER) {
 419         /* The backup job is cancelled unexpectedly */
 420         s->error = -EIO;
 421     }
 422
 423     backup_job_cleanup(bs);
 424 }
 425
 426 static bool check_top_bs(BlockDriverState *top_bs, BlockDriverState *bs)
 427 {
 428     BdrvChild *child;
 429
 430     /* The bs itself is the top_bs */
 431     if (top_bs == bs) {
 432         return true;
 433     }
 434
 435     /* Iterate over top_bs's children */
 436     QLIST_FOREACH(child, &top_bs->children, next) {
 437         if (child->bs == bs || check_top_bs(child->bs, bs)) {
 438             return true;
 439         }
 440     }
 441
 442     return false;
 443 }
 444
 445 static void replication_start(ReplicationState *rs, ReplicationMode mode,
 446                               Error **errp)
 447 {
 448     BlockDriverState *bs = rs->opaque;
 449     BDRVReplicationState *s;
 450     BlockDriverState *top_bs;
 451     int64_t active_length, hidden_length, disk_length;
 452     AioContext *aio_context;
 453     Error *local_err = NULL;
 454     BlockJob *job;
 455
 456     aio_context = bdrv_get_aio_context(bs);
 457     aio_context_acquire(aio_context);
 458     s = bs->opaque;
 459
 460     if (s->stage != BLOCK_REPLICATION_NONE) {
 461         error_setg(errp, "Block replication is running or done");
 462         aio_context_release(aio_context);
 463         return;
 464     }
 465
 466     if (s->mode != mode) {
 467         error_setg(errp, "The parameter mode's value is invalid, needs %d,"
 468                    " but got %d", s->mode, mode);
 469         aio_context_release(aio_context);
 470         return;
 471     }
 472
 473     switch (s->mode) {
 474     case REPLICATION_MODE_PRIMARY:
 475         break;
 476     case REPLICATION_MODE_SECONDARY:
 477         s->active_disk = bs->file;
 478         if (!s->active_disk || !s->active_disk->bs ||
 479                                     !s->active_disk->bs->backing) {
 480             error_setg(errp, "Active disk doesn't have backing file");
 481             aio_context_release(aio_context);
 482             return;
 483         }
 484
 485         s->hidden_disk = s->active_disk->bs->backing;
 486         if (!s->hidden_disk->bs || !s->hidden_disk->bs->backing) {
 487             error_setg(errp, "Hidden disk doesn't have backing file");
 488             aio_context_release(aio_context);
 489             return;
 490         }
 491
 492         s->secondary_disk = s->hidden_disk->bs->backing;
 493         if (!s->secondary_disk->bs || !bdrv_has_blk(s->secondary_disk->bs)) {
 494             error_setg(errp, "The secondary disk doesn't have block backend");
 495             aio_context_release(aio_context);
 496             return;
 497         }
 498
 499         /* verify the length */
 500         active_length = bdrv_getlength(s->active_disk->bs);
 501         hidden_length = bdrv_getlength(s->hidden_disk->bs);
 502         disk_length = bdrv_getlength(s->secondary_disk->bs);
 503         if (active_length < 0 || hidden_length < 0 || disk_length < 0 ||
 504             active_length != hidden_length || hidden_length != disk_length) {
 505             error_setg(errp, "Active disk, hidden disk, secondary disk's length"
 506                        " are not the same");
 507             aio_context_release(aio_context);
 508             return;
 509         }
 510
 511         if (!s->active_disk->bs->drv->bdrv_make_empty ||
 512             !s->hidden_disk->bs->drv->bdrv_make_empty) {
 513             error_setg(errp,
 514                        "Active disk or hidden disk doesn't support make_empty");
 515             aio_context_release(aio_context);
 516             return;
 517         }
 518
 519         /* reopen the backing file in r/w mode */
 520         reopen_backing_file(bs, true, &local_err);
 521         if (local_err) {
 522             error_propagate(errp, local_err);
 523             aio_context_release(aio_context);
 524             return;
 525         }
 526
 527         /* start backup job now */
 528         error_setg(&s->blocker,
 529                    "Block device is in use by internal backup job");
 530
 531         top_bs = bdrv_lookup_bs(s->top_id, s->top_id, NULL);
 532         if (!top_bs || !bdrv_is_root_node(top_bs) ||
 533             !check_top_bs(top_bs, bs)) {
 534             error_setg(errp, "No top_bs or it is invalid");
 535             reopen_backing_file(bs, false, NULL);
 536             aio_context_release(aio_context);
 537             return;
 538         }
 539         bdrv_op_block_all(top_bs, s->blocker);
 540         bdrv_op_unblock(top_bs, BLOCK_OP_TYPE_DATAPLANE, s->blocker);
 541
 542         job = backup_job_create(NULL, s->secondary_disk->bs, s->hidden_disk->bs,
 543                                 0, MIRROR_SYNC_MODE_NONE, NULL, false,
 544                                 BLOCKDEV_ON_ERROR_REPORT,
 545                                 BLOCKDEV_ON_ERROR_REPORT, BLOCK_JOB_INTERNAL,
 546                                 backup_job_completed, bs, NULL, &local_err);
 547         if (local_err) {
 548             error_propagate(errp, local_err);
 549             backup_job_cleanup(bs);
 550             aio_context_release(aio_context);
 551             return;
 552         }
 553         block_job_start(job);
 554         break;
 555     default:
 556         aio_context_release(aio_context);
 557         abort();
 558     }
 559
 560     s->stage = BLOCK_REPLICATION_RUNNING;
 561
 562     if (s->mode == REPLICATION_MODE_SECONDARY) {
 563         secondary_do_checkpoint(s, errp);
 564     }
 565
 566     s->error = 0;
 567     aio_context_release(aio_context);
 568 }
 569
 570 static void replication_do_checkpoint(ReplicationState *rs, Error **errp)
 571 {
 572     BlockDriverState *bs = rs->opaque;
 573     BDRVReplicationState *s;
 574     AioContext *aio_context;
 575
 576     aio_context = bdrv_get_aio_context(bs);
 577     aio_context_acquire(aio_context);
 578     s = bs->opaque;
 579
 580     if (s->mode == REPLICATION_MODE_SECONDARY) {
 581         secondary_do_checkpoint(s, errp);
 582     }
 583     aio_context_release(aio_context);
 584 }
 585
 586 static void replication_get_error(ReplicationState *rs, Error **errp)
 587 {
 588     BlockDriverState *bs = rs->opaque;
 589     BDRVReplicationState *s;
 590     AioContext *aio_context;
 591
 592     aio_context = bdrv_get_aio_context(bs);
 593     aio_context_acquire(aio_context);
 594     s = bs->opaque;
 595
 596     if (s->stage != BLOCK_REPLICATION_RUNNING) {
 597         error_setg(errp, "Block replication is not running");
 598         aio_context_release(aio_context);
 599         return;
 600     }
 601
 602     if (s->error) {
 603         error_setg(errp, "I/O error occurred");
 604         aio_context_release(aio_context);
 605         return;
 606     }
 607     aio_context_release(aio_context);
 608 }
 609
 610 static void replication_done(void *opaque, int ret)
 611 {
 612     BlockDriverState *bs = opaque;
 613     BDRVReplicationState *s = bs->opaque;
 614
 615     if (ret == 0) {
 616         s->stage = BLOCK_REPLICATION_DONE;
 617
 618         /* refresh top bs's filename */
 619         bdrv_refresh_filename(bs);
 620         s->active_disk = NULL;
 621         s->secondary_disk = NULL;
 622         s->hidden_disk = NULL;
 623         s->error = 0;
 624     } else {
 625         s->stage = BLOCK_REPLICATION_FAILOVER_FAILED;
 626         s->error = -EIO;
 627     }
 628 }
 629
 630 static void replication_stop(ReplicationState *rs, bool failover, Error **errp)
 631 {
 632     BlockDriverState *bs = rs->opaque;
 633     BDRVReplicationState *s;
 634     AioContext *aio_context;
 635
 636     aio_context = bdrv_get_aio_context(bs);
 637     aio_context_acquire(aio_context);
 638     s = bs->opaque;
 639
 640     if (s->stage != BLOCK_REPLICATION_RUNNING) {
 641         error_setg(errp, "Block replication is not running");
 642         aio_context_release(aio_context);
 643         return;
 644     }
 645
 646     switch (s->mode) {
 647     case REPLICATION_MODE_PRIMARY:
 648         s->stage = BLOCK_REPLICATION_DONE;
 649         s->error = 0;
 650         break;
 651     case REPLICATION_MODE_SECONDARY:
 652         /*
 653          * This BDS will be closed, and the job should be completed
 654          * before the BDS is closed, because we will access hidden
 655          * disk, secondary disk in backup_job_completed().
 656          */
 657         if (s->secondary_disk->bs->job) {
 658             block_job_cancel_sync(s->secondary_disk->bs->job);
 659         }
 660
 661         if (!failover) {
 662             secondary_do_checkpoint(s, errp);
 663             s->stage = BLOCK_REPLICATION_DONE;
 664             aio_context_release(aio_context);
 665             return;
 666         }
 667
 668         s->stage = BLOCK_REPLICATION_FAILOVER;
 669         commit_active_start(NULL, s->active_disk->bs, s->secondary_disk->bs,
 670                             BLOCK_JOB_INTERNAL, 0, BLOCKDEV_ON_ERROR_REPORT,
 671                             NULL, replication_done, bs, true, errp);
 672         break;
 673     default:
 674         aio_context_release(aio_context);
 675         abort();
 676     }
 677     aio_context_release(aio_context);
 678 }
 679
 680 BlockDriver bdrv_replication = {
 681     .format_name                = "replication",
 682     .protocol_name              = "replication",
 683     .instance_size              = sizeof(BDRVReplicationState),
 684
 685     .bdrv_open                  = replication_open,
 686     .bdrv_close                 = replication_close,
 687     .bdrv_child_perm            = replication_child_perm,
 688
 689     .bdrv_getlength             = replication_getlength,
 690     .bdrv_co_readv              = replication_co_readv,
 691     .bdrv_co_writev             = replication_co_writev,
 692
 693     .is_filter                  = true,
 694     .bdrv_recurse_is_first_non_filter = replication_recurse_is_first_non_filter,
 695
 696     .has_variable_length        = true,
 697 };
 698
 699 static void bdrv_replication_init(void)
 700 {
 701     bdrv_register(&bdrv_replication);
 702 }
 703
 704 block_init(bdrv_replication_init);