blockjob.c

   1 /*
   2  * QEMU System Emulator block driver
   3  *
   4  * Copyright (c) 2011 IBM Corp.
   5  * Copyright (c) 2012 Red Hat, Inc.
   6  *
   7  * Permission is hereby granted, free of charge, to any person obtaining a copy
   8  * of this software and associated documentation files (the "Software"), to deal
   9  * in the Software without restriction, including without limitation the rights
  10  * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  11  * copies of the Software, and to permit persons to whom the Software is
  12  * furnished to do so, subject to the following conditions:
  13  *
  14  * The above copyright notice and this permission notice shall be included in
  15  * all copies or substantial portions of the Software.
  16  *
  17  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  18  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  19  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
  20  * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  21  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  22  * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
  23  * THE SOFTWARE.
  24  */
  25
  26 #include "qemu/osdep.h"
  27 #include "qemu-common.h"
  28 #include "block/block.h"
  29 #include "block/blockjob_int.h"
  30 #include "block/block_int.h"
  31 #include "sysemu/block-backend.h"
  32 #include "qapi/qmp/qerror.h"
  33 #include "qapi/qmp/qjson.h"
  34 #include "qemu/coroutine.h"
  35 #include "qemu/id.h"
  36 #include "qmp-commands.h"
  37 #include "qemu/timer.h"
  38 #include "qapi-event.h"
  39
  40 static void block_job_event_cancelled(BlockJob *job);
  41 static void block_job_event_completed(BlockJob *job, const char *msg);
  42
  43 /* Transactional group of block jobs */
  44 struct BlockJobTxn {
  45
  46     /* Is this txn being cancelled? */
  47     bool aborting;
  48
  49     /* List of jobs */
  50     QLIST_HEAD(, BlockJob) jobs;
  51
  52     /* Reference count */
  53     int refcnt;
  54 };
  55
  56 static QLIST_HEAD(, BlockJob) block_jobs = QLIST_HEAD_INITIALIZER(block_jobs);
  57
  58 static char *child_job_get_parent_desc(BdrvChild *c)
  59 {
  60     BlockJob *job = c->opaque;
  61     return g_strdup_printf("%s job '%s'",
  62                            BlockJobType_lookup[job->driver->job_type],
  63                            job->id);
  64 }
  65
  66 static const BdrvChildRole child_job = {
  67     .get_parent_desc    = child_job_get_parent_desc,
  68     .stay_at_node       = true,
  69 };
  70
  71 BlockJob *block_job_next(BlockJob *job)
  72 {
  73     if (!job) {
  74         return QLIST_FIRST(&block_jobs);
  75     }
  76     return QLIST_NEXT(job, job_list);
  77 }
  78
  79 BlockJob *block_job_get(const char *id)
  80 {
  81     BlockJob *job;
  82
  83     QLIST_FOREACH(job, &block_jobs, job_list) {
  84         if (job->id && !strcmp(id, job->id)) {
  85             return job;
  86         }
  87     }
  88
  89     return NULL;
  90 }
  91
  92 static void block_job_attached_aio_context(AioContext *new_context,
  93                                            void *opaque)
  94 {
  95     BlockJob *job = opaque;
  96
  97     if (job->driver->attached_aio_context) {
  98         job->driver->attached_aio_context(job, new_context);
  99     }
 100
 101     block_job_resume(job);
 102 }
 103
 104 static void block_job_drain(BlockJob *job)
 105 {
 106     /* If job is !job->busy this kicks it into the next pause point. */
 107     block_job_enter(job);
 108
 109     blk_drain(job->blk);
 110     if (job->driver->drain) {
 111         job->driver->drain(job);
 112     }
 113 }
 114
 115 static void block_job_detach_aio_context(void *opaque)
 116 {
 117     BlockJob *job = opaque;
 118
 119     /* In case the job terminates during aio_poll()... */
 120     block_job_ref(job);
 121
 122     block_job_pause(job);
 123
 124     while (!job->paused && !job->completed) {
 125         block_job_drain(job);
 126     }
 127
 128     block_job_unref(job);
 129 }
 130
 131 int block_job_add_bdrv(BlockJob *job, const char *name, BlockDriverState *bs,
 132                        uint64_t perm, uint64_t shared_perm, Error **errp)
 133 {
 134     BdrvChild *c;
 135
 136     c = bdrv_root_attach_child(bs, name, &child_job, perm, shared_perm,
 137                                job, errp);
 138     if (c == NULL) {
 139         return -EPERM;
 140     }
 141
 142     job->nodes = g_slist_prepend(job->nodes, c);
 143     bdrv_ref(bs);
 144     bdrv_op_block_all(bs, job->blocker);
 145
 146     return 0;
 147 }
 148
 149 void *block_job_create(const char *job_id, const BlockJobDriver *driver,
 150                        BlockDriverState *bs, uint64_t perm,
 151                        uint64_t shared_perm, int64_t speed, int flags,
 152                        BlockCompletionFunc *cb, void *opaque, Error **errp)
 153 {
 154     BlockBackend *blk;
 155     BlockJob *job;
 156     int ret;
 157
 158     if (bs->job) {
 159         error_setg(errp, QERR_DEVICE_IN_USE, bdrv_get_device_name(bs));
 160         return NULL;
 161     }
 162
 163     if (job_id == NULL && !(flags & BLOCK_JOB_INTERNAL)) {
 164         job_id = bdrv_get_device_name(bs);
 165         if (!*job_id) {
 166             error_setg(errp, "An explicit job ID is required for this node");
 167             return NULL;
 168         }
 169     }
 170
 171     if (job_id) {
 172         if (flags & BLOCK_JOB_INTERNAL) {
 173             error_setg(errp, "Cannot specify job ID for internal block job");
 174             return NULL;
 175         }
 176
 177         if (!id_wellformed(job_id)) {
 178             error_setg(errp, "Invalid job ID '%s'", job_id);
 179             return NULL;
 180         }
 181
 182         if (block_job_get(job_id)) {
 183             error_setg(errp, "Job ID '%s' already in use", job_id);
 184             return NULL;
 185         }
 186     }
 187
 188     blk = blk_new(perm, shared_perm);
 189     ret = blk_insert_bs(blk, bs, errp);
 190     if (ret < 0) {
 191         blk_unref(blk);
 192         return NULL;
 193     }
 194
 195     job = g_malloc0(driver->instance_size);
 196     error_setg(&job->blocker, "block device is in use by block job: %s",
 197                BlockJobType_lookup[driver->job_type]);
 198     block_job_add_bdrv(job, "main node", bs, 0, BLK_PERM_ALL, &error_abort);
 199     bdrv_op_unblock(bs, BLOCK_OP_TYPE_DATAPLANE, job->blocker);
 200
 201     job->driver        = driver;
 202     job->id            = g_strdup(job_id);
 203     job->blk           = blk;
 204     job->cb            = cb;
 205     job->opaque        = opaque;
 206     job->busy          = false;
 207     job->paused        = true;
 208     job->pause_count   = 1;
 209     job->refcnt        = 1;
 210     bs->job = job;
 211
 212     QLIST_INSERT_HEAD(&block_jobs, job, job_list);
 213
 214     blk_add_aio_context_notifier(blk, block_job_attached_aio_context,
 215                                  block_job_detach_aio_context, job);
 216
 217     /* Only set speed when necessary to avoid NotSupported error */
 218     if (speed != 0) {
 219         Error *local_err = NULL;
 220
 221         block_job_set_speed(job, speed, &local_err);
 222         if (local_err) {
 223             block_job_unref(job);
 224             error_propagate(errp, local_err);
 225             return NULL;
 226         }
 227     }
 228     return job;
 229 }
 230
 231 bool block_job_is_internal(BlockJob *job)
 232 {
 233     return (job->id == NULL);
 234 }
 235
 236 static bool block_job_started(BlockJob *job)
 237 {
 238     return job->co;
 239 }
 240
 241 void block_job_start(BlockJob *job)
 242 {
 243     assert(job && !block_job_started(job) && job->paused &&
 244            !job->busy && job->driver->start);
 245     job->co = qemu_coroutine_create(job->driver->start, job);
 246     if (--job->pause_count == 0) {
 247         job->paused = false;
 248         job->busy = true;
 249         qemu_coroutine_enter(job->co);
 250     }
 251 }
 252
 253 void block_job_ref(BlockJob *job)
 254 {
 255     ++job->refcnt;
 256 }
 257
 258 void block_job_unref(BlockJob *job)
 259 {
 260     if (--job->refcnt == 0) {
 261         GSList *l;
 262         BlockDriverState *bs = blk_bs(job->blk);
 263         bs->job = NULL;
 264         for (l = job->nodes; l; l = l->next) {
 265             BdrvChild *c = l->data;
 266             bdrv_op_unblock_all(c->bs, job->blocker);
 267             bdrv_root_unref_child(c);
 268         }
 269         g_slist_free(job->nodes);
 270         blk_remove_aio_context_notifier(job->blk,
 271                                         block_job_attached_aio_context,
 272                                         block_job_detach_aio_context, job);
 273         blk_unref(job->blk);
 274         error_free(job->blocker);
 275         g_free(job->id);
 276         QLIST_REMOVE(job, job_list);
 277         g_free(job);
 278     }
 279 }
 280
 281 static void block_job_completed_single(BlockJob *job)
 282 {
 283     if (!job->ret) {
 284         if (job->driver->commit) {
 285             job->driver->commit(job);
 286         }
 287     } else {
 288         if (job->driver->abort) {
 289             job->driver->abort(job);
 290         }
 291     }
 292     if (job->driver->clean) {
 293         job->driver->clean(job);
 294     }
 295
 296     if (job->cb) {
 297         job->cb(job->opaque, job->ret);
 298     }
 299
 300     /* Emit events only if we actually started */
 301     if (block_job_started(job)) {
 302         if (block_job_is_cancelled(job)) {
 303             block_job_event_cancelled(job);
 304         } else {
 305             const char *msg = NULL;
 306             if (job->ret < 0) {
 307                 msg = strerror(-job->ret);
 308             }
 309             block_job_event_completed(job, msg);
 310         }
 311     }
 312
 313     if (job->txn) {
 314         QLIST_REMOVE(job, txn_list);
 315         block_job_txn_unref(job->txn);
 316     }
 317     block_job_unref(job);
 318 }
 319
 320 static void block_job_completed_txn_abort(BlockJob *job)
 321 {
 322     AioContext *ctx;
 323     BlockJobTxn *txn = job->txn;
 324     BlockJob *other_job, *next;
 325
 326     if (txn->aborting) {
 327         /*
 328          * We are cancelled by another job, which will handle everything.
 329          */
 330         return;
 331     }
 332     txn->aborting = true;
 333     /* We are the first failed job. Cancel other jobs. */
 334     QLIST_FOREACH(other_job, &txn->jobs, txn_list) {
 335         ctx = blk_get_aio_context(other_job->blk);
 336         aio_context_acquire(ctx);
 337     }
 338     QLIST_FOREACH(other_job, &txn->jobs, txn_list) {
 339         if (other_job == job || other_job->completed) {
 340             /* Other jobs are "effectively" cancelled by us, set the status for
 341              * them; this job, however, may or may not be cancelled, depending
 342              * on the caller, so leave it. */
 343             if (other_job != job) {
 344                 other_job->cancelled = true;
 345             }
 346             continue;
 347         }
 348         block_job_cancel_sync(other_job);
 349         assert(other_job->completed);
 350     }
 351     QLIST_FOREACH_SAFE(other_job, &txn->jobs, txn_list, next) {
 352         ctx = blk_get_aio_context(other_job->blk);
 353         block_job_completed_single(other_job);
 354         aio_context_release(ctx);
 355     }
 356 }
 357
 358 static void block_job_completed_txn_success(BlockJob *job)
 359 {
 360     AioContext *ctx;
 361     BlockJobTxn *txn = job->txn;
 362     BlockJob *other_job, *next;
 363     /*
 364      * Successful completion, see if there are other running jobs in this
 365      * txn.
 366      */
 367     QLIST_FOREACH(other_job, &txn->jobs, txn_list) {
 368         if (!other_job->completed) {
 369             return;
 370         }
 371     }
 372     /* We are the last completed job, commit the transaction. */
 373     QLIST_FOREACH_SAFE(other_job, &txn->jobs, txn_list, next) {
 374         ctx = blk_get_aio_context(other_job->blk);
 375         aio_context_acquire(ctx);
 376         assert(other_job->ret == 0);
 377         block_job_completed_single(other_job);
 378         aio_context_release(ctx);
 379     }
 380 }
 381
 382 void block_job_completed(BlockJob *job, int ret)
 383 {
 384     assert(blk_bs(job->blk)->job == job);
 385     assert(!job->completed);
 386     job->completed = true;
 387     job->ret = ret;
 388     if (!job->txn) {
 389         block_job_completed_single(job);
 390     } else if (ret < 0 || block_job_is_cancelled(job)) {
 391         block_job_completed_txn_abort(job);
 392     } else {
 393         block_job_completed_txn_success(job);
 394     }
 395 }
 396
 397 void block_job_set_speed(BlockJob *job, int64_t speed, Error **errp)
 398 {
 399     Error *local_err = NULL;
 400
 401     if (!job->driver->set_speed) {
 402         error_setg(errp, QERR_UNSUPPORTED);
 403         return;
 404     }
 405     job->driver->set_speed(job, speed, &local_err);
 406     if (local_err) {
 407         error_propagate(errp, local_err);
 408         return;
 409     }
 410
 411     job->speed = speed;
 412 }
 413
 414 void block_job_complete(BlockJob *job, Error **errp)
 415 {
 416     /* Should not be reachable via external interface for internal jobs */
 417     assert(job->id);
 418     if (job->pause_count || job->cancelled ||
 419         !block_job_started(job) || !job->driver->complete) {
 420         error_setg(errp, "The active block job '%s' cannot be completed",
 421                    job->id);
 422         return;
 423     }
 424
 425     job->driver->complete(job, errp);
 426 }
 427
 428 void block_job_pause(BlockJob *job)
 429 {
 430     job->pause_count++;
 431 }
 432
 433 void block_job_user_pause(BlockJob *job)
 434 {
 435     job->user_paused = true;
 436     block_job_pause(job);
 437 }
 438
 439 static bool block_job_should_pause(BlockJob *job)
 440 {
 441     return job->pause_count > 0;
 442 }
 443
 444 bool block_job_user_paused(BlockJob *job)
 445 {
 446     return job ? job->user_paused : 0;
 447 }
 448
 449 void coroutine_fn block_job_pause_point(BlockJob *job)
 450 {
 451     assert(job && block_job_started(job));
 452
 453     if (!block_job_should_pause(job)) {
 454         return;
 455     }
 456     if (block_job_is_cancelled(job)) {
 457         return;
 458     }
 459
 460     if (job->driver->pause) {
 461         job->driver->pause(job);
 462     }
 463
 464     if (block_job_should_pause(job) && !block_job_is_cancelled(job)) {
 465         job->paused = true;
 466         job->busy = false;
 467         qemu_coroutine_yield(); /* wait for block_job_resume() */
 468         job->busy = true;
 469         job->paused = false;
 470     }
 471
 472     if (job->driver->resume) {
 473         job->driver->resume(job);
 474     }
 475 }
 476
 477 void block_job_resume(BlockJob *job)
 478 {
 479     assert(job->pause_count > 0);
 480     job->pause_count--;
 481     if (job->pause_count) {
 482         return;
 483     }
 484     block_job_enter(job);
 485 }
 486
 487 void block_job_user_resume(BlockJob *job)
 488 {
 489     if (job && job->user_paused && job->pause_count > 0) {
 490         job->user_paused = false;
 491         block_job_resume(job);
 492     }
 493 }
 494
 495 void block_job_enter(BlockJob *job)
 496 {
 497     if (job->co && !job->busy) {
 498         qemu_coroutine_enter(job->co);
 499     }
 500 }
 501
 502 void block_job_cancel(BlockJob *job)
 503 {
 504     if (block_job_started(job)) {
 505         job->cancelled = true;
 506         block_job_iostatus_reset(job);
 507         block_job_enter(job);
 508     } else {
 509         block_job_completed(job, -ECANCELED);
 510     }
 511 }
 512
 513 bool block_job_is_cancelled(BlockJob *job)
 514 {
 515     return job->cancelled;
 516 }
 517
 518 void block_job_iostatus_reset(BlockJob *job)
 519 {
 520     job->iostatus = BLOCK_DEVICE_IO_STATUS_OK;
 521     if (job->driver->iostatus_reset) {
 522         job->driver->iostatus_reset(job);
 523     }
 524 }
 525
 526 static int block_job_finish_sync(BlockJob *job,
 527                                  void (*finish)(BlockJob *, Error **errp),
 528                                  Error **errp)
 529 {
 530     Error *local_err = NULL;
 531     int ret;
 532
 533     assert(blk_bs(job->blk)->job == job);
 534
 535     block_job_ref(job);
 536
 537     finish(job, &local_err);
 538     if (local_err) {
 539         error_propagate(errp, local_err);
 540         block_job_unref(job);
 541         return -EBUSY;
 542     }
 543     /* block_job_drain calls block_job_enter, and it should be enough to
 544      * induce progress until the job completes or moves to the main thread.
 545     */
 546     while (!job->deferred_to_main_loop && !job->completed) {
 547         block_job_drain(job);
 548     }
 549     while (!job->completed) {
 550         aio_poll(qemu_get_aio_context(), true);
 551     }
 552     ret = (job->cancelled && job->ret == 0) ? -ECANCELED : job->ret;
 553     block_job_unref(job);
 554     return ret;
 555 }
 556
 557 /* A wrapper around block_job_cancel() taking an Error ** parameter so it may be
 558  * used with block_job_finish_sync() without the need for (rather nasty)
 559  * function pointer casts there. */
 560 static void block_job_cancel_err(BlockJob *job, Error **errp)
 561 {
 562     block_job_cancel(job);
 563 }
 564
 565 int block_job_cancel_sync(BlockJob *job)
 566 {
 567     return block_job_finish_sync(job, &block_job_cancel_err, NULL);
 568 }
 569
 570 void block_job_cancel_sync_all(void)
 571 {
 572     BlockJob *job;
 573     AioContext *aio_context;
 574
 575     while ((job = QLIST_FIRST(&block_jobs))) {
 576         aio_context = blk_get_aio_context(job->blk);
 577         aio_context_acquire(aio_context);
 578         block_job_cancel_sync(job);
 579         aio_context_release(aio_context);
 580     }
 581 }
 582
 583 int block_job_complete_sync(BlockJob *job, Error **errp)
 584 {
 585     return block_job_finish_sync(job, &block_job_complete, errp);
 586 }
 587
 588 void block_job_sleep_ns(BlockJob *job, QEMUClockType type, int64_t ns)
 589 {
 590     assert(job->busy);
 591
 592     /* Check cancellation *before* setting busy = false, too!  */
 593     if (block_job_is_cancelled(job)) {
 594         return;
 595     }
 596
 597     job->busy = false;
 598     if (!block_job_should_pause(job)) {
 599         co_aio_sleep_ns(blk_get_aio_context(job->blk), type, ns);
 600     }
 601     job->busy = true;
 602
 603     block_job_pause_point(job);
 604 }
 605
 606 void block_job_yield(BlockJob *job)
 607 {
 608     assert(job->busy);
 609
 610     /* Check cancellation *before* setting busy = false, too!  */
 611     if (block_job_is_cancelled(job)) {
 612         return;
 613     }
 614
 615     job->busy = false;
 616     if (!block_job_should_pause(job)) {
 617         qemu_coroutine_yield();
 618     }
 619     job->busy = true;
 620
 621     block_job_pause_point(job);
 622 }
 623
 624 BlockJobInfo *block_job_query(BlockJob *job, Error **errp)
 625 {
 626     BlockJobInfo *info;
 627
 628     if (block_job_is_internal(job)) {
 629         error_setg(errp, "Cannot query QEMU internal jobs");
 630         return NULL;
 631     }
 632     info = g_new0(BlockJobInfo, 1);
 633     info->type      = g_strdup(BlockJobType_lookup[job->driver->job_type]);
 634     info->device    = g_strdup(job->id);
 635     info->len       = job->len;
 636     info->busy      = job->busy;
 637     info->paused    = job->pause_count > 0;
 638     info->offset    = job->offset;
 639     info->speed     = job->speed;
 640     info->io_status = job->iostatus;
 641     info->ready     = job->ready;
 642     return info;
 643 }
 644
 645 static void block_job_iostatus_set_err(BlockJob *job, int error)
 646 {
 647     if (job->iostatus == BLOCK_DEVICE_IO_STATUS_OK) {
 648         job->iostatus = error == ENOSPC ? BLOCK_DEVICE_IO_STATUS_NOSPACE :
 649                                           BLOCK_DEVICE_IO_STATUS_FAILED;
 650     }
 651 }
 652
 653 static void block_job_event_cancelled(BlockJob *job)
 654 {
 655     if (block_job_is_internal(job)) {
 656         return;
 657     }
 658
 659     qapi_event_send_block_job_cancelled(job->driver->job_type,
 660                                         job->id,
 661                                         job->len,
 662                                         job->offset,
 663                                         job->speed,
 664                                         &error_abort);
 665 }
 666
 667 static void block_job_event_completed(BlockJob *job, const char *msg)
 668 {
 669     if (block_job_is_internal(job)) {
 670         return;
 671     }
 672
 673     qapi_event_send_block_job_completed(job->driver->job_type,
 674                                         job->id,
 675                                         job->len,
 676                                         job->offset,
 677                                         job->speed,
 678                                         !!msg,
 679                                         msg,
 680                                         &error_abort);
 681 }
 682
 683 void block_job_event_ready(BlockJob *job)
 684 {
 685     job->ready = true;
 686
 687     if (block_job_is_internal(job)) {
 688         return;
 689     }
 690
 691     qapi_event_send_block_job_ready(job->driver->job_type,
 692                                     job->id,
 693                                     job->len,
 694                                     job->offset,
 695                                     job->speed, &error_abort);
 696 }
 697
 698 BlockErrorAction block_job_error_action(BlockJob *job, BlockdevOnError on_err,
 699                                         int is_read, int error)
 700 {
 701     BlockErrorAction action;
 702
 703     switch (on_err) {
 704     case BLOCKDEV_ON_ERROR_ENOSPC:
 705     case BLOCKDEV_ON_ERROR_AUTO:
 706         action = (error == ENOSPC) ?
 707                  BLOCK_ERROR_ACTION_STOP : BLOCK_ERROR_ACTION_REPORT;
 708         break;
 709     case BLOCKDEV_ON_ERROR_STOP:
 710         action = BLOCK_ERROR_ACTION_STOP;
 711         break;
 712     case BLOCKDEV_ON_ERROR_REPORT:
 713         action = BLOCK_ERROR_ACTION_REPORT;
 714         break;
 715     case BLOCKDEV_ON_ERROR_IGNORE:
 716         action = BLOCK_ERROR_ACTION_IGNORE;
 717         break;
 718     default:
 719         abort();
 720     }
 721     if (!block_job_is_internal(job)) {
 722         qapi_event_send_block_job_error(job->id,
 723                                         is_read ? IO_OPERATION_TYPE_READ :
 724                                         IO_OPERATION_TYPE_WRITE,
 725                                         action, &error_abort);
 726     }
 727     if (action == BLOCK_ERROR_ACTION_STOP) {
 728         /* make the pause user visible, which will be resumed from QMP. */
 729         block_job_user_pause(job);
 730         block_job_iostatus_set_err(job, error);
 731     }
 732     return action;
 733 }
 734
 735 typedef struct {
 736     BlockJob *job;
 737     AioContext *aio_context;
 738     BlockJobDeferToMainLoopFn *fn;
 739     void *opaque;
 740 } BlockJobDeferToMainLoopData;
 741
 742 static void block_job_defer_to_main_loop_bh(void *opaque)
 743 {
 744     BlockJobDeferToMainLoopData *data = opaque;
 745     AioContext *aio_context;
 746
 747     /* Prevent race with block_job_defer_to_main_loop() */
 748     aio_context_acquire(data->aio_context);
 749
 750     /* Fetch BDS AioContext again, in case it has changed */
 751     aio_context = blk_get_aio_context(data->job->blk);
 752     aio_context_acquire(aio_context);
 753
 754     data->job->deferred_to_main_loop = false;
 755     data->fn(data->job, data->opaque);
 756
 757     aio_context_release(aio_context);
 758
 759     aio_context_release(data->aio_context);
 760
 761     g_free(data);
 762 }
 763
 764 void block_job_defer_to_main_loop(BlockJob *job,
 765                                   BlockJobDeferToMainLoopFn *fn,
 766                                   void *opaque)
 767 {
 768     BlockJobDeferToMainLoopData *data = g_malloc(sizeof(*data));
 769     data->job = job;
 770     data->aio_context = blk_get_aio_context(job->blk);
 771     data->fn = fn;
 772     data->opaque = opaque;
 773     job->deferred_to_main_loop = true;
 774
 775     aio_bh_schedule_oneshot(qemu_get_aio_context(),
 776                             block_job_defer_to_main_loop_bh, data);
 777 }
 778
 779 BlockJobTxn *block_job_txn_new(void)
 780 {
 781     BlockJobTxn *txn = g_new0(BlockJobTxn, 1);
 782     QLIST_INIT(&txn->jobs);
 783     txn->refcnt = 1;
 784     return txn;
 785 }
 786
 787 static void block_job_txn_ref(BlockJobTxn *txn)
 788 {
 789     txn->refcnt++;
 790 }
 791
 792 void block_job_txn_unref(BlockJobTxn *txn)
 793 {
 794     if (txn && --txn->refcnt == 0) {
 795         g_free(txn);
 796     }
 797 }
 798
 799 void block_job_txn_add_job(BlockJobTxn *txn, BlockJob *job)
 800 {
 801     if (!txn) {
 802         return;
 803     }
 804
 805     assert(!job->txn);
 806     job->txn = txn;
 807
 808     QLIST_INSERT_HEAD(&txn->jobs, job, txn_list);
 809     block_job_txn_ref(txn);
 810 }