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