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