aio-posix.c

   1 /*
   2  * QEMU aio implementation
   3  *
   4  * Copyright IBM, Corp. 2008
   5  *
   6  * Authors:
   7  *  Anthony Liguori   <aliguori@us.ibm.com>
   8  *
   9  * This work is licensed under the terms of the GNU GPL, version 2.  See
  10  * the COPYING file in the top-level directory.
  11  *
  12  * Contributions after 2012-01-13 are licensed under the terms of the
  13  * GNU GPL, version 2 or (at your option) any later version.
  14  */
  15
  16 #include "qemu/osdep.h"
  17 #include "qemu-common.h"
  18 #include "block/block.h"
  19 #include "qemu/rcu_queue.h"
  20 #include "qemu/sockets.h"
  21 #include "qemu/cutils.h"
  22 #include "trace-root.h"
  23 #ifdef CONFIG_EPOLL_CREATE1
  24 #include <sys/epoll.h>
  25 #endif
  26
  27 struct AioHandler
  28 {
  29     GPollFD pfd;
  30     IOHandler *io_read;
  31     IOHandler *io_write;
  32     AioPollFn *io_poll;
  33     IOHandler *io_poll_begin;
  34     IOHandler *io_poll_end;
  35     int deleted;
  36     void *opaque;
  37     bool is_external;
  38     QLIST_ENTRY(AioHandler) node;
  39 };
  40
  41 #ifdef CONFIG_EPOLL_CREATE1
  42
  43 /* The fd number threashold to switch to epoll */
  44 #define EPOLL_ENABLE_THRESHOLD 64
  45
  46 static void aio_epoll_disable(AioContext *ctx)
  47 {
  48     ctx->epoll_available = false;
  49     if (!ctx->epoll_enabled) {
  50         return;
  51     }
  52     ctx->epoll_enabled = false;
  53     close(ctx->epollfd);
  54 }
  55
  56 static inline int epoll_events_from_pfd(int pfd_events)
  57 {
  58     return (pfd_events & G_IO_IN ? EPOLLIN : 0) |
  59            (pfd_events & G_IO_OUT ? EPOLLOUT : 0) |
  60            (pfd_events & G_IO_HUP ? EPOLLHUP : 0) |
  61            (pfd_events & G_IO_ERR ? EPOLLERR : 0);
  62 }
  63
  64 static bool aio_epoll_try_enable(AioContext *ctx)
  65 {
  66     AioHandler *node;
  67     struct epoll_event event;
  68
  69     QLIST_FOREACH_RCU(node, &ctx->aio_handlers, node) {
  70         int r;
  71         if (node->deleted || !node->pfd.events) {
  72             continue;
  73         }
  74         event.events = epoll_events_from_pfd(node->pfd.events);
  75         event.data.ptr = node;
  76         r = epoll_ctl(ctx->epollfd, EPOLL_CTL_ADD, node->pfd.fd, &event);
  77         if (r) {
  78             return false;
  79         }
  80     }
  81     ctx->epoll_enabled = true;
  82     return true;
  83 }
  84
  85 static void aio_epoll_update(AioContext *ctx, AioHandler *node, bool is_new)
  86 {
  87     struct epoll_event event;
  88     int r;
  89     int ctl;
  90
  91     if (!ctx->epoll_enabled) {
  92         return;
  93     }
  94     if (!node->pfd.events) {
  95         ctl = EPOLL_CTL_DEL;
  96     } else {
  97         event.data.ptr = node;
  98         event.events = epoll_events_from_pfd(node->pfd.events);
  99         ctl = is_new ? EPOLL_CTL_ADD : EPOLL_CTL_MOD;
 100     }
 101
 102     r = epoll_ctl(ctx->epollfd, ctl, node->pfd.fd, &event);
 103     if (r) {
 104         aio_epoll_disable(ctx);
 105     }
 106 }
 107
 108 static int aio_epoll(AioContext *ctx, GPollFD *pfds,
 109                      unsigned npfd, int64_t timeout)
 110 {
 111     AioHandler *node;
 112     int i, ret = 0;
 113     struct epoll_event events[128];
 114
 115     assert(npfd == 1);
 116     assert(pfds[0].fd == ctx->epollfd);
 117     if (timeout > 0) {
 118         ret = qemu_poll_ns(pfds, npfd, timeout);
 119     }
 120     if (timeout <= 0 || ret > 0) {
 121         ret = epoll_wait(ctx->epollfd, events,
 122                          sizeof(events) / sizeof(events[0]),
 123                          timeout);
 124         if (ret <= 0) {
 125             goto out;
 126         }
 127         for (i = 0; i < ret; i++) {
 128             int ev = events[i].events;
 129             node = events[i].data.ptr;
 130             node->pfd.revents = (ev & EPOLLIN ? G_IO_IN : 0) |
 131                 (ev & EPOLLOUT ? G_IO_OUT : 0) |
 132                 (ev & EPOLLHUP ? G_IO_HUP : 0) |
 133                 (ev & EPOLLERR ? G_IO_ERR : 0);
 134         }
 135     }
 136 out:
 137     return ret;
 138 }
 139
 140 static bool aio_epoll_enabled(AioContext *ctx)
 141 {
 142     /* Fall back to ppoll when external clients are disabled. */
 143     return !aio_external_disabled(ctx) && ctx->epoll_enabled;
 144 }
 145
 146 static bool aio_epoll_check_poll(AioContext *ctx, GPollFD *pfds,
 147                                  unsigned npfd, int64_t timeout)
 148 {
 149     if (!ctx->epoll_available) {
 150         return false;
 151     }
 152     if (aio_epoll_enabled(ctx)) {
 153         return true;
 154     }
 155     if (npfd >= EPOLL_ENABLE_THRESHOLD) {
 156         if (aio_epoll_try_enable(ctx)) {
 157             return true;
 158         } else {
 159             aio_epoll_disable(ctx);
 160         }
 161     }
 162     return false;
 163 }
 164
 165 #else
 166
 167 static void aio_epoll_update(AioContext *ctx, AioHandler *node, bool is_new)
 168 {
 169 }
 170
 171 static int aio_epoll(AioContext *ctx, GPollFD *pfds,
 172                      unsigned npfd, int64_t timeout)
 173 {
 174     assert(false);
 175 }
 176
 177 static bool aio_epoll_enabled(AioContext *ctx)
 178 {
 179     return false;
 180 }
 181
 182 static bool aio_epoll_check_poll(AioContext *ctx, GPollFD *pfds,
 183                           unsigned npfd, int64_t timeout)
 184 {
 185     return false;
 186 }
 187
 188 #endif
 189
 190 static AioHandler *find_aio_handler(AioContext *ctx, int fd)
 191 {
 192     AioHandler *node;
 193
 194     QLIST_FOREACH(node, &ctx->aio_handlers, node) {
 195         if (node->pfd.fd == fd)
 196             if (!node->deleted)
 197                 return node;
 198     }
 199
 200     return NULL;
 201 }
 202
 203 void aio_set_fd_handler(AioContext *ctx,
 204                         int fd,
 205                         bool is_external,
 206                         IOHandler *io_read,
 207                         IOHandler *io_write,
 208                         AioPollFn *io_poll,
 209                         void *opaque)
 210 {
 211     AioHandler *node;
 212     bool is_new = false;
 213     bool deleted = false;
 214
 215     qemu_lockcnt_lock(&ctx->list_lock);
 216
 217     node = find_aio_handler(ctx, fd);
 218
 219     /* Are we deleting the fd handler? */
 220     if (!io_read && !io_write && !io_poll) {
 221         if (node == NULL) {
 222             qemu_lockcnt_unlock(&ctx->list_lock);
 223             return;
 224         }
 225
 226         g_source_remove_poll(&ctx->source, &node->pfd);
 227
 228         /* If the lock is held, just mark the node as deleted */
 229         if (qemu_lockcnt_count(&ctx->list_lock)) {
 230             node->deleted = 1;
 231             node->pfd.revents = 0;
 232         } else {
 233             /* Otherwise, delete it for real.  We can't just mark it as
 234              * deleted because deleted nodes are only cleaned up while
 235              * no one is walking the handlers list.
 236              */
 237             QLIST_REMOVE(node, node);
 238             deleted = true;
 239         }
 240
 241         if (!node->io_poll) {
 242             ctx->poll_disable_cnt--;
 243         }
 244     } else {
 245         if (node == NULL) {
 246             /* Alloc and insert if it's not already there */
 247             node = g_new0(AioHandler, 1);
 248             node->pfd.fd = fd;
 249             QLIST_INSERT_HEAD_RCU(&ctx->aio_handlers, node, node);
 250
 251             g_source_add_poll(&ctx->source, &node->pfd);
 252             is_new = true;
 253
 254             ctx->poll_disable_cnt += !io_poll;
 255         } else {
 256             ctx->poll_disable_cnt += !io_poll - !node->io_poll;
 257         }
 258
 259         /* Update handler with latest information */
 260         node->io_read = io_read;
 261         node->io_write = io_write;
 262         node->io_poll = io_poll;
 263         node->opaque = opaque;
 264         node->is_external = is_external;
 265
 266         node->pfd.events = (io_read ? G_IO_IN | G_IO_HUP | G_IO_ERR : 0);
 267         node->pfd.events |= (io_write ? G_IO_OUT | G_IO_ERR : 0);
 268     }
 269
 270     aio_epoll_update(ctx, node, is_new);
 271     qemu_lockcnt_unlock(&ctx->list_lock);
 272     aio_notify(ctx);
 273
 274     if (deleted) {
 275         g_free(node);
 276     }
 277 }
 278
 279 void aio_set_fd_poll(AioContext *ctx, int fd,
 280                      IOHandler *io_poll_begin,
 281                      IOHandler *io_poll_end)
 282 {
 283     AioHandler *node = find_aio_handler(ctx, fd);
 284
 285     if (!node) {
 286         return;
 287     }
 288
 289     node->io_poll_begin = io_poll_begin;
 290     node->io_poll_end = io_poll_end;
 291 }
 292
 293 void aio_set_event_notifier(AioContext *ctx,
 294                             EventNotifier *notifier,
 295                             bool is_external,
 296                             EventNotifierHandler *io_read,
 297                             AioPollFn *io_poll)
 298 {
 299     aio_set_fd_handler(ctx, event_notifier_get_fd(notifier), is_external,
 300                        (IOHandler *)io_read, NULL, io_poll, notifier);
 301 }
 302
 303 void aio_set_event_notifier_poll(AioContext *ctx,
 304                                  EventNotifier *notifier,
 305                                  EventNotifierHandler *io_poll_begin,
 306                                  EventNotifierHandler *io_poll_end)
 307 {
 308     aio_set_fd_poll(ctx, event_notifier_get_fd(notifier),
 309                     (IOHandler *)io_poll_begin,
 310                     (IOHandler *)io_poll_end);
 311 }
 312
 313 static void poll_set_started(AioContext *ctx, bool started)
 314 {
 315     AioHandler *node;
 316
 317     if (started == ctx->poll_started) {
 318         return;
 319     }
 320
 321     ctx->poll_started = started;
 322
 323     qemu_lockcnt_inc(&ctx->list_lock);
 324     QLIST_FOREACH_RCU(node, &ctx->aio_handlers, node) {
 325         IOHandler *fn;
 326
 327         if (node->deleted) {
 328             continue;
 329         }
 330
 331         if (started) {
 332             fn = node->io_poll_begin;
 333         } else {
 334             fn = node->io_poll_end;
 335         }
 336
 337         if (fn) {
 338             fn(node->opaque);
 339         }
 340     }
 341     qemu_lockcnt_dec(&ctx->list_lock);
 342 }
 343
 344
 345 bool aio_prepare(AioContext *ctx)
 346 {
 347     /* Poll mode cannot be used with glib's event loop, disable it. */
 348     poll_set_started(ctx, false);
 349
 350     return false;
 351 }
 352
 353 bool aio_pending(AioContext *ctx)
 354 {
 355     AioHandler *node;
 356     bool result = false;
 357
 358     /*
 359      * We have to walk very carefully in case aio_set_fd_handler is
 360      * called while we're walking.
 361      */
 362     qemu_lockcnt_inc(&ctx->list_lock);
 363
 364     QLIST_FOREACH_RCU(node, &ctx->aio_handlers, node) {
 365         int revents;
 366
 367         revents = node->pfd.revents & node->pfd.events;
 368         if (revents & (G_IO_IN | G_IO_HUP | G_IO_ERR) && node->io_read &&
 369             aio_node_check(ctx, node->is_external)) {
 370             result = true;
 371             break;
 372         }
 373         if (revents & (G_IO_OUT | G_IO_ERR) && node->io_write &&
 374             aio_node_check(ctx, node->is_external)) {
 375             result = true;
 376             break;
 377         }
 378     }
 379     qemu_lockcnt_dec(&ctx->list_lock);
 380
 381     return result;
 382 }
 383
 384 static bool aio_dispatch_handlers(AioContext *ctx)
 385 {
 386     AioHandler *node, *tmp;
 387     bool progress = false;
 388
 389     /*
 390      * We have to walk very carefully in case aio_set_fd_handler is
 391      * called while we're walking.
 392      */
 393     qemu_lockcnt_inc(&ctx->list_lock);
 394
 395     QLIST_FOREACH_SAFE_RCU(node, &ctx->aio_handlers, node, tmp) {
 396         int revents;
 397
 398         revents = node->pfd.revents & node->pfd.events;
 399         node->pfd.revents = 0;
 400
 401         if (!node->deleted &&
 402             (revents & (G_IO_IN | G_IO_HUP | G_IO_ERR)) &&
 403             aio_node_check(ctx, node->is_external) &&
 404             node->io_read) {
 405             node->io_read(node->opaque);
 406
 407             /* aio_notify() does not count as progress */
 408             if (node->opaque != &ctx->notifier) {
 409                 progress = true;
 410             }
 411         }
 412         if (!node->deleted &&
 413             (revents & (G_IO_OUT | G_IO_ERR)) &&
 414             aio_node_check(ctx, node->is_external) &&
 415             node->io_write) {
 416             node->io_write(node->opaque);
 417             progress = true;
 418         }
 419
 420         if (node->deleted) {
 421             if (qemu_lockcnt_dec_if_lock(&ctx->list_lock)) {
 422                 QLIST_REMOVE(node, node);
 423                 g_free(node);
 424                 qemu_lockcnt_inc_and_unlock(&ctx->list_lock);
 425             }
 426         }
 427     }
 428
 429     qemu_lockcnt_dec(&ctx->list_lock);
 430     return progress;
 431 }
 432
 433 /*
 434  * Note that dispatch_fds == false has the side-effect of post-poning the
 435  * freeing of deleted handlers.
 436  */
 437 bool aio_dispatch(AioContext *ctx, bool dispatch_fds)
 438 {
 439     bool progress;
 440
 441     /*
 442      * If there are callbacks left that have been queued, we need to call them.
 443      * Do not call select in this case, because it is possible that the caller
 444      * does not need a complete flush (as is the case for aio_poll loops).
 445      */
 446     progress = aio_bh_poll(ctx);
 447
 448     if (dispatch_fds) {
 449         progress |= aio_dispatch_handlers(ctx);
 450     }
 451
 452     /* Run our timers */
 453     progress |= timerlistgroup_run_timers(&ctx->tlg);
 454
 455     return progress;
 456 }
 457
 458 /* These thread-local variables are used only in a small part of aio_poll
 459  * around the call to the poll() system call.  In particular they are not
 460  * used while aio_poll is performing callbacks, which makes it much easier
 461  * to think about reentrancy!
 462  *
 463  * Stack-allocated arrays would be perfect but they have size limitations;
 464  * heap allocation is expensive enough that we want to reuse arrays across
 465  * calls to aio_poll().  And because poll() has to be called without holding
 466  * any lock, the arrays cannot be stored in AioContext.  Thread-local data
 467  * has none of the disadvantages of these three options.
 468  */
 469 static __thread GPollFD *pollfds;
 470 static __thread AioHandler **nodes;
 471 static __thread unsigned npfd, nalloc;
 472 static __thread Notifier pollfds_cleanup_notifier;
 473
 474 static void pollfds_cleanup(Notifier *n, void *unused)
 475 {
 476     g_assert(npfd == 0);
 477     g_free(pollfds);
 478     g_free(nodes);
 479     nalloc = 0;
 480 }
 481
 482 static void add_pollfd(AioHandler *node)
 483 {
 484     if (npfd == nalloc) {
 485         if (nalloc == 0) {
 486             pollfds_cleanup_notifier.notify = pollfds_cleanup;
 487             qemu_thread_atexit_add(&pollfds_cleanup_notifier);
 488             nalloc = 8;
 489         } else {
 490             g_assert(nalloc <= INT_MAX);
 491             nalloc *= 2;
 492         }
 493         pollfds = g_renew(GPollFD, pollfds, nalloc);
 494         nodes = g_renew(AioHandler *, nodes, nalloc);
 495     }
 496     nodes[npfd] = node;
 497     pollfds[npfd] = (GPollFD) {
 498         .fd = node->pfd.fd,
 499         .events = node->pfd.events,
 500     };
 501     npfd++;
 502 }
 503
 504 static bool run_poll_handlers_once(AioContext *ctx)
 505 {
 506     bool progress = false;
 507     AioHandler *node;
 508
 509     QLIST_FOREACH_RCU(node, &ctx->aio_handlers, node) {
 510         if (!node->deleted && node->io_poll &&
 511             aio_node_check(ctx, node->is_external) &&
 512             node->io_poll(node->opaque)) {
 513             progress = true;
 514         }
 515
 516         /* Caller handles freeing deleted nodes.  Don't do it here. */
 517     }
 518
 519     return progress;
 520 }
 521
 522 /* run_poll_handlers:
 523  * @ctx: the AioContext
 524  * @max_ns: maximum time to poll for, in nanoseconds
 525  *
 526  * Polls for a given time.
 527  *
 528  * Note that ctx->notify_me must be non-zero so this function can detect
 529  * aio_notify().
 530  *
 531  * Note that the caller must have incremented ctx->list_lock.
 532  *
 533  * Returns: true if progress was made, false otherwise
 534  */
 535 static bool run_poll_handlers(AioContext *ctx, int64_t max_ns)
 536 {
 537     bool progress;
 538     int64_t end_time;
 539
 540     assert(ctx->notify_me);
 541     assert(qemu_lockcnt_count(&ctx->list_lock) > 0);
 542     assert(ctx->poll_disable_cnt == 0);
 543
 544     trace_run_poll_handlers_begin(ctx, max_ns);
 545
 546     end_time = qemu_clock_get_ns(QEMU_CLOCK_REALTIME) + max_ns;
 547
 548     do {
 549         progress = run_poll_handlers_once(ctx);
 550     } while (!progress && qemu_clock_get_ns(QEMU_CLOCK_REALTIME) < end_time);
 551
 552     trace_run_poll_handlers_end(ctx, progress);
 553
 554     return progress;
 555 }
 556
 557 /* try_poll_mode:
 558  * @ctx: the AioContext
 559  * @blocking: busy polling is only attempted when blocking is true
 560  *
 561  * ctx->notify_me must be non-zero so this function can detect aio_notify().
 562  *
 563  * Note that the caller must have incremented ctx->list_lock.
 564  *
 565  * Returns: true if progress was made, false otherwise
 566  */
 567 static bool try_poll_mode(AioContext *ctx, bool blocking)
 568 {
 569     if (blocking && ctx->poll_max_ns && ctx->poll_disable_cnt == 0) {
 570         /* See qemu_soonest_timeout() uint64_t hack */
 571         int64_t max_ns = MIN((uint64_t)aio_compute_timeout(ctx),
 572                              (uint64_t)ctx->poll_ns);
 573
 574         if (max_ns) {
 575             poll_set_started(ctx, true);
 576
 577             if (run_poll_handlers(ctx, max_ns)) {
 578                 return true;
 579             }
 580         }
 581     }
 582
 583     poll_set_started(ctx, false);
 584
 585     /* Even if we don't run busy polling, try polling once in case it can make
 586      * progress and the caller will be able to avoid ppoll(2)/epoll_wait(2).
 587      */
 588     return run_poll_handlers_once(ctx);
 589 }
 590
 591 bool aio_poll(AioContext *ctx, bool blocking)
 592 {
 593     AioHandler *node;
 594     int i;
 595     int ret = 0;
 596     bool progress;
 597     int64_t timeout;
 598     int64_t start = 0;
 599
 600     aio_context_acquire(ctx);
 601     progress = false;
 602
 603     /* aio_notify can avoid the expensive event_notifier_set if
 604      * everything (file descriptors, bottom halves, timers) will
 605      * be re-evaluated before the next blocking poll().  This is
 606      * already true when aio_poll is called with blocking == false;
 607      * if blocking == true, it is only true after poll() returns,
 608      * so disable the optimization now.
 609      */
 610     if (blocking) {
 611         atomic_add(&ctx->notify_me, 2);
 612     }
 613
 614     qemu_lockcnt_inc(&ctx->list_lock);
 615
 616     if (ctx->poll_max_ns) {
 617         start = qemu_clock_get_ns(QEMU_CLOCK_REALTIME);
 618     }
 619
 620     if (try_poll_mode(ctx, blocking)) {
 621         progress = true;
 622     } else {
 623         assert(npfd == 0);
 624
 625         /* fill pollfds */
 626
 627         if (!aio_epoll_enabled(ctx)) {
 628             QLIST_FOREACH_RCU(node, &ctx->aio_handlers, node) {
 629                 if (!node->deleted && node->pfd.events
 630                     && aio_node_check(ctx, node->is_external)) {
 631                     add_pollfd(node);
 632                 }
 633             }
 634         }
 635
 636         timeout = blocking ? aio_compute_timeout(ctx) : 0;
 637
 638         /* wait until next event */
 639         if (timeout) {
 640             aio_context_release(ctx);
 641         }
 642         if (aio_epoll_check_poll(ctx, pollfds, npfd, timeout)) {
 643             AioHandler epoll_handler;
 644
 645             epoll_handler.pfd.fd = ctx->epollfd;
 646             epoll_handler.pfd.events = G_IO_IN | G_IO_OUT | G_IO_HUP | G_IO_ERR;
 647             npfd = 0;
 648             add_pollfd(&epoll_handler);
 649             ret = aio_epoll(ctx, pollfds, npfd, timeout);
 650         } else  {
 651             ret = qemu_poll_ns(pollfds, npfd, timeout);
 652         }
 653         if (timeout) {
 654             aio_context_acquire(ctx);
 655         }
 656     }
 657
 658     if (blocking) {
 659         atomic_sub(&ctx->notify_me, 2);
 660     }
 661
 662     /* Adjust polling time */
 663     if (ctx->poll_max_ns) {
 664         int64_t block_ns = qemu_clock_get_ns(QEMU_CLOCK_REALTIME) - start;
 665
 666         if (block_ns <= ctx->poll_ns) {
 667             /* This is the sweet spot, no adjustment needed */
 668         } else if (block_ns > ctx->poll_max_ns) {
 669             /* We'd have to poll for too long, poll less */
 670             int64_t old = ctx->poll_ns;
 671
 672             if (ctx->poll_shrink) {
 673                 ctx->poll_ns /= ctx->poll_shrink;
 674             } else {
 675                 ctx->poll_ns = 0;
 676             }
 677
 678             trace_poll_shrink(ctx, old, ctx->poll_ns);
 679         } else if (ctx->poll_ns < ctx->poll_max_ns &&
 680                    block_ns < ctx->poll_max_ns) {
 681             /* There is room to grow, poll longer */
 682             int64_t old = ctx->poll_ns;
 683             int64_t grow = ctx->poll_grow;
 684
 685             if (grow == 0) {
 686                 grow = 2;
 687             }
 688
 689             if (ctx->poll_ns) {
 690                 ctx->poll_ns *= grow;
 691             } else {
 692                 ctx->poll_ns = 4000; /* start polling at 4 microseconds */
 693             }
 694
 695             if (ctx->poll_ns > ctx->poll_max_ns) {
 696                 ctx->poll_ns = ctx->poll_max_ns;
 697             }
 698
 699             trace_poll_grow(ctx, old, ctx->poll_ns);
 700         }
 701     }
 702
 703     aio_notify_accept(ctx);
 704
 705     /* if we have any readable fds, dispatch event */
 706     if (ret > 0) {
 707         for (i = 0; i < npfd; i++) {
 708             nodes[i]->pfd.revents = pollfds[i].revents;
 709         }
 710     }
 711
 712     npfd = 0;
 713     qemu_lockcnt_dec(&ctx->list_lock);
 714
 715     /* Run dispatch even if there were no readable fds to run timers */
 716     if (aio_dispatch(ctx, ret > 0)) {
 717         progress = true;
 718     }
 719
 720     aio_context_release(ctx);
 721
 722     return progress;
 723 }
 724
 725 void aio_context_setup(AioContext *ctx)
 726 {
 727     /* TODO remove this in final patch submission */
 728     if (getenv("QEMU_AIO_POLL_MAX_NS")) {
 729         fprintf(stderr, "The QEMU_AIO_POLL_MAX_NS environment variable has "
 730                 "been replaced with -object iothread,poll-max-ns=NUM\n");
 731         exit(1);
 732     }
 733
 734 #ifdef CONFIG_EPOLL_CREATE1
 735     assert(!ctx->epollfd);
 736     ctx->epollfd = epoll_create1(EPOLL_CLOEXEC);
 737     if (ctx->epollfd == -1) {
 738         fprintf(stderr, "Failed to create epoll instance: %s", strerror(errno));
 739         ctx->epoll_available = false;
 740     } else {
 741         ctx->epoll_available = true;
 742     }
 743 #endif
 744 }
 745
 746 void aio_context_set_poll_params(AioContext *ctx, int64_t max_ns,
 747                                  int64_t grow, int64_t shrink, Error **errp)
 748 {
 749     /* No thread synchronization here, it doesn't matter if an incorrect value
 750      * is used once.
 751      */
 752     ctx->poll_max_ns = max_ns;
 753     ctx->poll_ns = 0;
 754     ctx->poll_grow = grow;
 755     ctx->poll_shrink = shrink;
 756
 757     aio_notify(ctx);
 758 }