util/aio-wait.c

   1 /*
   2  * AioContext wait support
   3  *
   4  * Copyright (C) 2018 Red Hat, Inc.
   5  *
   6  * Permission is hereby granted, free of charge, to any person obtaining a copy
   7  * of this software and associated documentation files (the "Software"), to deal
   8  * in the Software without restriction, including without limitation the rights
   9  * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  10  * copies of the Software, and to permit persons to whom the Software is
  11  * furnished to do so, subject to the following conditions:
  12  *
  13  * The above copyright notice and this permission notice shall be included in
  14  * all copies or substantial portions of the Software.
  15  *
  16  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  17  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  18  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
  19  * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  20  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  21  * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
  22  * THE SOFTWARE.
  23  */
  24
  25 #include "qemu/osdep.h"
  26 #include "qemu/main-loop.h"
  27 #include "block/aio-wait.h"
  28
  29 AioWait global_aio_wait;
  30
  31 static void dummy_bh_cb(void *opaque)
  32 {
  33     /* The point is to make AIO_WAIT_WHILE()'s aio_poll() return */
  34 }
  35
  36 void aio_wait_kick(void)
  37 {
  38     /*
  39      * Paired with smp_mb in AIO_WAIT_WHILE. Here we have:
  40      * write(condition);
  41      * aio_wait_kick() {
  42      *      smp_mb();
  43      *      read(num_waiters);
  44      * }
  45      *
  46      * And in AIO_WAIT_WHILE:
  47      * write(num_waiters);
  48      * smp_mb();
  49      * read(condition);
  50      */
  51     smp_mb();
  52
  53     if (qatomic_read(&global_aio_wait.num_waiters)) {
  54         aio_bh_schedule_oneshot(qemu_get_aio_context(), dummy_bh_cb, NULL);
  55     }
  56 }
  57
  58 typedef struct {
  59     bool done;
  60     QEMUBHFunc *cb;
  61     void *opaque;
  62 } AioWaitBHData;
  63
  64 /* Context: BH in IOThread */
  65 static void aio_wait_bh(void *opaque)
  66 {
  67     AioWaitBHData *data = opaque;
  68
  69     data->cb(data->opaque);
  70
  71     data->done = true;
  72     aio_wait_kick();
  73 }
  74
  75 void aio_wait_bh_oneshot(AioContext *ctx, QEMUBHFunc *cb, void *opaque)
  76 {
  77     AioWaitBHData data = {
  78         .cb = cb,
  79         .opaque = opaque,
  80     };
  81
  82     assert(qemu_get_current_aio_context() == qemu_get_aio_context());
  83
  84     aio_bh_schedule_oneshot(ctx, aio_wait_bh, &data);
  85     AIO_WAIT_WHILE_UNLOCKED(NULL, !data.done);
  86 }