LXR qemu/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
  29AioWait global_aio_wait;
  30
  31static void dummy_bh_cb(void *opaque)
  32{
  33    /* The point is to make AIO_WAIT_WHILE()'s aio_poll() return */
  34}
  35
  36void 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
  58typedef struct {
  59    bool done;
  60    QEMUBHFunc *cb;
  61    void *opaque;
  62} AioWaitBHData;
  63
  64/* Context: BH in IOThread */
  65static 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
  75void 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(ctx, !data.done);
  86}
  87