qemu

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/*
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 * AioContext wait support
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 *
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 * Copyright (C) 2018 Red Hat, Inc.
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 *
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 * Permission is hereby granted, free of charge, to any person obtaining a copy
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 * of this software and associated documentation files (the "Software"), to deal
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 * in the Software without restriction, including without limitation the rights
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 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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 * copies of the Software, and to permit persons to whom the Software is
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 * furnished to do so, subject to the following conditions:
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 *
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 * The above copyright notice and this permission notice shall be included in
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 * all copies or substantial portions of the Software.
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 *
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 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
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 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
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 * THE SOFTWARE.
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 */
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#include "qemu/osdep.h"
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#include "qemu/main-loop.h"
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#include "block/aio-wait.h"
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AioWait global_aio_wait;
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static void dummy_bh_cb(void *opaque)
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{
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    /* The point is to make AIO_WAIT_WHILE()'s aio_poll() return */
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}
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void aio_wait_kick(void)
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{
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    /*
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     * Paired with smp_mb in AIO_WAIT_WHILE. Here we have:
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     * write(condition);
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     * aio_wait_kick() {
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     *      smp_mb();
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     *      read(num_waiters);
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     * }
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     *
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     * And in AIO_WAIT_WHILE:
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     * write(num_waiters);
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     * smp_mb();
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     * read(condition);
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     */
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    smp_mb();
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    if (qatomic_read(&global_aio_wait.num_waiters)) {
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        aio_bh_schedule_oneshot(qemu_get_aio_context(), dummy_bh_cb, NULL);
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    }
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}
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typedef struct {
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    bool done;
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    QEMUBHFunc *cb;
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    void *opaque;
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} AioWaitBHData;
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/* Context: BH in IOThread */
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static void aio_wait_bh(void *opaque)
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{
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    AioWaitBHData *data = opaque;
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    data->cb(data->opaque);
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    data->done = true;
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    aio_wait_kick();
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}
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void aio_wait_bh_oneshot(AioContext *ctx, QEMUBHFunc *cb, void *opaque)
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{
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    AioWaitBHData data = {
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        .cb = cb,
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        .opaque = opaque,
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    };
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    assert(qemu_get_current_aio_context() == qemu_get_aio_context());
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    aio_bh_schedule_oneshot(ctx, aio_wait_bh, &data);
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    AIO_WAIT_WHILE_UNLOCKED(NULL, !data.done);
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}
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