async.c 8.25 KB
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/*
 * QEMU System Emulator
 *
 * Copyright (c) 2003-2008 Fabrice Bellard
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */

#include "qemu-common.h"
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#include "block/aio.h"
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#include "block/thread-pool.h"
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#include "qemu/main-loop.h"
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#include "qemu/atomic.h"
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/***********************************************************/
/* bottom halves (can be seen as timers which expire ASAP) */

struct QEMUBH {
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    AioContext *ctx;
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    QEMUBHFunc *cb;
    void *opaque;
    QEMUBH *next;
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    bool scheduled;
    bool idle;
    bool deleted;
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};

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QEMUBH *aio_bh_new(AioContext *ctx, QEMUBHFunc *cb, void *opaque)
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{
    QEMUBH *bh;
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    bh = g_malloc0(sizeof(QEMUBH));
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    bh->ctx = ctx;
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    bh->cb = cb;
    bh->opaque = opaque;
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    qemu_mutex_lock(&ctx->bh_lock);
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    bh->next = ctx->first_bh;
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    /* Make sure that the members are ready before putting bh into list */
    smp_wmb();
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    ctx->first_bh = bh;
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    qemu_mutex_unlock(&ctx->bh_lock);
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    return bh;
}

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/* Multiple occurrences of aio_bh_poll cannot be called concurrently */
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int aio_bh_poll(AioContext *ctx)
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{
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    QEMUBH *bh, **bhp, *next;
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    int ret;
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    ctx->walking_bh++;
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    ret = 0;
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    for (bh = ctx->first_bh; bh; bh = next) {
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        /* Make sure that fetching bh happens before accessing its members */
        smp_read_barrier_depends();
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        next = bh->next;
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        if (!bh->deleted && bh->scheduled) {
            bh->scheduled = 0;
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            /* Paired with write barrier in bh schedule to ensure reading for
             * idle & callbacks coming after bh's scheduling.
             */
            smp_rmb();
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            if (!bh->idle)
                ret = 1;
            bh->idle = 0;
            bh->cb(bh->opaque);
        }
    }

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    ctx->walking_bh--;
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    /* remove deleted bhs */
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    if (!ctx->walking_bh) {
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        qemu_mutex_lock(&ctx->bh_lock);
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        bhp = &ctx->first_bh;
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        while (*bhp) {
            bh = *bhp;
            if (bh->deleted) {
                *bhp = bh->next;
                g_free(bh);
            } else {
                bhp = &bh->next;
            }
        }
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        qemu_mutex_unlock(&ctx->bh_lock);
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    }

    return ret;
}

void qemu_bh_schedule_idle(QEMUBH *bh)
{
    if (bh->scheduled)
        return;
    bh->idle = 1;
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    /* Make sure that idle & any writes needed by the callback are done
     * before the locations are read in the aio_bh_poll.
     */
    smp_wmb();
    bh->scheduled = 1;
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}

void qemu_bh_schedule(QEMUBH *bh)
{
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    AioContext *ctx;

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    if (bh->scheduled)
        return;
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    ctx = bh->ctx;
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    bh->idle = 0;
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    /* Make sure that:
     * 1. idle & any writes needed by the callback are done before the
     *    locations are read in the aio_bh_poll.
     * 2. ctx is loaded before scheduled is set and the callback has a chance
     *    to execute.
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     */
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    smp_mb();
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    bh->scheduled = 1;
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    aio_notify(ctx);
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}

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/* This func is async.
 */
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void qemu_bh_cancel(QEMUBH *bh)
{
    bh->scheduled = 0;
}

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/* This func is async.The bottom half will do the delete action at the finial
 * end.
 */
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void qemu_bh_delete(QEMUBH *bh)
{
    bh->scheduled = 0;
    bh->deleted = 1;
}

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int64_t
aio_compute_timeout(AioContext *ctx)
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{
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    int64_t deadline;
    int timeout = -1;
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    QEMUBH *bh;

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    for (bh = ctx->first_bh; bh; bh = bh->next) {
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        if (!bh->deleted && bh->scheduled) {
            if (bh->idle) {
                /* idle bottom halves will be polled at least
                 * every 10ms */
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                timeout = 10000000;
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            } else {
                /* non-idle bottom halves will be executed
                 * immediately */
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                return 0;
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            }
        }
    }
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    deadline = timerlistgroup_deadline_ns(&ctx->tlg);
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    if (deadline == 0) {
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        return 0;
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    } else {
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        return qemu_soonest_timeout(timeout, deadline);
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    }
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}
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static gboolean
aio_ctx_prepare(GSource *source, gint    *timeout)
{
    AioContext *ctx = (AioContext *) source;

    /* We assume there is no timeout already supplied */
    *timeout = qemu_timeout_ns_to_ms(aio_compute_timeout(ctx));
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    if (aio_prepare(ctx)) {
        *timeout = 0;
    }

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    return *timeout == 0;
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}

static gboolean
aio_ctx_check(GSource *source)
{
    AioContext *ctx = (AioContext *) source;
    QEMUBH *bh;

    for (bh = ctx->first_bh; bh; bh = bh->next) {
        if (!bh->deleted && bh->scheduled) {
            return true;
	}
    }
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    return aio_pending(ctx) || (timerlistgroup_deadline_ns(&ctx->tlg) == 0);
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}

static gboolean
aio_ctx_dispatch(GSource     *source,
                 GSourceFunc  callback,
                 gpointer     user_data)
{
    AioContext *ctx = (AioContext *) source;

    assert(callback == NULL);
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    aio_dispatch(ctx);
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    return true;
}

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static void
aio_ctx_finalize(GSource     *source)
{
    AioContext *ctx = (AioContext *) source;

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    thread_pool_free(ctx->thread_pool);
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    aio_set_event_notifier(ctx, &ctx->notifier, NULL);
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    event_notifier_cleanup(&ctx->notifier);
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    rfifolock_destroy(&ctx->lock);
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    qemu_mutex_destroy(&ctx->bh_lock);
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    g_array_free(ctx->pollfds, TRUE);
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    timerlistgroup_deinit(&ctx->tlg);
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}

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static GSourceFuncs aio_source_funcs = {
    aio_ctx_prepare,
    aio_ctx_check,
    aio_ctx_dispatch,
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    aio_ctx_finalize
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};

GSource *aio_get_g_source(AioContext *ctx)
{
    g_source_ref(&ctx->source);
    return &ctx->source;
}
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ThreadPool *aio_get_thread_pool(AioContext *ctx)
{
    if (!ctx->thread_pool) {
        ctx->thread_pool = thread_pool_new(ctx);
    }
    return ctx->thread_pool;
}

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void aio_set_dispatching(AioContext *ctx, bool dispatching)
{
    ctx->dispatching = dispatching;
    if (!dispatching) {
        /* Write ctx->dispatching before reading e.g. bh->scheduled.
         * Optimization: this is only needed when we're entering the "unsafe"
         * phase where other threads must call event_notifier_set.
         */
        smp_mb();
    }
}

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void aio_notify(AioContext *ctx)
{
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    /* Write e.g. bh->scheduled before reading ctx->dispatching.  */
    smp_mb();
    if (!ctx->dispatching) {
        event_notifier_set(&ctx->notifier);
    }
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}

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static void aio_timerlist_notify(void *opaque)
{
    aio_notify(opaque);
}

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static void aio_rfifolock_cb(void *opaque)
{
    /* Kick owner thread in case they are blocked in aio_poll() */
    aio_notify(opaque);
}

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AioContext *aio_context_new(Error **errp)
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{
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    int ret;
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    AioContext *ctx;
    ctx = (AioContext *) g_source_new(&aio_source_funcs, sizeof(AioContext));
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    ret = event_notifier_init(&ctx->notifier, false);
    if (ret < 0) {
        g_source_destroy(&ctx->source);
        error_setg_errno(errp, -ret, "Failed to initialize event notifier");
        return NULL;
    }
    aio_set_event_notifier(ctx, &ctx->notifier,
                           (EventNotifierHandler *)
                           event_notifier_test_and_clear);
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    ctx->pollfds = g_array_new(FALSE, FALSE, sizeof(GPollFD));
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    ctx->thread_pool = NULL;
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    qemu_mutex_init(&ctx->bh_lock);
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    rfifolock_init(&ctx->lock, aio_rfifolock_cb, ctx);
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    timerlistgroup_init(&ctx->tlg, aio_timerlist_notify, ctx);
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    return ctx;
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}

void aio_context_ref(AioContext *ctx)
{
    g_source_ref(&ctx->source);
}

void aio_context_unref(AioContext *ctx)
{
    g_source_unref(&ctx->source);
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}
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void aio_context_acquire(AioContext *ctx)
{
    rfifolock_lock(&ctx->lock);
}

void aio_context_release(AioContext *ctx)
{
    rfifolock_unlock(&ctx->lock);
}