Archipelago » qemu

/*

 * 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"

#include "qemu-aio.h"

/*

 * An AsyncContext protects the callbacks of AIO requests and Bottom Halves

 * against interfering with each other. A typical example is qcow2 that accepts

 * asynchronous requests, but relies for manipulation of its metadata on

 * synchronous bdrv_read/write that doesn't trigger any callbacks.

 *

 * However, these functions are often emulated using AIO which means that AIO

 * callbacks must be run - but at the same time we must not run callbacks of

 * other requests as they might start to modify metadata and corrupt the

 * internal state of the caller of bdrv_read/write.

 *

 * To achieve the desired semantics we switch into a new AsyncContext.

 * Callbacks must only be run if they belong to the current AsyncContext.

 * Otherwise they need to be queued until their own context is active again.

 * This is how you can make qemu_aio_wait() wait only for your own callbacks.

 *

 * The AsyncContexts form a stack. When you leave a AsyncContexts, you always

 * return to the old ("parent") context.

 */

struct AsyncContext {

    /* Consecutive number of the AsyncContext (position in the stack) */

    int id;

    /* Anchor of the list of Bottom Halves belonging to the context */

    struct QEMUBH *first_bh;

    /* Link to parent context */

    struct AsyncContext *parent;

};

/* The currently active AsyncContext */

static struct AsyncContext *async_context = &(struct AsyncContext) { 0 };

/*

 * Enter a new AsyncContext. Already scheduled Bottom Halves and AIO callbacks

 * won't be called until this context is left again.

 */

void async_context_push(void)

{

    struct AsyncContext *new = qemu_mallocz(sizeof(*new));

    new->parent = async_context;

    new->id = async_context->id + 1;

    async_context = new;

}

/* Run queued AIO completions and destroy Bottom Half */

static void bh_run_aio_completions(void *opaque)

{

    QEMUBH **bh = opaque;

    qemu_bh_delete(*bh);

    qemu_free(bh);

    qemu_aio_process_queue();

}

/*

 * Leave the currently active AsyncContext. All Bottom Halves belonging to the

 * old context are executed before changing the context.

 */

void async_context_pop(void)

{

    struct AsyncContext *old = async_context;

    QEMUBH **bh;

    /* Flush the bottom halves, we don't want to lose them */

    while (qemu_bh_poll());

    /* Switch back to the parent context */

    async_context = async_context->parent;

    qemu_free(old);

    if (async_context == NULL) {

        abort();

    }

    /* Schedule BH to run any queued AIO completions as soon as possible */

    bh = qemu_malloc(sizeof(*bh));

    *bh = qemu_bh_new(bh_run_aio_completions, bh);

    qemu_bh_schedule(*bh);

}

/*

 * Returns the ID of the currently active AsyncContext

 */

int get_async_context_id(void)

{

    return async_context->id;

}

/***********************************************************/

/* bottom halves (can be seen as timers which expire ASAP) */

struct QEMUBH {

    QEMUBHFunc *cb;

    void *opaque;

    int scheduled;

    int idle;

    int deleted;

    QEMUBH *next;

};

QEMUBH *qemu_bh_new(QEMUBHFunc *cb, void *opaque)

{

    QEMUBH *bh;

    bh = qemu_mallocz(sizeof(QEMUBH));

    bh->cb = cb;

    bh->opaque = opaque;

    bh->next = async_context->first_bh;

    async_context->first_bh = bh;

    return bh;

}

int qemu_bh_poll(void)

{

    QEMUBH *bh, **bhp, *next;

    int ret;

    ret = 0;

    for (bh = async_context->first_bh; bh; bh = next) {

        next = bh->next;

        if (!bh->deleted && bh->scheduled) {

            bh->scheduled = 0;

            if (!bh->idle)

                ret = 1;

            bh->idle = 0;

            bh->cb(bh->opaque);

        }

    }

    /* remove deleted bhs */

    bhp = &async_context->first_bh;

    while (*bhp) {

        bh = *bhp;

        if (bh->deleted) {

            *bhp = bh->next;

            qemu_free(bh);

        } else

            bhp = &bh->next;

    }

    return ret;

}

void qemu_bh_schedule_idle(QEMUBH *bh)

{

    if (bh->scheduled)

        return;

    bh->scheduled = 1;

    bh->idle = 1;

}

void qemu_bh_schedule(QEMUBH *bh)

{

    if (bh->scheduled)

        return;

    bh->scheduled = 1;

    bh->idle = 0;

    /* stop the currently executing CPU to execute the BH ASAP */

    qemu_notify_event();

}

void qemu_bh_cancel(QEMUBH *bh)

{

    bh->scheduled = 0;

}

void qemu_bh_delete(QEMUBH *bh)

{

    bh->scheduled = 0;

    bh->deleted = 1;

}

void qemu_bh_update_timeout(int *timeout)

{

    QEMUBH *bh;

    for (bh = async_context->first_bh; bh; bh = bh->next) {

        if (!bh->deleted && bh->scheduled) {

            if (bh->idle) {

                /* idle bottom halves will be polled at least

                 * every 10ms */

                *timeout = MIN(10, *timeout);

            } else {

                /* non-idle bottom halves will be executed

                 * immediately */

                *timeout = 0;

                break;

            }

        }

    }

}