Archipelago » qemu

/*

 * Linux native AIO support.

 *

 * Copyright (C) 2009 IBM, Corp.

 * Copyright (C) 2009 Red Hat, Inc.

 *

 * This work is licensed under the terms of the GNU GPL, version 2 or later.

 * See the COPYING file in the top-level directory.

 */

#include "qemu-common.h"

#include "qemu-aio.h"

#include "block_int.h"

#include "block/raw-posix-aio.h"

#include <sys/eventfd.h>

#include <libaio.h>

/*

 * Queue size (per-device).

 *

 * XXX: eventually we need to communicate this to the guest and/or make it

 *      tunable by the guest.  If we get more outstanding requests at a time

 *      than this we will get EAGAIN from io_submit which is communicated to

 *      the guest as an I/O error.

 */

#define MAX_EVENTS 128

struct qemu_laiocb {

    BlockDriverAIOCB common;

    struct qemu_laio_state *ctx;

    struct iocb iocb;

    ssize_t ret;

    size_t nbytes;

    int async_context_id;

    QLIST_ENTRY(qemu_laiocb) node;

};

struct qemu_laio_state {

    io_context_t ctx;

    int efd;

    int count;

    QLIST_HEAD(, qemu_laiocb) completed_reqs;

};

static inline ssize_t io_event_ret(struct io_event *ev)

{

    return (ssize_t)(((uint64_t)ev->res2 << 32) | ev->res);

}

/*

 * Completes an AIO request (calls the callback and frees the ACB).

 * Be sure to be in the right AsyncContext before calling this function.

 */

static void qemu_laio_process_completion(struct qemu_laio_state *s,

    struct qemu_laiocb *laiocb)

{

    int ret;

    s->count--;

    ret = laiocb->ret;

    if (ret != -ECANCELED) {

        if (ret == laiocb->nbytes)

            ret = 0;

        else if (ret >= 0)

            ret = -EINVAL;

        laiocb->common.cb(laiocb->common.opaque, ret);

    }

    qemu_aio_release(laiocb);

}

/*

 * Processes all queued AIO requests, i.e. requests that have return from OS

 * but their callback was not called yet. Requests that cannot have their

 * callback called in the current AsyncContext, remain in the queue.

 *

 * Returns 1 if at least one request could be completed, 0 otherwise.

 */

static int qemu_laio_process_requests(void *opaque)

{

    struct qemu_laio_state *s = opaque;

    struct qemu_laiocb *laiocb, *next;

    int res = 0;

    QLIST_FOREACH_SAFE (laiocb, &s->completed_reqs, node, next) {

        if (laiocb->async_context_id == get_async_context_id()) {

            qemu_laio_process_completion(s, laiocb);

            QLIST_REMOVE(laiocb, node);

            res = 1;

        }

    }

    return res;

}

/*

 * Puts a request in the completion queue so that its callback is called the

 * next time when it's possible. If we already are in the right AsyncContext,

 * the request is completed immediately instead.

 */

static void qemu_laio_enqueue_completed(struct qemu_laio_state *s,

    struct qemu_laiocb* laiocb)

{

    if (laiocb->async_context_id == get_async_context_id()) {

        qemu_laio_process_completion(s, laiocb);

    } else {

        QLIST_INSERT_HEAD(&s->completed_reqs, laiocb, node);

    }

}

static void qemu_laio_completion_cb(void *opaque)

{

    struct qemu_laio_state *s = opaque;

    while (1) {

        struct io_event events[MAX_EVENTS];

        uint64_t val;

        ssize_t ret;

        struct timespec ts = { 0 };

        int nevents, i;

        do {

            ret = read(s->efd, &val, sizeof(val));

        } while (ret == -1 && errno == EINTR);

        if (ret == -1 && errno == EAGAIN)

            break;

        if (ret != 8)

            break;

        do {

            nevents = io_getevents(s->ctx, val, MAX_EVENTS, events, &ts);

        } while (nevents == -EINTR);

        for (i = 0; i < nevents; i++) {

            struct iocb *iocb = events[i].obj;

            struct qemu_laiocb *laiocb =

                    container_of(iocb, struct qemu_laiocb, iocb);

            laiocb->ret = io_event_ret(&events[i]);

            qemu_laio_enqueue_completed(s, laiocb);

        }

    }

}

static int qemu_laio_flush_cb(void *opaque)

{

    struct qemu_laio_state *s = opaque;

    return (s->count > 0) ? 1 : 0;

}

static void laio_cancel(BlockDriverAIOCB *blockacb)

{

    struct qemu_laiocb *laiocb = (struct qemu_laiocb *)blockacb;

    struct io_event event;

    int ret;

    if (laiocb->ret != -EINPROGRESS)

        return;

    /*

     * Note that as of Linux 2.6.31 neither the block device code nor any

     * filesystem implements cancellation of AIO request.

     * Thus the polling loop below is the normal code path.

     */

    ret = io_cancel(laiocb->ctx->ctx, &laiocb->iocb, &event);

    if (ret == 0) {

        laiocb->ret = -ECANCELED;

        return;

    }

    /*

     * We have to wait for the iocb to finish.

     *

     * The only way to get the iocb status update is by polling the io context.

     * We might be able to do this slightly more optimal by removing the

     * O_NONBLOCK flag.

     */

    while (laiocb->ret == -EINPROGRESS)

        qemu_laio_completion_cb(laiocb->ctx);

}

static AIOPool laio_pool = {

    .aiocb_size         = sizeof(struct qemu_laiocb),

    .cancel             = laio_cancel,

};

BlockDriverAIOCB *laio_submit(BlockDriverState *bs, void *aio_ctx, int fd,

        int64_t sector_num, QEMUIOVector *qiov, int nb_sectors,

        BlockDriverCompletionFunc *cb, void *opaque, int type)

{

    struct qemu_laio_state *s = aio_ctx;

    struct qemu_laiocb *laiocb;

    struct iocb *iocbs;

    off_t offset = sector_num * 512;

    laiocb = qemu_aio_get(&laio_pool, bs, cb, opaque);

    if (!laiocb)

        return NULL;

    laiocb->nbytes = nb_sectors * 512;

    laiocb->ctx = s;

    laiocb->ret = -EINPROGRESS;

    laiocb->async_context_id = get_async_context_id();

    iocbs = &laiocb->iocb;

    switch (type) {

    case QEMU_AIO_WRITE:

        io_prep_pwritev(iocbs, fd, qiov->iov, qiov->niov, offset);

        break;

    case QEMU_AIO_READ:

        io_prep_preadv(iocbs, fd, qiov->iov, qiov->niov, offset);

        break;

    default:

        fprintf(stderr, "%s: invalid AIO request type 0x%x.\n",

                        __func__, type);

        goto out_free_aiocb;

    }

    io_set_eventfd(&laiocb->iocb, s->efd);

    s->count++;

    if (io_submit(s->ctx, 1, &iocbs) < 0)

        goto out_dec_count;

    return &laiocb->common;

out_free_aiocb:

    qemu_aio_release(laiocb);

out_dec_count:

    s->count--;

    return NULL;

}

void *laio_init(void)

{

    struct qemu_laio_state *s;

    s = qemu_mallocz(sizeof(*s));

    QLIST_INIT(&s->completed_reqs);

    s->efd = eventfd(0, 0);

    if (s->efd == -1)

        goto out_free_state;

    fcntl(s->efd, F_SETFL, O_NONBLOCK);

    if (io_setup(MAX_EVENTS, &s->ctx) != 0)

        goto out_close_efd;

    qemu_aio_set_fd_handler(s->efd, qemu_laio_completion_cb, NULL,

        qemu_laio_flush_cb, qemu_laio_process_requests, s);

    return s;

out_close_efd:

    close(s->efd);

out_free_state:

    qemu_free(s);

    return NULL;

}