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/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;

    QEMUIOVector *qiov;

    bool is_read;

    QLIST_ENTRY(qemu_laiocb) node;

};

struct qemu_laio_state {

    io_context_t ctx;

    int efd;

    int count;

};

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).

 */

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) {

            /* Short reads mean EOF, pad with zeros. */

            if (laiocb->is_read) {

                qemu_iovec_memset_skip(laiocb->qiov, 0,

                    laiocb->qiov->size - ret, ret);

            } else {

                ret = -EINVAL;

            }

        }

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

    }

    qemu_aio_release(laiocb);

}

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_process_completion(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);

    laiocb->nbytes = nb_sectors * 512;

    laiocb->ctx = s;

    laiocb->ret = -EINPROGRESS;

    laiocb->is_read = (type == QEMU_AIO_READ);

    laiocb->qiov = qiov;

    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;

    /* Currently Linux kernel does not support other operations */

    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_dec_count:

    s->count--;

out_free_aiocb:

    qemu_aio_release(laiocb);

    return NULL;

}

void *laio_init(void)

{

    struct qemu_laio_state *s;

    s = g_malloc0(sizeof(*s));

    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, NULL, s);

    return s;

out_close_efd:

    close(s->efd);

out_free_state:

    g_free(s);

    return NULL;

}