hw/block/dataplane/virtio-blk.c

/*
 * Dedicated thread for virtio-blk I/O processing
 *
 * Copyright 2012 IBM, Corp.
 * Copyright 2012 Red Hat, Inc. and/or its affiliates
 *
 * Authors:
 *   Stefan Hajnoczi <stefanha@redhat.com>
 *
 * 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 "trace.h"
#include "qemu/iov.h"
#include "qemu/thread.h"
#include "qemu/error-report.h"
#include "hw/virtio/dataplane/vring.h"
#include "block/block.h"
#include "hw/virtio/virtio-blk.h"
#include "virtio-blk.h"
#include "block/aio.h"
#include "hw/virtio/virtio-bus.h"
#include "qom/object_interfaces.h"

typedef struct {
    VirtIOBlockDataPlane *s;
    QEMUIOVector *inhdr;            /* iovecs for virtio_blk_inhdr */
    VirtQueueElement *elem;         /* saved data from the virtqueue */
    QEMUIOVector qiov;              /* original request iovecs */
    struct iovec bounce_iov;        /* used if guest buffers are unaligned */
    QEMUIOVector bounce_qiov;       /* bounce buffer iovecs */
    bool read;                      /* read or write? */
} VirtIOBlockRequest;

struct VirtIOBlockDataPlane {
    bool started;
    bool starting;
    bool stopping;

    VirtIOBlkConf *blk;

    VirtIODevice *vdev;
    Vring vring;                    /* virtqueue vring */
    EventNotifier *guest_notifier;  /* irq */

    /* Note that these EventNotifiers are assigned by value.  This is
     * fine as long as you do not call event_notifier_cleanup on them
     * (because you don't own the file descriptor or handle; you just
     * use it).
     */
    IOThread *iothread;
    IOThread internal_iothread_obj;
    AioContext *ctx;
    EventNotifier host_notifier;    /* doorbell */

    /* Operation blocker on BDS */
    Error *blocker;
};

/* Raise an interrupt to signal guest, if necessary */
static void notify_guest(VirtIOBlockDataPlane *s)
{
    if (!vring_should_notify(s->vdev, &s->vring)) {
        return;
    }

    event_notifier_set(s->guest_notifier);
}

static void complete_rdwr(void *opaque, int ret)
{
    VirtIOBlockRequest *req = opaque;
    struct virtio_blk_inhdr hdr;
    int len;

    if (likely(ret == 0)) {
        hdr.status = VIRTIO_BLK_S_OK;
        len = req->qiov.size;
    } else {
        hdr.status = VIRTIO_BLK_S_IOERR;
        len = 0;
    }

    trace_virtio_blk_data_plane_complete_request(req->s, req->elem->index, ret);

    if (req->read && req->bounce_iov.iov_base) {
        qemu_iovec_from_buf(&req->qiov, 0, req->bounce_iov.iov_base, len);
    }

    if (req->bounce_iov.iov_base) {
        qemu_vfree(req->bounce_iov.iov_base);
    }

    qemu_iovec_from_buf(req->inhdr, 0, &hdr, sizeof(hdr));
    qemu_iovec_destroy(req->inhdr);
    g_slice_free(QEMUIOVector, req->inhdr);

    /* According to the virtio specification len should be the number of bytes
     * written to, but for virtio-blk it seems to be the number of bytes
     * transferred plus the status bytes.
     */
    vring_push(&req->s->vring, req->elem, len + sizeof(hdr));
    notify_guest(req->s);
    g_slice_free(VirtIOBlockRequest, req);
}

static void complete_request_early(VirtIOBlockDataPlane *s, VirtQueueElement *elem,
                                   QEMUIOVector *inhdr, unsigned char status)
{
    struct virtio_blk_inhdr hdr = {
        .status = status,
    };

    qemu_iovec_from_buf(inhdr, 0, &hdr, sizeof(hdr));
    qemu_iovec_destroy(inhdr);
    g_slice_free(QEMUIOVector, inhdr);

    vring_push(&s->vring, elem, sizeof(hdr));
    notify_guest(s);
}

/* Get disk serial number */
static void do_get_id_cmd(VirtIOBlockDataPlane *s,
                          struct iovec *iov, unsigned int iov_cnt,
                          VirtQueueElement *elem, QEMUIOVector *inhdr)
{
    char id[VIRTIO_BLK_ID_BYTES];

    /* Serial number not NUL-terminated when longer than buffer */
    strncpy(id, s->blk->serial ? s->blk->serial : "", sizeof(id));
    iov_from_buf(iov, iov_cnt, 0, id, sizeof(id));
    complete_request_early(s, elem, inhdr, VIRTIO_BLK_S_OK);
}

static void do_rdwr_cmd(VirtIOBlockDataPlane *s, bool read,
                        struct iovec *iov, unsigned iov_cnt,
                        int64_t sector_num, VirtQueueElement *elem,
                        QEMUIOVector *inhdr)
{
    VirtIOBlockRequest *req = g_slice_new0(VirtIOBlockRequest);
    QEMUIOVector *qiov;
    int nb_sectors;

    /* Fill in virtio block metadata needed for completion */
    req->s = s;
    req->elem = elem;
    req->inhdr = inhdr;
    req->read = read;
    qemu_iovec_init_external(&req->qiov, iov, iov_cnt);

    qiov = &req->qiov;

    if (!bdrv_qiov_is_aligned(s->blk->conf.bs, qiov)) {
        void *bounce_buffer = qemu_blockalign(s->blk->conf.bs, qiov->size);

        /* Populate bounce buffer with data for writes */
        if (!read) {
            qemu_iovec_to_buf(qiov, 0, bounce_buffer, qiov->size);
        }

        /* Redirect I/O to aligned bounce buffer */
        req->bounce_iov.iov_base = bounce_buffer;
        req->bounce_iov.iov_len = qiov->size;
        qemu_iovec_init_external(&req->bounce_qiov, &req->bounce_iov, 1);
        qiov = &req->bounce_qiov;
    }

    nb_sectors = qiov->size / BDRV_SECTOR_SIZE;

    if (read) {
        bdrv_aio_readv(s->blk->conf.bs, sector_num, qiov, nb_sectors,
                       complete_rdwr, req);
    } else {
        bdrv_aio_writev(s->blk->conf.bs, sector_num, qiov, nb_sectors,
                        complete_rdwr, req);
    }
}

static void complete_flush(void *opaque, int ret)
{
    VirtIOBlockRequest *req = opaque;
    unsigned char status;

    if (ret == 0) {
        status = VIRTIO_BLK_S_OK;
    } else {
        status = VIRTIO_BLK_S_IOERR;
    }

    complete_request_early(req->s, req->elem, req->inhdr, status);
    g_slice_free(VirtIOBlockRequest, req);
}

static void do_flush_cmd(VirtIOBlockDataPlane *s, VirtQueueElement *elem,
                         QEMUIOVector *inhdr)
{
    VirtIOBlockRequest *req = g_slice_new(VirtIOBlockRequest);
    req->s = s;
    req->elem = elem;
    req->inhdr = inhdr;

    bdrv_aio_flush(s->blk->conf.bs, complete_flush, req);
}

static void do_scsi_cmd(VirtIOBlockDataPlane *s, VirtQueueElement *elem,
                        QEMUIOVector *inhdr)
{
    int status;

    status = virtio_blk_handle_scsi_req(VIRTIO_BLK(s->vdev), elem);
    complete_request_early(s, elem, inhdr, status);
}

static int process_request(VirtIOBlockDataPlane *s, VirtQueueElement *elem)
{
    struct iovec *iov = elem->out_sg;
    struct iovec *in_iov = elem->in_sg;
    unsigned out_num = elem->out_num;
    unsigned in_num = elem->in_num;
    struct virtio_blk_outhdr outhdr;
    QEMUIOVector *inhdr;
    size_t in_size;

    /* Copy in outhdr */
    if (unlikely(iov_to_buf(iov, out_num, 0, &outhdr,
                            sizeof(outhdr)) != sizeof(outhdr))) {
        error_report("virtio-blk request outhdr too short");
        return -EFAULT;
    }
    iov_discard_front(&iov, &out_num, sizeof(outhdr));

    /* Grab inhdr for later */
    in_size = iov_size(in_iov, in_num);
    if (in_size < sizeof(struct virtio_blk_inhdr)) {
        error_report("virtio_blk request inhdr too short");
        return -EFAULT;
    }
    inhdr = g_slice_new(QEMUIOVector);
    qemu_iovec_init(inhdr, 1);
    qemu_iovec_concat_iov(inhdr, in_iov, in_num,
            in_size - sizeof(struct virtio_blk_inhdr),
            sizeof(struct virtio_blk_inhdr));
    iov_discard_back(in_iov, &in_num, sizeof(struct virtio_blk_inhdr));

    /* TODO Linux sets the barrier bit even when not advertised! */
    outhdr.type &= ~VIRTIO_BLK_T_BARRIER;

    switch (outhdr.type) {
    case VIRTIO_BLK_T_IN:
        do_rdwr_cmd(s, true, in_iov, in_num,
                    outhdr.sector * 512 / BDRV_SECTOR_SIZE,
                    elem, inhdr);
        return 0;

    case VIRTIO_BLK_T_OUT:
        do_rdwr_cmd(s, false, iov, out_num,
                    outhdr.sector * 512 / BDRV_SECTOR_SIZE,
                    elem, inhdr);
        return 0;

    case VIRTIO_BLK_T_SCSI_CMD:
        do_scsi_cmd(s, elem, inhdr);
        return 0;

    case VIRTIO_BLK_T_FLUSH:
        do_flush_cmd(s, elem, inhdr);
        return 0;

    case VIRTIO_BLK_T_GET_ID:
        do_get_id_cmd(s, in_iov, in_num, elem, inhdr);
        return 0;

    default:
        error_report("virtio-blk unsupported request type %#x", outhdr.type);
        qemu_iovec_destroy(inhdr);
        g_slice_free(QEMUIOVector, inhdr);
        return -EFAULT;
    }
}

static void handle_notify(EventNotifier *e)
{
    VirtIOBlockDataPlane *s = container_of(e, VirtIOBlockDataPlane,
                                           host_notifier);

    VirtQueueElement *elem;
    int ret;

    event_notifier_test_and_clear(&s->host_notifier);
    for (;;) {
        /* Disable guest->host notifies to avoid unnecessary vmexits */
        vring_disable_notification(s->vdev, &s->vring);

        for (;;) {
            ret = vring_pop(s->vdev, &s->vring, &elem);
            if (ret < 0) {
                assert(elem == NULL);
                break; /* no more requests */
            }

            trace_virtio_blk_data_plane_process_request(s, elem->out_num,
                                                        elem->in_num, elem->index);

            if (process_request(s, elem) < 0) {
                vring_set_broken(&s->vring);
                vring_free_element(elem);
                ret = -EFAULT;
                break;
            }
        }

        if (likely(ret == -EAGAIN)) { /* vring emptied */
            /* Re-enable guest->host notifies and stop processing the vring.
             * But if the guest has snuck in more descriptors, keep processing.
             */
            if (vring_enable_notification(s->vdev, &s->vring)) {
                break;
            }
        } else { /* fatal error */
            break;
        }
    }
}

/* Context: QEMU global mutex held */
void virtio_blk_data_plane_create(VirtIODevice *vdev, VirtIOBlkConf *blk,
                                  VirtIOBlockDataPlane **dataplane,
                                  Error **errp)
{
    VirtIOBlockDataPlane *s;
    Error *local_err = NULL;

    *dataplane = NULL;

    if (!blk->data_plane) {
        return;
    }

    /* If dataplane is (re-)enabled while the guest is running there could be
     * block jobs that can conflict.
     */
    if (bdrv_op_is_blocked(blk->conf.bs, BLOCK_OP_TYPE_DATAPLANE, &local_err)) {
        error_report("cannot start dataplane thread: %s",
                      error_get_pretty(local_err));
        error_free(local_err);
        return;
    }

    s = g_new0(VirtIOBlockDataPlane, 1);
    s->vdev = vdev;
    s->blk = blk;

    if (blk->iothread) {
        s->iothread = blk->iothread;
        object_ref(OBJECT(s->iothread));
    } else {
        /* Create per-device IOThread if none specified.  This is for
         * x-data-plane option compatibility.  If x-data-plane is removed we
         * can drop this.
         */
        object_initialize(&s->internal_iothread_obj,
                          sizeof(s->internal_iothread_obj),
                          TYPE_IOTHREAD);
        user_creatable_complete(OBJECT(&s->internal_iothread_obj), &error_abort);
        s->iothread = &s->internal_iothread_obj;
    }
    s->ctx = iothread_get_aio_context(s->iothread);

    error_setg(&s->blocker, "block device is in use by data plane");
    bdrv_op_block_all(blk->conf.bs, s->blocker);

    *dataplane = s;
}

/* Context: QEMU global mutex held */
void virtio_blk_data_plane_destroy(VirtIOBlockDataPlane *s)
{
    if (!s) {
        return;
    }

    virtio_blk_data_plane_stop(s);
    bdrv_op_unblock_all(s->blk->conf.bs, s->blocker);
    error_free(s->blocker);
    object_unref(OBJECT(s->iothread));
    g_free(s);
}

/* Context: QEMU global mutex held */
void virtio_blk_data_plane_start(VirtIOBlockDataPlane *s)
{
    BusState *qbus = BUS(qdev_get_parent_bus(DEVICE(s->vdev)));
    VirtioBusClass *k = VIRTIO_BUS_GET_CLASS(qbus);
    VirtQueue *vq;

    if (s->started) {
        return;
    }

    if (s->starting) {
        return;
    }

    s->starting = true;

    vq = virtio_get_queue(s->vdev, 0);
    if (!vring_setup(&s->vring, s->vdev, 0)) {
        s->starting = false;
        return;
    }

    /* Set up guest notifier (irq) */
    if (k->set_guest_notifiers(qbus->parent, 1, true) != 0) {
        fprintf(stderr, "virtio-blk failed to set guest notifier, "
                "ensure -enable-kvm is set\n");
        exit(1);
    }
    s->guest_notifier = virtio_queue_get_guest_notifier(vq);

    /* Set up virtqueue notify */
    if (k->set_host_notifier(qbus->parent, 0, true) != 0) {
        fprintf(stderr, "virtio-blk failed to set host notifier\n");
        exit(1);
    }
    s->host_notifier = *virtio_queue_get_host_notifier(vq);

    s->starting = false;
    s->started = true;
    trace_virtio_blk_data_plane_start(s);

    bdrv_set_aio_context(s->blk->conf.bs, s->ctx);

    /* Kick right away to begin processing requests already in vring */
    event_notifier_set(virtio_queue_get_host_notifier(vq));

    /* Get this show started by hooking up our callbacks */
    aio_context_acquire(s->ctx);
    aio_set_event_notifier(s->ctx, &s->host_notifier, handle_notify);
    aio_context_release(s->ctx);
}

/* Context: QEMU global mutex held */
void virtio_blk_data_plane_stop(VirtIOBlockDataPlane *s)
{
    BusState *qbus = BUS(qdev_get_parent_bus(DEVICE(s->vdev)));
    VirtioBusClass *k = VIRTIO_BUS_GET_CLASS(qbus);
    if (!s->started || s->stopping) {
        return;
    }
    s->stopping = true;
    trace_virtio_blk_data_plane_stop(s);

    aio_context_acquire(s->ctx);

    /* Stop notifications for new requests from guest */
    aio_set_event_notifier(s->ctx, &s->host_notifier, NULL);

    /* Drain and switch bs back to the QEMU main loop */
    bdrv_set_aio_context(s->blk->conf.bs, qemu_get_aio_context());

    aio_context_release(s->ctx);

    /* Sync vring state back to virtqueue so that non-dataplane request
     * processing can continue when we disable the host notifier below.
     */
    vring_teardown(&s->vring, s->vdev, 0);

    k->set_host_notifier(qbus->parent, 0, false);

    /* Clean up guest notifier (irq) */
    k->set_guest_notifiers(qbus->parent, 1, false);

    s->started = false;
    s->stopping = false;
}