Re: [Qemu-devel] [PATCH v5 3/6] libvhost-user: Support tracking inflight I/O in shared memory

[Jason Wang <jasowang@redhat.com>]

On 2019/1/22 下午4:31, elohimes@gmail.com wrote:
> +static int
> +vu_queue_inflight_get(VuDev *dev, VuVirtq *vq, int desc_idx)
> +{
> +    if (!has_feature(dev->protocol_features,
> +        VHOST_USER_PROTOCOL_F_INFLIGHT_SHMFD)) {
> +        return 0;
> +    }
> +
> +    if (unlikely(!vq->inflight)) {
> +        return -1;
> +    }
> +
> +    vq->inflight->desc[desc_idx].inuse = 1;
> +
> +    vq->inflight->desc[desc_idx].avail_idx = vq->last_avail_idx;
> +
> +    return 0;
> +}
> +
> +static int
> +vu_queue_inflight_pre_put(VuDev *dev, VuVirtq *vq, int desc_idx)
> +{
> +    if (!has_feature(dev->protocol_features,
> +        VHOST_USER_PROTOCOL_F_INFLIGHT_SHMFD)) {
> +        return 0;
> +    }
> +
> +    if (unlikely(!vq->inflight)) {
> +        return -1;
> +    }
> +
> +    vq->inflight->desc[desc_idx].used_idx = vq->used_idx;
> +
> +    barrier();
> +
> +    vq->inflight->desc[desc_idx].version++;
> +
> +    return 0;
> +}


You probably need WRITE_ONCE() semantic (e.g volatile) to make sure the 
value reach memory.

Thanks