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

[Jason Wang]

On 2019/1/30 上午11:58, Yongji Xie wrote:
> On Wed, 30 Jan 2019 at 10:32, Jason Wang <address@hidden> wrote:
> > On 2019/1/22 下午4:31, address@hidden 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.
> Is it enough to declare those variables as volatile?
>
> Thanks,
> Yongji


I think so.

Thanks