On Tue, Jun 29, 2021 at 11:29 AM Jason Wang <jasowang@xxxxxxxxxx> wrote: > > > 在 2021/6/29 上午10:26, Yongji Xie 写道: > > On Mon, Jun 28, 2021 at 12:40 PM Jason Wang <jasowang@xxxxxxxxxx> wrote: > >> > >> 在 2021/6/25 下午12:19, Yongji Xie 写道: > >>>> 2b) for set_status(): simply relay the message to userspace, reply is no > >>>> needed. Userspace will use a command to update the status when the > >>>> datapath is stop. The the status could be fetched via get_stats(). > >>>> > >>>> 2b looks more spec complaint. > >>>> > >>> Looks good to me. And I think we can use the reply of the message to > >>> update the status instead of introducing a new command. > >>> > >> Just notice this part in virtio_finalize_features(): > >> > >> virtio_add_status(dev, VIRTIO_CONFIG_S_FEATURES_OK); > >> status = dev->config->get_status(dev); > >> if (!(status & VIRTIO_CONFIG_S_FEATURES_OK)) { > >> > >> So we no reply doesn't work for FEATURES_OK. > >> > >> So my understanding is: > >> > >> 1) We must not use noreply for set_status() > >> 2) We can use noreply for get_status(), but it requires a new ioctl to > >> update the status. > >> > >> So it looks to me we need synchronize for both get_status() and > >> set_status(). > >> > > We should not send messages to userspace in the FEATURES_OK case. So > > the synchronization is not necessary. > > > As discussed previously, there could be a device that mandates some > features (VIRTIO_F_RING_PACKED). So it can choose to not accept > FEATURES_OK is packed virtqueue is not negotiated. > > In this case we need to relay the message to userspace. > OK, I see. If so, I prefer to only use noreply for set_status(). We do not set the status bit if the message is failed. In this way, we don't need to change lots of virtio core codes to handle the failure of set_status()/get_status(). Thanks, Yongji