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Date: Tue, 29 Jun 2021 11:29:25 +0800 From: Jason Wang <jasowang@...hat.com> To: Yongji Xie <xieyongji@...edance.com> Cc: "Michael S. Tsirkin" <mst@...hat.com>, Stefan Hajnoczi <stefanha@...hat.com>, Stefano Garzarella <sgarzare@...hat.com>, Parav Pandit <parav@...dia.com>, Christoph Hellwig <hch@...radead.org>, Christian Brauner <christian.brauner@...onical.com>, Randy Dunlap <rdunlap@...radead.org>, Matthew Wilcox <willy@...radead.org>, Al Viro <viro@...iv.linux.org.uk>, Jens Axboe <axboe@...nel.dk>, bcrl@...ck.org, Jonathan Corbet <corbet@....net>, Mika Penttilä <mika.penttila@...tfour.com>, Dan Carpenter <dan.carpenter@...cle.com>, joro@...tes.org, Greg KH <gregkh@...uxfoundation.org>, songmuchun@...edance.com, virtualization <virtualization@...ts.linux-foundation.org>, netdev@...r.kernel.org, kvm <kvm@...r.kernel.org>, linux-fsdevel@...r.kernel.org, iommu@...ts.linux-foundation.org, linux-kernel <linux-kernel@...r.kernel.org> Subject: Re: [PATCH v8 09/10] vduse: Introduce VDUSE - vDPA Device in Userspace 在 2021/6/29 上午10:26, Yongji Xie 写道: > On Mon, Jun 28, 2021 at 12:40 PM Jason Wang <jasowang@...hat.com> 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. Thanks > > Thanks, > Yongji >
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