netdev - Re: [PATCH v8 09/10] vduse: Introduce VDUSE

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Date:   Mon, 28 Jun 2021 12:40:14 +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 2021/6/25 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().

Thanks