On Mon, Dec 26, 2016 at 06:55:16AM +0000, Tan, Jianfeng wrote:
>
>
> > -----Original Message-----
> > From: Yuanhan Liu [mailto:yuanhan....@linux.intel.com]
> > Sent: Monday, December 26, 2016 2:27 PM
> > To: Tan, Jianfeng
> > Cc: dev@dpdk.org; Yigit, Ferruh; Liang, Cunming
> > Subject: Re: [PATCH v2 2/7] net/virtio_user: postpone DRIVER OK notification
> >
> > On Fri, Dec 23, 2016 at 07:14:21AM +0000, Jianfeng Tan wrote:
> > > In driver probe phase, we obtain device information; and then virtio
> > > driver will initialize device and stores info, like negotiated
> > > features, in vhost_user layer; finally, vhost_user gets DRIVER_OK
> > > notification from virtio driver, and then sync with backend device.
> > >
> > > Previously, DRIVER_OK could be sent twice: 1. when ether layer invokes
> > > eth_device_init to initialize device; 2. when user configures it with
> > > different configuration from that of previous.
> >
> > Yes, but that's wrong. Now only 1) will be taken.
>
> >From code in virtio_dev_configure() as below, if hw_ip_checksum or
> >enable_lro is configured, the device will be reset and re-initialized.
> if (rxmode->hw_ip_checksum)
> req_features |= (1ULL << VIRTIO_NET_F_GUEST_CSUM);
> if (rxmode->enable_lro)
> req_features |=
> (1ULL << VIRTIO_NET_F_GUEST_TSO4) |
> (1ULL << VIRTIO_NET_F_GUEST_TSO6);
>
> /* if request features changed, reinit the device */
> if (req_features != hw->req_guest_features) {
> ret = virtio_init_device(dev, req_features);
> if (ret < 0)
> return ret;
> }
Yes, I know. But virtio_init_device() will call vtpci_reinit_complete()
at the end, doesn't it?
> > > Since we can only depend on DRIVER_OK notification to sync with backend
> > > device, we postpone it to virtio_dev_start when everything is settled.
> >
> > I don't quite understand what you were going to fix here; you don't
> > state it in the commit log after all. Normally, when everything is
> > negotiated (when DRIVER_OK is set), we should not set it again, unless
> > a reset has been happened.
>
> I agree that DRIVER_OK should be set only if everything is settled. Under the
> case of hw_ip_checksum or enable_lro, a reset will be sent and the device
> will be re-initialized.
>
> So my point is that since the configuration might be changed in
> dev_configure(), why not just send DRIVER_OK after everything is done.
>
> >
> > If you look at QEMU, qemu will simply ignore it once vhost has already
> > started.
>
> It does not apply here. The configuration is changed, and it cannot be
> ignored.
Why it doesn't apply here? What makes virtio_user special? If it works
to QEMU and it doesn't to virtio_user, it basically means the virtio_user
is broken ...
--yliu
