Re: [PATCH v2 2/7] net/virtio_user: postpone DRIVER OK notification

From: "Tan, Jianfeng" <jianfeng.tan@intel.com>
To: Yuanhan Liu <yuanhan.liu@linux.intel.com>
Cc: "dev@dpdk.org" <dev@dpdk.org>,
	"Yigit, Ferruh" <ferruh.yigit@intel.com>,
	"Liang, Cunming" <cunming.liang@intel.com>
Subject: Re: [PATCH v2 2/7] net/virtio_user: postpone DRIVER OK notification
Date: Mon, 26 Dec 2016 08:26:03 +0000	[thread overview]
Message-ID: <ED26CBA2FAD1BF48A8719AEF02201E36510FC938@SHSMSX103.ccr.corp.intel.com> (raw)
In-Reply-To: <20161226080208.GG19288@yliu-dev.sh.intel.com>

As discussed offline, this will lead to many DRIVER OK among dev_stop()/dev_start(). I'll remove this patch.

Thanks,
Jianfeng

> -----Original Message-----
> From: Yuanhan Liu [mailto:yuanhan.liu@linux.intel.com]
> Sent: Monday, December 26, 2016 4:02 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 Mon, Dec 26, 2016 at 06:55:16AM +0000, Tan, Jianfeng wrote:
> >
> >
> > > -----Original Message-----
> > > From: Yuanhan Liu [mailto:yuanhan.liu@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