Re: [dpdk-dev] [PATCH] net/virtio-user: fix feature setting with vhost-net backend

["Hu, Jiayu" <jiayu.hu@intel.com>]

Hi Tiwei,

> -----Original Message-----
> From: Bie, Tiwei
> Sent: Thursday, May 10, 2018 1:05 PM
> To: Hu, Jiayu <jiayu.hu@intel.com>
> Cc: dev@dpdk.org; Yang, Zhiyong <zhiyong.yang@intel.com>;
> maxime.coquelin@redhat.com
> Subject: Re: [dpdk-dev] [PATCH] net/virtio-user: fix feature setting with
> vhost-net backend
> 
> On Tue, May 08, 2018 at 03:44:22PM +0800, Jiayu Hu wrote:
> > Hi Tiwei,
> >
> > On Tue, May 08, 2018 at 10:49:50AM +0800, Tiwei Bie wrote:
> > > On Mon, May 07, 2018 at 02:50:06PM +0800, Jiayu Hu wrote:
> > > > Currently, when the backend is vhost-net, which implies
> > > > virtio-user works in client mode, virtio-user is assigned
> > > > to the default feature VIRTIO_USER_SUPPORTED_FEATURES.
> > > > However, virtio-user should request features from the
> > > > backend in this case.
> > > >
> > > > Fixes: bd8f50a45d0f ("net/virtio-user: support server mode")
> > > > Signed-off-by: Jiayu Hu <jiayu.hu@intel.com>
> > > > ---
> > > >  drivers/net/virtio/virtio_user/virtio_user_dev.c | 15 +++++++--------
> > > >  1 file changed, 7 insertions(+), 8 deletions(-)
> > > >
> > > > diff --git a/drivers/net/virtio/virtio_user/virtio_user_dev.c
> b/drivers/net/virtio/virtio_user/virtio_user_dev.c
> > > > index 38b8bc9..f745163 100644
> > > > --- a/drivers/net/virtio/virtio_user/virtio_user_dev.c
> > > > +++ b/drivers/net/virtio/virtio_user/virtio_user_dev.c
> > > > @@ -353,20 +353,22 @@ virtio_user_dev_init(struct virtio_user_dev
> *dev, char *path, int queues,
> > > >  		return -1;
> > > >  	}
> > > >
> > > > -	if (dev->vhostfd >= 0) {
> > > > +	if (!dev->is_server) {
> > >
> > > Server mode also needs to run below code when the
> > > connection to the backend is established.
> >
> > For server mode, the below code is called by virtio_user_start_device(),
> > instead of virtio_user_dev_init(). Only client mode virtio-user
> > needs to call it when init.
> 
> Okay. So in server mode, virtio-user never get a chance
> to do GET_FEATURES.

In current design, virtio-user server mode always has no way to do GET_FEATURES.
I think it's the design problem of virtio-user server mode. This patch is just for solving
client mode virtio-user feature setting.

> 
> >
> > >
> > > >  		if (dev->ops->send_request(dev,
> VHOST_USER_SET_OWNER,
> > > > -					   NULL) < 0) {
> > > > +					NULL) < 0) {
> > >
> > > There is no need to change the indent.
> >
> > Thanks, change in the next patch.
> >
> > >
> > > >  			PMD_INIT_LOG(ERR, "set_owner fails: %s",
> > > > -				     strerror(errno));
> > > > +					strerror(errno));
> > >
> > > There is no need to change the indent.
> >
> > ditto.
> >
> > >
> > > >  			return -1;
> > > >  		}
> > > >
> > > >  		if (dev->ops->send_request(dev,
> VHOST_USER_GET_FEATURES,
> > > > -					   &dev->device_features) < 0) {
> > > > +					&dev->device_features) < 0) {
> > >
> > > There is no need to change the indent.
> >
> > ditto.
> >
> > >
> > > >  			PMD_INIT_LOG(ERR, "get_features failed: %s",
> > > > -				     strerror(errno));
> > > > +					strerror(errno));
> > >
> > > There is no need to change the indent.
> >
> > ditto.
> >
> > >
> > > >  			return -1;
> > > >  		}
> > > > +		if (dev->mac_specified)
> > > > +			dev->device_features |= (1ull <<
> VIRTIO_NET_F_MAC);
> > >
> > > Why move above code?
> >
> > The server mode virtio-user is assigned the default features, which include
> > VIRTIO_NET_F_MAC. So checking if support VIRTIO_NET_F_MAC is only
> necessary
> > for client mode.
> 
> I think we should set this bit only when mac is
> specified. And in server mode, we need to clear
> this bit when mac isn't specified. So instead
> of moving it, it should be changed to something
> like this:
> 
> 	if (dev->mac_specified)
> 		dev->device_features |= (1ull << VIRTIO_NET_F_MAC);
> 	else
> 		dev->device_features &= ~(1ull << VIRTIO_NET_F_MAC);
> 

Make sense. It shouldn't change in this patch. I will change it. Thanks.

Jiayu
> Thanks
> 
> >
> > Thanks,
> > Jiayu
> >
> > >
> > > >  	} else {
> > > >  		/* We just pretend vhost-user can support all these
> features.
> > > >  		 * Note that this could be problematic that if some feature
> is
> > > > @@ -376,9 +378,6 @@ virtio_user_dev_init(struct virtio_user_dev
> *dev, char *path, int queues,
> > > >  		dev->device_features =
> VIRTIO_USER_SUPPORTED_FEATURES;
> > > >  	}
> > > >
> > > > -	if (dev->mac_specified)
> > > > -		dev->device_features |= (1ull << VIRTIO_NET_F_MAC);
> > > > -
> > > >  	if (cq) {
> > > >  		/* device does not really need to know anything about CQ,
> > > >  		 * so if necessary, we just claim to support CQ
> > > > --
> > > > 2.7.4
> > > >