Re: [RFC PATCH net-next v5 3/4] virtio_net: Extend virtio to use VF datapath when available

["Samudrala, Sridhar" <sridhar.samudrala@intel.com>]

On 4/10/2018 3:55 AM, Jiri Pirko wrote:
> Mon, Apr 09, 2018 at 08:47:06PM CEST, sridhar.samudrala@intel.com wrote:
> > On 4/9/2018 1:07 AM, Jiri Pirko wrote:
> > > Sat, Apr 07, 2018 at 12:59:14AM CEST, sridhar.samudrala@intel.com wrote:
> > > > On 4/6/2018 5:48 AM, Jiri Pirko wrote:
> > > > > Thu, Apr 05, 2018 at 11:08:22PM CEST, sridhar.samudrala@intel.com wrote:
> > > [...]
> > >
> > > > > > +static int virtnet_bypass_join_child(struct net_device *bypass_netdev,
> > > > > > +				     struct net_device *child_netdev)
> > > > > > +{
> > > > > > +	struct virtnet_bypass_info *vbi;
> > > > > > +	bool backup;
> > > > > > +
> > > > > > +	vbi = netdev_priv(bypass_netdev);
> > > > > > +	backup = (child_netdev->dev.parent == bypass_netdev->dev.parent);
> > > > > > +	if (backup ? rtnl_dereference(vbi->backup_netdev) :
> > > > > > +			rtnl_dereference(vbi->active_netdev)) {
> > > > > > +		netdev_info(bypass_netdev,
> > > > > > +			    "%s attempting to join bypass dev when %s already present\n",
> > > > > > +			    child_netdev->name, backup ? "backup" : "active");
> > > > > Bypass module should check if there is already some other netdev
> > > > > enslaved and refuse right there.
> > > > This will work for virtio-net with 3 netdev model, but this check has to be done by netvsc
> > > > as its bypass_netdev is same as the backup_netdev.
> > > > Will add a flag while registering with the bypass module to indicate if the driver is doing
> > > > a 2 netdev or 3 netdev model and based on that flag this check can be done in bypass module
> > > > for 3 netdev scenario.
> > > Just let me undestand it clearly. What I expect the difference would be
> > > between 2netdev and3 netdev model is this:
> > > 2netdev:
> > >     bypass_master
> > >        /
> > >       /
> > > VF_slave
> > >
> > > 3netdev:
> > >     bypass_master
> > >        /     \
> > >       /       \
> > > VF_slave   backup_slave
> > >
> > > Is that correct? If not, how does it look like?
> > Looks correct.
> > VF_slave and backup_slave are the original netdevs and are present in both the models.
> > In the 3 netdev model, bypass_master netdev is created and VF_slave and backup_slave are
> > marked as the 2 slaves of this new netdev.
> You say it looks correct and in another sentence you provide completely
> different description. Could you please look again?
To be exact, 2 netdev model with netvsc looks like this.

    netvsc_netdev
      /
     /
 VF_slave

With virtio_net, 3 netdev model

  bypass_netdev
      /     \
     /       \
VF_slave   virtio_net netdev