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

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Date:   Mon, 9 Apr 2018 10:07:51 +0200
From:   Jiri Pirko <jiri@...nulli.us>
To:     "Samudrala, Sridhar" <sridhar.samudrala@...el.com>
Cc:     mst@...hat.com, stephen@...workplumber.org, davem@...emloft.net,
        netdev@...r.kernel.org, virtualization@...ts.linux-foundation.org,
        virtio-dev@...ts.oasis-open.org, jesse.brandeburg@...el.com,
        alexander.h.duyck@...el.com, kubakici@...pl, jasowang@...hat.com,
        loseweigh@...il.com
Subject: Re: [RFC PATCH net-next v5 3/4] virtio_net: Extend virtio to use VF
 datapath when available

Sat, Apr 07, 2018 at 12:59:14AM CEST, sridhar.samudrala@...el.com wrote:
>On 4/6/2018 5:48 AM, Jiri Pirko wrote:
>> Thu, Apr 05, 2018 at 11:08:22PM CEST, sridhar.samudrala@...el.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?

Thanks!