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

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Message-ID: <20180410152205.GF2028@nanopsycho>
Date:   Tue, 10 Apr 2018 17:22:05 +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

Tue, Apr 10, 2018 at 05:13:40PM CEST, sridhar.samudrala@...el.com wrote:
>On 4/10/2018 3:55 AM, Jiri Pirko wrote:
>> Mon, Apr 09, 2018 at 08:47:06PM CEST, sridhar.samudrala@...el.com wrote:
>> > On 4/9/2018 1:07 AM, Jiri Pirko wrote:
>> > > 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?
>> > > 
>> > > 
>> > 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

Could you also mark the original netdev which is there now? is it
bypass_netdev or virtio_net_netdev ?