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

On 4/10/2018 11:03 PM, Jiri Pirko wrote:
Tue, Apr 10, 2018 at 05:59:02PM CEST, sridhar.samudrala@intel.com wrote:
On 4/10/2018 8:43 AM, Jiri Pirko wrote:
Tue, Apr 10, 2018 at 05:27:48PM CEST, sridhar.samudrala@intel.com wrote:
On 4/10/2018 8:22 AM, Jiri Pirko wrote:
Tue, Apr 10, 2018 at 05:13:40PM CEST, sridhar.samudrala@intel.com wrote:
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:

          /     \
         /       \
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.


With virtio_net, 3 netdev model

        /     \
       /       \
VF_slave   virtio_net netdev
Could you also mark the original netdev which is there now? is it
bypass_netdev or virtio_net_netdev ?
      /     \
     /       \
VF_slave   virtio_net netdev (original)
That does not make sense.
1) You diverge from the behaviour of the netvsc, where the original
     netdev is a master of the VF
2) If the original netdev is a slave, you cannot have any IP address
     configured on it (well you could, but the rx_handler would eat every
     incoming packet). So you will break the user bacause he would have to
     move the configuration to the new master device.
This only makes sense that the original netdev becomes the master for both
netvsc and virtio_net.
Forgot to mention that bypass_netdev takes over the name of the original
netdev and
virtio_net netdev will get the backup name.
What do you mean by "name"?

bypass_netdev also is associated with the same pci device as the original virtio_net
netdev via SET_NETDEV_DEV().  Also, we added ndo_get_phys_port_name() to virtio_net
that will return _bkup when BACKUP feature is enabled.

So for ex: if virtio_net inteface was getting 'ens12' as the name assigned by udev
without BACKUP feature,  when BACKUP feature is enabled,  the  bypass_netdev will be
named 'ens12' and the original virtio_net will get named as ens12n_bkup.

So the userspace network configuration doesn't need to change.

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