[dpdk-dev] vtap0 device creation (bug)?

[Tiwei Bie]

On Fri, Nov 08, 2019 at 03:44:07PM -0800, Stephen Hemminger wrote:
> When I create a virtio-user device with rte_hotplug it creates a kernel device (ie vtap0).
> This is normal an the device has ifindex N.
> 
> But later when device is configured an started the original vtap0 device is deleted
> and a new one is created (with ifindex N+1).  This seems like a bug, if nothing
> else it unnecessary overhead and link flapping for routing daemons.
> 
> Noticed only while tracking down a bug where after vtap was created the
> address was being set, but then disappearing.
> 
> Is this intentional? Is it documented?

Thanks for catching this.
I think it's caused by the fact that tapfds will be closed
each time when the queue pairs are disabled [1]. We may need
a way to keep tapfds open to fix it.

[1] https://github.com/DPDK/dpdk/blob/6bbc5a923625/drivers/net/virtio/virtio_user/vhost_kernel.c#L333-L338

Thanks,
Tiwei