Re: [Qemu-devel] snabbswitch integration with QEMU for userspace ethernet I/O

[Stefan Hajnoczi]

On Sun, May 26, 2013 at 11:32:49AM +0200, Luke Gorrie wrote:
> Stefan put us onto the highly promising track of vhost/virtio. We have
> implemented this between Snabb Switch and the Linux kernel, but not
> directly between Snabb Switch and QEMU guests. The "roadblock" we have hit
> is embarrasingly basic: QEMU is using user-to-kernel system calls to setup
> vhost (open /dev/net/tun and /dev/vhost-net, ioctl()s) and I haven't found
> a good way to map these towards Snabb Switch instead of the kernel.

vhost_net is about connecting the a virtio-net speaking process to a
tun-like device.  The problem you are trying to solve is connecting a
virtio-net speaking process to Snabb Switch.

Either you need to replace vhost or you need a tun-like device
interface.

Replacing vhost would mean that your switch implements virtio-net,
shares guest RAM with the guest, and shares the ioeventfd and irqfd
which are used to signal with the guest.  At that point your switch is
similar to the virtio-net data plane work that Ping Fan Liu is working
on but your switch is in a separate process rather than a thread.

How does your switch talk to hardware?  If you have userspace NIC
drivers that bypass the Linux network stack then the approach I
mentioned fits well.

If you are using the Linux network stack then it might be better to
integrate with vhost maybe as a tun-like device driver.

Stefan