On Wed, Oct 6, 2010 at 7:43 AM, devi thapa [off-list ref] wrote:

      I dont know how to put this question, but bear with me.   My
query is how to invoke the ioctl request "VHOST_NET_SET_BACKEND"  or
how to set the backend, and when ?

Look at the QEMU side vhost-net code:
http://git.qemu.org/qemu.git/tree/hw/vhost_net.c#n145

Where does the backend fd come from?  It's the host network device
file descriptor that gets fetched by vhost_net_get_fd().  Currently it
must be a tap device file descriptor.

Stefan