Specifying names for tap interfaces

[Roger Pau Monne <roger.pau%citrix.com@localhost>]

Hello,

New Xen versions will ship with upstream Qemu, which means we have to 
get ready to support new Qemu features not present in the previous 
versions of Qemu used by Xen. This also means that Xen developers are 
not allowing to post Qemu-xen specific changes, so all changes should be 
first committed and approved to regular Qemu and then backported to the 
Qemu Xen repository.

So far we are doing quite good, and new Qemu upstream seems to be 
working fine with Xen under NetBSD. The only remaining issue is with tap 
interfaces, so we can at least have a working basic HVM guest. New Qemu 
does not longer support the deprecated "bridge" parameter that NetBSD 
was using to attach the created tap interface to a given bridge.

Linux does this by passing the name of the tap interface Qemu has to 
create, so when the interface is created its name is known and can be 
used outside of Qemu.

From what I see, NetBSD has the option to fetch the name of the 
interface created, using the TAPGIFNAME ioctl, but this is not really 
helpful because we create the interface from Qemu, but the scripts that 
attach the network interface are launched from the toolstack (xl).

Will it be possible to provide a TAPSIFNAME ioctl to set the name of the 
created interface? I will start looking into this, but I would also like 
some feedback.

Thanks, Roger.