networkManager bridge functionality

[Ben Klopfenstein <benklop gmail com>]

Hello, I have an application that i think could benefit from integration with 
NetworkManager, but it needs a bit more functionality i think.

I am hacking on QtEmu, a frontend to qemu, and I have been working on how to 
implement proper network functionality. intially I was intending to do the 
parts that needed to be done as root by running commands through sudo with a 
NOPASSWD setting in sudoers, but i have decided this is too insecure and 
troublesome.

I decided that it would be best to run a daemon that configures device 
settings, talks to NetworkManager, and limits the allowed actions of the 
clients, but now i am wondering whether the necessary functionality could be 
added directly to NetworkManager, thus also benefiting other projects as 
well.

my needs mean the following:

- when a machine starts, make a tun/tap device with a specific name
- make a specified bridge if it does not exist
- connect the tun/tap to that bridge
optionally (depending on machine settings)
- connect that bridge to the primary ethernet interface
- move the IP address settings from the primary interface to the bridge if it 
was just created
- make sure default routes are correct
 - OR -
- run dhcpd on the bridge
- set up routing between the bridge and the primary interface

some of this, like creating the tun/tap device, could be done in my 
application, but the rest i think belongs elsewhere.

Would it be too hard to add this to NetworkManager? Is this the right place 
for it, or should it be in a related daemon that communicates with NM? If 
this is the right place to put the functionality, is there a primer for 
hacking on NM? 

if done well i think this sort of functionality would be very useful for 
system control panels, and would help make NM more useful even on servers.

Thanks for your help and knowledge!

-Ben