I want to find a way to do that.
The network options in documentation:http://qemu.weilnetz.de/qemu-doc.htm...005finvocation
I have tried one of them and could start an interface in linux.img, but couldn't do it again :/ (I forgot how I could do)
Of course this guest interface also did not connect to any interface in host OS.
After that I tested the scripts here: http://en.wikibooks.org/wiki/QEMU/Networking
The qemu-ifup made a virtual interface. (Of course by some edits in script like "/sbin/ifdown eth0" > "ifconfig eth0 down")
I can not understand what the script qemu-ifup does exactly, and also how to connect my guest interface to host interface. (the last commands couldn't do it for me)