This is the Plan 9 port of lguest. The very first version in the repo is the 
working lguest for 2.6.25. Interface churn being a fact of life in Linux, 
this port does not work on later Linuxes. I will have to tag each working 
version with the kernel it works on I guess. 

To build, 
cd /sys/src/9/lg

You'll get a 9lguestcpu.elf suitable for booting with Linux. 

On Linux, 

modprobe lg syscall_vector=64
lguest <some memory size> 9lguestcpu.elf <some options>

For a venti disk, you can do, e.g.:
lguest  512 /tmp/9lguestcpu.elf --block=/u3/thx9.img --tunnet=bridge:lg0 'venti=#S/sd00/arenas;bootdisk=local!#S/sd00/fossil;bootargs=local!#S/sd00/fossil'

thx9.img in this case I think came from qemu.