This allows us to do modifications to the kernel tree and rebuild that kernel
using make-testing. We can even have a git kernel tree in a directory to
do kernel development.
Passthrough mode only works as expected when running as root. On
Debian/Ubuntu systems qemu runs as user 'libvirt-qemu' and group 'kvm'
so all shared files must be chowned to grant access from guests.
Symlinks created on the host are still problematic because the Plan 9
filesystem has no direct notion of symbolic links, see [1].
[1] - http://ericvh.github.com/9p-rfc/rfc9p2000.u.html