libvirt users - Sep 2013 - Can I run a KVM guest with a btrfs subvolume as file system?

Hi,	

I want to run a virtualized Debian stable KVM guest on a Debian stable host 
(to run untrusted stuff like Skype, Flash or eclipse with third-party plugins). 
Naturally host and guest will have many files in common and it would be nice to 
make us of btrfs deduplication.

Now I found "direct kernel boot" but I could not find any
documentation about
it. Does it allow me to hand a btrfs subvolume of the host file system to the 
guest and the guest uses this subvolume as its own file system?

I already asked this question here:

http://serverfault.com/questions/536752/can-i-run-a-kvm-guest-with-a-btrfs-
subvolume-as-file-system

Regards, Thomas Koch

Hi again,

I've read and thought a bit more. Is the following possible:

1. create a folder (say /virtroot) on the host that should hold the root 
filesystem for the virtual machine
2. pass /bin, /sbin, /usr, /lib and /lib64 and /virtroot to the guest via 
virtfs[1]. Only the latter is passed writable.
3. create an initrd for the guest with an fstab that mounts the above folders 
at the right locations.
4. start the virtual machine without storage attached and use -kernel to pass 
a kernel from the host system

[1] http://www.linux-kvm.org/page/9p_virtio

As a result I could have a very lightweight debian stable virtual machine to 
run untrusted applications.

Regards, Thomas Koch