I had a go at writing a patch, but I think it's possible already without any patch. After launch you can get the PID of the qemu subprocess:  guestfs_get_pid (g);  --> returns PID You can use Linux to map this to a list of thread IDs:  ls /proc/$PID/task/  --> returns a list of thread IDs [Yes, this is potentially racy, but in reality qemu has already started up fully after guestfs_launch returns and is almost quiescent when you're not issuing commands.] Then you can assign the threads to the cgroup:  for tid in $(ls -1 /proc/$PID/task); do    echo $tid > /cgroup/blkio/$group/tasks  done This is more cumbersome if you're using guestfish instead of some scripting language, and it's difficult if you want to port to non-Linux, but should work in the common case AFAICS.  I've not tried it though ... Rich. -- Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones libguestfs lets you edit virtual machines.  Supports shell scripting, bindings from many languages.  http://et.redhat.com/~rjones/libguestfs/ See what it can do: http://et.redhat.com/~rjones/libguestfs/recipes.html