title: Next free device option for qemu-nbd
body: <p>Is there an option for the <strong>qemu-nbd</strong> command to get the next free, i.e. unused NBD like <strong>losetup -f</strong> does? The manpage of 0.0.1 (which is version of the currently stable release 1.7.0 of qemu) doesn't mention anything.</p>