kvm tools: Add optional callback on disk op completion

This patch adds an optional callback to be called when a disk op completes.

Currently theres not much use for it, but it is the infrastructure for adding
aio support.

Signed-off-by: Sasha Levin <levinsasha928@gmail.com>
Signed-off-by: Pekka Enberg <penberg@kernel.org>
5 files changed