This allows a front-end to request for a callback when the backend
is writable again.
Signed-off-by: NAnthony Liguori <aliguori@us.ibm.com>
Signed-off-by: NAmit Shah <amit.shah@redhat.com>
Message-id: 96f93c0f741064604bbb6389ce962191120af8b7.1362505276.git.amit.shah@redhat.com
Signed-off-by: NAnthony Liguori <aliguori@us.ibm.com>