[libvirt] NBD TLS support in QEMU

Hi, QEMU offers both NBD client and server functionality. The NBD protocol runs unencrypted, which is a problem when the client and server communicate over an untrusted network. The particular use case that prompted this mail is storage migration in OpenStack. The goal is to encrypt the NBD connection between source and destination hosts during storage migration. I think we can integrate TLS into the NBD protocol as an optional flag. A quick web search does not reveal existing open source SSL/TLS NBD implementations. I do see a VMware NBDSSL protocol but there is no specification so I guess it is proprietary. The NBD protocol starts with a negotiation phase. This would be the appropriate place to indicate that TLS will be used. After client and server complete TLS setup the connection can continue as normal. Besides QEMU, the userspace NBD tools (http://nbd.sf.net/) can also be extended to support TLS. In this case the kernel needs a localhost socket and userspace handles TLS. Thoughts? Stefan