[Libguestfs] Point-in-time snapshots

[Richard W.M. Jones]

On Fri, Mar 27, 2015 at 01:27:39PM -0600, Eric Blake wrote:
> Is NBD bi-directional, in that the target can receive write requests at
> the same time it is sending read requests?

It's unidirectional.  It's a very simple protocol - you can't even
answer requests out of order:

  https://github.com/yoe/nbd/blob/master/doc/proto.txt

In an ideal world for libguestfs we'd have qemu be the NBD server,
with some sort of monitor command like:

  drive-point-in-time-snapshot device:virtio-disk1 port:1000 id:123

then you'd connect to <qemu-server>:1000 and it'd give you access to
the drive at that instant in time until there was a further command to
discard the snapshot:

  drive-discard-point-in-time-snapshot id:123

Rich.

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