[Nbd] nbd protocol specification?

[Andreas Klauer <Andreas.Klauer@...1264...>]

Hi,

I need to implement a block device in user space with my own idea
of read and write (like a selective copy-on-write layer). The thing 
would be machine-local, network is not important.

I'm currently using FUSE + loop for that, but googling I came across 
a [1]BUSE discussion on LKML which in turn referred to NBD. 
(never even heard of NBD before... *blush*)

I experimented a bit with it and it seems like an interesting 
alternative for me, but to use it, it appears I have to implement 
the protocol myself since there doesn't seem to be a C library like 
the one FUSE offers? Or is there one I have missed?

Is there a protocol specification for NBD available anywhere, 
however brief, other than reading the very fine source of course? 
Reverse engineering has always the risk of missing some detail...

Thank you & Regards
Andreas Klauer

[1] https://lkml.org/lkml/2009/7/28/1