[Nbd] NBD server not working with qemu

[Alex King <alex@...2850...>]

I'm writing a simple NBD server in rust as a learning project.  I have something 
simple working with the kernel NBC client, however, it does not work with the 
QEMU client.

I'm using Debian Jessie versions to test against.

So far my server uses only the "un-fixed" new protocol (I'm working from 
proto.md), without NBD_FLAG_NO_ZEROES.

I'm wondering, since I can seem to work with the kernel client, if the QEMU 
client (version 1:2.1+dfsg-12+deb8u6) is incompatible with that protocol?  The 
handshaking completes (from my server's perspective), and then everything stops 
with my server waiting for client requests which never come.

I'll implement the fixed newstyle protocol and see if that fixes things.  But 
would be interested to know if QEMU is supposed to support the unfixed protocol.

Thanks,

Alex