Re: [Qemu-block] [PATCH for-4.0 00/14] nbd: add qemu-nbd --list

[Eric Blake]

On 12/1/18 1:42 AM, Richard W.M. Jones wrote:
> On Fri, Nov 30, 2018 at 04:03:29PM -0600, Eric Blake wrote:
> > I note that upstream NBD has 'nbd-client -l $host' for querying
> > just export names (with no quoting, so you have to know that
> > a blank line means the default export), but it wasn't powerful
> > enough, so I implemented 'qemu-nbd -L' to document everything.
> > Upstream NBD has separate 'nbd-client' and 'nbd-server' binaries,
> > while we only have 'qemu-nbd' (which is normally just a server,
> > but 'qemu-nbd -c' also operates a second thread as a client).
> > Our other uses of qemu as NBD client are for consuming a block
> > device (as in qemu-io, qemu-img, or a drive to qemu) - but those
> > binaries are less suited to something so specific to the NBD
> > protocol.
>
> I tried it against nbdkit and it works (obviously):
>
> $ ./qemu-nbd -L
> exports available: 1
>   export: ''
>    size:  67108864
>    flags: 0x61 ( trim zeroes )
>
> What I couldn't work out is how to connect to other hosts.  It's
> possible to add -p or -k to change the localhost port number or to use
> a Unix domain socket (and I checked both work).  However can we
> connect to remote hosts?

Should work by adding '-b host' (if -b is omitted, it defaults to 
0.0.0.0).  However, I admit that so far I have only tested '-b 
localhost' or '-b 127.0.0.1' (per the iotest additions at the end of the 
series), so it could well be something that I missed in setting up the 
client socket in nbd_build_socket_address().

--
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org