Re: [Qemu-devel] [Qemu-block] block/ssh:Allow blockdev-add for ssh

[Daniel P. Berrange]

On Thu, Sep 29, 2016 at 12:42:34PM +0200, Kevin Wolf wrote:
> Am 29.09.2016 um 10:07 hat Richard W.M. Jones geschrieben:
> > On Thu, Sep 29, 2016 at 01:05:48PM +0530, Ashijeet Acharya wrote:
> > > Hi all,
> > > 
> > > I was trying to convert SSH driver to support 'blockdev-add' and so
> > > far I have tried to figure out what the struct 'BlockdevOptionsSsh' in
> > > block-core.json should look like,
> > > 
> > > { 'struct': 'BlockdevOptionsSsh',
> > >   'data': { 'tcp': 'InetSocketAddress',
> > >              'path': 'str' } }
> > > 
> > > Naive question but I have to ask, Am I missing something?
> > > 
> > > As far as I know, ssh only supports 'tcp' right? So using
> > > 'InetSocketAddress' should be good enough. (like the TODO says)
> > > 
> > > I had a discussion with Kevin about this and he thinks, maybe
> > > 'SocketAddress' can be used too because the restriction comes from the
> > > qemu block driver rather than the backend. He advised me to get an
> > > opinion on this one from the maintainers of SSH.
> > 
> > I have no idea.
> 
> I searched the net a bit and it seems that SSH over Unix domain sockets
> isn't a thing. So it might actually be okay to restrict the QEMU block
> driver to TCP, too, and therefore use InetSocketAddress.

SSH over UNIX sockets isn't common, but it is possible. eg say you want
to connect to a remote machine that isn't directly acessible. You might
use SSH tunnelling to setup a local UNIX domain socket that is connected
to the remote machine eg

   ssh -L /tmp/catbus-sock:catbus.mydomain.com:22 domokun

Now, connecting to the UNIX domain socket /tmp/catbus-sock would in
fact forward traffic to the remote TCP server.

This isn't specific to SSH really - any network protocol could be tunnelled
in this way, so from that POV there is value in all the network block
drivers being able to accept UNIX domain socket addresses.

Regards,
Daniel
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