Re: [Qemu-devel] bidirectional data exchange between guest and host without network

[Jamie Lokier <jamie@shareable.org>]

Richard W.M. Jones wrote:
> On Sat, Jul 11, 2009 at 01:04:00AM +0100, Jamie Lokier wrote:
> > Anthony Lannuzel wrote:
> > > > Can you not create _another_ network device and use that?
> > > > QEMU lets you create lots of network devices.
> > >
> > > No, I do not want the guest to be able to communicate with the host
> > > network, so that is not an option.
> > 
> > So create a network device that is only used for the private
> > communication, and isolate from the rest of the host network with
> > firewall rules.
> > 
> > I'll admit that can be a lot of work, if the host has a complex
> > network, or a dynamic one where IP addresses are unpredictable.
> 
> This is precisely the reason why vmchannel is a good thing.
> 
> There is no IPv4 address you can give to the new interface which won't
> have the potential to conflict with some other IPv4 address already in
> use.  Extra network devices require special handling in firewall rules
> and changes to the configuration of every network daemon in the
> system.

A network interface with no IPv4 or IPv6 addresses assigned would
avoid most daemon problems.  Using a non-ethernet MAC type and
point-to-point would probably avoid the rest, even routing daemons,
NetworkManager and the like.  Use raw sockets over the interfaces.

Just a thought.

> If you don't add an extra network device to the guest, then you rely
> on the host and guest being on the same network, which is not always
> true.
> 
> While it's possible to configure the guest specially to avoid this,
> that doesn't look much like our promise to run any vanilla guest as a
> virtual machine.

I don't see how "any vanilla guest" can use vmchannel, since it
requires specific kernel support doesn't it, and therefore the guest
tools can only use vmchannel on new guest kernels built for it?

-- Jamie