Re: socket.c added support for unix domain socket datagram transport

[Daniel P . Berrangé]

On Fri, Apr 23, 2021 at 08:56:48AM +0200, Ralph Schmieder wrote:
> Hey...  new to this list.  I was looking for a way to use Unix domain sockets 
> as a network transport between local VMs.
> 
> I'm part of a team where we run dozens if not hundreds of VMs on a single 
> compute instance which are highly interconnected.
> 
> In the current implementation, I use UDP sockets (e.g. something like 
> 
> -netdev id=bla,type=socket,udp=localhost:1234,localaddr=localhost:5678) 
> 
> which works great.
> 
> The downside of this approach is that I need to keep track of all the UDP 
> ports in use and that there's a potential for clashes.  Clearly, having Unix 
> domain sockets where I could store the sockets in the VM's directory would be 
> much easier to manage.
> 
> However, even though there is some AF_UNIX support in net/socket.c, it's
> 
> - not configurable
> - it doesn't work
> 
> As a side note, I tried to pass in an already open FD, but that didn't work 
> either.
> 
> So, I added some code which does work for me... e.g.
> 
> - can specify the socket paths like -netdev 
> id=bla,type=socket,unix=/tmp/in:/tmp/out
> - it does forward packets between two Qemu instances running back-to-back
> 
> I'm wondering if this is of interest for the wider community and, if so, how 
> to proceed.

As a general rule, any place in QEMU that supports sockets, ought to
support all of IPv4, IPv6 and UNIX sockets.   Where there are gaps
it generally just needs someone motivated to provide a patch.

Regards,
Daniel
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