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

[Ralph Schmieder]

> On Apr 23, 2021, at 11:16, Daniel P. Berrangé <berrange@redhat.com> wrote:
> 
> 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.

OK, great... The code basically works afaict, so I am wondering if you guys are 
OK with the CLI "unix=path1:path2" approach and also whether patches are sent 
to this list or whether it's better to open a PR on github/gitlab?


Thanks,
-ralph