Re: [RFC PATCH 0/6] qapi: net: add unix socket type support to netdev backend

["Daniel P. Berrangé" <berrange@redhat.com>]

On Mon, May 09, 2022 at 07:36:12PM +0200, Laurent Vivier wrote:
> "-netdev socket" only supports inet sockets.
> 
> It's not a complex task to add support for unix sockets, but
> the socket netdev parameters are not defined to manage well unix
> socket parameters.
> 
> As discussed in:
> 
>   "socket.c added support for unix domain socket datagram transport"
>   https://lore.kernel.org/qemu-devel/1C0E1BC5-904F-46B0-8044-68E43E67BE60@gmail.com/
> 
> This series adds support of unix socket type using SocketAddress QAPI structure.
> 
> A new netdev backend "socket-ng" is added, that is barely a copy of "socket"
> backend but it uses the SocketAddress QAPI to provide socket parameters.
> And then it also implement unix sockets (TCP and UDP).

So pulling in the QAPI from patch 2

   { 'enum': 'NetdevSocketNGMode',
     'data':  [ 'dgram', 'server', 'client' ] }

   { 'struct': 'NetdevSocketNGOptions',
     'data': {
       'mode':    'NetdevSocketNGMode',
       '*addr':   'SocketAddress',
       '*remote': 'SocketAddress',
       '*local':  'SocketAddress' } }

> Some examples of CLI syntax:
> 
>   for TCP:
> 
>   -netdev socket-ng,id=socket0,mode=server,addr.type=inet,addr.host=localhost,addr.port=1234
>   -netdev socket-ng,id=socket0,mode=client,addr.type=inet,addr.host=localhost,addr.port=1234
> 
>   -netdev socket-ng,id=socket0,mode=dgram,\
>           local.type=inet,local.host=localhost,local.port=1234,\
>           remote.type=inet,remote.host=localhost,remote.port=1235
> 
>   for UNIX:
> 
>   -netdev socket-ng,id=socket0,mode=server,addr.type=unix,addr.path=/tmp/qemu0
>   -netdev socket-ng,id=socket0,mode=client,addr.type=unix,addr.path=/tmp/qemu0
> 
>   -netdev socket-ng,id=socket0,mode=dgram,\
>           local.type=unix,local.path=/tmp/qemu0,\
>           remote.type=unix,remote.path=/tmp/qemu1
> 
>   for FD:
> 
>   -netdev socket-ng,id=socket0,mode=server,addr.type=fd,addr.str=4
>   -netdev socket-ng,id=socket0,mode=client,addr.type=fd,addr.str=5
> 
>   -netdev socket-ng,id=socket0,mode=dgram,local.type=fd,addr.str=4

                                                          ^^^ local.str=4

I notice that in all these examples, mode=client/server always use
the 'addr' field, and mode=dgram always uses the 'local'/'remote'
fields. IOW, there is almost no commonality between the dgram scenario
and the stream scenario, which feels sub-optimal.

Two alternatives come to mind

 - mode=client could use 'remote' and mode=server could use 'local',
   removing the 'addr' field entirely

 - Have completely separate backends, ie '-netdev stream' for
   client/server TCP/UNIX sockets, and '-netdev dgram' for UDP
   sockets, removing 'mode' field.

I'd have a slight preference for the second, since I'm not thrilled
by the 'socket-ng' name :-) 

With regards,
Daniel
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