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

[Stefano Brivio <sbrivio@redhat.com>]

On Tue, 10 May 2022 09:26:39 +0100
Daniel P. Berrangé <berrange@redhat.com> wrote:

> 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

To me, "mode is client, address is x" sounds more intuitive than "mode
is client, remote is x". I mean, of course it's the remote address --
that's a bit redundant.

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

...this won't work, though, because UNIX domain sockets can be
stream-oriented or datagram-oriented.

-- 
Stefano