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

[Stefano Brivio]

On Tue, 10 May 2022 10:22:48 +0100
Daniel P. Berrangé <berrange@redhat.com> wrote:

> On Tue, May 10, 2022 at 10:59:08AM +0200, Stefano Brivio wrote:
> > 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.  

Well, this ^^^ is one thing ('-netdev stream' for UNIX sockets),

> > ...this won't work, though, because UNIX domain sockets can be
> > stream-oriented or datagram-oriented.  
> 
> Sure it can work, both the 'stream' and 'dgram' backends would
> allow the full range of addr types as they're independant config
> dimensions
> 
> 
>     -netdev stream,server=no,addr.type=inet,addr.host=localhost,addr.port=1234
>     -netdev stream,server=no,addr.type=unix,addr.path=/some/stream/sock
> 
> 
>     -netdev dgram,id=ndev0,\
>             local.type=inet,local.host=localhost,local.port=1234,\
>             remote.type=inet,remote.host=localhost,remote.port=1235
>     -netdev dgram,id=ndev0,\
>             local.type=unix,local.path=/some/dgram/sock0,
>             remote.type=unix,remote.path=/some/dgram/sock1

...and this ('-netdev dgram' for UNIX sockets) is another one. :)

Indeed they're independent though, so I also prefer this version (with
the details Laurent just provided).

-- 
Stefano