On Mon, Apr 29, 2019 at 09:12:43AM +0200, Gerd Hoffmann wrote: > Hi, > > > > What questions for example? > > > > This opens up different kind of possible replies, and error handling. > > > > With current proposal and needs, the reply (or absence of reply) is > > entirely driven by the request. > > > > With your proposal, should all request have a reply? > > Yes. > > > which makes a lot > > more code synchronous, > > Why? You don't have to wait for the reply before sending the next > request. > > Adding a request id to the messages might be useful, so it is possible > to wait for a reply to a specific message without having to keeping > track of all in-flight messages. > > > and complicates both sides unnecessarily. > > Having headers in the reply allows it to process them in generic code. > There is a size header for the reply, so you can parse the stream > without knowing what replay to expect. You can use the status field to > indicate the payload, simliar to virtio-gpu which has response code > OK_NODATA, some OK_$whatpayload and some ERR_$failure codes. > > You can dispatch based on the response/status code and run *fully* > asynchronous without too much trouble. > > > > > Can we leave that for future protocol extensions negotiated with > > > > GET/SET_PROTOCOL_FEATURES ? > > > > > > I don't think negotiating such a basic protocol change is a good idea. > > > > Well, then I would rather focus on improving protocol negociation, > > rather than adding unnecessary protocol changes. > > > > Given that GET/SET_PROTOCOL_FEATURES is the first messages being sent, > > why couldn't it have flags indicating new protocol revision? > > A properly structed reply allows a different approach in reply > processing (see above). But that only works if it is in the protocol > right from the start. As add-on feature it can't provide the benefits > because the reply parser must be able to handle both protocol variants. > > cheers, > Gerd
I think it can in theory - but if we know we want a feature we should just add it as mandatory. More options does imply more overhead. -- MST
