From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([209.51.188.92]:52948) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1hL7mj-0000mO-2j for qemu-devel@nongnu.org; Mon, 29 Apr 2019 11:01:38 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1hL7mf-0001hU-CI for qemu-devel@nongnu.org; Mon, 29 Apr 2019 11:01:37 -0400 Received: from mail-qt1-f177.google.com ([209.85.160.177]:33900) by eggs.gnu.org with esmtps (TLS1.0:RSA_AES_128_CBC_SHA1:16) (Exim 4.71) (envelope-from ) id 1hL7mV-0001bU-VQ for qemu-devel@nongnu.org; Mon, 29 Apr 2019 11:01:27 -0400 Received: by mail-qt1-f177.google.com with SMTP id j6so12307043qtq.1 for ; Mon, 29 Apr 2019 08:01:17 -0700 (PDT) Date: Mon, 29 Apr 2019 11:01:14 -0400 From: "Michael S. Tsirkin" Message-ID: <20190429105933-mutt-send-email-mst@kernel.org> References: <20190423132004.13725-1-marcandre.lureau@redhat.com> <20190423132004.13725-6-marcandre.lureau@redhat.com> <20190426072446.r7b7wsm4qghd7pzr@sirius.home.kraxel.org> <20190426120558.vh66gugqtvcc6tm5@sirius.home.kraxel.org> <20190429071243.icqw3qbzcxbcz7ph@sirius.home.kraxel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190429071243.icqw3qbzcxbcz7ph@sirius.home.kraxel.org> Subject: Re: [Qemu-devel] [PATCH v6 05/11] vhost-user: add vhost_user_gpu_set_socket() List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Gerd Hoffmann Cc: =?iso-8859-1?Q?Marc-Andr=E9?= Lureau , QEMU 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