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Tsirkin" To: Johannes Berg Message-ID: <20190909094609-mutt-send-email-mst@kernel.org> References: <20190902121233.13382-1-johannes@sipsolutions.net> <20190906121350.29202-1-johannes@sipsolutions.net> <20190906102217-mutt-send-email-mst@kernel.org> <20190906110340-mutt-send-email-mst@kernel.org> <20190908091207-mutt-send-email-mst@kernel.org> <8a9cf8a1726afce7fed8992a4f19fc808004ef88.camel@sipsolutions.net> <20190909083902-mutt-send-email-mst@kernel.org> <89f25546ffa71c799c533e50658a3a58e066f436.camel@sipsolutions.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <89f25546ffa71c799c533e50658a3a58e066f436.camel@sipsolutions.net> X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 209.132.183.28 Subject: Re: [Qemu-devel] [RFC] libvhost-user: implement VHOST_USER_PROTOCOL_F_KICK_CALL_MSGS X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: qemu-devel@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Mon, Sep 09, 2019 at 03:05:08PM +0200, Johannes Berg wrote: > On Mon, 2019-09-09 at 08:41 -0400, Michael S. Tsirkin wrote: > > > > The only thing we could do is crash if it wants to use this feature > > > without the others, but would that really be helpful? > > > > We can return failure from SET_PROTOCOL_FEATURES. > > We can also fail all following messages. > > Only if we have F_REPLY_ACK, I think? > > I suppose we could fail a later command that already needs a reply > without REPLY_ACK, but that seems difficult to debug? Next command is GET_FEATURES. Return an error response from that and device init will fail. > Anyway, if you feel that we should have this as some sort of safeguard I > can try to do that; to me it feels rather pointless as libvhost-user is > more of a sample implementation than anything else. Exactly for this reason :) > Unless you also wanted to write into the spec that F_KICK_CALL_MSGS > absolutely *requires* F_REPLY_ACK, yep > and add some text that tells a device > how to behave when F_KICK_CALL_MSGS is negotiated without F_REPLY_ACK? > > johannes We can document how to behave in case of inconsistent protocol features, yes.