From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:47371) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1fYWZJ-0007Ck-Vp for qemu-devel@nongnu.org; Thu, 28 Jun 2018 09:02:42 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1fYWZE-0001oV-5E for qemu-devel@nongnu.org; Thu, 28 Jun 2018 09:02:38 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:35676 helo=mx1.redhat.com) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1fYWZE-0001o3-0l for qemu-devel@nongnu.org; Thu, 28 Jun 2018 09:02:32 -0400 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.rdu2.redhat.com [10.11.54.5]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 45A7C8151D6F for ; Thu, 28 Jun 2018 13:02:31 +0000 (UTC) From: Markus Armbruster References: <20180620073223.31964-1-peterx@redhat.com> <871sctea4y.fsf@dusky.pond.sub.org> <87tvpoadcc.fsf_-_@dusky.pond.sub.org> <87wouk8vul.fsf@dusky.pond.sub.org> <87h8lo74oa.fsf@dusky.pond.sub.org> <20180627132853.GO30628@redhat.com> Date: Thu, 28 Jun 2018 15:02:27 +0200 In-Reply-To: <20180627132853.GO30628@redhat.com> ("Daniel P. =?utf-8?Q?Ber?= =?utf-8?Q?rang=C3=A9=22's?= message of "Wed, 27 Jun 2018 14:28:53 +0100") Message-ID: <8736x7hxng.fsf@dusky.pond.sub.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Subject: Re: [Qemu-devel] monitor: enable OOB by default List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "Daniel P. =?utf-8?Q?Berrang=C3=A9?=" Cc: Markus Armbruster , qemu-devel@nongnu.org, Peter Xu Daniel P. Berrang=C3=A9 writes: > On Wed, Jun 27, 2018 at 03:13:57PM +0200, Markus Armbruster wrote: >> Monitor behavior changes even when the client rejects capability "oob". >>=20 >> Traditionally, the monitor reads, executes and responds to one command >> after the other. If the client sends in-band commands faster than the >> server can execute them, the kernel will eventually refuse to buffer >> more, and sending blocks or fails with EAGAIN. >>=20 >> To make OOB possible, we need to read and queue commands as we receive >> them. If the client sends in-band commands faster than the server can >> execute them, the server will eventually drop commands to limit the >> queue length. The sever sends event COMMAND_DROPPED then. >>=20 >> However, we get the new behavior even when the client rejects capability >> "oob". We get the traditional behavior only when the server doesn't >> offer "oob". >>=20 >> Is this what we want? > > IMHO the key benefit of allowing the client to reject the capability > is to enable backwards compat support. So this behaviour feels wrong. > Rejecting OOB should have same semantics as previous QEMU's without > OOB available, otherwise we now have 3 distinct ways the monitor > operates (no OOB, OOB rejected, OOB accepted). This can only ever > lead to more bugs due to lack of testing of no OOB vs OOB rejected > scenarios. Agreed. We have three configuration cases * OOB not offered (because MUX) * OOB offered, but rejected by client * OOB offered and accepted We want to map them to two run time cases * OOB off * OOB on We may use "server offered OOB" only for configuration purposes. Keep that in mind when reading my reply to Peter's reply. Aside: it would be nice to get rid of the configuration case "OOB not offered", but that's for later.