From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:33224) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Xu12x-000886-1v for qemu-devel@nongnu.org; Thu, 27 Nov 2014 10:32:04 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Xu12o-0004VQ-1Q for qemu-devel@nongnu.org; Thu, 27 Nov 2014 10:31:55 -0500 Received: from e06smtp14.uk.ibm.com ([195.75.94.110]:33844) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Xu12n-0004VC-Q9 for qemu-devel@nongnu.org; Thu, 27 Nov 2014 10:31:45 -0500 Received: from /spool/local by e06smtp14.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Thu, 27 Nov 2014 15:31:44 -0000 Received: from b06cxnps4076.portsmouth.uk.ibm.com (d06relay13.portsmouth.uk.ibm.com [9.149.109.198]) by d06dlp03.portsmouth.uk.ibm.com (Postfix) with ESMTP id 2DF341B08040 for ; Thu, 27 Nov 2014 15:31:57 +0000 (GMT) Received: from d06av06.portsmouth.uk.ibm.com (d06av06.portsmouth.uk.ibm.com [9.149.37.217]) by b06cxnps4076.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id sARFVf5T17039540 for ; Thu, 27 Nov 2014 15:31:41 GMT Received: from d06av06.portsmouth.uk.ibm.com (localhost [127.0.0.1]) by d06av06.portsmouth.uk.ibm.com (8.14.4/8.14.4/NCO v10.0 AVout) with ESMTP id sARASg6k016282 for ; Thu, 27 Nov 2014 05:28:42 -0500 Date: Thu, 27 Nov 2014 16:31:39 +0100 From: Cornelia Huck Message-ID: <20141127163139.7db48144.cornelia.huck@de.ibm.com> In-Reply-To: <20141127152422.GA26747@redhat.com> References: <1417101409-29482-1-git-send-email-cornelia.huck@de.ibm.com> <20141127152422.GA26747@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH RFC v4 00/16] qemu: towards virtio-1 host support List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "Michael S. Tsirkin" Cc: thuth@linux.vnet.ibm.com, rusty@rustcorp.com.au, qemu-devel@nongnu.org, kvm@vger.kernel.org, virtualization@lists.linux-foundation.org On Thu, 27 Nov 2014 17:24:22 +0200 "Michael S. Tsirkin" wrote: > On Thu, Nov 27, 2014 at 04:16:33PM +0100, Cornelia Huck wrote: > > Yet another version of the virtio-1 support patches. > > > > This one has seen some (very) light testing with the virtio-1 guest > > support patches currently on vhost-next. > > > > Changes from v3: > > > > - Add support for FEATURES_OK. We refuse to set features after the > > driver has set this in the status field, and we allow to fail > > setting the status if the features are inconsistent. > > - Add missing virtio-1 changes for virtio-net (header size and mac). > > - Dropped setting the VERSION_1 bit for virtio-blk: There's still > > some stuff missing. > > > > For virtio-blk, we need to validate the feature bits if version 1 is > > negotiated: some legacy features are not allowed in that case. I'm not > > quite sure how to handle this, though. We could use the new > > validate_features callback to verify that the driver negotiated a > > sensible feature set, but that would require us to offer a superset > > of legacy and version 1 bits, which feels wrong. Any ideas? > > No, that's violating the spec. > I think the simplest way is to have separate features and > legacy_features fields. Present the correct one depending on which > revision was negotiated. But revisions are a virtio-ccw only thing - what can other transports do here? The basic problem is that we decide via a feature bit that needs to be negotiated which feature bits we want to present. pci and mmio don't have a way to know whether the driver wants to use 1.0 or legacy prior to feature negotiation, do they?