From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:34185) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZFM4y-00068F-Cg for qemu-devel@nongnu.org; Wed, 15 Jul 2015 08:46:29 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ZFM4v-0001dz-5f for qemu-devel@nongnu.org; Wed, 15 Jul 2015 08:46:28 -0400 Received: from e06smtp14.uk.ibm.com ([195.75.94.110]:41333) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZFM4u-0001c6-U5 for qemu-devel@nongnu.org; Wed, 15 Jul 2015 08:46:25 -0400 Received: from /spool/local by e06smtp14.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Wed, 15 Jul 2015 13:46:23 +0100 Received: from b06cxnps4076.portsmouth.uk.ibm.com (d06relay13.portsmouth.uk.ibm.com [9.149.109.198]) by d06dlp02.portsmouth.uk.ibm.com (Postfix) with ESMTP id C4EA1219005F for ; Wed, 15 Jul 2015 13:45:58 +0100 (BST) Received: from d06av02.portsmouth.uk.ibm.com (d06av02.portsmouth.uk.ibm.com [9.149.37.228]) by b06cxnps4076.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id t6FCkLY038535402 for ; Wed, 15 Jul 2015 12:46:21 GMT Received: from d06av02.portsmouth.uk.ibm.com (localhost [127.0.0.1]) by d06av02.portsmouth.uk.ibm.com (8.14.4/8.14.4/NCO v10.0 AVout) with ESMTP id t6FCkLGO025101 for ; Wed, 15 Jul 2015 06:46:21 -0600 Date: Wed, 15 Jul 2015 14:46:19 +0200 From: Cornelia Huck Message-ID: <20150715144619.681db0ff.cornelia.huck@de.ibm.com> In-Reply-To: <20150715145000-mutt-send-email-mst@redhat.com> References: <1436938201-16766-1-git-send-email-jasowang@redhat.com> <20150715111118.4d383807.cornelia.huck@de.ibm.com> <55A62A69.8060603@redhat.com> <20150715133842.2811cc67.cornelia.huck@de.ibm.com> <20150715145000-mutt-send-email-mst@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH V2 0/5] Set correct blk feature for virtio 1.0 List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "Michael S. Tsirkin" Cc: kwolf@redhat.com, pbonzini@redhat.com, Jason Wang , qemu-devel@nongnu.org, stefanha@redhat.com On Wed, 15 Jul 2015 14:52:11 +0300 "Michael S. Tsirkin" wrote: > On Wed, Jul 15, 2015 at 01:38:42PM +0200, Cornelia Huck wrote: > > On Wed, 15 Jul 2015 17:39:53 +0800 > > Jason Wang wrote: > > > > > > > > > > > On 07/15/2015 05:11 PM, Cornelia Huck wrote: > > > > On Wed, 15 Jul 2015 13:29:56 +0800 > > > > Jason Wang wrote: > > > > > > > >> Hi all: > > > >> > > > >> This series tries to set feature correctly for virtio-blk when virtio > > > >> 1.0 is supported. Two isssues were addressed according to the spec: > > > >> > > > >> - scsi passthrough was not support in 1.0. This is done by, 1) disable > > > >> scsi by defautl for 2.4 machine type and fail the initialization > > > >> when both scsi and 1.0 were set. > > > >> - any layout must be set for transitional device. This is done by set > > > >> any layout when 1.0 is supported. > > > >> > > > >> Please review > > > >> > > > >> Changes from V1: > > > >> - Split virtio-net changes out of the series > > > >> - Enable VIRTIO_BLK_F_SCSI only when scsi is set > > > >> - Disable scsi by default and compat it for legacy machine types > > > >> - Let get_features() can fail and fail the initialization of > > > >> virito-blk when both 1.0 and scsi were supported. > > > > Hm, this seems confusing to me mainly due to the different way > > > > transitional devices are handled by pci and ccw. > > > > > > > > For virtio-pci: (please correct me if I misunderstood) > > > > - devices (except input) are transitional by default > > > > - user can disable legacy or modern support > > > > - drivers can use method they prefer, depending on VERSION_1 > > > > > > > > For virtio-ccw: > > > > - transitional means "in limbo" regarding legacy or modern > > > > - devices become legacy if features are read without negotiation of a > > > > revision, or if revision 0 is negotiated > > > > - they become modern if revision 1 is negotiated > > > > > > > > That implies that for ccw, a transitional device does not offer any > > > > features: It either transitions to the legacy or modern state if a > > > > revision was negotiated, or it becomes a legacy device by reading > > > > features (which are the legacy features, then). While pci has "real" > > > > transitional devices needing to offer a certain feature set. > > > > > > > > I'm not sure what the solution is here: basically, ccw needs a dynamic > > > > feature set, while pci does not. > > > > > > > > > > So, if I understand correctly. All virtio-ccw devices are transitional > > > since user can disable neither legacy nor modern. It looks to me then we > > > can set VIRTIO_F_VERSION_1 unconditionally for ccw. Then there's no > > > issue left? > > > > I think the base problem is that "transitional" for pci means something > > slightly different than "transitional" for ccw - it's more transient > > for ccw. > > > > Setting VERSION_1 is not really the problem (as legacy guests will only > > retrieve the first 32 bits of features anyway), but any decicions about > > other feature bits that are made based upon the presence of VERSION_1. > > Are we talking about the scsi bit here, again? > Or are there other examples? > The scsi bit is the one I thought about here; I'd need to check the spec whether there are others (for other device types).