From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:49495) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZFLSX-0000QB-51 for qemu-devel@nongnu.org; Wed, 15 Jul 2015 08:06:51 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ZFLST-0007Q3-Um for qemu-devel@nongnu.org; Wed, 15 Jul 2015 08:06:45 -0400 Received: from mx1.redhat.com ([209.132.183.28]:54580) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZFLEY-0002GP-NK for qemu-devel@nongnu.org; Wed, 15 Jul 2015 07:52:18 -0400 Date: Wed, 15 Jul 2015 14:52:11 +0300 From: "Michael S. Tsirkin" Message-ID: <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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150715133842.2811cc67.cornelia.huck@de.ibm.com> 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: Cornelia Huck Cc: kwolf@redhat.com, pbonzini@redhat.com, Jason Wang , qemu-devel@nongnu.org, stefanha@redhat.com 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? -- MST