From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:59522) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZFJAa-0007U1-3P for qemu-devel@nongnu.org; Wed, 15 Jul 2015 05:40:05 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ZFJAV-0003mH-09 for qemu-devel@nongnu.org; Wed, 15 Jul 2015 05:40:04 -0400 Received: from mx1.redhat.com ([209.132.183.28]:47130) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZFJAU-0003lr-Rs for qemu-devel@nongnu.org; Wed, 15 Jul 2015 05:39:58 -0400 Message-ID: <55A62A69.8060603@redhat.com> Date: Wed, 15 Jul 2015 17:39:53 +0800 From: Jason Wang MIME-Version: 1.0 References: <1436938201-16766-1-git-send-email-jasowang@redhat.com> <20150715111118.4d383807.cornelia.huck@de.ibm.com> In-Reply-To: <20150715111118.4d383807.cornelia.huck@de.ibm.com> Content-Type: text/plain; charset=windows-1252 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: Cornelia Huck Cc: kwolf@redhat.com, pbonzini@redhat.com, qemu-devel@nongnu.org, stefanha@redhat.com, mst@redhat.com 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?