From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:47884) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZFIiw-0000Jk-CC for qemu-devel@nongnu.org; Wed, 15 Jul 2015 05:11:31 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ZFIiq-00068A-Jm for qemu-devel@nongnu.org; Wed, 15 Jul 2015 05:11:30 -0400 Received: from e06smtp14.uk.ibm.com ([195.75.94.110]:45338) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZFIiq-00067r-BZ for qemu-devel@nongnu.org; Wed, 15 Jul 2015 05:11:24 -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 10:11:22 +0100 Received: from b06cxnps4075.portsmouth.uk.ibm.com (d06relay12.portsmouth.uk.ibm.com [9.149.109.197]) by d06dlp01.portsmouth.uk.ibm.com (Postfix) with ESMTP id 4DD8717D8059 for ; Wed, 15 Jul 2015 10:12:39 +0100 (BST) Received: from d06av11.portsmouth.uk.ibm.com (d06av11.portsmouth.uk.ibm.com [9.149.37.252]) by b06cxnps4075.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id t6F9BJQT34668600 for ; Wed, 15 Jul 2015 09:11:19 GMT Received: from d06av11.portsmouth.uk.ibm.com (localhost [127.0.0.1]) by d06av11.portsmouth.uk.ibm.com (8.14.4/8.14.4/NCO v10.0 AVout) with ESMTP id t6F9BJxn003920 for ; Wed, 15 Jul 2015 03:11:19 -0600 Date: Wed, 15 Jul 2015 11:11:18 +0200 From: Cornelia Huck Message-ID: <20150715111118.4d383807.cornelia.huck@de.ibm.com> In-Reply-To: <1436938201-16766-1-git-send-email-jasowang@redhat.com> References: <1436938201-16766-1-git-send-email-jasowang@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: Jason Wang Cc: kwolf@redhat.com, pbonzini@redhat.com, qemu-devel@nongnu.org, stefanha@redhat.com, mst@redhat.com 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.