From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:43462) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZFLCD-0001Fk-Ol for qemu-devel@nongnu.org; Wed, 15 Jul 2015 07:49:54 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ZFLC8-0001AJ-PI for qemu-devel@nongnu.org; Wed, 15 Jul 2015 07:49:53 -0400 Received: from mx1.redhat.com ([209.132.183.28]:39914) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZFLC8-0001AD-Jd for qemu-devel@nongnu.org; Wed, 15 Jul 2015 07:49:48 -0400 Date: Wed, 15 Jul 2015 14:49:43 +0300 From: "Michael S. Tsirkin" Message-ID: <20150715143130-mutt-send-email-mst@redhat.com> References: <1436938201-16766-1-git-send-email-jasowang@redhat.com> <20150715111118.4d383807.cornelia.huck@de.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150715111118.4d383807.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 11:11:18AM +0200, 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. I think the issue is theoretical since linux guests do not read feature bits > 31 unless revision 1 is negotiated. In any case, won't the following solve it nicely? if (revision >= 1) return d->host_features else return d->host_features & 0xffffffff; -- MST