From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:42588) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZFL9H-0006JG-M1 for qemu-devel@nongnu.org; Wed, 15 Jul 2015 07:46:52 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ZFL9F-0008OL-0F for qemu-devel@nongnu.org; Wed, 15 Jul 2015 07:46:51 -0400 Received: from e06smtp13.uk.ibm.com ([195.75.94.109]:59713) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZFL9E-0008OB-Nz for qemu-devel@nongnu.org; Wed, 15 Jul 2015 07:46:48 -0400 Received: from /spool/local by e06smtp13.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Wed, 15 Jul 2015 12:46:43 +0100 Date: Wed, 15 Jul 2015 13:46:38 +0200 From: Cornelia Huck Message-ID: <20150715134638.065bbd03.cornelia.huck@de.ibm.com> In-Reply-To: <20150715135237-mutt-send-email-mst@redhat.com> References: <20150713104051-mutt-send-email-mst@redhat.com> <55A37E43.6060403@redhat.com> <20150713095651.GA5893@noname.redhat.com> <20150713135156.0d32ef1e.cornelia.huck@de.ibm.com> <20150713151705-mutt-send-email-mst@redhat.com> <20150713143024.3b102b9c.cornelia.huck@de.ibm.com> <20150713153319-mutt-send-email-mst@redhat.com> <20150713152059.69b373ee.cornelia.huck@de.ibm.com> <20150713182901-mutt-send-email-mst@redhat.com> <20150714194344.529a6ea4.cornelia.huck@de.ibm.com> <20150715135237-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 2/5] virtio-blk: disable scsi passthrough for 1.0 device List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "Michael S. Tsirkin" Cc: Kevin Wolf , qemu-block@nongnu.org, Jason Wang , qemu-devel@nongnu.org, Stefan Hajnoczi , pbonzini@redhat.com On Wed, 15 Jul 2015 13:59:00 +0300 "Michael S. Tsirkin" wrote: > On Tue, Jul 14, 2015 at 07:43:44PM +0200, Cornelia Huck wrote: > > > Yes, and that's because as written, transitional devices must set > > > ANY_LAYOUT, but that's incompatible with scsi. > > > > Hm, I had a patch before that dynamically allowed different feature > > sets for legacy or modern, not only a subset. Probably won't apply > > anymore, but I'd like to able to do the following: > > > > - driver reads features without negotiating a revision: driver is > > legacy, offer legacy bits > > - driver negotiates revision 0: dito > > - driver negotiates revision >= 1: driver is modern, offer modern bits > > > > That way we could offer SCSI and !ANY_LAYOUT (if scsi is enabled) in the > > first two cases, and a new qemu could still offer scsi to old guests. > > > > Would it be worth pursuing that idea? > > Frankly, I don't think so: I don't see why it makes sense > to expose more features on the legacy interface than > on the modern one. Imagine updating drivers to fix a bug > and losing some features. How does this make sense? I don't think one should be a strict subset of the other. But I think we don't want to withdraw features from legacy guests on qemu updates either? > > I think the virtio TC's assumption was that the scsi passthrough was a > bad idea, so in QEMU we only keep it around for legacy devices to avoid > regressions. I'm not opposing this :) > > If you disagree and think transitional devices need the SCSI feature, > either try to convince pbonzini or rewrite the spec youself > to support it in the virtio 1 mode. This seems to boil down to the different meaning of "transitional" for ccw and pci, see the other thread.