From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:41461) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZHvP8-0000He-JQ for qemu-devel@nongnu.org; Wed, 22 Jul 2015 10:53:56 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ZHvP5-000310-7D for qemu-devel@nongnu.org; Wed, 22 Jul 2015 10:53:54 -0400 Received: from mx1.redhat.com ([209.132.183.28]:33576) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZHvP4-00030u-W9 for qemu-devel@nongnu.org; Wed, 22 Jul 2015 10:53:51 -0400 Date: Wed, 22 Jul 2015 17:53:47 +0300 From: "Michael S. Tsirkin" Message-ID: <20150722175008-mutt-send-email-mst@redhat.com> References: <1437544792-3949-1-git-send-email-jasowang@redhat.com> <1437544792-3949-3-git-send-email-jasowang@redhat.com> <20150722105843.41d22942.cornelia.huck@de.ibm.com> <20150722121913-mutt-send-email-mst@redhat.com> <20150722122531.5f0218e7.cornelia.huck@de.ibm.com> <20150722132638-mutt-send-email-mst@redhat.com> <20150722123840.0fcb9b95.cornelia.huck@de.ibm.com> <20150722133908-mutt-send-email-mst@redhat.com> <20150722125522.25109a04.cornelia.huck@de.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150722125522.25109a04.cornelia.huck@de.ibm.com> Subject: Re: [Qemu-devel] [PATCH V3 2/3] virtio-blk: fail get_features when both scsi and 1.0 were set List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Cornelia Huck Cc: pbonzini@redhat.com, Jason Wang , qemu-devel@nongnu.org On Wed, Jul 22, 2015 at 12:55:22PM +0200, Cornelia Huck wrote: > On Wed, 22 Jul 2015 13:44:14 +0300 > "Michael S. Tsirkin" wrote: > > > On Wed, Jul 22, 2015 at 12:38:40PM +0200, Cornelia Huck wrote: > > > On Wed, 22 Jul 2015 13:32:17 +0300 > > > "Michael S. Tsirkin" wrote: > > > > > > > On Wed, Jul 22, 2015 at 12:25:31PM +0200, Cornelia Huck wrote: > > > > > On Wed, 22 Jul 2015 12:21:32 +0300 > > > > > "Michael S. Tsirkin" wrote: > > > > > > > > > > > On Wed, Jul 22, 2015 at 10:58:43AM +0200, Cornelia Huck wrote: > > > > > > > On Wed, 22 Jul 2015 13:59:51 +0800 > > > > > > > Jason Wang wrote: > > > > > > > > > > > > > > > SCSI passthrough was no longer supported in virtio 1.0, so this patch > > > > > > > > fail the get_features() when both 1.0 and scsi is set. And also only > > > > > > > > advertise VIRTIO_BLK_F_SCSI for legacy virtio-blk device. > > > > > > > > > > > > > > > > Signed-off-by: Jason Wang > > > > > > > > --- > > > > > > > > hw/block/virtio-blk.c | 9 ++++++++- > > > > > > > > 1 file changed, 8 insertions(+), 1 deletion(-) > > > > > > > > > > > > > > > > diff --git a/hw/block/virtio-blk.c b/hw/block/virtio-blk.c > > > > > > > > index 4c27974..4716c3e 100644 > > > > > > > > --- a/hw/block/virtio-blk.c > > > > > > > > +++ b/hw/block/virtio-blk.c > > > > > > > > @@ -731,7 +731,14 @@ static uint64_t virtio_blk_get_features(VirtIODevice *vdev, uint64_t features, > > > > > > > > virtio_add_feature(&features, VIRTIO_BLK_F_GEOMETRY); > > > > > > > > virtio_add_feature(&features, VIRTIO_BLK_F_TOPOLOGY); > > > > > > > > virtio_add_feature(&features, VIRTIO_BLK_F_BLK_SIZE); > > > > > > > > - virtio_add_feature(&features, VIRTIO_BLK_F_SCSI); > > > > > > > > + if (__virtio_has_feature(features, VIRTIO_F_VERSION_1)) { > > > > > > > > + if (s->conf.scsi) { > > > > > > > > + error_setg(errp, "Virtio 1.0 does not support scsi passthrough!"); > > > > > > > > + return 0; > > > > > > > > + } > > > > > > > > + } else { > > > > > > > > + virtio_add_feature(&features, VIRTIO_BLK_F_SCSI); > > > > > > > > + } > > > > > > > > > > > > > > > > if (s->conf.config_wce) { > > > > > > > > virtio_add_feature(&features, VIRTIO_BLK_F_CONFIG_WCE); > > > > > > > > > > > > > > Do we advertise F_SCSI even if scsi is not configured in order to keep > > > > > > > the same bits as before? I'm afraid I don't remember, that thread was > > > > > > > long :/ > > > > > > > > > > > > > > I'm asking because I'd like to depend on that bit to decide whether I > > > > > > > can negotiate revision 1 for ccw and subsequently offer VERSION_1. It > > > > > > > would be an easy thing to do, and I'd like to avoid mucking around with > > > > > > > device-specific configuration from the transport. > > > > > > > > > > > > > > To illustrate what I'm talking about, my current patchset for virtio-1 > > > > > > > on ccw is here: > > > > > > > > > > > > > > git://github.com/cohuck/qemu virtio-1-ccw-2.5 > > > > > > > > > > > > > > > > > > I still think you are over-engineering it. > > > > > > > > > > > > Just add a property to disable the modern interface. > > > > > > Anyone using scsi passthrough will have to set that, > > > > > > if not - above patch will make initialization fail. > > > > > > > > > > And I still think requiring user action and not having this work > > > > > transparently is a bad idea... > > > > > > > > Having what work transparently? SCSI passthrough? > > > > Look, either you agree with Paolo or not. > > > > Paolo thinks it's a deprecated hack not really worth supporting long term. > > > > If you agree, I don't see why is asking for an extra property > > > > such a bit deal. If you don't agree - please open a new thread > > > > and argue about that. > > > > > > I sometimes wonder whether we're arguing about the same thing :( > > > > > > Dropping scsi for virtio-1 is fine. Dropping backwards-compatibility is > > > not. If I upgrade the host, I want the guests to be able to continue > > > using scsi without needing to fence virtio-1 off manually. > > > > Paolo's argument is that no one should be using scsi passthrough. > > > > If the feature has users, we should bring it back into virtio 1. > > > > If almost one uses it, then no one will suffer too much from getting > > an error message saying "please set disable-modern=on". > > And here's where we disagree. Even if it's exotic, I don't want to > break existing users. You should take this disagreement to the virtio TC. QEMU merely implements what the spec voted by TC says. > > And there's no reason to make it behave differently > > between ccw and pci. > > > > > > > > > > > > > > > > > Moreover, I will need a revision-fencing mechanism in any case, when we > > > > > introduce further revisions. > > > > > > > > Why? Assuming we drop more features in the future? > > > > > > Revisions != features. Think new or changed channel commands, for > > > example. > > > > You likely can just add these unconditionally. > > Backwards compatibility? Compatibility is built-in to revision negotiation, isn't it? > > How is this related to virtio blk at all? > > It isn't, revision handling is generic. It's just the scsi bit that > triggered it. -- MST