On Wed, 15 Jul 2015 14:52:11 +0300 "Michael S. Tsirkin" <m...@redhat.com> wrote:
> On Wed, Jul 15, 2015 at 01:38:42PM +0200, Cornelia Huck wrote: > > On Wed, 15 Jul 2015 17:39:53 +0800 > > Jason Wang <jasow...@redhat.com> wrote: > > > > > > > > > > > On 07/15/2015 05:11 PM, Cornelia Huck wrote: > > > > On Wed, 15 Jul 2015 13:29:56 +0800 > > > > Jason Wang <jasow...@redhat.com> 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? > > > > I think the base problem is that "transitional" for pci means something > > slightly different than "transitional" for ccw - it's more transient > > for ccw. > > > > Setting VERSION_1 is not really the problem (as legacy guests will only > > retrieve the first 32 bits of features anyway), but any decicions about > > other feature bits that are made based upon the presence of VERSION_1. > > Are we talking about the scsi bit here, again? > Or are there other examples? > The scsi bit is the one I thought about here; I'd need to check the spec whether there are others (for other device types).