On Wed, 15 Jul 2015 14:49:43 +0300 "Michael S. Tsirkin" <m...@redhat.com> wrote:
> On Wed, Jul 15, 2015 at 11:11:18AM +0200, 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. > > I think the issue is theoretical since linux guests > do not read feature bits > 31 unless revision 1 > is negotiated. Again, VERSION_1 is not really the problem. (qemu clears it for revisions < 1, and I plan to send a patch that effectively clears all bits > 31.) I'm caring about the legacy bits (scsi, in that case) that are not send to legacy drivers.