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. In any case, won't the following solve it nicely? if (revision >= 1) return d->host_features else return d->host_features & 0xffffffff; -- MST