> From: Jason Gunthorpe <jgg@xxxxxxxxxx> > Sent: Wednesday, April 28, 2021 1:12 AM > [...] > One option is VFIO can keep its group FD but nothing else will have > anthing like it. However I don't much like the idea that VFIO will > have a special and unique programming model to do that same things > other subsystem will do. That will make it harder for userspace to > implement. Hi, Jason, I have a question here. Based on discussions so far, it's clearly that the new ioasid uAPI will differ from existing VFIO uAPI a lot, e.g. ioasid- centric operations, no group fd, no incompatible domains, etc. Then I wonder how we plan to support legacy VFIO applications in this transition phase. Earlier you ever mentioned the desire of directly replacing /dev/vfio/vfio with /dev/ioasid and having ioasid to present both VFIO and new uAPI. Doesn't it imply that we have to copy the VFIO container/group semantics into /dev/ioasid although it's a special programming model only for VFIO? Alternatively we could keep all the container/group legacy within VFIO and having /dev/ioasid support only the new uAPI semantics. In this case VFIO will include a shim iommu backend to connect its legacy uAPI into drivers/ioasid backend functions for backward compatibility. Then VFIO will also support a new model which only uses its device uAPI to bind to new ioasid fd w/o using any legacy container/group/iommu uAPI. Does this sound a plan? Thanks Kevin
