Keir Fraser wrote: > Do the same as you did with blkback. Add a protocol version or bitwidth > field to xenstore. Update frontend driver to write that field. Make tools > write a default value for pv guests for backward compat. This is even better > than with blkfront/blkback because there are definitely no PV-on-HVM pvfb > driver frontends out in the wild (and it's HVM that makes things harder). Ok, point taken, forgot about the pv-on-hvm issue. Why put the protocol into xenstore btw? The framebuffer configuration is in the shared page instead of xenstore anyway. I'd place protocol next to the configuration, it is the natural location IMHO. We can still sneak it in without breaking the struct layout as we have alignment holes in there anyway. > Speaking of which, we should add the protocol/bitwidth field to blkfront > asap... It is sitting in my 32-on-64 patch queue emmanuel is looking at. The blkback bits shouldn't have any dependencies to the other patches though, so I can submit it right away if you are willing to take it now. Patch for unstable attached. I can prepare a minimal one with just the frontend bits for 3.0.4 if you want. cheers, Gerd -- Gerd Hoffmann