On Mon, Oct 16, 2017 at 12:44:31PM -0700, Dan Williams wrote: > > While I agree with the need for a per-MR notification mechanism, one > > thing we lose by walking away from MAP_DIRECT is a way for a > > hypervisor to coordinate pass through of a DAX mapping to an RDMA > > device in a guest. That will remain a case where we will still need to > > use device-dax. I'm fine if that's the answer, but just want to be > > clear about all the places we need to protect a DAX mapping against > > RDMA from a non-ODP device. > > For this specific issue perhaps we promote FL_LAYOUT as a lease-type > that can be set by fcntl(). I don't think it is a good userspace interface, mostly because it is about things that don't matter for userspace (block mappings). It makes sense as a kernel interface for callers that want to pin down a memory long-term, but for userspace the fact that the block mapping changes doesn't matter - it matters that their long term pin is broken by something.
