On Thu, Feb 19, 2015 at 08:55:23AM +1100, Dave Chinner wrote:

And speaking of phony BHs, the pnfs block layout changes introduce
an struct iomap and a "map_blocks" method to the export_ops in
exportfs.h. This is the model what we should be using instead of
phony BHs for block mapping/allocation operations...

I've got some WIP patches to move the direct I/O code over to that,
DAX would be another natural fit.