The pNFS block server support for the NFSD kernel code allow for an NFS client connected to a shared disk to do block I/O to that disk in place of NFS reads and writes. pNFS is short for Parallel NFS. By being able to do I/O directly to the shared disk, performance and its parallel abilities can be boosted.
For those not familiar with the pNFS block work, see these older PDF slides or visit pNFS.com. The pNFS block server code has been out there for a while now but up until now has been in an out-of-tree kernel Git repository.
The nfsd changes were submitted early for the Linux 4.0/3.20 merge window while this weekend is when a XFS pull request was submitted for pNFS block layout support. There's just shy of 400 lines of code to change the file-system for supporting the PNFS block layout server. For Linux 4.0/3.20, XFS is the only file-system supporting this feature.