Sparse file support in FreeBSD NFSv4.2 server

Could you please implement sparse file support in the FreeBSD NFS server?

Typical users are databases, High Performance Computing, Big Data,
distributed systems and so on.

Required are:
- NFSv4.2 operation "SEEK", to list sections with data, and sections with holes
- NFSv4.2 operation "ALLOCATE", to allocate disk space
- NFSv4.2 operation "DEALLOCATE", to free/deallocate disk space, aka
punching a hole (which does not alter a file's size)
- NFSv4.2 operation "READPLUS", to read from sparse files. The
returned data are a list of unions, each union either containing the
block data, or the size of the hole
- NFSv4.2 operation "WRITESAME", to fill (and thus allocate) files
with repeated patterns (typical fill with zeros, or "empty pattern"
for databases)

Caveats:
- Sparse files contain sections called "holes" which do not contain
data, but for backwards compatibility read as 0x00 bytes. But valid
data can contain long sequences of 0x00 bytes, which are NOT holes
-- 
Aurélien