mmap MAP_FIXED, Linux 4.17

[Howard Chu <hyc@symas.com>]

There's a new mmap option MAP_FIXED_NOREPLACE added in the Linux 4.17 kernel. 
This will check if the requested mapping overlaps any existing maps and fail 
if so, allowing fixed address mappings to be used more safely. Funny to see 
since we already worked around this danger in LMDB a long time ago.

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=a4ff8e8620d3f4f50ac4b41e8067b7d395056843

As usual, adding more stuff to the kernel even though userland solutions 
already existed.

--
  -- Howard Chu
  CTO, Symas Corp.           http://www.symas.com
  Director, Highland Sun     http://highlandsun.com/hyc/
  Chief Architect, OpenLDAP  http://www.openldap.org/project/