Copy stable/9 to releng/9.3 as part of the 9.3-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

MFC r233648:
Remove trailing whitespace per mdoc lint warning

Approved by: cperciva (implicit)

MFC 228509,228620,228533:
Add a helper API to allow in-kernel code to map portions of shared memory
objects created by shm_open(2) into the kernel's address space. This
provides a convenient way for creating shared memory buffers between
userland and the kernel without requiring custom character devices.

Add a helper API to allow in-kernel code to map portions of shared memory
objects created by shm_open(2) into the kernel's address space. This
provides a convenient way for creating shared memory buffers between
userland and the kernel without requiring custom character devices.