MFC r312110:

Fix -Wsign-compare warnings

The loop index (i) doesn't need to be size_t as its comparison is signed

Copy head@r302406 to stable/11 as part of the 11.0-RELEASE cycle.
Prune svn:mergeinfo from the new branch, as nothing has been merged
here.

Additional commits post-branch will follow.

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

Fix leaks and test for getpagesize() returning == -1

- close file descriptors after use.
- Always munmap memory regions after mmap'ing them.
- Make sure getpagesize() returns a value greater than 0 and use a
cached value instead of always calling getpagesize(3).

CID: 1331374-1331377, 1331653-1331662
Differential Revision: https://reviews.freebsd.org/D6011
MFC after: 2 weeks
Reported by: Coverity
Reviewed by: cem
Sponsored by: EMC / Isilon Storage Division

Add more mmap tests related to character devices.
- Add cdev-related tests for bad args.
- Add two simple tests cases for mapping /dev/zero that test for
MAP_ANON-like behavior.

Reviewed by: alc, kib
MFC after: 1 week
Differential Revision: https://reviews.freebsd.org/D3323

Add various tests to ensure that invalid arguments passed to mmap()
trigger failures.

Reviewed by: kib
Differential Revision: https://reviews.freebsd.org/D3269

Convert the map_at_zero test case to ATF. In particular, this will
facilitate adding more mmap() tests.

MFC after: 2 weeks
Differential Revision: https://reviews.freebsd.org/D3268

Move tests/sys/kern/mmap_test to tests/sys/vm/mmap_test

As jhb noted, the actual mmap(2) implementation is under sys/vm, not
sys/kern/, so the correct logical place is tests/sys/vm/, not
tests/sys/kern/

X-MFC with: r282076
MFC after: 6 days

Integrate tools/regression/mmap into the FreeBSD test suite as
tests/sys/kern/mmap_test

MFC after: 1 week

Convert this testcase over to a TAP format testcase

MFC after: 1 week

Replace the name of the sysctl to security.bsd.map_at_zero and to be
consistent updated the name of the variable as well, after the change
in r197711.

Add a simple C program to check mmap calls to various different addresses.
The most important test is the mapping fixed at address 0 depending on the
new sysctl.

Things will be updated and possibly converted to m4/.t style once the
details about the kernel patch will be shaken out.

Submitted by: simon (initial version)