Copy stable/10@r272459 to releng/10.1 as part of
the 10.1-RELEASE process.

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

MFC 261517,261520:
Convert the license on files where I am the sole copyright holder to
2 clause BSD licenses.

Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

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

Add assertion for refcount overflow.

Submitted by: Andrey Zonov <andrey zonov.org>
Reviewed by: kib

Remove debugging cruft.

pjd@'s r180759 was intended to revert r180755 due to ipfilter breakage,
but removed too much, breaking the build in other places instead. Now
that the ipfilter issue has been fixed (or hacked around), address the
second issue by restoring r180755, with one small change. I don't feel
comfortable using assert(3) in a header that will be included in userland
code that may or may not already have an assertion mechanism in place,
so KASSERT() evaluates to a no-op in the !_KERNEL case.

Back out this change, as it breaks the build and I don't have time for
a better fix today.

Check for negative reference count.

Reviewed by: des

Add a simple reference count API that is simply a thin wrapper API around
atomic operations on ints.

Reviewed by: arch@
MFC after: 1 week