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

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

Added ZFS TRIM support which is enabled by default. To disable
ZFS TRIM support set vfs.zfs.trim.enabled=0 in loader.conf.

Creating new ZFS pools and adding new devices to existing pools
first performs a full device level TRIM which can take a significant
amount of time. The sysctl vfs.zfs.vdev.trim_on_init can be set to 0
to disable this behaviour.

ZFS TRIM requires the underlying device support BIO_DELETE which
is currently provided by methods such as ATA TRIM and SCSI UNMAP
via CAM, which are typically supported by SSD's.

Stats for ZFS TRIM can be monitored by looking at the sysctl's
under kstat.zfs.misc.zio_trim.

MFC r240868: Add TRIM support
MFC r244155: Renamed zfs trim stats
MFC r244187: Upgrade TRIM free request sizes optimisation
MFC r244188: Added vfs.zfs.vdev.trim_on_init sysctl
MFC r248572: Add TRIM support for L2ARC
MFC r248574: Improve TXG handling in the TRIM module
MFC r248575: TRIM cache devices based on time instead of TXGs
MFC r248576: Names the ZFS TRIM thread
MFC r248577: Optimisation of TRIM processing
MFC r248602: Fix for building libzpool under i386
MFC r249921: Enabled ZFS TRIM by default

Copy head to stable/9 as part of 9.0-RELEASE release cycle.

Approved by: re (implicit)

Remove C constructs that are incompatible with C++ from various
OpenSolaris and ZFS header files. These changes are sufficient
to allow a C++ program to use the libzfs library.

Note: The majority of these files already included 'extern "C"'
declarations, so the intention of providing C++ compatibility
already existed even if it wasn't provided.

cddl/compat/opensolaris/include/assert.h:
Wrap our compatibility assert implementation in
'extern "C"'. Since this is a compatibility header
I matched the Solaris style of doing this explicitly
rather than rely on FreeBSD's __BEGIN/END_DECLS macro.

sys/cddl/compat/opensolaris/sys/kstat.h:
sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/arc.h:
sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/dsl_pool.h:
sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/ddt.h:
sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/spa.h:
sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/zio.h:
Rename parameters in function declarations that conflict
with C++ keywords. This was the solution preferred by
members of the Illumos community.

sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/zfs_ioctl.h:
In C, nested structures are visible in the global namespace,
but in C++, they take on the namespace of the structure in
which they are contained. Flatten nested structure
definitions within struct zfs_cmd so these structures are
visible in the global namespace when compiled in both
languages.

Sponsored by: Spectra Logic Corporation

Forced commit to note that these files were repo copied.

Please welcome ZFS - The last word in file systems.

ZFS file system was ported from OpenSolaris operating system. The code in under
CDDL license.

I'd like to thank all SUN developers that created this great piece of software.

Supported by: Wheel LTD (http://www.wheel.pl/)
Supported by: The FreeBSD Foundation (http://www.freebsdfoundation.org/)
Supported by: Sentex (http://www.sentex.net/)