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 r253996,253997: opensolaris code: translate INVARIANTS to DEBUG and ZFS_DEBUG

Please note that support for compiling ZFS into a kernel is not in this
branch as of now.

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

Approved by: re (implicit)

Finally... Import the latest open-source ZFS version - (SPA) 28.

Few new things available from now on:

- Data deduplication.
- Triple parity RAIDZ (RAIDZ3).
- zfs diff.
- zpool split.
- Snapshot holds.
- zpool import -F. Allows to rewind corrupted pool to earlier
transaction group.
- Possibility to import pool in read-only mode.

MFC after: 1 month

Reverse the logic for ADAPTIVE_SX option and enable it by default.
Introduce for this operation the reverse NO_ADAPTIVE_SX option.
The flag SX_ADAPTIVESPIN to be passed to sx_init_flags(9) gets suppressed
and the new flag, offering the reversed logic, SX_NOADAPTIVE is added.

Additively implements adaptive spininning for sx held in shared mode.
The spinning limit can be handled through sysctls in order to be tuned
while the code doesn't reach the release, after which time they should
be dropped probabilly.

This change has made been necessary by recent benchmarks where it does
improve concurrency of workloads in presence of high contention
(ie. ZFS).

KPI breakage is documented by __FreeBSD_version bumping, manpage and
UPDATING updates.

Requested by: jeff, kmacy
Reviewed by: jeff
Tested by: pho

enable adaptive spinning on zfs locks

Forced commit to note that these files were repo copied.

Remove "zfs:" prefix from lock and condvar names and also skip non-letter
characters (mostly "&"). Because top(1) shows only first six characters of
wait channel, without this change we saw only one meaningful character.

Requested by: kris & others
MFC after: 1 week

There are too many false positive LORs reported by WITNESS, so when ZFS
debug is turned off, initialize locks with NOWITNESS flag.
At some point I'll get back to them, we would probably need BLESSING
functionality, which is currently turned off by default.

Instead of detecting if lock is already initialized based on standard 1 bit
check, use more accurate 13 bits check. We had too many false-positives with
the standard check.

Reported by: mlaier

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/)