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 r247187,247265,247348,247398,247540,247585,247852,248265,248267
Merge various ZFS improvements and bugfixes

MFC r247187:
Import vendor change to avoid "unitialized variable" warnings.

Illumos ZFS issues:
3522 zfs module should not allow uninitialized variables

MFC r247265:
Merge the ZFS I/O deadman thread from vendor (illumos).
This feature panics the system on hanging ZFS I/O, helps debugging
and resumes failed service.

The panic behavior can be controlled with the loader-only tunables:
vfs.zfs.deadman_enabled (enable or disable panic on stalled ZFS I/O)
vfs.zfs.deadman_synctime (expiration time for stalled ZFS I/O)

By default, ZFS I/O deadman is enabled by default on amd64 and i386
excluding virtual guest machines.

MFC r247348:
Be more verbose on ZFS deadman I/O panic
Patch suggested upstream.

MFC r247398:
Import metaslab_sync() speedup from vendor (illumos).

Illumos ZFS issues:
3552 condensing one space map burns 3 seconds of CPU in spa_sync() thread
3564 spa_sync() spends 5-10% of its time in metaslab_sync() (when not
condensing)
3578 transferring the freed map to the defer map should be constant time
3579 ztest trips assertion in metaslab_weight()

MFC r247540:
Fix the zfs_ioctl compat layer to support zfs_cmd size change introduced
in r247265 (ZFS deadman thread). Both new utilities now support the old
kernel and new kernel properly detects old utilities.

For future backwards compatibility, the vfs.zfs.version.ioctl read-only
sysctl has been introduced. With this sysctl zfs utilities will be able
to detect the ioctl interface version of the currently loaded zfs module.

MFC r247585:
Merge new read-only zfs properties from vendor (illumos)

Illumos ZFS issues:
3588 provide zfs properties for logical (uncompressed) space used and
referenced

MFC r247852:
Import ZFS bpobj bugfix from vendor.

Illumos ZFS issues:
3603 panic from bpobj_enqueue_subobj()
3604 zdb should print bpobjs more verbosely

MFC r248265:
Update zfs.8 manpage date (missing in r247585)

MFC r248267:
Import minor ZFS changes from vendor

Illumos ZFS issues:
3604 zdb should print bpobjs more verbosely (fix zdb hang)
3606 zpool status -x shouldn't warn about old on-disk format

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

Update ZFS from version 6 to 13 and bring some FreeBSD-specific changes.

This bring huge amount of changes, I'll enumerate only user-visible changes:

- Delegated Administration

Allows regular users to perform ZFS operations, like file system
creation, snapshot creation, etc.

- L2ARC

Level 2 cache for ZFS - allows to use additional disks for cache.
Huge performance improvements mostly for random read of mostly
static content.

- slog

Allow to use additional disks for ZFS Intent Log to speed up
operations like fsync(2).

- vfs.zfs.super_owner

Allows regular users to perform privileged operations on files stored
on ZFS file systems owned by him. Very careful with this one.

- chflags(2)

Not all the flags are supported. This still needs work.

- ZFSBoot

Support to boot off of ZFS pool. Not finished, AFAIK.

Submitted by: dfr

- Snapshot properties

- New failure modes

Before if write requested failed, system paniced. Now one
can select from one of three failure modes:
- panic - panic on write error
- wait - wait for disk to reappear
- continue - serve read requests if possible, block write requests

- Refquota, refreservation properties

Just quota and reservation properties, but don't count space consumed
by children file systems, clones and snapshots.

- Sparse volumes

ZVOLs that don't reserve space in the pool.

- External attributes

Compatible with extattr(2).

- NFSv4-ACLs

Not sure about the status, might not be complete yet.

Submitted by: trasz

- Creation-time properties

- Regression tests for zpool(8) command.

Obtained from: OpenSolaris