- Copy stable/10 (r259064) to releng/10.0 as part of the
10.0-RELEASE cycle.
- Update __FreeBSD_version [1]
- Set branch name to -RC1

[1] 10.0-CURRENT __FreeBSD_version value ended at '55', so
start releng/10.0 at '100' so the branch is started with
a value ending in zero.

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

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

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

MFV r251620:

ZFS comments need cleaner, more consistent style

Illumos ZFS issues:
3741 zfs comments need cleaner, more consistent style

MFC after: 2 weeks

MFV r248217:
Merge change from vendor to reduce diff only.
ZFS dtrace probes are not supported on FreeBSD yet.

Illumos ZFS issues:
3598 want to dtrace when errors are generated in zfs

MFC after: 3 weeks

Merge libzfs_core branch:
includes MFV 238590, 238592, 247580

MFV 238590, 238592:
In the first zfs ioctl restructuring phase, the libzfs_core library was
introduced. It is a new thin library that wraps around kernel ioctl's.
The idea is to provide a forward-compatible way of dealing with new
features. Arguments are passed in nvlists and not random zfs_cmd fields,
new-style ioctls are logged to pool history using a new method of
history logging.

http://blog.delphix.com/matt/2012/01/17/the-future-of-libzfs/

MFV 247580 [1]:
To address issues of several deadlocks and race conditions the locking
code around dsl_dataset was rewritten and the interface to synctasks
was changed.

User-Visible Changes:
"zfs snapshot" can create more arbitrary snapshots at once (atomically)
"zfs destroy" destroys multiple snapshots at once
"zfs recv" has improved performance

Backward Compatibility:
I have extended the compatibility layer to support full backward
compatibility by remapping or rewriting the responsible ioctl arguments.
Old utilities are fully supported by the new kernel module.

Forward Compatibility:
New utilities work with old kernels with the following restrictions:
- creating, destroying, holding and releasing of multiple snapshots
at once is not supported, this includes recursive (-r) commands

Illumos ZFS issues:
2882 implement libzfs_core
2900 "zfs snapshot" should be able to create multiple,
arbitrary snapshots at once
3464 zfs synctask code needs restructuring

References:
https://www.illumos.org/issues/2882
https://www.illumos.org/issues/2900
https://www.illumos.org/issues/3464 [1]

MFC after: 1 month
Sponsored by: Hybrid Logic Inc. [1]

MFV r246653:
Import vendor change to avoid "unitialized variable" warnings.

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

References:
https://www.illumos.org/issues/3522

MFV r246633:
Import vendor bugfixes regarding SA rounding, header size and layout.
This was already partially fixed by avg.

Illumos ZFS issues:
3512 rounding discrepancy in sa_find_sizes()
3513 mismatch between SA header size and layout

References:
https://www.illumos.org/issues/3512
https://www.illumos.org/issues/3513

MFC after: 2 weeks

zfs: correctly calculate dn_bonuslen for saving SAs to disk

Since all attribute values start at 8-byte aligned boundary, we would
previously incorrectly calculate dn_bonuslen if any attribute but the
last had a variable-length value with length not multiple of 8.

Reported by: Nicolas Rachinsky <fbsd-mas-0@ml.turing-complete.org>
Tested by: Nicolas Rachinsky <fbsd-mas-0@ml.turing-complete.org>
Reviewed by: Matthew Ahrens <mahrens@delphix.com> (for upstream)
MFC after: 2 weeks

zfs: fix sa_modify_attrs handling of variable-sized attributes

- skip length_idx index for a replaced variable-sized attribute
- skip length_idx index for a removed variable-sized attribute
- also re-arranged code to make sure that length_idx is always
incremented for variable-sized attributes
- additionally add an assertion that the number of actually produced
attributes is the same as the expected number of resulting
attributes

In cooperation with: Matthew Ahrens <mahrens@delphix.com>
Tested by: Trent Nelson <trent@snakebite.org>
Reviewed by: Matthew Ahrens <mahrens@delphix.com> (for upstream)
To do: get this upstreamed
MFC after: 2 weeks

Introduce "feature flags" for ZFS pools (bump SPA version to 5000).
Add first feature "com.delphix:async_destroy" (asynchronous destroy
of ZFS datasets).
Implement features support in ZFS boot code.

Illumos revisions merged:
13700:2889e2596bd6
13701:1949b688d5fb
2619 asynchronous destruction of ZFS file systems
2747 SPA versioning with zfs feature flags

References:
https://www.illumos.org/issues/2619
https://www.illumos.org/issues/2747

Obtained from: illumos (issue #2619, #2747)
MFC after: 1 month

Update copyright information in several ZFS files, as the clause 3.3
of the CDDL licence explicitly requires every Contributor to add
a copyright notice.

This also reflects the copyright notices for the changes recently
added by Illumos.

MFC after: 3 days

Fix a bug in sa_find_sizes() which could lead to panic:

When calculating space needed for SA_BONUS buffers,
hdrsize is always rounded up to next 8-aligned boundary.
However, in two places the round up was done against
sum of 'total' plus hdrsize. On the other hand,
hdrsize increments by 4 each time, which means in
certain conditions, we would end up returning with
will_spill == 0 and (total + hdrsize) larger than
full_space, leading to a failed assertion because
it's invalid for dmu_set_bonus.

Sponsored by: iXsystems, Inc.
Reviewed by: mm
MFC after: 3 days

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