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 r268473: MFV r268455:

Use reserved space for ZFS administrative commands.

MFC r268075: MFV r267565:

4757 ZFS embedded-data block pointers ("zero block compression")
4913 zfs release should not be subject to space checks

MFC r258294:
Fix ZFS deadlock when sending a snapshot which is mounted.

Approved by: re (glebius)
Sponsored by: Multiplay

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

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

MFV r252215:

Restore a previous behavior before r251646, where when destructing
ZFS snapshot, the ioctl would return ENOENT when it hit any of
them in the errlist (the new behavior was only return ENOENT when
all returns error).

Illumos ZFS issues:
3829 fix for 3740 changed behavior of zfs destroy/hold/release ioctl

MFC after: 1 week

MFV r251644:

Poor ZFS send / receive performance due to snapshot
hold / release processing (by smh@)

Illumos ZFS issues:
3740 Poor ZFS send / receive performance due to snapshot
hold / release processing

MFC after: 2 weeks

MFV r251622:

ZFS shouldn't ignore errors unmounting snapshots

Illumos ZFS issues:
3744 zfs shouldn't ignore errors unmounting snapshots

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 r247580:
Merge synctask code restructuring from vendor.

Modify forward and backward compatibility to support new change.

Illumos ZFS issues:
3464 zfs synctask code needs restructuring

Sponsored by: Hybrid Logic Ltd.

Update vendor/illumos/dist and vendor-sys/illumos/dist
to illumos-gate 13973:4972ab336f54

Illumos ZFS issues:
3464 zfs synctask code needs restructuring