Prevent upgrading root pool.

Ticket:	#6312
Do not fill syslog with Unknown USB device messages

Ticket 5512
Fix a bug introduced in changeset cea7002: when doing 'zpool status'
without -x, don't return early but instead override the returned
error message.

Ticket:	#6312
Revert "support for devfs long symlinks"

This reverts commit ef141829dd7424e7d9fdc50c2844e2d82ede1c43.
Make VPD 80h (Serial Number) transfer length match serial number length.

MFC after:	1 week

(cherry picked from commit 18b36a84027f81186796361079b04c0d28c14b37)

Ticket:	#6369
Add another PCI ID for JMB368 PATA controller.

MFC after:	1 week
Ticket:		#6382

(cherry picked from commit 04644ebb8427df9654fe6a1d3ad835d57926b04b)
Limit default maximum blocks to be freed in one single transaction
group, vfs.zfs.free_max_blocks at 131072 blocks (=512M @ 4k block size,
or =16GiB @ 128k block size).  This helps to prevent foot shooting for
destroying large datasets.
MFV r272493:

Show individual disk capacity when doing zpool list -v.

Illumos issue:
    5147 zpool list -v should show individual disk capacity

MFC after:	1 week

(cherry picked from commit 33caf06b8f97faa86800b3207971b177f5a78fc5)
MFV r272494:

Make space_map_truncate() always do space_map_reallocate().  Without
this, setting space_map_max_blksz would cause panic for existing pool,
as dmu_objset_set_blocksize would fail if the object have multiple blocks.

Illumos issues:
   5164 space_map_max_blksz causes panic, does not work
   5165 zdb fails assertion when run on pool with recently-enabled
	spacemap_histogram feature

MFC after:	2 weeks

(cherry picked from commit 64595536f12e0c6835b51d11556e9fda8cc7596d)
MFV r272495:

In arc_kmem_reap_now(), reap range_seg_cache too to reclaim memory in
response of memory pressure.

Illumos issue:
    5163 arc should reap range_seg_cache

MFC after:	1 week

(cherry picked from commit 3dd244b4585ee134de54a563e36294f12da835a5)
Don't make nested definition for range_seg_cache.

Reported by:	ian
MFC after:	1 week
X-MFC-With:	r272506

(cherry picked from commit 60bf73506ecd9b277bfeb5eaa63fa80715d98698)
MFV r272496:

Add tunable for number of metaslabs per vdev
(vfs.zfs.vdev.metaslabs_per_vdev).  The default remains
at 200.

Illumos issue:
    5161 add tunable for number of metaslabs per vdev

MFC after:	2 weeks

(cherry picked from commit 096b5dca2146c061317f69289592b55c29e33c20)
Diff reduction with upstream.  The code change is not really applicable
to FreeBSD.

Illumos issue:
    5148 zvol's DKIOCFREE holds zfsdev_state_lock too long

MFC after:	1 month

(cherry picked from commit cd42e24ad69c0a9ba1e765d5401cfc7739996fc5)
Add a new sysctl, vfs.zfs.vol.unmap_enabled, which allows the system
administrator to toggle whether ZFS should ignore UNMAP requests.

Illumos issue:
    5149 zvols need a way to ignore DKIOCFREE

MFC after:	2 weeks

(cherry picked from commit 8bbc3504dc7ab4846f39c308c7df786d8e105fd9)
MFV r272499:

Illumos issue:
    5174 add sdt probe for blocked read in dbuf_read()

MFC after:	2 weeks

(cherry picked from commit 87516a919a377c41145bcbb6d0b7f9b69d15c658)
MFV r272500:

Don't inherit flags other than DS_FLAG_CI_DATASET and DS_FLAG_INCONSISTENT
when cloning.  This prevents DS_FLAG_DEFER_DESTROY being inherited from a
clone that is marked for deferred destroy, which causes snapshots of the
clone being destroyed when getting a hold or clone.

Illumos issue:
    5150 zfs clone of a defer_destroy snapshot causes strangeness

MFC after:	1 week

(cherry picked from commit bd5e6432da9c175a419ce63c6835ec5e61a58451)
MFV r272501:

Illumos issue:
    5177 remove dead code from dsl_scan.c

MFC after:	2 weeks

(cherry picked from commit 37185e7390a0c255ae105ae62e8e8135235f9367)
MFV r272585:

Split the godfather zio into CPU number's to reduce lock
contention.

Illumos issue:
    5176 lock contention on godfather zio

MFC after:	2 weeks

(cherry picked from commit 3f54b74af40b22333965b536b8a9aad1dba482e9)
MFV r272588:

Handle old format deadlist.

Illumos issue:
    5178 zdb -vvvvv on old-format pool fails in dump_deadlist()

MFC after:	2 weeks

(cherry picked from commit 72b086c52ce1483b4a1a258fce3db32ce687df75)
MFV r272591:

Use loaned ARC buffer for zfs receive to avoid copy.

Illumos issue:
    5162 zfs recv should use loaned arc buffer to avoid copy

MFC after:	2 weeks

(cherry picked from commit 004a50f8bdd69852eaf09dfea3316483d61f950a)