Add object type checking to zap_lockdir()

If a non-ZAP object is passed to zap_lockdir() it will be treated
as a valid ZAP object.  This can result in zap_lockdir() attempting
to read what it believes are leaf blocks from invalid disk locations.
The SCSI layer will eventually generate errors for these bogus IOs
but the caller will hang in zap_get_leaf_byblk().

The good news is that is a situation which can not occur unless the
pool has been damaged.  The bad news is that there are reports from
both FreeBSD and Solaris of damaged pools.  Specifically, there are
normal files in the filesystem which reference another normal file
as their parent.

Since pools like this are known to exist the zap_lockdir() function
has been updated to verify the type of the object.  If a non-ZAP
object has been passed it EINVAL will be returned immediately.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Issue #2597
Issue #2602
Illumos 5117 - spacemap reallocation can cause corruption

5117 space map reallocation can cause corruption
Reviewed by: Matthew Ahrens <mahrens@delphix.com>
Reviewed by: Sebastien Roy <sebastien.roy@delphix.com>
Reviewed by: Richard Elling <richard.elling@gmail.com>
Approved by: Richard Lowe <richlowe@richlowe.net>

References:
  https://www.illumos.org/projects/illumos-gate/issues/5117
  https://github.com/illumos/illumos-gate/commit/e503a68

Ported by: Turbo Fredriksson <turbo@bayour.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #2662
Implement fallocate FALLOC_FL_PUNCH_HOLE

Add support for the FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE mode of
fallocate(2).  Mimic the behavior of other native file systems such as
ext4 in cases where the file might be extended. If the offset is beyond
the end of the file, return success without changing the file. If the
extent of the punched hole would extend the file, only the existing tail
of the file is punched.

Add the zfs_zero_partial_page() function, modeled after update_page(),
to handle zeroing partial pages in a hole-punching operation.  It must
be used under a range lock for the requested region in order that the
ARC and page cache stay in sync.

Move the existing page cache truncation via truncate_setsize() into
zfs_freesp() for better source structure compatibility with upstream code.

Add page cache truncation to zfs_freesp() and zfs_free_range() to handle
hole punching.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Tim Chase <tim@chase2k.com>
Closes #2619
Document the "readonly" pool property

This documentation is based FreeBSD's zpool(8) man page.

Signed-off-by: Tim Chase <tim@chase2k.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #2682
Fix z_teardown_inactive_lock deadlock

When rolling back a mounted filesystem zfs_suspend() is called
which acquires the z_teardown_inactive_lock.  This lock can not
be dropped until the filesystem has been rolled back and resumed
in zfs_resume_fs().

Therefore, we must not call iput() under this lock because it
may result in the inode->evict() handler being called which also
takes this lock.  Instead use zfs_iput_async() to ensure dropping
the last reference is deferred and runs in a safe context.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #2670
Document environment variables for zdb, zfs, zinject and zpool.

Signed-off-by: Turbo Fredriksson <turbo@bayour.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #2691
Illumos 5140 - message about "%recv could not be opened" is printed when booting after crash

Reviewed by: Christopher Siden <christopher.siden@delphix.com>
Reviewed by: George Wilson <george.wilson@delphix.com>
Reviewed by: Max Grossman <max.grossman@delphix.com>
Reviewed by: Richard Elling <richard.elling@gmail.com>
Approved by: Dan McDonald <danmcd@omniti.com>

References:
  https://www.illumos.org/projects/illumos-gate//issues/5140
  https://github.com/illumos/illumos-gate/commit/2243853

Ported by: Turbo Fredriksson <turbo@bayour.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #2676
Illumos 5138 - add tunable for maximum number of blocks freed in one txg

Reviewed by: Mattew Ahrens mahrens@delphix.com
Reviewed by: Adam Leventhal adam.leventhal@delphix.com

References:
  https://www.illumos.org/issues/5138
  https://github.com/illumos/illumos-gate/commit/af3465d

Porting notes:

Because exposing a uint64_t parameter, we require v3.17-rc1 which
complicates the whole code. Instead, just use an ulong.

The worst thing that can happen is we're limited to freeing 2^32
blocks in a single pass. This is already far far far far more than we
can reasonably do.

Ported by: Turbo Fredriksson <turbo@bayour.com>