Fixing a bug related to set_capacity() before add_disk().

See these references:
  http://osdir.com/ml/linux.enbd.general/2002-10/msg00176.html
  http://osdir.com/ml/linux.enbd.general/2002-10/msg00177.html
  http://stackoverflow.com/questions/13518404/add-disk-hangs-on-insmod
Illumos #3006

3006 VERIFY[S,U,P] and ASSERT[S,U,P] frequently check if first argument
     is zero

Reviewed by Matt Ahrens <matthew.ahrens@delphix.com>
Reviewed by George Wilson <george.wilson@delphix.com>
Approved by Eric Schrock <eric.schrock@delphix.com>

References:
  illumos/illumos-gate@fb09f5aad449c97fe309678f3f604982b563a96f
  https://illumos.org/issues/3006

Ported-by: Brian Behlendorf <behlendorf1@llnl.gov>
Use kmem_cache for zil_vdev_node_t objects

Signed-off-by: Richard Yao <ryao@gentoo.org>
Use bitfields for boolean values in znode_t

znode_t uses 1312 bytes in length on Linux 3.9.6 amd64. Switching to
bitfields for boolean values reduces the size to 1296 bytes. Further
reductions should be possible if padding were removed, but saving 16
bytes per struct can translate into megabytes of savings when hundreds
of thousands of znodes are cached. While the savings is relatively
small in comparison to memory used, the small efficiency gain is
practically free.

Signed-off-by: Richard Yao <ryao@gentoo.org>
Remove unused option -r from zpool

Signed-off-by: Richard Yao <ryao@gentoo.org>
Implement -t option to zpool import for temporary pool names

Specifying newname to a pool import currently changes the pool name. We
implement option -t. Specifying option -t in conjuction with newpool to
zpool import will make the name change temporary. In specific, the
original pool name will be used in all label updates and therefore is
retained upon export.

This is useful in any situation where maintenance on a system's root
pool is done from another system. A good example is environments using
virtualization, where it is more desireable to do rollback of the root
dataset of a guest's root pool than it is to rollback of the zvol
hosting the guest's root pool when an issue prevents the guest from
booting properly. Other examples include maintenance on root pools
hosted on iSCSI and operating system installations on USB keys that are
used to rescue non-bootable sytems.

Signed-off-by: Richard Yao <ryao@gentoo.org>
Make dmu_sync_arg_cache

Signed-off-by: Richard Yao <ryao@gentoo.org>
Make zio_gang_node_t cache

Signed-off-by: Richard Yao <ryao@gentoo.org>
User namespace compatibility

Signed-off-by: Richard Yao <ryao@gentoo.org>
Move ARC allocations to slab caches

Signed-off-by: Richard Yao <ryao@gentoo.org>
Illumos #3603, #3604: bobj improvements

3603 panic from bpobj_enqueue_subobj()
3604 zdb should print bpobjs more verbosely
3871 GCC 4.5.3 does not like issue 3604 patch

https://www.illumos.org/issues/3603
https://www.illumos.org/issues/3604
https://www.illumos.org/issues/3871

Reviewed by: Henrik Mattson <henrik.mattson@delphix.com>
Reviewed by: Adam Leventhal <ahl@delphix.com>
Reviewed by: Christopher Siden <christopher.siden@delphix.com>
Reviewed by: George Wilson <george.wilson@delphix.com>
Reviewed by: Garrett D'Amore <garrett@damore.org>
Approved by: Dan McDonald <danmcd@nexenta.com>
Ported-by: Richard Yao <ryao@gentoo.org>

Note that the patch from Illumos issue 3871 is not accepted into Illumos
at the time of this writing. It is something that I wrote when porting
this. Documentation is in the Illumos issue.
Make SLAB caches for dmu_tx_* operations

Signed-off-by: Richard Yao <ryao@gentoo.org>
Make slab cache for rl_t

Signed-off-by: Richard Yao <ryao@gentoo.org>
Make deadman thread panic on hung IO

Signed-off-by: Richard Yao <ryao@gentoo.org>
Linux 3.11 compat: fops->iterate()

Commit torvalds/linux@2233f31aade393641f0eaed43a71110e629bb900 replaced
->readdir() with ->iterate() in struct file_operations.

Signed-off-by: Richard Yao <ryao@gentoo.org>