vdev_file_io_start() to use taskq_dispatch(TQ_PUSHPAGE)

The vdev_file_io_start() function may be processing a zio that the
txg_sync thread is waiting on.  In this case it is not safe to perform
memory allocations that may generate new I/O since this could cause a
deadlock.  To avoid this, call taskq_dispatch() with TQ_PUSHPAGE
instead of TQ_SLEEP.

Signed-off-by: Ned Bass <bass6@llnl.gov>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Issue #1928
Allow chown/chgrp when no ACL SAs exist.

From the comment in the commit:

Some ZFS implementations (ZEVO) create neither a ZNODE_ACL nor a DACL_ACES
SA in which case ENOENT is returned from zfs_acl_node_read() when the
SA can't be located.  Allow chown/chgrp to succeed in these cases rather
than returning an error that makes no sense in the context of the caller.

Signed-off-by: Tim Chase <tim@chase2k.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Issue zfs-osx/zfs#86
Closes #1911
Closes #2029
Use enum type(zfetch_dirn_t) instead

Fix code with zfetch_dirn_t, which is more readable and clear.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #2068
Add additional state TXG_STATE_WAIT_FOR_SYNC for txg.

In several cases when digging into kstats we can found two txgs
in SYNC state, e.g.

txg     birth            state  nreserved  nread      nwritten ...
985452  258127184872561  C      0          373948416  2376272384 ...
985453  258129016180616  C      0          378173440  28793344 ...
985454  258129016271523  S      0          0          0 ...
985455  258130864245986  S      0          0          0 ...
985456  258130867458851  O      0          0          0 ...

However only first txg (985454) is really syncing at this moment.
The other one (985455) marked as SYNCED is actually in a post-QUIESCED
state and waiting to start sync.   So, the new TXG_STATE_WAIT_FOR_SYNC
state between TXG_STATE_QUIESCED and TXG_STATE_SYNCED was added to
reveal this situation.

txg     birth            state  nreserved  nread      nwritten ...
1086896 235261068743969  C      0          163577856  8437248 ...
1086897 235262870830801  C      0          280625152  822594048 ...
1086898 235264172219064  S      0          0          0 ...
1086899 235264936134407  W      0          0          0 ...
1086900 235264936296156  O      0          0          0 ...

Signed-off-by: Igor Lvovsky <ilvovsky@gmail.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Issue #2075
Call gethrtime() only once per new txg creation

When transitioning current open TXG into QUIESCE state and opening
a new one txg_quiesce() calls gethrtime():
  - to mark the birth time of the new TXG
  - to record the SPA txg history kstat
  - implicitely inside spa_txg_history_add()

These timestamps are practically the same, so that the first one
can be used instead of the other two.  The only visible difference
is that inside spa_txg_history_add() the time spent in kmem_zalloc()
will be counted towards the opened TXG.

Since at this point the new TXG already exists (tx->tx_open_txg
has been already incremented) it is actually a correct accounting.

In any case this extra work is only happening when spa_txg_history
kstat is activated (i.e. zfs_txg_history > 0) and doesn't affect
the normal processing in any way.

Signed-off-by: Cyril Plisko <cyril.plisko@mountall.com>
Issue #2075