Illumos #2671: zpool import should not fail if vdev ashift has increased

Reviewed by: Adam Leventhal <ahl@delphix.com>
Reviewed by: Eric Schrock <eric.schrock@delphix.com>
Reviewed by: Richard Elling <richard.elling@richardelling.com>
Reviewed by: Gordon Ross <gwr@nexenta.com>
Reviewed by: Garrett D'Amore <garrett@damore.org>
Approved by: Richard Lowe <richlowe@richlowe.net>

Refererces to Illumos issue:
      https://www.illumos.org/issues/2671

This patch has been slightly modified from the upstream Illumos
version.  In the upstream implementation a warning message is
logged to the console.  To prevent pointless console noise this
notification is now posted as a "ereport.fs.zfs.vdev.bad_ashift"
event.

The event indicates a non-optimial (but entirely safe) ashift
value was used to create the pool.  Depending on your workload
this may impact pool performance.  Unfortunately, the only way
to correct the issue is to recreate the pool with a new ashift.

NOTE: The unrelated fix to the comment in zpool_main.c appears
in the upstream commit and was preserved for consistnecy.

Ported-by: Cyril Plisko <cyril.plisko@mountall.com>
Reworked-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #955
Improve AF hard disk detection

Use the bdev_physical_block_size() interface to determine the
minimize write size which can be issued without incurring a
read-modify-write operation.  This is used to set the ashift
correctly to prevent a performance penalty when using AF hard
disks.

Unfortunately, this interface isn't entirely reliable because
it's not uncommon for disks to misreport this value.  For this
reason you may still need to manually set your ashift with:

  zpool create -o ashift=12 ...

The solution to this in the upstream Illumos source was to add
a white list of known offending drives.  Maintaining such a list
will be a burden, but it still may be worth doing if we can
detect a large number of these drives.  This should be considered
as future work.

Reported-by: Richard Yao <ryao@cs.stonybrook.edu>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #916
Add "-o ashift" to zpool add and zpool attach

When adding devices to an existing pool "ashift" property is
auto-detected.  However, if this property was overridden at
the pool creation time (i.e. zpool create -o ashift=12 tank ...)
this may not be what the user wants.  This commit lets the user
specify the value of "ashift" property to be used with newly
added drives. For example,

    zpool add -o ashift=12 tank disk1
    zpool attach -o ashift=12 tank disk1 disk2

Signed-off-by: Cyril Plisko <cyril.plisko@mountall.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #566
Merge branch 'ashift'

This branch adds some overdue ashift improvements.

  * Add '-o ashift' to 'zpool add' and 'zpool attach'
  * Improve AF hard disk detection
  * Allow 'zpool import' to handle increases in ashift

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
mount.zfs: canonicalize mount point for mtab

Canonicalize the mount point passed to the mount.zfs helper.
This way a clean path is always added to mtab which ensures
the umount can properly locate and remove the entry.

Test case:
$ mkdir /mnt/foo
$ mount -t zfs zpool/foo /mnt/../mnt/foo////
$ umount /mnt/foo
$ cat /etc/mtab | grep zpool/foo
zpool/foo /mnt/../mnt/foo//// zfs rw 0 0

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #573
Merge branch 'master' of git://github.com/zfsonlinux/zfs