From: Brian Behlendorf <behlendorf1@llnl.gov>
Subject: [PATCH] feature commit cb

ZFS commit callbacks (v3) some version of this support is expected
to appear in an official release from the core ZFS team.

NOTE: The ztest test case was dropped because it assumed userspace
pthreads support.  We should certainly keep the test case but the
user space modification should be properly written to handle and
kernel space build as well.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>