Both ext4 and ZFS allow storing the file creation time in the
on-disk inode, and the new statx() API allows returning it to
userspace, but as yet we do not have any mechanism to send it
from the servers to the client.

Add fields into struct mdt_body and an OBD_MD_FLBTIME flag to
allow it to be requested and returned directly from MDTs. It
does not need to get it from the OSTs or in the LVB since those
objects are precreated and their creation time (birth time) is
not accurate.

This patch also adds support to lfs find to query on this field.

Signed-off-by: Qian Yingjin <qian@ddn.com>
Change-Id: Ib122b336695cde511fa6d8fb9eca95a4da701430
Reviewed-on: https://review.whamcloud.com/36507


Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Li Xi <lixi@ddn.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Reviewed-by: Oleg Drokin <green@whamcloud.com>