LU-9538 mdt: Lazy size on MDT

LU-9538 mdt: Lazy size on MDT

The design of Lazy size on MDT (LSOM) does not guarantee the
accuracy. A file that is being opened for a long time might
cause inaccurate LSOM for a very long time. And also eviction or
crash of client might cause incomplete process of closing a file,
thus might cause inaccurate LSOM. A precise LSOM could only be read
from MDT when 1) all possible corruption and inconsistency caused
by client eviction or client/server crash have all been fixed by
LFSCK and 2) the file is not being opened for write.
In the first step of implementing LSOM, LSOM will not be accessible
from client. Instead, LSOM values can only be accessed on MDT. Thus,
no interface or logic codes will be added on client side to enabled
the access of LSOM from client side.
The LSOM will be saved as an EA value on MDT.
LSOM includes both the apparent size and also the disk usage of
the file.
Whenever a file is being truncated, the LSOM of the file on MDT
will be updated.
Whenever a client is closing a file, ll_prepare_close() will send
the size and blocks to the MDS. The MDS will update the LSOM of
the file if the file size or block size is being increased.

Signed-off-by: Qian Yingjin <qian@ddn.com>
Change-Id: If4032a55f448a65235a6b3db58f857c74222faa3
Reviewed-on: https://review.whamcloud.com/29960
Reviewed-by: Vitaly Fertman <c17818@cray.com>
Reviewed-by: Jinshan Xiong <jinshan.xiong@gmail.com>
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>