Transaction Number
~~~~~~~~~~~~~~~~~~
[[transno]]

For each target there is a sequence of values (a strictly increasing
series of numbers) where each operation that can modify the file
system is assigned the next number in the series. This is the
transaction number, and it imposes a strict serial ordering for all
file system modifying operations.  For file system modifying
requests the server assigns the next value in the sequence and
informs the client of the value in the 'pb_transno' field of the
'ptlrpc_body' of its reply to the client's request. For replys to
requests that do not modify the file system the 'pb_transno' field in
the 'ptlrpc_body' is just set to 0.