ocfs2: add ocfs2_overwrite_io()

ocfs2: add ocfs2_overwrite_io()

Add ocfs2_overwrite_io function, which is used to judge if overwrite
allocated blocks, otherwise, the write will bring extra block allocation
overhead.

[[email protected]: v3]
Link: http://lkml.kernel.org/r/[email protected]
[[email protected]: v2]
Link: http://lkml.kernel.org/r/[email protected]
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Gang He <[email protected]>
Reviewed-by: Changwei Ge <[email protected]>
Cc: Mark Fasheh <[email protected]>
Cc: Joel Becker <[email protected]>
Cc: Junxiao Bi <[email protected]>
Cc: Joseph Qi <[email protected]>
Cc: Jun Piao <[email protected]>
Cc: alex chen <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>