ocfs2: add ocfs2_write_type_t type to identify the caller of write

Patchset: fix ocfs2 direct io code patch to support sparse file and data
ordering semantics

The idea is to use buffer io(more precisely use the interface
ocfs2_write_begin_nolock & ocfs2_write_end_nolock) to do the zero work
beyond block size.  And clear UNWRITTEN flag until direct io data has
been written to disk, which can prevent data corruption when system
crashed during direct write.

And we will also archive a better performance: eg.  dd direct write new
file with block size 4KB: before this patchset:
  2.5 MB/s
after this patchset:
  66.4 MB/s

This patch (of 8):

To support direct io in ocfs2_write_begin_nolock &
ocfs2_write_end_nolock.

Remove unused args filp & flags.  Add new arg type.  The type is one of
buffer/direct/mmap.  Indicate 3 way to perform write.  buffer/mmap type
has implemented.  direct type will be implemented later.

Signed-off-by: Ryan Ding <ryan.ding@oracle.com>
Reviewed-by: Junxiao Bi <junxiao.bi@oracle.com>
Cc: Joseph Qi <joseph.qi@huawei.com>
Cc: Mark Fasheh <mfasheh@suse.de>
Cc: Joel Becker <jlbec@evilplan.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>