Btrfs: wait ordered range before doing direct io

Btrfs: wait ordered range before doing direct io

My recent truncate patch uncovered this bug, but I can reproduce it without the
truncate patch.  If you mount with -o compress-force, do a direct write to some
area, do a buffered write to some other area, and then do a direct read you will
get the wrong data for where you did the buffered write.  This is because the
generic direct io helpers only call filemap_write_and_wait once, and for
compression we need it twice.  So to be safe add the btrfs_wait_ordered_range to
the start of the direct io function to make sure any compressed writes have
truly been written.  This patch makes xfstests 130 pass when you mount with -o
compress-force=lzo.  Thanks,

Signed-off-by: Josef Bacik <jbacik@fusionio.com>