nilfs2: switch O_DIRECT to iomap based operations

The patch eliminates blockdev_direct_IO() from
nilfs2 entirely:

 - nilfs_file_open() now sets FMODE_CAN_ODIRECT explicitly, since
   permission to open the file O_DIRECT was previously implied by
   aops->direct_IO being non-NULL.
 - nilfs_file_read_iter() dispatches O_DIRECT reads to iomap_dio_rw()
   using nilfs_iomap_ops; everything else still goes through
   generic_file_read_iter() as before.
 - nilfs_file_write_iter() strips IOCB_DIRECT and falls through to
   generic_file_write_iter()'s ordinary buffered path. NILFS2 cannot
   perform true direct I/O writes: new blocks are delay-allocated and
   only given a real disk address by the segment constructor, which
   works on buffer_head lists, not iomap. This reproduces today's
   actual behavior: the old nilfs_direct_IO() already just returned 0
   for WRITE.
 - nilfs_direct_IO() and the .direct_IO callback on nilfs_aops are
   removed.
 - drop the unnecessary "select LEGACY_DIRECT_IO" from Kconfig
   in favor of "select FS_IOMAP".

cc: Christoph Hellwig <hch@lst.de>
cc: Ryusuke Konishi <konishi.ryusuke@gmail.com>
cc: linux-nilfs@vger.kernel.org
cc: linux-fsdevel@vger.kernel.org
Acked-by: Ryusuke Konishi <konishi.ryusuke@gmail.com>
Signed-off-by: Viacheslav Dubeyko <slava@dubeyko.com>

0 files changed, 0 insertions, 0 deletions