Please do not add a new ->direct_IO method. I'm currently working hard on removing it, just set FMODE_CAN_ODIRECT and handle the fallback in your read_iter/write_iter methods. But if we just start claiming direct I/O support for file systems that don't actually support it, I'm starting to seriously wonder why we bother with the flag at all and don't just allow O_DIRECT opens to always succeed..
