confuse about generic_file_read_iter

Hello everyone,

I'm trying to figure out how asyncchronous I/O implemented, but I'm confusing about the generic_file_read_iter in mm/filemap.c. major file systems use this function as read_iter for it's file_operations structure(eg, ext3).

And it's called by syscall io_submit(fs/aio.c:1359):
sys_io_submit -> do_io_submit -> io_submit_one -> aio_run_iocb

The point I'm confusing is generic_file_read_iter seems do noting about asyncchronous I/O at all, as I see what generic_file_read_iter does:
if opened with O_DIRECT

     flush pages;
	 call direct_IO;
   else
     call do_generic_file_read();

Actually, I think it's syncchronous.

It's that means file systems using generic_file_read_iter does not support aio(such as ext3)?

I also tried git log fs/aio.c. I found retry-based AIO is removed at commit 41003a7bcfed1255032e1e7c7b487e505b22e298(Tue May 7 16:18:25 2013) Could anyone tell me how does linux AIO implement now?

I'm working on linux-next(20140502)
thanks.