buffered asynchronous file I/O on linux

I am looking for the most efficient way to do asynchronous file I/O on linux.

The POSIX glibc implementation uses threads in userland.

The native aio kernel api only works with unbuffered operations, patches for the kernel to add support for buffered operations exist, but those are >3 years old and no one seems to care about integrating them into the mainline.

I found plenty of other ideas, concepts, patches that would allow asynchronous I/O, though most of them in articles that are also >3 years old. What of all this is really available in todays kernel? I've read about servlets, acalls, stuff with kernel threads and more things I don't even remember right now.

What is the most efficient way to do buffered asynchronous file input/output in todays kernel?