Which API are you referring to? If you're referring to `aio_` that's just glibc's user-space thread-pool emulation of the POSIX's asynchronous IO + many operations needed for the truly async IO are not supported (such as `stat` and `open`). There's `io_` syscalls family, but that's not in the ready-to-use state yet, judging by the manpages and various patches being submitted every month.
I'm referring to `fcntl(fd, F_SETFL, flags | O_NONBLOCK)`. `stat`, `open` are blocking, yes, didn't think about that. Also according to [1] file operations will always block, even in non-blocking mode, so I was wrong, sorry.
