O_DIRECT is a non-standard option that is available on Linux 2.4 (at
least some subrevisions of it). Passed to open(2), it tells the OS to
bypass the page cache for read(2) and write(2) operations on that file
descriptor. That's almost everything I know about it.

So I googled a little bit and got some hits on that topic that confused
me more that they cleared up anything

What I would like to know is:
- is this option still actively supported on current Linux
implementations (although Linus T. strongly recommends against it)?
- what other OSs support this option (possibly with a different name)?
- are there alternative ways to bypass kernel caches when writing to a
file descriptor on Linux and *BSD, like e.g. Solaris directio(3c) and
sendfile(3ext), apart from madvise(3c) and posix_fadvise(2)?

Basically, I'm searching for an equivalent of
'directio(fd,DIRECTIO_ON)', if any such thing exists.

Any pointer would be highly appreciated...