FreeBSD 4.9 was released today. In the release notes was:
2.2.6 File Systems
A new DIRECTIO kernel option enables support for read operations that
bypass the buffer cache and put data directly into a userland buffer.
This feature requires that the O_DIRECT flag is set on the file
descriptor and that both the offset and length for the read operation
are multiples of the physical media sector size.
Is that of any use?
Chris