hi folks,

I've finished the initial implementation of direct I/O,
there's an updated diff in:

ftp://ftp.netbsd.org/pub/NetBSD/misc/chs/dio/diff.directio.3

this version does not allow concurrent writes to files, it's only
intended to provide the ability to prevent caching fs data in the
kernel.  I'll add support for concurrency of non-overlapping writes
in a separate change.

if no one sees any problems with this part of the work,
I'll check it in (along with associated doc changes) later this week.

-Chuck