fadvise syscall?

[Jeff Garzik]

Has anyone ever done an madvise(2)-type syscall for file descriptors?
(or does the capability exist and I'm missing it?)

I was thinking, in playing around with stuff like cp(1) I've found that 
standard read(2) and write(2) of a 4-8K buffer is the fastest solution 
overall, in addition to providing the useful side effect of better error 
reporting, such as ENOSPC report.  Better error reporting than the 
alternative I see anyway, mmap(2).

So... we have madvise, why not fadvise?  I would love the capability for 
applications to provide hints to the OS like madvise, but for file 
descriptors...

    Jeff