As someone else noted, this doesn't belong in the filesystem (rather the kernel's block I/O layer/buffer cache). But I agree, an API by which we can tell the kernel what kind of I/O behavior to expect would be good.
The closest API to what you're describing that I'm aware of is posix_fadvise(). While that is technically-speaking a POSIX standard, it is not widely implemented (I know Linux 2.6 implements it; based on some quick googling, it looks like AIX does too).

Don't forget about the existence/usefulness/widely implemented madvise(2)/posix_madvise(2) call, which can give the OS the following hints: MADV_NORMAL, MADV_SEQUENTIAL, MADV_RANDOM, MADV_WILLNEED, MADV_DONTNEED, and MADV_FREE. :) -sc

Sean Chittenden

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