Re: Is sendfile all that sexy?

[Andreas Dilger]

Roger Wolff writes:
> I'd prefer an interface that says "copy this fd to that one, and
> optimize that if you can".
> 
> For example, copying a file from one disk to another. I'm pretty sure
> that some efficiency can be gained if you don't need to handle the
> possibility of the userspace program accessing the data in between the
> read and the write. Sure this may not qualify as a "trivial
> optimization, that can be done with the existing infrastructure" right
> now, but programs that want to indicate "kernel, please optimize this
> if you can" can say so.

Actually, this is a great example, because at one point I was working
on a device interface which would offload all of the disk-disk copying
overhead to the disks themselves, and not involve the CPU/RAM at all.

I seem to recall that I2O promised something along these lines as well
(i.e. direct device-device communication).

Cheers, Andreas
-- 
Andreas Dilger  \ "If a man ate a pound of pasta and a pound of antipasto,
                 \  would they cancel out, leaving him still hungry?"
http://www-mddsp.enel.ucalgary.ca/People/adilger/               -- Dogbert