To:	davem@dm.cobaltmicro.com, sct@redhat.com, alan@lxorguk.ukuu.org.uk, linux-kernel@vger.rutgers.edu, number6@the-village.bc.nu, torvalds@transmeta.com,
Subject: Re: PATCH: Raw device IO for 2.1.131
From:	lm@bitmover.com (Larry McVoy)
Date:	Sat, 12 Dec 1998 10:44:38 -0800

> > Finally, I'd put all this lock down pages stuff into a mm/*.c file.
> > I want to use it for networking if it goes in (zero copy TCP, NFS
> > directly into page cache, etc.).
> 
> Well for sendfile() it seems ideal for zero copying. I'd second it being in
> mm/*.c - I want it for video capture

I came into this late but I want this too.  I need to bring you up to date
on some stuff I'm trying to make happen with the disk/network people.
I'm working with one of the big disk drive companies.  They want to
put networking on the disk drives.  In order for this not to be a joke,
there needs to be a way to essentially do DMA over the network - standard
networking won't be fast enough (in other words, if a 386 can set up a
DMA to move data off the disk at 20MB/sec, then the same 386 had better
be able to do the same thing with a network disk - that isn't true today).

There is a way of accomplishing the goal - SGI does it with
something called scheduled transfer (you can sort of read about it at
http://bitmover.com/talks/pp/slide01.html ) - they can do 791MBytes/sec
over their GSN network using this technique.

The technique requires that you can lock down pages and set things up
such that the card does all the work - the OS sets up the "descriptors"
and then stands back and lets the "network DMA" happen.

I've agreed to work with SGI and the disk & networking people to try and
make a ST-lite specification which would work for everyone.  Linux is the
primary target for this, so as soon as there is an implementation, you'll
all get it.

So, Linus, I know you haven't been thrilled about "raw I/O" and that you
have some very valid reasons for not wanting it in the kernel.  Does the 
patch for raw device I/O come anywhere near being good enough that you 
are OK with it?  If not, can you suggest what it would need to look like?

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