Re: PATCH: Raw device IO for 2.1.131

[Linus Torvalds]

On Sat, 12 Dec 1998, Alan Cox wrote:
> 
> Frame capture into a file is uninteresting for serious video people because
> a) we have this toy computer 2Gig file limit[1] and b) performance is a colossal
> issue. a) is easy to work around [apple worked around it nicely with Qt,
> intel forgot] b) is a problem. Video people really don't care about throwing
> an 80Gig FCAL array at a video problem. No file system who cares - saves fscking

Alan, let me clue you in: we're going to be living in the 21st century in
not too long.

We're going to have mom-and-pop users who want to capture their
grandchildren in HDTV on their computer from their camera. And yes, their
computers _are_ going to be able to handle it, and the 2G file limit won't
be there. 

Anybody who seriously thinks that raw device access is worthwhile had
better think again. It's not. It's a special case thing that will never be
acceptable to any real target audience. 

Right now you might be able to do it on current hardware only with raw
device access, but designing for it is a piece of shit design. 

> We need memory locking for stuff like video capture DMA. The demonstration
> HDTV chipsets want capture to DMA 1600x1200x24bit data to memory targets.
> The existing bttv sick 'vmalloc and look the other way' approach isnt as
> good as locking pages for this (Disk I/O issues aside)

Umm.. That's what I said. You can lock down pages _easily_ in the page
cache. You just increment their usage count.

And that has absolutely NOTHING to do with raw device access. What you do
is you make "sendfile()" work for the "copy to page cache" case too. 

		Linus