Re: Syslets, Threadlets, generic AIO support, v6

[Linus Torvalds <torvalds@linux-foundation.org>]

On Wed, 30 May 2007, Ulrich Drepper wrote:
> 
> I don't like special cases.  For me things better come in quantities 0,
> 1, and unlimited (well, reasonable high limit).  Otherwise, who gets to
> use that special namespace?  The C library is not the only body of code
> which would want to use descriptors.

Well, don't think of it as a special case at all: think of bit 30 as a 
"the user asked for a non-linear fd".

In fact, to make it effective, I'd suggest literally scrambling the low 
bits (using, for example, some silly per-boot xor value to to actually 
generate the "true" index - the equivalent of a really stupid randomizer). 

That way you'd have the legacy "linear" space, and a separate "non-linear 
space" where people simply *cannot* make assumptions about contiguous fd 
allocations. There's no special case there - it's just an extension which 
explicitly allows us to say "if you do that, your fd's won't be allocated 
the traditional way any more, but you *can* mix the traditional and the 
non-linear allocation".

> And then the semantics: do these descriptors should show up in
> /proc/self/fd?  Are there separate directories for each namespace?  Do
> they count against the rlimit?

Oh, absolutely. The'd be real fd's in every way. People could use them 
100% equivalently (and concurrently) with the traditional ones. The whole, 
and the _only_ point, would be that it breaks the legacy guarantees of a 
dense fd space.

Most apps don't actually *need* that dense fd space in any case. But by 
defaulting to it, we wouldn't break those (few) apps that actually depend 
on it.

		Linus
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